fix(acp): validate a permission reply against the options that were sent

CodeRabbit caught a hole on the same seam this PR already fixes, in the
other direction.

buildPermissionOptions drops PermissionDecisionCancel, because ACP
expresses cancellation through the outcome rather than an option. But
ZERO enumerates cancel in AvailableDecisions for shell commands and
apply_patch — the two commonest prompts — so validating against the
decisions accepted {"outcome":"selected","optionId":"cancel"}: an
identifier no client was ever shown, aborting the whole turn.

Rather than reject cancel by name, decisionFromOutcome now takes the
[]PermissionOption that were actually sent, and requestPermission builds
that list once and uses it for both halves. "What we offered" and "what we
accept" become the same slice instead of two things kept in step, so
anything optionKindFor declines to render is excluded structurally — the
next such action is covered the day it is added.

The regression test is written over every option-less decision rather
than over cancel specifically, for the same reason. Cancelling through
the outcome still works, which is asserted separately: closing the
selected-id route must not close the real one.

Also adds the cancellation coverage CodeRabbit asked for on the two
sandbox-retry paths. Both wrap ErrPermissionApprovalCanceled and each is
reached by a different denial, and the ACP mapping in this PR depends on
them producing something recognisable. They also assert the escalated
retry does not run: a cancelled prompt that still ran it would run the
command the user had just declined.

.release-please-manifest.json

@@ -1 +1 @@
-{".":"0.6.0"}
+{".":"0.7.0"}

AGENTS.md

@@ -91,6 +91,14 @@ These classes drive multi-round reviews. Fix them before requesting review:
   final-component-only no-follow is insufficient. On multi-step setup, roll back
   only what this run created; never destroy pre-existing resources you did
   not create; never report success when cleanup or unlock failed.
+- **Normalize before matching:** Any transform that REMOVES bytes without
+  leaving a gap is also a reassembler, so it has to run before whatever matches
+  on the result. Redacting by shape and then stripping control bytes lets a
+  credential split by a NUL, an ESC or a C1 byte pass the patterns as two
+  fragments and be rejoined on the way out; comparing a path against a form
+  produced by the same resolver the kernel just used makes a redirect agree with
+  itself. Strip, decode, or canonicalize first, then match. The unsplit value
+  passing is not evidence, so the test needs a split case.
 - **Atomic shared state:** Write a complete temporary file, then atomically
   replace the destination so concurrent readers never see a partial write.
   Exclusive create or a write lock alone is not enough for readers. Serialize

CHANGELOG.md

@@ -6,6 +6,42 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 aims to follow [Semantic Versioning](https://semver.org/spec/v2.0.0.html) once the first release is
 tagged. Until then, source builds report the version `dev`.
 
+## [0.7.0](https://github.com/Gitlawb/zero/compare/v0.6.0...v0.7.0) (2026-08-10)
+
+
+### Features
+
+* **agent:** add PermissionModePlan for interactive read-only planning ([#853](https://github.com/Gitlawb/zero/issues/853)) ([0176ee4](https://github.com/Gitlawb/zero/commit/0176ee49ffddcff6f7edf6ae2ade4967e5b22cc3))
+* **providers:** live model lists for OpenRouter and OpenGateway ([#860](https://github.com/Gitlawb/zero/issues/860)) ([fb4f293](https://github.com/Gitlawb/zero/commit/fb4f293c20eb860ca388a10d22fd566ce282ba1f))
+* **tools:** give tool results an image channel and add view_image ([#843](https://github.com/Gitlawb/zero/issues/843)) ([cd0eb19](https://github.com/Gitlawb/zero/commit/cd0eb194e4df4b844785796c0701216740a56344))
+* **tui:** replace /retitle with local /rename ([#826](https://github.com/Gitlawb/zero/issues/826)) ([5886354](https://github.com/Gitlawb/zero/commit/588635487f22ef4d62d350140a219b7b8bb24119))
+
+
+### Bug Fixes
+
+* **agent:** end the additional_permissions retry loop ([#864](https://github.com/Gitlawb/zero/issues/864)) ([4ca4fa7](https://github.com/Gitlawb/zero/commit/4ca4fa75d31b139dbe55a3badf17da86892ab001))
+* **agent:** tell the user a prefix approval leaves the sandbox ([#885](https://github.com/Gitlawb/zero/issues/885)) ([2ec5c3a](https://github.com/Gitlawb/zero/commit/2ec5c3ae6b8fb543887bdeafdb34c4da057b8d36))
+* **cli:** report MCP servers that failed to start ([#822](https://github.com/Gitlawb/zero/issues/822)) ([#827](https://github.com/Gitlawb/zero/issues/827)) ([021281e](https://github.com/Gitlawb/zero/commit/021281ebbab3f2bbe6a77b2dab4bf121bcfe6b52))
+* **lsp:** dispatch notifications off read loop ([#759](https://github.com/Gitlawb/zero/issues/759)) ([936aa4e](https://github.com/Gitlawb/zero/commit/936aa4e77cf49738560a89395b8ba4d22263a396))
+* **mcp:** name the non-text blocks a tool result drops ([#874](https://github.com/Gitlawb/zero/issues/874)) ([027a670](https://github.com/Gitlawb/zero/commit/027a67080bea511b876c284bc911ef011eceb308))
+* **sandbox:** deny reads of Zero credential stores ([#681](https://github.com/Gitlawb/zero/issues/681)) ([55fa05f](https://github.com/Gitlawb/zero/commit/55fa05f0ab5a01b495345d43464606cd19a31b4f))
+* **sandbox:** stop the Windows write jail honouring Everyone-granted paths ([#865](https://github.com/Gitlawb/zero/issues/865)) ([91b413c](https://github.com/Gitlawb/zero/commit/91b413c514cc1607d5b4e7936780d40569239814))
+* **secrets,worktrees:** fix secret redaction leakage and prune stale worktrees ([#855](https://github.com/Gitlawb/zero/issues/855)) ([ff62f73](https://github.com/Gitlawb/zero/commit/ff62f73b7f4dc5e2472db21acba43cf6140c06d1))
+* **specialist:** make overwrites atomic ([#757](https://github.com/Gitlawb/zero/issues/757)) ([30f6d8f](https://github.com/Gitlawb/zero/commit/30f6d8f591a0b81638b4182ff56c86c8a50a5c70))
+* suppress gosec G204 warning for trusted local config commands ([#848](https://github.com/Gitlawb/zero/issues/848)) ([c52db05](https://github.com/Gitlawb/zero/commit/c52db055b0b213758a33c5c5627a411e052f8de4))
+* **tui:** a copied NUL byte no longer panics the TUI on Windows ([#876](https://github.com/Gitlawb/zero/issues/876)) ([cae0269](https://github.com/Gitlawb/zero/commit/cae0269e77e7a0a493cf799b41c653c9ff9a19de)), closes [#875](https://github.com/Gitlawb/zero/issues/875)
+* **tui:** exclude permission waits from turn time ([#820](https://github.com/Gitlawb/zero/issues/820)) ([15eb16f](https://github.com/Gitlawb/zero/commit/15eb16f736f903c94203207032f98aacbcf06318))
+* **tui:** fall back to CellMotion where AllMotion is unreliable ([#872](https://github.com/Gitlawb/zero/issues/872)) ([7fbd864](https://github.com/Gitlawb/zero/commit/7fbd864e91433441489902571ea394ebc5b7bd0d))
+* **tui:** fill alt-screen frame with theme panel background ([#850](https://github.com/Gitlawb/zero/issues/850)) ([020c28e](https://github.com/Gitlawb/zero/commit/020c28eaf95e2f38853f99fc06a13cd1568bf3c9))
+* **tui:** hide unavailable sidebar shortcut ([#821](https://github.com/Gitlawb/zero/issues/821)) ([845df6c](https://github.com/Gitlawb/zero/commit/845df6c7d28e02f475e90acfe838733eb37e6aa2))
+* use OAuth credentials in provider health checks ([#828](https://github.com/Gitlawb/zero/issues/828)) ([d37de92](https://github.com/Gitlawb/zero/commit/d37de9214b1ba86542f4f5ef3b060bb96849763b))
+
+
+### Performance Improvements
+
+* compact common test output ([#846](https://github.com/Gitlawb/zero/issues/846)) ([edf660a](https://github.com/Gitlawb/zero/commit/edf660ab85131f90a452cee51dc2c3a5cf62d632))
+* improve harness context efficiency ([#838](https://github.com/Gitlawb/zero/issues/838)) ([8e26679](https://github.com/Gitlawb/zero/commit/8e266797a8305e689806eadcf9698da2796481ab))
+
 ## [0.6.0](https://github.com/Gitlawb/zero/compare/v0.5.0...v0.6.0) (2026-07-29)
 
 

README.md

@@ -8,6 +8,7 @@
   <a href="LICENSE"><img alt="license" src="https://img.shields.io/badge/license-MIT-blue"></a>
   <img alt="Go 1.26.5+" src="https://img.shields.io/badge/Go-1.26.5+-00ADD8?logo=go&logoColor=white">
   <img alt="25+ providers" src="https://img.shields.io/badge/providers-25+-34E2EA">
+  <a href="https://discord.gg/CaQDS6wdFn"><img alt="Discord" src="https://img.shields.io/badge/Discord-join-5865F2?logo=discord&logoColor=white"></a>
   <br>
   <strong>English</strong> | <a href="README_ZH.md">中文</a>
 </p>
@@ -212,6 +213,7 @@ Common slash commands:
 | `/spec`, `/plan` | draft and review a plan before building |
 | `/image` | attach an image for vision-capable models |
 | `/resume`, `/rewind` | continue or roll back local sessions |
+| `/new` | start a fresh session in place (previous session stays on disk) |
 | `/btw [question]` | ask in an isolated fork without adding the side conversation to the main session |
 | `/loop` | repeat a prompt or custom `/command` on an interval (`/loop 5m /babysit-prs`) or self-paced |
 | `/compact`, `/context` | manage context usage |
@@ -308,7 +310,8 @@ zero verify           detect and run local verification checks
 zero changes          inspect and commit local git changes
 zero usage            token usage and estimated cost
 zero cron             scheduled agent jobs
-zero update           check for newer releases
+zero update --check   check for newer releases
+zero upgrade          download, verify, and install the latest release
 ```
 
 ## Extending Zero
@@ -415,6 +418,8 @@ go run ./cmd/zero-release build --goos windows --goarch amd64 --output dist/zero
 
 ## Community
 
+Real-time chat happens on the [Discord server](https://discord.gg/CaQDS6wdFn).
+
 Questions, setup help, ideas, and sharing all live in
 [GitHub Discussions](https://github.com/Gitlawb/zero/discussions):
 

README_ZH.md

@@ -8,6 +8,7 @@
   <a href="LICENSE"><img alt="license" src="https://img.shields.io/badge/license-MIT-blue"></a>
   <img alt="Go 1.26.5+" src="https://img.shields.io/badge/Go-1.26.5+-00ADD8?logo=go&logoColor=white">
   <img alt="25+ providers" src="https://img.shields.io/badge/providers-25+-34E2EA">
+  <a href="https://discord.gg/CaQDS6wdFn"><img alt="Discord" src="https://img.shields.io/badge/Discord-join-5865F2?logo=discord&logoColor=white"></a>
   <br>
   <a href="README.md">English</a> | <strong>中文</strong>
 </p>
@@ -141,6 +142,7 @@ zero
 | `/spec`、`/plan` | 在构建之前起草和审查计划 |
 | `/image` | 为视觉模型附加图片 |
 | `/resume`、`/rewind` | 继续或回滚本地会话 |
+| `/new` | 原地开始一个新会话（之前的会话仍保留在磁盘上） |
 | `/compact`、`/context` | 管理上下文使用 |
 | `/permissions`、`/tools` | 检查可用工具和策略 |
 | `/add-dir` | 为此会话授予额外的写入目录 |
@@ -226,7 +228,8 @@ zero verify           检测和运行本地验证检查
 zero changes          检查和提交本地 Git 变更
 zero usage            Token 使用量和估算成本
 zero cron             定时智能体任务
-zero update           检查更新版本
+zero update --check   检查更新版本
+zero upgrade          下载、验证并安装最新版本
 ```
 
 ## 外观和无障碍
@@ -269,6 +272,20 @@ go run ./cmd/zero-release build --goos windows --goarch amd64 --output dist/zero
 - [性能](docs/PERFORMANCE.md)
 - [智能体评估](docs/AGENT_EVALS.md)
 
+## 社区
+
+实时交流在 [Discord 服务器](https://discord.gg/CaQDS6wdFn) 进行。
+
+提问、安装帮助、想法和分享都在
+[GitHub Discussions](https://github.com/Gitlawb/zero/discussions)：
+
+| 分类 | 用途 |
+|---|---|
+| [Q&A](https://github.com/Gitlawb/zero/discussions/categories/q-a) | 安装帮助、提供商/模型配置、"如何做"类问题 |
+| [Ideas](https://github.com/Gitlawb/zero/discussions/categories/ideas) | 功能提议和 PR 之前的设计讨论 |
+| [Show and tell](https://github.com/Gitlawb/zero/discussions/categories/show-and-tell) | 你的技能、插件、MCP 配置、主题和工作流 |
+| [Announcements](https://github.com/Gitlawb/zero/discussions/categories/announcements) | 维护者发布的版本和项目动态 |
+
 ## 贡献
 
 欢迎贡献。阅读 [CONTRIBUTING.md](CONTRIBUTING.md)，运行相关测试，然后提交一个聚焦的拉取请求。

docs/INSTALL.md

@@ -234,10 +234,11 @@ directory.
 
 ## Updating
 
-Check for a newer release:
+Check for a newer release, then download, verify, and install it in place:
 
 ```bash
 zero update --check
+zero upgrade
 ```
 
-Then reinstall with npm or rerun the install script for the version you want.
+See the [update guide](UPDATE.md) for update modes, flags, and platform details.

docs/SPECIALISTS.md

@@ -138,3 +138,45 @@ output or stop a still-running task by id.
 If Zero is restarted while a background task is still marked `running`, the new
 manager marks that task `error` and clears its PID. This avoids sending
 `TaskStop` to a stale PID that may now belong to an unrelated process.
+
+## Recovering an Interrupted Overwrite
+
+Zero writes and flushes a complete temporary file before publishing an overwrite,
+so a write failure before publication leaves the existing manifest unchanged
+instead of truncating it. On Unix, publication uses a same-directory rename and
+preserves the existing file's permission bits.
+
+On Windows, Zero uses `ReplaceFileW` to preserve the destination DACL instead of
+silently replacing it with the temporary file's inherited DACL. `ReplaceFileW`
+is not observer-atomic: another process can briefly observe the destination path
+as absent during replacement. Zero serializes specialist loads and managed
+mutations within one process, but cannot synchronize external processes or
+editors.
+
+Windows errors 1176 (`ERROR_UNABLE_TO_MOVE_REPLACEMENT`) and 1177
+(`ERROR_UNABLE_TO_MOVE_REPLACEMENT_2`) are partial replacement failures. With
+Zero's managed backup, 1176 leaves the original names intact and needs no manual
+recovery. For 1177, Zero has moved the original aside and tries to move it back.
+That rollback almost always succeeds, and the failed write changes nothing.
+
+If the rollback itself fails — typically because another process is holding a
+lock on the file — the original is not lost, but it is left under a name Zero
+does not read:
+
+```text
+<specialist dir>/.zero-replace-<random>.backup
+```
+
+Only `*.md` files are loaded as specialists, so until that file is renamed the
+specialist will not appear in `zero specialist list` or resolve by name. Zero's
+error message includes both the backup path and destination path. Recover by
+closing whatever holds the lock and renaming the backup back:
+
+```powershell
+Move-Item .zero-replace-<random>.backup <name>.md
+```
+
+A `.zero-replace-*.backup` can also linger after a *successful* overwrite if the
+backup could not be deleted afterward. That case is reported as a warning rather
+than an error — the new manifest is already in place, and the leftover file is
+safe to delete.

docs/UPDATE.md

@@ -1,16 +1,23 @@
 # Update Flow
 
 `zero update --check` checks the latest GitHub release and compares it with the
-local CLI version.
+local CLI version. `zero update --apply` (or its shorthand, `zero upgrade`)
+downloads, verifies, and installs it.
 
 ```bash
 zero update --check
 zero update --check --json
 zero update --check --repo Gitlawb/zero
 zero update --check --target windows-x64
+
+zero upgrade
+zero update --apply
 ```
 
-The command is intentionally check-only:
+`--check` and `--apply` are mutually exclusive. `zero update` requires one of
+them explicitly; `zero upgrade` is `zero update` with `--apply` implied.
+
+`--check` is check-only:
 
 - It does not replace the running binary.
 - It exits with code `0` when the check succeeds, even when an update is
@@ -19,14 +26,35 @@ The command is intentionally check-only:
 - `--json` prints the same result in a machine-readable format for scripts and
   CI.
 
+`--apply` installs the update in place:
+
+- npm installs delegate to `npm install -g @gitlawb/zero@latest`.
+- Standalone installs download the release archive, verify its checksum,
+  extract it, and atomically replace the running binary plus any installed
+  optional sandbox helpers.
+- On Windows, the running executable is renamed aside and cleaned up on the
+  next `zero update --apply` or `zero upgrade`, since it can't be overwritten
+  while running.
+- `--target` cannot be combined with `--apply`; it only applies to `--check`,
+  since applying always installs onto the current machine.
+- `--repo` and `--endpoint` are ignored when applying to an npm-managed
+  install: that path delegates to `npm install -g @gitlawb/zero@latest` and
+  takes its release from the npm registry, not from GitHub. They still apply to
+  `--check` there.
+- `--json` serializes Zero's final result. For npm-managed installs, npm may
+  also write progress output to stdout, so neither
+  `zero update --apply --json` nor `zero upgrade --json` is guaranteed to
+  produce a single parseable JSON document. Use `--check --json` for
+  machine-readable automation.
+
 Useful flags:
 
 | Flag | Purpose |
 |---|---|
-| `--repo <owner/repo>` | Check another GitHub repository. |
-| `--endpoint <url|owner/repo>` | Check a specific release API URL or repository slug. |
+| `--repo <owner/repo>` | Use another GitHub repository for `--check` and `--apply`/`upgrade`. Ignored by an npm-managed apply. |
+| `--endpoint <url\|owner/repo>` | Use a specific release API URL or repository slug for `--check` and `--apply`/`upgrade`. Ignored by an npm-managed apply. |
 | `--timeout <duration>` | Override the default release check timeout. |
-| `--target <platform-arch>` | Validate release metadata for another supported target. |
+| `--target <platform-arch>` | Validate release metadata for another supported target (`--check` only). |
 
 Supported targets are `linux-x64`, `linux-arm64`, `macos-x64`, `macos-arm64`,
 `windows-x64`, and `windows-arm64`. Without `--target`, Zero checks the current
@@ -40,5 +68,45 @@ Endpoint resolution order:
 4. `https://api.github.com/repos/Gitlawb/zero/releases/latest`
 
 Installer scripts download the matching release asset for the local platform and
-verify its `.sha256` file. If Zero is already installed, run `zero update --check`
-before reinstalling.
+verify its `.sha256` file. If Zero is already installed, run `zero upgrade`
+instead of reinstalling.
+
+## Windows recovery state (standalone installs)
+
+This section describes Windows only. On Linux and macOS a standalone update
+renames the staged file directly over the executable path through the
+installation directory's file descriptor, so the replacement is atomic and no
+aside copy, marker, or recovery record is ever created — a failed update leaves
+the previous binary in place and nothing to resolve.
+
+On Windows, a running executable cannot be replaced in place, so the previous
+binary is moved aside to `<binary>.zero-update-<random>.old` first. The updater
+records that exact file — bound to its filesystem identity, in per-user state
+outside the installation directory — and deletes only that recorded copy after
+the next update is verified in place. Backups it did not create are never
+removed, so a file such as `zero.exe.before-manual-patch.old` is left alone. A
+recorded copy that something else holds open (an on-access scanner, an editor)
+stays recorded and is removed by a later update instead.
+
+An update **refuses to run** while unresolved recovery state exists beside the
+binary:
+
+| State on disk | Meaning |
+|---|---|
+| `<binary>.old` (or `<binary>.<suffix>.old`) plus a `.keep` marker | A previous update could not restore the original binary. The `.old` file may be the last binary the updater verified; the installed one may be unverified. |
+| `<binary>.…old.<suffix>.recovery` | A previous update could not even write the marker, so it moved the last verified binary to that name. |
+| The binary is missing and one or more `*.old` files exist | The previous attempt was interrupted between moves. |
+
+The refusal names the paths involved and the two moves that end the state:
+either move the recovery binary back over the executable path, or — if the
+installed binary is the one you want — delete the `.keep` marker (or the
+`.recovery` copy, once you have verified the installed binary) and update again.
+
+This is deliberately fail-closed and differs from older releases, which deleted
+`<binary>.old` and proceeded. The trade-off is that anyone who can write in the
+installation directory can plant `<binary>.old` and `<binary>.old.keep` there
+and make every subsequent update refuse until an operator clears them. That is
+the safe direction: the alternative is an update that overwrites the only
+verified copy of the previous binary. If updates start refusing, inspect those
+files before removing them — an installation directory that a lower-privileged
+account can write to is itself worth fixing.

go.mod

@@ -1,25 +1,27 @@
 module github.com/Gitlawb/zero
 
-go 1.26.5
+go 1.26.6
 
 require (
 	charm.land/bubbles/v2 v2.1.1
 	charm.land/bubbletea/v2 v2.0.8
 	charm.land/lipgloss/v2 v2.0.5
+	github.com/Microsoft/go-winio v0.6.2
 	github.com/alecthomas/chroma/v2 v2.27.0
 	github.com/atotto/clipboard v0.1.4
 	github.com/aymanbagabas/go-udiff v0.4.1
 	github.com/charmbracelet/colorprofile v0.4.3
+	github.com/charmbracelet/ultraviolet v0.0.0-20260703014108-f5a850f9c2b7
 	github.com/charmbracelet/x/ansi v0.11.7
 	github.com/charmbracelet/x/term v0.2.2
 	github.com/coder/websocket v1.8.15
 	github.com/ledongthuc/pdf v0.0.0-20250511090121-5959a4027728
+	golang.org/x/image v0.45.0
 	golang.org/x/sys v0.47.0
 	mvdan.cc/sh/v3 v3.13.1
 )
 
 require (
-	github.com/charmbracelet/ultraviolet v0.0.0-20260703014108-f5a850f9c2b7 // indirect
 	github.com/charmbracelet/x/exp/golden v0.0.0-20260615092313-b57e5e6d29bb // indirect
 	github.com/charmbracelet/x/termios v0.1.1 // indirect
 	github.com/charmbracelet/x/windows v0.2.2 // indirect

go.sum

@@ -4,6 +4,8 @@ charm.land/bubbletea/v2 v2.0.8 h1:SxTJMhCAI3lbPmy4SgX5LWZ24AdINr4I6UEqzZvYJuY=
 charm.land/bubbletea/v2 v2.0.8/go.mod h1:2SkdgoTXluXJHOUwAoRlRXF/28vklb1rFl6GcgV1/ss=
 charm.land/lipgloss/v2 v2.0.5 h1:kbNxgeeUOYv5J0YdpxFjfvf3dFvqH8Aci4zB6xqFtrY=
 charm.land/lipgloss/v2 v2.0.5/go.mod h1:9oqhxt4yxIMe6q5A4kHr44DremZk7J9UNh74GlWa5nc=
+github.com/Microsoft/go-winio v0.6.2 h1:F2VQgta7ecxGYO8k3ZZz3RS8fVIXVxONVUPlNERoyfY=
+github.com/Microsoft/go-winio v0.6.2/go.mod h1:yd8OoFMLzJbo9gZq8j5qaps8bJ9aShtEA8Ipt1oGCvU=
 github.com/alecthomas/assert/v2 v2.11.0 h1:2Q9r3ki8+JYXvGsDyBXwH3LcJ+WK5D0gc5E8vS6K3D0=
 github.com/alecthomas/assert/v2 v2.11.0/go.mod h1:Bze95FyfUr7x34QZrjL+XP+0qgp/zg8yS+TtBj1WA3k=
 github.com/alecthomas/chroma/v2 v2.27.0 h1:FodwmyOBgJULFYmDqibcp9pvfDLWdtPRh9v/r5BXYZs=
@@ -62,6 +64,10 @@ github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e h1:JVG44RsyaB9T2KIHavM
 github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e/go.mod h1:RbqR21r5mrJuqunuUZ/Dhy/avygyECGrLceyNeo4LiM=
 golang.org/x/exp v0.0.0-20260611194520-c48552f49976 h1:X8Hz2ImujgbmetVuW+w2YkyZChE3cBpZi2P158rTG9M=
 golang.org/x/exp v0.0.0-20260611194520-c48552f49976/go.mod h1:vnf4pv9iKZXY58sQE1L86zmNWJ4159e1RkcWiLCkeEY=
+golang.org/x/image v0.44.0 h1:+tDekMZED9+LrtB3G5xzRggpVh9CARjZqROla3R3R+I=
+golang.org/x/image v0.44.0/go.mod h1:V8K3KE9KKKE+pLpQDOeN18w9oacNSvy1tDOirTu4xtY=
+golang.org/x/image v0.45.0 h1:FMb1nTbH5H9vF55SriQHgFw5GnNL9Jg6L25BwXKzhB0=
+golang.org/x/image v0.45.0/go.mod h1:n62x/7RqlwXDvGsSU4u6IUTUf6KghUZ9Bt7cG/T9Fx4=
 golang.org/x/sync v0.22.0 h1:SZjpbeLmrCk4xhRSZFNZW5gFUeCeFgjekvI/+gfScek=
 golang.org/x/sync v0.22.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
 golang.org/x/sys v0.47.0 h1:o7XGOvZQCADBQQ4Y7VNq2dRWQR7JmOUW8Kxx4ZsNgWs=

internal/acp/agent.go

@@ -296,6 +296,16 @@ func stopReasonFor(result agent.Result, err error) (string, error) {
 		if errors.Is(err, context.Canceled) {
 			return StopCancelled, nil
 		}
+		// A CLIENT THAT CANCELLED A PERMISSION PROMPT DID NOT FAIL. Only
+		// context.Canceled was matched here, so dismissing a permission dialog —
+		// a deliberate action, and for apply_patch the only refusal a client is
+		// offered — came back as JSON-RPC -32603 carrying the internal sentinel
+		// text. Editors and the desktop app both render that as a crashed turn,
+		// so declining a tool looked like ZERO falling over. It is a
+		// cancellation, and StopCancelled is what ACP has for saying so.
+		if errors.Is(err, agent.ErrPermissionApprovalCanceled) {
+			return StopCancelled, nil
+		}
 		return "", err
 	}
 	if result.FinishReason == "length" {
@@ -311,10 +321,14 @@ func stopReasonFor(result agent.Result, err error) (string, error) {
 // session/request_permission request and maps the outcome back. Failure to reach
 // the client fails closed to deny.
 func (a *Agent) requestPermission(ctx context.Context, sessionID string, req agent.PermissionRequest) (agent.PermissionDecision, error) {
+	// Built ONCE and used for both halves. Sending one list and validating the
+	// reply against another is the defect this whole path had; see
+	// decisionFromOutcome.
+	options := buildPermissionOptions(req)
 	params := RequestPermissionParams{
 		SessionID: sessionID,
 		ToolCall:  permissionToolCall(req),
-		Options:   buildPermissionOptions(req),
+		Options:   options,
 	}
 	var result RequestPermissionResult
 	if err := a.conn.Call(ctx, MethodSessionRequestPerm, params, &result); err != nil {
@@ -323,7 +337,7 @@ func (a *Agent) requestPermission(ctx context.Context, sessionID string, req age
 		}
 		return agent.PermissionDecision{Action: agent.PermissionDecisionDeny, Reason: "permission request failed: " + err.Error()}, nil
 	}
-	return decisionFromOutcome(result.Outcome, req.AvailableDecisions), nil
+	return decisionFromOutcome(result.Outcome, options), nil
 }
 
 func (a *Agent) emitPlan(registry *tools.Registry, note *notifier) {
@@ -349,9 +363,11 @@ func (a *Agent) handleSetMode(_ context.Context, params json.RawMessage) (any, e
 	if sess == nil {
 		return nil, RPCError(codeInvalidParams, "unknown session: "+p.SessionID)
 	}
+	sess.turnMu.Lock()
+	defer sess.turnMu.Unlock()
 	mode := agent.PermissionMode(p.ModeID)
 	switch mode {
-	case agent.PermissionModeAuto, agent.PermissionModeAsk:
+	case agent.PermissionModeAuto, agent.PermissionModeAsk, agent.PermissionModePlan:
 		sess.setMode(mode)
 		(&notifier{conn: a.conn, sessionID: sess.id}).currentMode(string(mode))
 		return SetSessionModeResult{}, nil
@@ -381,9 +397,13 @@ func (a *Agent) handleSetConfigOption(_ context.Context, params json.RawMessage)
 			return nil, err
 		}
 	case configIDMode:
+		// Same turnMu as handleSetMode so the two advertised mode doors (session
+		// set_mode and set_config_option) serialize mode flips consistently.
+		sess.turnMu.Lock()
+		defer sess.turnMu.Unlock()
 		mode := agent.PermissionMode(p.Value)
 		switch mode {
-		case agent.PermissionModeAuto, agent.PermissionModeAsk:
+		case agent.PermissionModeAuto, agent.PermissionModeAsk, agent.PermissionModePlan:
 			sess.setMode(mode)
 			(&notifier{conn: a.conn, sessionID: sess.id}).currentMode(string(mode))
 		case agent.PermissionModeUnsafe:
@@ -439,13 +459,16 @@ func (a *Agent) handleCancel(_ context.Context, params json.RawMessage) {
 // ---- advertising helpers ----
 
 func (a *Agent) modeState(s *acpSession) *SessionModeState {
-	// Only auto/ask are offered over ACP; Unsafe is gated to the operator (see
-	// handleSetMode) so a client can't grant itself no-prompt host access.
+	// auto/ask/plan are offered over ACP; Unsafe is gated to the operator (see
+	// handleSetMode) so a client can't grant itself no-prompt host access. Plan
+	// only narrows what a client can do (read-only, no write/shell tools), so
+	// unlike Unsafe there is no elevation risk in letting a client select it.
 	return &SessionModeState{
 		CurrentModeID: string(s.currentMode()),
 		AvailableModes: []SessionMode{
 			{ID: string(agent.PermissionModeAuto), Name: "Auto", Description: "Run safe tools automatically; ask before risky ones."},
 			{ID: string(agent.PermissionModeAsk), Name: "Ask", Description: "Ask before every tool that changes state."},
+			{ID: string(agent.PermissionModePlan), Name: "Plan", Description: "Read-only planning; write and shell tools are hidden."},
 		},
 	}
 }
@@ -516,6 +539,7 @@ func (a *Agent) configOptions(s *acpSession) []SessionConfigOption {
 		Options: []SessionConfigOptionValue{
 			{Value: string(agent.PermissionModeAuto), Name: "Auto", Description: "Run safe tools automatically; ask before risky ones."},
 			{Value: string(agent.PermissionModeAsk), Name: "Ask", Description: "Ask before every tool that changes state."},
+			{Value: string(agent.PermissionModePlan), Name: "Plan", Description: "Read-only planning; write and shell tools are hidden."},
 		},
 	}}
 }

internal/acp/agent_test.go

@@ -393,6 +393,32 @@ func TestACPSetModeUpdatesSession(t *testing.T) {
 	if got := configured.ConfigOptions[1].CurrentValue; got != string(agent.PermissionModeAuto) {
 		t.Fatalf("configured mode = %q", got)
 	}
+	// Plan is accepted: it only narrows capability (read-only), so unlike Unsafe
+	// there is no elevation risk in letting a client select it.
+	if err := h.client.Call(ctx, MethodSessionSetMode, SetSessionModeParams{SessionID: newRes.SessionID, ModeID: string(agent.PermissionModePlan)}, &SetSessionModeResult{}); err != nil {
+		t.Fatalf("set_mode plan: %v", err)
+	}
+	// Configuration path is a separate contract from MethodSessionSetMode: the
+	// mode option is advertised via configOptions and applied by handleSetConfigOption.
+	var planConfigured SetSessionConfigOptionResult
+	if err := h.client.Call(ctx, MethodSessionSetConfigOption, SetSessionConfigOptionParams{
+		SessionID: newRes.SessionID, ConfigID: configIDMode, Value: string(agent.PermissionModePlan),
+	}, &planConfigured); err != nil {
+		t.Fatalf("set_config_option plan: %v", err)
+	}
+	if got := planConfigured.ConfigOptions[1].CurrentValue; got != string(agent.PermissionModePlan) {
+		t.Fatalf("configured mode after plan = %q, want plan", got)
+	}
+	hasPlanOption := false
+	for _, opt := range planConfigured.ConfigOptions[1].Options {
+		if opt.Value == string(agent.PermissionModePlan) {
+			hasPlanOption = true
+			break
+		}
+	}
+	if !hasPlanOption {
+		t.Fatalf("config mode options missing plan: %#v", planConfigured.ConfigOptions[1].Options)
+	}
 	// Unsafe must be rejected over ACP — a client can't self-grant no-prompt host access.
 	if err := h.client.Call(ctx, MethodSessionSetMode, SetSessionModeParams{SessionID: newRes.SessionID, ModeID: string(agent.PermissionModeUnsafe)}, &SetSessionModeResult{}); err == nil {
 		t.Fatal("expected Unsafe mode to be rejected over ACP")
@@ -403,6 +429,37 @@ func TestACPSetModeUpdatesSession(t *testing.T) {
 	}
 }
 
+// TestACPPlanModeWiresPermissionModeIntoAgentOptions confirms selecting "plan"
+// over ACP actually reaches agent.Options.PermissionMode for the next turn —
+// the same gap this test's TUI counterpart covers for /plan on.
+func TestACPPlanModeWiresPermissionModeIntoAgentOptions(t *testing.T) {
+	deps := testDeps(t)
+	var captured agent.Options
+	deps.RunAgent = func(_ context.Context, _ string, _ zeroruntime.Provider, opts agent.Options) (agent.Result, error) {
+		captured = opts
+		return agent.Result{FinalAnswer: "ok"}, nil
+	}
+
+	h := newHarness(t, deps)
+	defer h.stop()
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	var newRes NewSessionResult
+	if err := h.client.Call(ctx, MethodSessionNew, NewSessionParams{Cwd: t.TempDir(), McpServers: []McpServer{}}, &newRes); err != nil {
+		t.Fatalf("session/new: %v", err)
+	}
+	if err := h.client.Call(ctx, MethodSessionSetMode, SetSessionModeParams{SessionID: newRes.SessionID, ModeID: string(agent.PermissionModePlan)}, &SetSessionModeResult{}); err != nil {
+		t.Fatalf("set_mode plan: %v", err)
+	}
+	if err := h.client.Call(ctx, MethodSessionPrompt, PromptParams{SessionID: newRes.SessionID, Prompt: []ContentBlock{TextBlock("plan it out")}}, &PromptResult{}); err != nil {
+		t.Fatalf("session/prompt: %v", err)
+	}
+	if captured.PermissionMode != agent.PermissionModePlan {
+		t.Fatalf("agent.Options.PermissionMode = %q, want plan", captured.PermissionMode)
+	}
+}
+
 // TestACPRunTurnWiresSandboxAndScopedRegistry proves the sandbox engine and the
 // scoped registry from BuildWorkspace actually reach agent.Options — i.e. ACP
 // shell tools run confined, not unconfined on the host.

internal/acp/desktopinterop_test.go

@@ -0,0 +1,217 @@
+package acp
+
+// desktopinterop_test.go covers three defects found by driving the real `zero
+// acp` binary from a desktop ACP client. Each is a case where ZERO and a
+// conforming client disagreed about the wire, and none of them failed loudly —
+// they produced a silent denial, a spurious crash, or two buttons the user
+// could not tell apart.
+//
+// A fourth, session/load restoring history without replaying it, is fixed by
+// #914 rather than here: that one also gives the replayed messages stable ids
+// and keeps session/resume replay-free, which this did not.
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+
+	"github.com/Gitlawb/zero/internal/agent"
+)
+
+// ---- an offered option is an acceptable answer ----
+
+// The list the options were BUILT from and the list the answer was CHECKED
+// against were different whenever ZERO did not enumerate: the client was sent
+// Allow and Reject, and its reply was validated against an empty slice, so
+// every button it could possibly show failed closed to deny. The user clicked
+// Allow and ZERO recorded a denial, with nothing on screen to say so.
+func TestAnOfferedOptionIsAccepted(t *testing.T) {
+	// No AvailableDecisions: the fallback path, which is every permission event
+	// that is not a prompt.
+	req := agent.PermissionRequest{ToolName: "bash"}
+
+	options := buildPermissionOptions(req)
+	if len(options) == 0 {
+		t.Fatal("no options were offered")
+	}
+
+	for _, option := range options {
+		decision := decisionFromOutcome(
+			RequestPermissionOutcome{Outcome: OutcomeSelected, OptionID: option.OptionID},
+			buildPermissionOptions(req),
+		)
+		if string(decision.Action) != option.OptionID {
+			t.Fatalf("option %q was answered with %q (%s) — an offered option must be accepted",
+				option.OptionID, decision.Action, decision.Reason)
+		}
+	}
+}
+
+// The narrowing this validation exists for still holds: a client must not be
+// able to return a broader grant than it was shown.
+func TestAnOptionThatWasNotOfferedIsStillRefused(t *testing.T) {
+	req := agent.PermissionRequest{ToolName: "bash"}
+
+	decision := decisionFromOutcome(
+		RequestPermissionOutcome{Outcome: OutcomeSelected, OptionID: string(agent.PermissionDecisionAlwaysAllow)},
+		buildPermissionOptions(req),
+	)
+	if decision.Action != agent.PermissionDecisionDeny {
+		t.Fatalf("an unoffered broader grant was accepted as %q", decision.Action)
+	}
+}
+
+// The resolver is the single source of truth for both sides, which is what
+// makes the two agree by construction rather than by being kept in step.
+func TestOfferedDecisionsMatchWhatWasSent(t *testing.T) {
+	for _, req := range []agent.PermissionRequest{
+		{ToolName: "bash"},
+		{ToolName: "bash", AvailableDecisions: []agent.PermissionDecisionAction{
+			agent.PermissionDecisionAllow,
+			agent.PermissionDecisionAllowForSession,
+			agent.PermissionDecisionDeny,
+		}},
+	} {
+		offered := buildPermissionOptions(req)
+		for _, option := range buildPermissionOptions(req) {
+			if !actionOffered(option.OptionID, offered) {
+				t.Fatalf("option %q was sent but is not in the offered set %v", option.OptionID, offered)
+			}
+		}
+	}
+}
+
+// ---- two options the user can tell apart ----
+
+// request_permissions offers plain allow and strict-review allow together, and
+// both were labelled "Allow". The label is the only thing an ACP client shows,
+// so the panel presented two identical buttons where one silently enabled
+// strict auto-review of what was granted.
+func TestEveryOfferedOptionHasADistinctLabel(t *testing.T) {
+	req := agent.PermissionRequest{
+		ToolName: "request_permissions",
+		AvailableDecisions: []agent.PermissionDecisionAction{
+			agent.PermissionDecisionAllow,
+			agent.PermissionDecisionAllowStrict,
+			agent.PermissionDecisionAllowForSession,
+			agent.PermissionDecisionDeny,
+		},
+	}
+
+	seen := map[string]string{}
+	for _, option := range buildPermissionOptions(req) {
+		if previous, clash := seen[option.Name]; clash {
+			t.Fatalf("options %q and %q share the label %q — a user cannot tell them apart",
+				previous, option.OptionID, option.Name)
+		}
+		seen[option.Name] = option.OptionID
+	}
+}
+
+// The two remain distinct decisions: the label changed, the round trip did not.
+func TestStrictAllowStillRoundTrips(t *testing.T) {
+	req := agent.PermissionRequest{
+		ToolName: "request_permissions",
+		AvailableDecisions: []agent.PermissionDecisionAction{
+			agent.PermissionDecisionAllow,
+			agent.PermissionDecisionAllowStrict,
+		},
+	}
+	decision := decisionFromOutcome(
+		RequestPermissionOutcome{Outcome: OutcomeSelected, OptionID: string(agent.PermissionDecisionAllowStrict)},
+		buildPermissionOptions(req),
+	)
+	if decision.Action != agent.PermissionDecisionAllowStrict {
+		t.Fatalf("strict allow round-tripped as %q", decision.Action)
+	}
+}
+
+// ---- cancelling a permission is a cancellation, not a crash ----
+
+// Only context.Canceled was recognised, so dismissing a permission dialog came
+// back as JSON-RPC -32603 carrying the internal sentinel text. Clients render
+// that as a failed turn, so declining a tool looked like ZERO falling over —
+// and for apply_patch, dismissing is the ONLY refusal a client is offered.
+func TestCancellingAPermissionEndsTheTurnAsCancelled(t *testing.T) {
+	canceled := fmt.Errorf("%w for apply_patch", agent.ErrPermissionApprovalCanceled)
+
+	reason, err := stopReasonFor(agent.Result{}, canceled)
+	if err != nil {
+		t.Fatalf("stopReasonFor returned an error for a cancellation: %v", err)
+	}
+	if reason != StopCancelled {
+		t.Fatalf("stop reason = %q, want %q", reason, StopCancelled)
+	}
+}
+
+// A genuine failure must still be an error. Mapping too much to cancelled would
+// hide real faults behind a clean ending, which is the opposite mistake.
+func TestARealFailureIsStillAnError(t *testing.T) {
+	failure := errors.New("provider exploded")
+
+	if _, err := stopReasonFor(agent.Result{}, failure); !errors.Is(err, failure) {
+		t.Fatalf("stopReasonFor(%v) = %v, want the failure preserved", failure, err)
+	}
+}
+
+// The sentinel is matched through errors.Is, so it survives the wrapping every
+// return site applies — each one adds the tool name.
+func TestPermissionCancellationSurvivesWrapping(t *testing.T) {
+	if !errors.Is(fmt.Errorf("%w for bash", agent.ErrPermissionApprovalCanceled), agent.ErrPermissionApprovalCanceled) {
+		t.Fatal("a wrapped permission cancellation was not recognised")
+	}
+	if errors.Is(errors.New("something else"), agent.ErrPermissionApprovalCanceled) {
+		t.Fatal("an unrelated error was reported as a permission cancellation")
+	}
+}
+
+// A decision that never became an option cannot be selected.
+//
+// PermissionDecisionCancel is the case that exists today: optionKindFor drops
+// it because ACP expresses cancellation through the outcome, yet ZERO
+// enumerates it in AvailableDecisions for shell commands and apply_patch. While
+// the reply was validated against the DECISIONS rather than the sent options, a
+// client could return {"outcome":"selected","optionId":"cancel"} — an id it was
+// never shown — and abort the whole turn.
+//
+// Written over every option-less decision rather than over "cancel", so a
+// future action that optionKindFor declines to render is covered the day it is
+// added rather than the day someone remembers this test.
+func TestADecisionThatIsNotAnOptionCannotBeSelected(t *testing.T) {
+	for _, toolName := range []string{"bash", "apply_patch"} {
+		req := agent.PermissionRequest{
+			ToolName: toolName,
+			AvailableDecisions: []agent.PermissionDecisionAction{
+				agent.PermissionDecisionAllow,
+				agent.PermissionDecisionDeny,
+				agent.PermissionDecisionCancel,
+			},
+		}
+		options := buildPermissionOptions(req)
+
+		for _, action := range req.AvailableDecisions {
+			if actionOffered(string(action), options) {
+				continue // it was sent; selecting it is legitimate
+			}
+			decision := decisionFromOutcome(
+				RequestPermissionOutcome{Outcome: OutcomeSelected, OptionID: string(action)},
+				options,
+			)
+			if decision.Action != agent.PermissionDecisionDeny {
+				t.Fatalf("%s: %q was never sent as an option but was accepted as %q",
+					toolName, action, decision.Action)
+			}
+		}
+	}
+}
+
+// Cancelling is still reachable — through the outcome, which is where ACP puts
+// it. Closing the selected-id route must not close the real one.
+func TestCancellingThroughTheOutcomeStillWorks(t *testing.T) {
+	options := buildPermissionOptions(agent.PermissionRequest{ToolName: "apply_patch"})
+
+	decision := decisionFromOutcome(RequestPermissionOutcome{Outcome: OutcomeCancelled}, options)
+	if decision.Action != agent.PermissionDecisionCancel {
+		t.Fatalf("outcome=cancelled gave %q, want cancel", decision.Action)
+	}
+}

internal/acp/permission.go

@@ -15,17 +15,10 @@ import (
 // PermissionOptions. Only the actions ZERO actually presented (AvailableDecisions)
 // are surfaced; the optionId is the ZERO action string for a clean round-trip.
 func buildPermissionOptions(req agent.PermissionRequest) []PermissionOption {
-	actions := req.AvailableDecisions
-	if len(actions) == 0 {
-		// Sensible default if ZERO didn't enumerate: allow once / reject.
-		actions = []agent.PermissionDecisionAction{
-			agent.PermissionDecisionAllow,
-			agent.PermissionDecisionDeny,
-		}
-	}
+	actions := offeredDecisions(req)
 	options := make([]PermissionOption, 0, len(actions))
 	for _, action := range actions {
-		kind, name := optionKindFor(action)
+		kind, name := optionKindFor(action, req.PrefixApprovalEscalates)
 		if kind == "" {
 			continue // skip actions that have no clean ACP option (e.g. cancel)
 		}
@@ -38,21 +31,61 @@ func buildPermissionOptions(req agent.PermissionRequest) []PermissionOption {
 	return options
 }
 
+// offeredDecisions resolves what this request actually offers the client.
+//
+// ONE RESOLVER, USED BY BOTH SIDES, and that is the entire point of it existing.
+// The fallback below used to live inside buildPermissionOptions while
+// requestPermission validated the client's answer against the raw
+// req.AvailableDecisions. When ZERO did not enumerate — which is every
+// permission event that is not a prompt, and includes a shell call whose sandbox
+// decision came back deny — the two disagreed completely: the client was sent
+// "Allow" and "Reject", and validation was performed against an EMPTY list, so
+// every option the client could possibly click failed closed to deny with
+// "permission option was not offered".
+//
+// The user clicked Allow and ZERO recorded a denial. Nothing surfaced it,
+// because a denial is a legitimate answer — the tool was simply refused and the
+// turn carried on as though the user had rejected it.
+func offeredDecisions(req agent.PermissionRequest) []agent.PermissionDecisionAction {
+	if len(req.AvailableDecisions) > 0 {
+		return req.AvailableDecisions
+	}
+	// Sensible default if ZERO didn't enumerate: allow once / reject.
+	return []agent.PermissionDecisionAction{
+		agent.PermissionDecisionAllow,
+		agent.PermissionDecisionDeny,
+	}
+}
+
 // optionKindFor maps a ZERO decision action to an ACP PermissionOptionKind and a
 // human label. Returns an empty kind for actions that ACP expresses through the
 // outcome rather than an option (cancel).
-func optionKindFor(action agent.PermissionDecisionAction) (kind, name string) {
+//
+// escalates reports that approving a command prefix will also run the command
+// outside the sandbox. The two prefix options say so in their label, since the
+// label is all an ACP client shows and the option id carries no room for it. An
+// editor user is deciding on exactly the same terms as a terminal user, so the
+// disclosure cannot be TUI-only.
+func optionKindFor(action agent.PermissionDecisionAction, escalates bool) (kind, name string) {
 	switch action {
-	case agent.PermissionDecisionAllow, agent.PermissionDecisionAllowStrict:
+	case agent.PermissionDecisionAllow:
 		return PermAllowOnce, "Allow"
+	case agent.PermissionDecisionAllowStrict:
+		// SPLIT FROM PLAIN ALLOW because the label is the only thing an ACP
+		// client shows. Both were labelled "Allow", and request_permissions
+		// offers them together — so the panel presented two identical buttons,
+		// and whichever the user picked looked the same while one of them
+		// silently turned on strict auto-review of what was granted. The option
+		// id carries no room for the distinction, so it has to be in the name.
+		return PermAllowOnce, "Allow with strict review"
 	case agent.PermissionDecisionAllowForSession:
 		return PermAllowAlways, "Allow for this session"
 	case agent.PermissionDecisionAllowPrefix:
-		return PermAllowAlways, "Allow this command for the session"
+		return PermAllowAlways, withSandboxEscalationNote("Allow this command for the session", escalates)
 	case agent.PermissionDecisionAlwaysAllow:
 		return PermAllowAlways, "Always allow"
 	case agent.PermissionDecisionAlwaysAllowPrefix:
-		return PermAllowAlways, "Always allow this command"
+		return PermAllowAlways, withSandboxEscalationNote("Always allow this command", escalates)
 	case agent.PermissionDecisionDeny:
 		return PermRejectOnce, "Reject"
 	case agent.PermissionDecisionCancel:
@@ -64,19 +97,31 @@ func optionKindFor(action agent.PermissionDecisionAction) (kind, name string) {
 
 // decisionFromOutcome maps the client's permission outcome back to a ZERO
 // decision. A cancelled outcome cancels the run; a selected option id is the ZERO
-// action verbatim (validated against what was offered); anything unrecognized
-// fails closed to deny.
-func decisionFromOutcome(outcome RequestPermissionOutcome, offered []agent.PermissionDecisionAction) agent.PermissionDecision {
+// action verbatim (validated against what was actually sent); anything
+// unrecognized fails closed to deny.
+//
+// IT TAKES THE OPTIONS THAT WERE SENT, not the decisions the request offered,
+// and the two are not the same list. Some actions never become options —
+// PermissionDecisionCancel is dropped by optionKindFor because ACP expresses
+// cancellation through the outcome instead — yet it IS enumerated in
+// AvailableDecisions for shell commands and apply_patch, the two commonest
+// prompts. Validating against the decisions therefore accepted
+// {"outcome":"selected","optionId":"cancel"}: an identifier no client was ever
+// shown, aborting the whole turn.
+//
+// Passing the sent options makes "what we offered" and "what we accept" the
+// same slice rather than two things kept in step, so anything optionKindFor
+// declines to render is excluded structurally instead of by name.
+func decisionFromOutcome(outcome RequestPermissionOutcome, offered []PermissionOption) agent.PermissionDecision {
 	switch outcome.Outcome {
 	case OutcomeCancelled:
 		return agent.PermissionDecision{Action: agent.PermissionDecisionCancel, Reason: "client cancelled"}
 	case OutcomeSelected:
-		action := agent.PermissionDecisionAction(outcome.OptionID)
 		// Bind to what was actually offered for THIS call: a client must not be able
 		// to return a broader grant (always_allow / allow_for_session) that wasn't
 		// presented. Anything not offered fails closed to deny.
-		if actionOffered(action, offered) {
-			return agent.PermissionDecision{Action: action}
+		if actionOffered(outcome.OptionID, offered) {
+			return agent.PermissionDecision{Action: agent.PermissionDecisionAction(outcome.OptionID)}
 		}
 		return agent.PermissionDecision{Action: agent.PermissionDecisionDeny, Reason: "permission option was not offered"}
 	default:
@@ -84,9 +129,9 @@ func decisionFromOutcome(outcome RequestPermissionOutcome, offered []agent.Permi
 	}
 }
 
-func actionOffered(action agent.PermissionDecisionAction, offered []agent.PermissionDecisionAction) bool {
-	for _, a := range offered {
-		if a == action {
+func actionOffered(optionID string, offered []PermissionOption) bool {
+	for _, option := range offered {
+		if option.OptionID == optionID {
 			return true
 		}
 	}
@@ -123,3 +168,13 @@ func rawInputBytes(data []byte) json.RawMessage {
 	}
 	return json.RawMessage(data)
 }
+
+// withSandboxEscalationNote appends the escalation disclosure to a prefix
+// option's label. Kept parallel to the TUI's wording so the same consequence is
+// not described two different ways depending on which client the user runs.
+func withSandboxEscalationNote(name string, escalates bool) string {
+	if !escalates {
+		return name
+	}
+	return name + " (runs outside the sandbox)"
+}

internal/acp/permission_escalation_test.go

@@ -0,0 +1,69 @@
+package acp
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/Gitlawb/zero/internal/agent"
+)
+
+func escalationRequest(escalates bool) agent.PermissionRequest {
+	return agent.PermissionRequest{
+		ToolName: "bash",
+		AvailableDecisions: []agent.PermissionDecisionAction{
+			agent.PermissionDecisionAllow,
+			agent.PermissionDecisionAllowPrefix,
+			agent.PermissionDecisionAlwaysAllowPrefix,
+			agent.PermissionDecisionDeny,
+		},
+		PrefixApprovalEscalates: escalates,
+	}
+}
+
+// An ACP client renders only Name, so if the escalation is not in the label the
+// editor user approves it blind. They face exactly the outcome a terminal user
+// faces, so the disclosure has to reach both clients or it is not a fix.
+func TestACPPrefixOptionsDiscloseLeavingTheSandbox(t *testing.T) {
+	found := 0
+	for _, option := range buildPermissionOptions(escalationRequest(true)) {
+		action := agent.PermissionDecisionAction(option.OptionID)
+		if action != agent.PermissionDecisionAllowPrefix && action != agent.PermissionDecisionAlwaysAllowPrefix {
+			if strings.Contains(option.Name, "sandbox") {
+				t.Errorf("option %q carries the disclosure but does not escalate", option.Name)
+			}
+			continue
+		}
+		found++
+		if !strings.Contains(option.Name, "outside the sandbox") {
+			t.Errorf("prefix option %q does not say the command leaves the sandbox", option.Name)
+		}
+	}
+	if found != 2 {
+		t.Fatalf("expected both prefix options, saw %d", found)
+	}
+}
+
+func TestACPPrefixOptionsStaySilentWithoutEscalation(t *testing.T) {
+	for _, option := range buildPermissionOptions(escalationRequest(false)) {
+		if strings.Contains(option.Name, "sandbox") {
+			t.Errorf("option %q warns about the sandbox when approving would not leave it", option.Name)
+		}
+	}
+}
+
+// The disclosure must live in the label only. The option id is the decision
+// action round-tripped verbatim, and decisionFromOutcome matches it against
+// what was offered, so decorating it would fail every prefix approval closed.
+func TestACPDisclosureDoesNotDisturbTheOptionIDRoundTrip(t *testing.T) {
+	request := escalationRequest(true)
+	options := buildPermissionOptions(request)
+	for _, option := range options {
+		decision := decisionFromOutcome(
+			RequestPermissionOutcome{Outcome: OutcomeSelected, OptionID: option.OptionID},
+			options,
+		)
+		if string(decision.Action) != option.OptionID {
+			t.Errorf("option id %q round-tripped to %q (%s)", option.OptionID, decision.Action, decision.Reason)
+		}
+	}
+}

internal/acp/permission_test.go

@@ -39,11 +39,14 @@ func TestBuildPermissionOptionsDefault(t *testing.T) {
 }
 
 func TestDecisionFromOutcome(t *testing.T) {
-	offered := []agent.PermissionDecisionAction{
-		agent.PermissionDecisionAllow,
-		agent.PermissionDecisionAlwaysAllow,
-		agent.PermissionDecisionDeny,
-	}
+	offered := buildPermissionOptions(agent.PermissionRequest{
+		ToolName: "bash",
+		AvailableDecisions: []agent.PermissionDecisionAction{
+			agent.PermissionDecisionAllow,
+			agent.PermissionDecisionAlwaysAllow,
+			agent.PermissionDecisionDeny,
+		},
+	})
 	if d := decisionFromOutcome(RequestPermissionOutcome{Outcome: OutcomeCancelled}, offered); d.Action != agent.PermissionDecisionCancel {
 		t.Errorf("cancelled -> %q, want cancel", d.Action)
 	}

internal/agent/compaction.go

@@ -38,8 +38,9 @@ const compactionTriggerRatio = 0.7
 // transcript (and so tests can assert on it).
 const summaryLabel = "[Summary of earlier conversation]"
 
-// summaryInstructions is the system prompt handed to the summarizer model.
-const summaryInstructions = "You are compacting a coding-assistant conversation to save context. " +
+// CompactionSummaryInstructions is the system prompt handed to both automatic
+// and manually requested compaction summarizers.
+const CompactionSummaryInstructions = "You are compacting a coding-assistant conversation to save context. " +
 	"Write a dense, factual summary of the conversation so far. Preserve: the user's goals and explicit constraints; " +
 	"decisions made and why; files created or modified (with paths) and key code changes; commands run and their important " +
 	"results; and anything still in progress or unresolved. Omit pleasantries. Use terse bullet points. Do not invent details. " +
@@ -75,6 +76,12 @@ type CompactionResult struct {
 	// summary message also includes summaryLabel and any preserved structured
 	// state needed by later compactions.
 	SummaryText string
+	// ProjectedChars is the text content sent to the summarizer after semantic
+	// projection, excluding provider protocol framing.
+	ProjectedChars int
+	// Truncated reports whether projection dropped content to satisfy its
+	// bounded brief or previous-summary limits.
+	Truncated bool
 	// Compacted reports whether Messages contains an injected summary.
 	Compacted bool
 }
@@ -216,11 +223,11 @@ func CompactMessages(messages []zeroruntime.Message, opts CompactionOptions) (Co
 		}, nil
 	}
 
-	summary, err := opts.Summarize(middle)
+	summaryResult, err := SummarizeCompactionMessages(middle, opts.Summarize)
 	if err != nil {
 		return CompactionResult{}, err
 	}
-	summary = strings.TrimSpace(summary)
+	summary := summaryResult.SummaryText
 
 	// Preserve structured state (active plan + loaded skills) from the elided
 	// middle verbatim, so it is not lost or paraphrased away by the prose summary.
@@ -238,10 +245,53 @@ func CompactMessages(messages []zeroruntime.Message, opts CompactionOptions) (Co
 		RemovedCount:   len(middle),
 		PreservedCount: len(messages) - len(middle),
 		SummaryText:    summary,
+		ProjectedChars: summaryResult.ProjectedChars,
+		Truncated:      summaryResult.Truncated,
 		Compacted:      true,
 	}, nil
 }
 
+// CompactionSummaryResult describes the shared summarization input and output.
+type CompactionSummaryResult struct {
+	SummaryText    string
+	ProjectedChars int
+	Truncated      bool
+}
+
+// SummarizeCompactionMessages applies the shared semantic projection before
+// invoking a caller-supplied summarizer. Automatic context-pressure compaction
+// and manual session compaction both use this path.
+func SummarizeCompactionMessages(messages []zeroruntime.Message, summarize func([]zeroruntime.Message) (string, error)) (CompactionSummaryResult, error) {
+	if summarize == nil {
+		return CompactionSummaryResult{}, errors.New("compaction requires a Summarize function")
+	}
+	projection := projectCompactionInput(messages)
+	summaryInput := projection.messages
+	if len(summaryInput) == 0 {
+		summaryInput = messages
+	}
+	summary, err := summarize(summaryInput)
+	if err != nil {
+		return CompactionSummaryResult{}, err
+	}
+	return CompactionSummaryResult{
+		SummaryText:    strings.TrimSpace(summary),
+		ProjectedChars: compactionMessageChars(summaryInput),
+		Truncated:      projection.truncated,
+	}, nil
+}
+
+func compactionMessageChars(messages []zeroruntime.Message) int {
+	total := 0
+	for _, message := range messages {
+		total += len(message.Content)
+		for _, call := range message.ToolCalls {
+			total += len(call.Name) + len(call.Arguments)
+		}
+	}
+	return total
+}
+
 // safeSuffixBoundary walks the preserve boundary backward (toward systemEnd) so
 // the preserved suffix begins on a user or assistant message rather than a
 // tool/tool_result message. A tool result with no preceding assistant tool call
@@ -331,6 +381,8 @@ type compactionState struct {
 	// but its token COST must still be counted so usage reports and budgets include it.
 	onUsage func(Usage)
 	task    *taskState
+	planner *contextPlanner
+	trace   *trace.Recorder
 
 	// calibrationRatio scales the raw byte/4 token estimate toward the provider's
 	// real prompt-token count. ApproxTextTokens over-counts code-heavy content by
@@ -377,6 +429,8 @@ func newCompactionState(options Options, task *taskState) *compactionState {
 		preserveLast: options.CompactionPreserveLast,
 		onUsage:      options.OnUsage,
 		task:         task,
+		planner:      newContextPlanner(contextPlannerConfig{contextWindow: options.ContextWindow, serviceTier: options.ServiceTier}),
+		trace:        options.Trace,
 	}
 	return state
 }
@@ -432,7 +486,7 @@ func (state *compactionState) maybeCompact(
 
 	compacted, err := Compact(messages, CompactionOptions{
 		PreserveLast: state.preserveLast,
-		Summarize:    summarizeClosure(ctx, provider, state.onUsage),
+		Summarize:    state.summarizeClosure(ctx, provider),
 		taskState:    state.task.snapshotForCompaction(messages),
 	})
 	if err != nil {
@@ -483,7 +537,7 @@ func (state *compactionState) recover(
 
 	result, compactErr := Compact(messages, CompactionOptions{
 		PreserveLast: state.preserveLast,
-		Summarize:    summarizeClosure(ctx, provider, state.onUsage),
+		Summarize:    state.summarizeClosure(ctx, provider),
 		taskState:    state.task.snapshotForCompaction(messages),
 	})
 	if compactErr != nil {
@@ -517,9 +571,12 @@ func (state *compactionState) recover(
 // provider call. The summary stream intentionally does NOT forward OnText (so
 // compaction stays invisible on the user-facing surface), but it DOES forward
 // OnUsage so the summarizer's token cost is still counted by usage/budgeting.
-func summarizeClosure(ctx context.Context, provider Provider, onUsage func(Usage)) func([]zeroruntime.Message) (string, error) {
+func (state *compactionState) summarizeClosure(ctx context.Context, provider Provider) func([]zeroruntime.Message) (string, error) {
+	if state.planner == nil {
+		state.planner = newContextPlanner(contextPlannerConfig{})
+	}
 	return func(toSummarize []zeroruntime.Message) (string, error) {
-		return summarizeWithFallback(ctx, provider, toSummarize, onUsage)
+		return summarizeWithPlanner(ctx, provider, toSummarize, state.onUsage, state.planner, state.trace)
 	}
 }
 
@@ -531,7 +588,11 @@ func summarizeClosure(ctx context.Context, provider Provider, onUsage func(Usage
 // Non-context-limit errors (and a single message that still won't fit) surface
 // to the caller unchanged.
 func summarizeWithFallback(ctx context.Context, provider Provider, messages []zeroruntime.Message, onUsage func(Usage)) (string, error) {
-	summary, err := summarizeMessagesOnce(ctx, provider, messages, onUsage)
+	return summarizeWithPlanner(ctx, provider, messages, onUsage, newContextPlanner(contextPlannerConfig{}), nil)
+}
+
+func summarizeWithPlanner(ctx context.Context, provider Provider, messages []zeroruntime.Message, onUsage func(Usage), planner *contextPlanner, recorder *trace.Recorder) (string, error) {
+	summary, err := summarizeMessagesOnce(ctx, provider, messages, onUsage, planner, recorder)
 	if err == nil {
 		return summary, nil
 	}
@@ -540,11 +601,11 @@ func summarizeWithFallback(ctx context.Context, provider Provider, messages []ze
 	}
 
 	mid := len(messages) / 2
-	left, leftErr := summarizeWithFallback(ctx, provider, messages[:mid], onUsage)
+	left, leftErr := summarizeWithPlanner(ctx, provider, messages[:mid], onUsage, planner, recorder)
 	if leftErr != nil {
 		return "", leftErr
 	}
-	right, rightErr := summarizeWithFallback(ctx, provider, messages[mid:], onUsage)
+	right, rightErr := summarizeWithPlanner(ctx, provider, messages[mid:], onUsage, planner, recorder)
 	if rightErr != nil {
 		return "", rightErr
 	}
@@ -557,7 +618,7 @@ func summarizeWithFallback(ctx context.Context, provider Provider, messages []ze
 	combined := strings.TrimSpace(left + "\n\n" + right)
 	reduced, reduceErr := summarizeMessagesOnce(ctx, provider, []zeroruntime.Message{
 		{Role: zeroruntime.MessageRoleUser, Content: combined},
-	}, onUsage)
+	}, onUsage, planner, recorder)
 	if reduceErr != nil {
 		if isContextLimitError(reduceErr.Error()) {
 			// Even the two combined partials don't fit (extreme): fall back to the
@@ -573,15 +634,15 @@ func summarizeWithFallback(ctx context.Context, provider Provider, messages []ze
 }
 
 // summarizeMessagesOnce performs a single tool-less summarization call.
-func summarizeMessagesOnce(ctx context.Context, provider Provider, messages []zeroruntime.Message, onUsage func(Usage)) (string, error) {
-	request := zeroruntime.CompletionRequest{
-		Messages: []zeroruntime.Message{
-			{Role: zeroruntime.MessageRoleSystem, Content: summaryInstructions},
-			{Role: zeroruntime.MessageRoleUser, Content: "Summarize this conversation:\n\n" + renderTranscript(messages)},
-		},
-		// No tools: this is a plain text summarization call.
+func summarizeMessagesOnce(ctx context.Context, provider Provider, messages []zeroruntime.Message, onUsage func(Usage), planner *contextPlanner, recorder *trace.Recorder) (string, error) {
+	requestMessages := []zeroruntime.Message{
+		{Role: zeroruntime.MessageRoleSystem, Content: CompactionSummaryInstructions},
+		{Role: zeroruntime.MessageRoleUser, Content: "Summarize this conversation:\n\n" + renderTranscript(messages)},
 	}
-	stream, err := provider.StreamCompletion(ctx, request)
+	parts := systemPromptParts{prompt: CompactionSummaryInstructions, baseInstructions: CompactionSummaryInstructions}
+	plan := planner.planWithPromptParts(requestMessages, nil, "", parts)
+	recordContextPlanTrace(recorder, plan)
+	stream, err := provider.StreamCompletion(ctx, plan.Request)
 	if err != nil {
 		return "", err
 	}

internal/agent/compaction_metadata_test.go

@@ -43,8 +43,14 @@ func TestCompactMessagesReturnsMetadataForManualCompaction(t *testing.T) {
 	if result.SummaryText != "manual summary" {
 		t.Fatalf("SummaryText = %q, want trimmed summary", result.SummaryText)
 	}
-	if len(captured) != 3 || captured[0].Content != "first question" || captured[2].Content != "second question" {
-		t.Fatalf("summarized middle = %#v, want the three non-preserved non-system messages", captured)
+	if result.ProjectedChars != compactionMessageChars(captured) || result.ProjectedChars == 0 {
+		t.Fatalf("ProjectedChars = %d, want %d", result.ProjectedChars, compactionMessageChars(captured))
+	}
+	if result.Truncated {
+		t.Fatal("Truncated = true for a projection within its limits")
+	}
+	if len(captured) != 1 || !strings.Contains(captured[0].Content, "first question") || !strings.Contains(captured[0].Content, "second question") {
+		t.Fatalf("summarized projection = %#v, want intent from the non-preserved middle", captured)
 	}
 	if len(result.Messages) != 4 {
 		t.Fatalf("compacted message count = %d, want 4", len(result.Messages))
@@ -96,11 +102,46 @@ func TestCompactMessagesNoopReturnsUncompactedMetadata(t *testing.T) {
 	if result.SummaryText != "" {
 		t.Fatalf("SummaryText = %q, want empty", result.SummaryText)
 	}
+	if result.ProjectedChars != 0 || result.Truncated {
+		t.Fatalf("no-op projection metadata = (%d, %t), want zero values", result.ProjectedChars, result.Truncated)
+	}
 	if !reflect.DeepEqual(result.Messages, messages) {
 		t.Fatalf("Messages changed on no-op: %#v", result.Messages)
 	}
 }
 
+func TestCompactMessagesReturnsTruncatedProjectionMetadata(t *testing.T) {
+	messages := []zeroruntime.Message{{Role: zeroruntime.MessageRoleSystem, Content: "system"}}
+	for index := range 20 {
+		messages = append(messages, zeroruntime.Message{
+			Role:    zeroruntime.MessageRoleUser,
+			Content: strings.Repeat("contextword ", 256) + string(rune('a'+index)),
+		})
+	}
+	messages = append(messages,
+		zeroruntime.Message{Role: zeroruntime.MessageRoleAssistant, Content: "recent answer"},
+		zeroruntime.Message{Role: zeroruntime.MessageRoleUser, Content: "latest question"},
+	)
+
+	var captured []zeroruntime.Message
+	result, err := CompactMessages(messages, CompactionOptions{
+		PreserveLast: 2,
+		Summarize: func(toSummarize []zeroruntime.Message) (string, error) {
+			captured = append([]zeroruntime.Message(nil), toSummarize...)
+			return "bounded summary", nil
+		},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !result.Compacted || !result.Truncated {
+		t.Fatalf("compaction metadata = compacted %t, truncated %t; want both true", result.Compacted, result.Truncated)
+	}
+	if result.ProjectedChars != compactionMessageChars(captured) || result.ProjectedChars == 0 {
+		t.Fatalf("ProjectedChars = %d, want %d", result.ProjectedChars, compactionMessageChars(captured))
+	}
+}
+
 func TestCompactMessagesPropagatesSummarizeError(t *testing.T) {
 	messages := []zeroruntime.Message{
 		{Role: zeroruntime.MessageRoleSystem, Content: "system"},

internal/agent/compaction_preserve.go

@@ -102,7 +102,7 @@ type skillEntry struct {
 	body string
 }
 
-// recentEdits returns the files mutated by write_file/edit_file calls in messages
+// recentEdits returns files mutated by editing calls in messages
 // — latest note per path, in last-seen order — as skillEntry{name: path, body:
 // note}. After compaction elides the editing turns, this tells the model WHAT it
 // changed in each file (from the tool's result) so it need not re-read to
@@ -113,6 +113,7 @@ type skillEntry struct {
 // rather than an earlier, now-stale entry.
 func recentEdits(messages []zeroruntime.Message) []skillEntry {
 	pathByID := map[string]string{}
+	noteByPath := map[string]string{}
 	sequence := make([]string, 0)
 	for _, message := range messages {
 		for _, call := range message.ToolCalls {
@@ -129,12 +130,24 @@ func recentEdits(messages []zeroruntime.Message) []skillEntry {
 			sequence = append(sequence, path)
 		}
 	}
+	for _, message := range messages {
+		if message.Role != zeroruntime.MessageRoleTool || len(message.ChangedFiles) == 0 {
+			continue
+		}
+		for _, path := range message.ChangedFiles {
+			path = strings.TrimSpace(path)
+			if path == "" {
+				continue
+			}
+			sequence = append(sequence, path)
+			noteByPath[path] = editNote(message.Content)
+		}
+	}
 	order := lastSeenOrder(sequence)
 	if len(order) == 0 {
 		return nil
 	}
 
-	noteByPath := map[string]string{}
 	for _, message := range messages {
 		if message.Role != zeroruntime.MessageRoleTool || message.ToolCallID == "" {
 			continue
@@ -425,15 +438,20 @@ type preservedState struct {
 }
 
 type preservedTaskState struct {
-	Objective           string     `json:"objective"`
-	Status              taskStatus `json:"status,omitempty"`
-	Pending             int        `json:"pending,omitempty"`
-	InProgress          int        `json:"in_progress,omitempty"`
-	Completed           int        `json:"completed,omitempty"`
-	Failed              int        `json:"failed,omitempty"`
-	VerificationPassed  int        `json:"verification_passed,omitempty"`
-	VerificationFailed  int        `json:"verification_failed,omitempty"`
-	VerificationOutcome Outcome    `json:"verification_outcome,omitempty"`
+	Objective           string              `json:"objective"`
+	Status              taskStatus          `json:"status,omitempty"`
+	Pending             int                 `json:"pending,omitempty"`
+	InProgress          int                 `json:"in_progress,omitempty"`
+	Completed           int                 `json:"completed,omitempty"`
+	Failed              int                 `json:"failed,omitempty"`
+	VerificationPassed  int                 `json:"verification_passed,omitempty"`
+	VerificationFailed  int                 `json:"verification_failed,omitempty"`
+	VerificationOutcome Outcome             `json:"verification_outcome,omitempty"`
+	Constraints         []string            `json:"constraints,omitempty"`
+	ChangedFiles        []string            `json:"changed_files,omitempty"`
+	UnresolvedFailures  []taskFailureState  `json:"unresolved_failures,omitempty"`
+	Approvals           []taskApprovalState `json:"approvals,omitempty"`
+	Artifacts           []taskArtifactState `json:"artifacts,omitempty"`
 }
 
 type preservedEdit struct {
@@ -468,7 +486,12 @@ func appendPreservedState(summary string, middle []zeroruntime.Message, taskSnap
 	task := priorState.Task
 	if taskSnapshot != nil {
 		task = &preservedTaskState{
-			Objective: capTaskObjective(taskSnapshot.Objective),
+			Objective:          capTaskObjective(taskSnapshot.Objective),
+			Constraints:        mergeBoundedComparable(priorTaskConstraints(priorState.Task), taskSnapshot.Constraints, maxTaskConstraints),
+			ChangedFiles:       mergeBoundedComparable(priorTaskChangedFiles(priorState.Task), taskSnapshot.ChangedFiles, maxTaskEvidenceEntries),
+			UnresolvedFailures: mergeTaskFailures(priorTaskFailures(priorState.Task), taskSnapshot.UnresolvedFailures, taskSnapshot.ResolvedFailureKeys),
+			Approvals:          mergeBoundedComparable(priorTaskApprovals(priorState.Task), taskSnapshot.Approvals, maxTaskEvidenceEntries),
+			Artifacts:          mergeBoundedComparable(priorTaskArtifacts(priorState.Task), taskSnapshot.Artifacts, maxTaskEvidenceEntries),
 		}
 		// Plan parity corroborates only the mutable task projection. The objective
 		// comes directly from the run prompt and is immutable, so it must survive
@@ -484,6 +507,13 @@ func appendPreservedState(summary string, middle []zeroruntime.Message, taskSnap
 			task.VerificationOutcome = taskSnapshot.Verification.LastOutcome
 		}
 	}
+	freshConstraints := explicitConstraintsFromMessages(middle)
+	if len(freshConstraints) > 0 {
+		if task == nil {
+			task = &preservedTaskState{}
+		}
+		task.Constraints = mergeBoundedComparable(task.Constraints, freshConstraints, maxTaskConstraints)
+	}
 
 	// Plan: a fresh update_plan in middle is authoritative; otherwise carry the
 	// plan preserved by an earlier compaction.
@@ -517,6 +547,95 @@ func appendPreservedState(summary string, middle []zeroruntime.Message, taskSnap
 	return summary
 }
 
+func explicitConstraintsFromMessages(messages []zeroruntime.Message) []string {
+	var constraints []string
+	for _, message := range messages {
+		if message.Role != zeroruntime.MessageRoleUser || strings.Contains(message.Content, preservedStateLabel) {
+			continue
+		}
+		if _, body := projectInstructionBlock(message.Content); body != "" {
+			continue
+		}
+		constraints = mergeBoundedComparable(constraints, extractExplicitConstraints(message.Content), maxTaskConstraints)
+	}
+	return constraints
+}
+
+func priorTaskConstraints(task *preservedTaskState) []string {
+	if task == nil {
+		return nil
+	}
+	return task.Constraints
+}
+
+func priorTaskChangedFiles(task *preservedTaskState) []string {
+	if task == nil {
+		return nil
+	}
+	return task.ChangedFiles
+}
+
+func priorTaskFailures(task *preservedTaskState) []taskFailureState {
+	if task == nil {
+		return nil
+	}
+	return task.UnresolvedFailures
+}
+
+func priorTaskApprovals(task *preservedTaskState) []taskApprovalState {
+	if task == nil {
+		return nil
+	}
+	return task.Approvals
+}
+
+func priorTaskArtifacts(task *preservedTaskState) []taskArtifactState {
+	if task == nil {
+		return nil
+	}
+	return task.Artifacts
+}
+
+func mergeTaskFailures(older, newer []taskFailureState, resolved []string) []taskFailureState {
+	resolvedSet := make(map[string]struct{}, len(resolved))
+	for _, key := range resolved {
+		resolvedSet[key] = struct{}{}
+	}
+	merged := make([]taskFailureState, 0, len(older)+len(newer))
+	for _, failure := range append(append([]taskFailureState(nil), older...), newer...) {
+		if _, ok := resolvedSet[failure.Key]; ok {
+			continue
+		}
+		withoutSameKey := make([]taskFailureState, 0, len(merged))
+		for _, existing := range merged {
+			if existing.Key != failure.Key {
+				withoutSameKey = append(withoutSameKey, existing)
+			}
+		}
+		merged = append(withoutSameKey, failure)
+	}
+	if len(merged) > maxTaskEvidenceEntries {
+		merged = merged[len(merged)-maxTaskEvidenceEntries:]
+	}
+	return merged
+}
+
+func mergeBoundedComparable[T comparable](older, newer []T, limit int) []T {
+	merged := make([]T, 0, len(older)+len(newer))
+	seen := make(map[T]struct{}, len(older)+len(newer))
+	for _, value := range append(append([]T(nil), older...), newer...) {
+		if _, ok := seen[value]; ok {
+			continue
+		}
+		seen[value] = struct{}{}
+		merged = append(merged, value)
+	}
+	if len(merged) > limit {
+		merged = merged[len(merged)-limit:]
+	}
+	return merged
+}
+
 func capTaskObjective(objective string) string {
 	objective = strings.TrimSpace(objective)
 	if len(objective) <= maxTaskObjectiveBytes {

internal/agent/compaction_preserve_test.go

@@ -6,6 +6,7 @@ import (
 	"testing"
 	"unicode/utf8"
 
+	"github.com/Gitlawb/zero/internal/tools"
 	"github.com/Gitlawb/zero/internal/zeroruntime"
 )
 
@@ -64,6 +65,9 @@ func TestCompactPreservesBoundedTaskContext(t *testing.T) {
 	objective := strings.Repeat("世", maxTaskObjectiveBytes)
 	task := newTaskState(objective, nil)
 	task.observe(taskStateEvent{kind: taskStateEventPlan, arguments: `{"plan":[{"content":"write code","status":"in_progress"},{"content":"add tests","status":"pending"}]}`})
+	task.observe(taskStateEvent{kind: taskStateEventToolResult, arguments: `{"patch":"*** Update File: internal/db.go"}`, toolResult: ToolResult{
+		Name: "apply_patch", Status: tools.StatusOK, Output: "Done!", ChangedFiles: []string{"internal/db.go"},
+	}})
 	messages := stateConversation()
 	compacted, err := Compact(messages, CompactionOptions{
 		PreserveLast: 2,
@@ -80,6 +84,69 @@ func TestCompactPreservesBoundedTaskContext(t *testing.T) {
 	if len(state.Task.Objective) > maxTaskObjectiveBytes || !utf8.ValidString(state.Task.Objective) {
 		t.Fatalf("objective was not safely bounded: %d bytes %q", len(state.Task.Objective), state.Task.Objective)
 	}
+	if len(state.Task.ChangedFiles) != 1 || state.Task.ChangedFiles[0] != "internal/db.go" {
+		t.Fatalf("changed files were not preserved: %#v", state.Task.ChangedFiles)
+	}
+}
+
+func TestCompactPreservesRuntimeEvidenceAcrossRepeatedCompaction(t *testing.T) {
+	task := newTaskState("Please keep the change focused.", nil)
+	task.observe(taskStateEvent{kind: taskStateEventToolResult, arguments: `{"cmd":"go test ./..."}`, toolResult: ToolResult{
+		Name: "exec_command", Status: tools.StatusError, Output: "Error: tests failed",
+		Meta: map[string]string{"spill_path": ".zero/artifacts/tests.txt"},
+	}})
+	task.observe(taskStateEvent{kind: taskStateEventPermission, permission: PermissionEvent{
+		ToolName: "exec_command", DecisionAction: PermissionDecisionAllowForSession, Scope: "/tmp",
+	}})
+	messages := stateConversation()
+
+	first, err := Compact(messages, CompactionOptions{
+		PreserveLast: 2,
+		Summarize:    func([]zeroruntime.Message) (string, error) { return "FIRST", nil },
+		taskState:    task.snapshotForCompaction(messages),
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	task.observe(taskStateEvent{kind: taskStateEventToolResult, arguments: `{"cmd":"go test ./..."}`, toolResult: ToolResult{
+		Name: "exec_command", Status: tools.StatusError, Output: "Error: tests still fail with newer evidence",
+		Meta: map[string]string{"spill_path": ".zero/artifacts/tests.txt"},
+	}})
+	secondInput := append(append([]zeroruntime.Message{}, first...),
+		zeroruntime.Message{Role: zeroruntime.MessageRoleUser, Content: "Never add background memory models."},
+		zeroruntime.Message{Role: zeroruntime.MessageRoleAssistant, Content: "understood"},
+		zeroruntime.Message{Role: zeroruntime.MessageRoleUser, Content: "continue"},
+		zeroruntime.Message{Role: zeroruntime.MessageRoleAssistant, Content: "working"},
+	)
+	second, err := Compact(secondInput, CompactionOptions{
+		PreserveLast: 2,
+		Summarize:    func([]zeroruntime.Message) (string, error) { return "SECOND", nil },
+		taskState:    task.snapshotForCompaction(secondInput),
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	state := parsePreservedStateBlock(second[1].Content)
+	if state.Task == nil || len(state.Task.UnresolvedFailures) != 1 || len(state.Task.Approvals) != 1 || len(state.Task.Artifacts) != 1 {
+		t.Fatalf("runtime evidence did not survive repeated compaction: %#v", state.Task)
+	}
+	if got := state.Task.UnresolvedFailures[0].Summary; got != "Error: tests still fail with newer evidence" {
+		t.Fatalf("newer failure evidence did not replace the older summary: %#v", state.Task.UnresolvedFailures)
+	}
+	for _, want := range []string{"Please keep the change focused.", "Never add background memory models."} {
+		if !containsString(state.Task.Constraints, want) {
+			t.Fatalf("constraint %q missing after repeated compaction: %#v", want, state.Task.Constraints)
+		}
+	}
+}
+
+func containsString(values []string, want string) bool {
+	for _, value := range values {
+		if value == want {
+			return true
+		}
+	}
+	return false
 }
 
 func TestCompactPreservesObjectiveAfterPlanParityMismatch(t *testing.T) {

internal/agent/compaction_projection.go

@@ -0,0 +1,315 @@
+package agent
+
+import (
+	"encoding/json"
+	"fmt"
+	"regexp"
+	"strings"
+
+	"github.com/Gitlawb/zero/internal/zeroruntime"
+)
+
+const (
+	compactionUserWordBudget       = 256
+	compactionAssistantWordBudget  = 200
+	compactionToolCallsPerTurn     = 8
+	compactionToolArgumentBytes    = 120
+	compactionErrorBytes           = 150
+	compactionResultBytes          = 1200
+	compactionPreviousSummaryBytes = 16 * 1024
+	compactionBriefMaxBytes        = 24 * 1024
+)
+
+var compactionWordPattern = regexp.MustCompile(`[\p{L}\p{N}]+`)
+
+type compactionProjection struct {
+	messages  []zeroruntime.Message
+	truncated bool
+}
+
+// projectCompactionInput removes reconstructible tool output before the model
+// summary call. It retains a bounded transcript of user intent, assistant
+// decisions, tool actions, and concise errors. Exact durable state is appended
+// separately from the original messages after the summary returns.
+func projectCompactionInput(messages []zeroruntime.Message) compactionProjection {
+	sections := make([]string, 0, len(messages))
+	previousSummary := ""
+	truncated := false
+	for index, message := range messages {
+		switch message.Role {
+		case zeroruntime.MessageRoleUser:
+			content := message.Content
+			if marker := strings.Index(content, preservedStateLabel); marker >= 0 {
+				content = content[:marker]
+			}
+			trimmed := strings.TrimSpace(content)
+			if strings.HasPrefix(trimmed, summaryLabel) {
+				fullSummary := strings.TrimSpace(strings.TrimPrefix(trimmed, summaryLabel))
+				previousSummary = clipHeadTailBytes(fullSummary, compactionPreviousSummaryBytes)
+				truncated = truncated || len(fullSummary) > compactionPreviousSummaryBytes
+				continue
+			}
+			if content = clipInformativeWords(content, compactionUserWordBudget); content != "" {
+				sections = append(sections, fmt.Sprintf("[user #%d]\n%s", index, content))
+			}
+		case zeroruntime.MessageRoleAssistant:
+			lines := make([]string, 0, 1+len(message.ToolCalls))
+			if content := clipInformativeWords(message.Content, compactionAssistantWordBudget); content != "" {
+				lines = append(lines, content)
+			}
+			calls := message.ToolCalls
+			omitted := 0
+			if len(calls) > compactionToolCallsPerTurn {
+				omitted = len(calls) - compactionToolCallsPerTurn
+				calls = calls[omitted:]
+			}
+			if omitted > 0 {
+				lines = append(lines, fmt.Sprintf("* (%d earlier tool calls omitted)", omitted))
+			}
+			for _, call := range calls {
+				lines = append(lines, compactionToolCallLine(call))
+			}
+			if len(lines) > 0 {
+				sections = append(sections, fmt.Sprintf("[assistant #%d]\n%s", index, strings.Join(lines, "\n")))
+			}
+		case zeroruntime.MessageRoleTool:
+			// New tool-result messages carry the execution status directly, as the
+			// source ToolResult does. Keep the text check for older session history
+			// created before Message exposed IsError.
+			name := toolNameForResult(messages, index)
+			mustPreserve := name == "ask_user" || len(message.ChangedFiles) > 0
+			if !mustPreserve && !message.IsError && !isLikelyToolError(message.Content) {
+				continue
+			}
+			if name == "" {
+				name = "tool"
+			}
+			switch {
+			case message.IsError || isLikelyToolError(message.Content):
+				sections = append(sections, fmt.Sprintf("[tool_error #%d] %s\n%s", index, name, clipBytes(firstLine(message.Content), compactionErrorBytes)))
+			case name == "ask_user":
+				sections = append(sections, fmt.Sprintf("[user_answer #%d] %s\n%s", index, name, clipBytes(message.Content, compactionResultBytes)))
+			default:
+				sections = append(sections, fmt.Sprintf("[tool_result #%d] %s changed %s\n%s", index, name,
+					clipBytes(strings.Join(message.ChangedFiles, ", "), compactionToolArgumentBytes), clipBytes(firstLine(message.Content), compactionErrorBytes)))
+			}
+		}
+	}
+	if len(sections) == 0 && previousSummary == "" {
+		return compactionProjection{}
+	}
+	brief, briefTruncated := capCompactionBrief(strings.Join(sections, "\n\n"))
+	truncated = truncated || briefTruncated
+	if previousSummary != "" {
+		brief = "[previous summary]\n" + previousSummary + "\n\n" + brief
+	}
+	return compactionProjection{
+		messages:  []zeroruntime.Message{{Role: zeroruntime.MessageRoleUser, Content: strings.TrimSpace(brief)}},
+		truncated: truncated,
+	}
+}
+
+func capCompactionBrief(brief string) (string, bool) {
+	if len(brief) <= compactionBriefMaxBytes {
+		return brief, false
+	}
+	marker := "\n\n...[middle transcript omitted to fit compaction budget]...\n\n"
+	available := compactionBriefMaxBytes - len(marker)
+	// Keep both chronological edges: the oldest material has not necessarily
+	// been summarized before, while the newest material is most actionable.
+	headBytes := available * 2 / 5
+	tailBytes := available - headBytes
+	head := clipPrefixAtBoundary(brief, headBytes)
+	tail := clipSuffixAtBoundary(brief, tailBytes)
+	return strings.TrimSpace(head) + marker + strings.TrimSpace(tail), true
+}
+
+func compactionToolCallLine(call zeroruntime.ToolCall) string {
+	detail := ""
+	var arguments map[string]any
+	if json.Unmarshal([]byte(strings.TrimSpace(call.Arguments)), &arguments) == nil {
+		for _, key := range []string{"file_path", "path", "url", "query", "pattern", "prompt", "description", "question"} {
+			if value, ok := arguments[key].(string); ok && strings.TrimSpace(value) != "" {
+				detail = value
+				break
+			}
+		}
+		if detail == "" && call.Name == "ask_user" {
+			detail = askUserQuestionsDetail(arguments)
+		}
+		if detail == "" && call.Name == "apply_patch" {
+			if patch, ok := arguments["patch"].(string); ok {
+				detail = strings.Join(patchPaths(patch), ", ")
+			}
+		}
+	}
+	if detail == "" {
+		detail = commandFromArguments(call.Arguments)
+	}
+	if detail == "" {
+		return "* " + call.Name
+	}
+	return fmt.Sprintf("* %s %q", call.Name, clipBytes(detail, compactionToolArgumentBytes))
+}
+
+func isLikelyToolError(content string) bool {
+	prefix := strings.TrimSpace(content)
+	if len(prefix) > compactionErrorBytes {
+		prefix = prefix[:compactionErrorBytes]
+	}
+	lower := strings.ToLower(prefix)
+	for _, prefix := range []string{"error:", "tool error:", "failed:", "permission denied", "command failed"} {
+		if strings.HasPrefix(lower, prefix) {
+			return true
+		}
+	}
+	return false
+}
+
+func clipInformativeWords(text string, limit int) string {
+	flat := strings.Join(strings.Fields(text), " ")
+	if flat == "" || limit <= 0 {
+		return ""
+	}
+	count := 0
+	for _, location := range compactionWordPattern.FindAllStringIndex(flat, -1) {
+		word := strings.ToLower(flat[location[0]:location[1]])
+		if compactionStopWords[word] {
+			continue
+		}
+		count++
+		if count > limit {
+			end := location[0]
+			return strings.TrimSpace(flat[:end]) + "...(truncated)"
+		}
+	}
+	return flat
+}
+
+func clipBytes(text string, limit int) string {
+	text = strings.TrimSpace(text)
+	if limit <= 0 {
+		return ""
+	}
+	if len(text) <= limit {
+		return text
+	}
+	if limit <= 3 {
+		end := limit
+		for end > 0 && end < len(text) && text[end]&0xc0 == 0x80 {
+			end--
+		}
+		return text[:end]
+	}
+	end := limit - 3
+	for end > 0 && end < len(text) && text[end]&0xc0 == 0x80 {
+		end--
+	}
+	return strings.TrimSpace(text[:end]) + "..."
+}
+
+func clipHeadTailBytes(text string, limit int) string {
+	text = strings.TrimSpace(text)
+	if len(text) <= limit {
+		return text
+	}
+	if limit <= 0 {
+		return ""
+	}
+	marker := "\n...[middle omitted]...\n"
+	if limit <= len(marker) {
+		return clipBytes(text, limit)
+	}
+	available := limit - len(marker)
+	head := clipPrefixAtBoundary(text, available/2)
+	tail := clipSuffixAtBoundary(text, available-available/2)
+	return strings.TrimSpace(head) + marker + strings.TrimSpace(tail)
+}
+
+func clipPrefixAtBoundary(text string, limit int) string {
+	if limit <= 0 {
+		return ""
+	}
+	if len(text) <= limit {
+		return text
+	}
+	end := limit
+	for end > 0 && text[end]&0xc0 == 0x80 {
+		end--
+	}
+	if boundary := strings.LastIndex(text[:end], "\n\n["); boundary > 0 {
+		end = boundary
+	}
+	return text[:end]
+}
+
+func clipSuffixAtBoundary(text string, limit int) string {
+	if limit <= 0 {
+		return ""
+	}
+	if len(text) <= limit {
+		return text
+	}
+	start := len(text) - limit
+	for start < len(text) && text[start]&0xc0 == 0x80 {
+		start++
+	}
+	if boundary := strings.Index(text[start:], "\n\n["); boundary >= 0 {
+		start += boundary + 2
+	}
+	return text[start:]
+}
+
+func askUserQuestionsDetail(arguments map[string]any) string {
+	raw, ok := arguments["questions"].([]any)
+	if !ok {
+		return ""
+	}
+	questions := make([]string, 0, len(raw))
+	for _, item := range raw {
+		object, ok := item.(map[string]any)
+		if !ok {
+			continue
+		}
+		if question, ok := object["question"].(string); ok && strings.TrimSpace(question) != "" {
+			questions = append(questions, strings.TrimSpace(question))
+		}
+	}
+	return strings.Join(questions, " | ")
+}
+
+func patchPaths(patch string) []string {
+	var paths []string
+	seen := map[string]bool{}
+	for _, line := range strings.Split(patch, "\n") {
+		for _, prefix := range []string{"*** Add File: ", "*** Update File: ", "*** Delete File: ", "*** Move to: "} {
+			if !strings.HasPrefix(line, prefix) {
+				continue
+			}
+			path := strings.TrimSpace(strings.TrimPrefix(line, prefix))
+			if path != "" && !seen[path] {
+				seen[path] = true
+				paths = append(paths, path)
+			}
+		}
+	}
+	return paths
+}
+
+var compactionStopWords = map[string]bool{
+	"a": true, "an": true, "the": true, "is": true, "are": true, "was": true, "were": true,
+	"be": true, "been": true, "being": true, "have": true, "has": true, "had": true,
+	"do": true, "does": true, "did": true, "will": true, "would": true, "could": true,
+	"should": true, "may": true, "might": true, "shall": true, "can": true, "need": true, "must": true,
+	"to": true, "of": true, "in": true, "for": true, "on": true, "with": true, "at": true,
+	"by": true, "from": true, "as": true, "into": true, "through": true, "during": true,
+	"before": true, "after": true, "above": true, "below": true, "between": true, "under": true, "over": true,
+	"and": true, "but": true, "or": true, "nor": true, "not": true, "so": true, "yet": true,
+	"both": true, "either": true, "neither": true, "each": true, "every": true, "all": true,
+	"any": true, "few": true, "more": true, "most": true, "other": true, "some": true, "such": true, "no": true,
+	"that": true, "this": true, "these": true, "those": true, "it": true, "its": true,
+	"i": true, "me": true, "my": true, "we": true, "our": true, "you": true, "your": true,
+	"he": true, "him": true, "his": true, "she": true, "her": true, "they": true, "them": true, "their": true,
+	"who": true, "which": true, "what": true, "if": true, "then": true, "than": true,
+	"when": true, "where": true, "how": true, "just": true, "also": true,
+}

internal/agent/compaction_projection_test.go

@@ -0,0 +1,130 @@
+package agent
+
+import (
+	"strings"
+	"testing"
+	"unicode/utf8"
+
+	"github.com/Gitlawb/zero/internal/zeroruntime"
+)
+
+func TestClipBytesHandlesTinyLimitsOnRuneBoundaries(t *testing.T) {
+	for _, limit := range []int{0, 1, 2, 3} {
+		if clipped := clipBytes("世界", limit); len(clipped) > limit || !utf8.ValidString(clipped) {
+			t.Fatalf("clipBytes limit %d returned invalid result %q", limit, clipped)
+		}
+	}
+}
+
+func TestBoundaryClippersHandleNonPositiveLimits(t *testing.T) {
+	for _, clip := range []func(string, int) string{clipPrefixAtBoundary, clipSuffixAtBoundary} {
+		for _, limit := range []int{-1, 0} {
+			if got := clip("世界", limit); got != "" {
+				t.Fatalf("clipper limit %d = %q, want empty", limit, got)
+			}
+		}
+	}
+}
+
+func TestProjectCompactionInputDropsRecoverableToolBodies(t *testing.T) {
+	largeBody := strings.Repeat("recoverable source line\n", 1000)
+	messages := []zeroruntime.Message{
+		{Role: zeroruntime.MessageRoleUser, Content: "Inspect the parser and preserve its current behavior."},
+		{Role: zeroruntime.MessageRoleAssistant, Content: "I will inspect before editing.", ToolCalls: []zeroruntime.ToolCall{{ID: "read", Name: "read_file", Arguments: `{"path":"internal/parser.go"}`}}},
+		{Role: zeroruntime.MessageRoleTool, ToolCallID: "read", Content: largeBody},
+		{Role: zeroruntime.MessageRoleAssistant, ToolCalls: []zeroruntime.ToolCall{{ID: "test", Name: "exec_command", Arguments: `{"cmd":"go test ./internal/parser"}`}}},
+		{Role: zeroruntime.MessageRoleTool, ToolCallID: "test", Content: "Error: parser regression\nlong diagnostic details"},
+	}
+
+	projection := projectCompactionInput(messages)
+	projected := projection.messages
+	if len(projected) != 1 {
+		t.Fatalf("projection = %#v, want one compact message", projected)
+	}
+	content := projected[0].Content
+	for _, want := range []string{"Inspect the parser", `read_file "internal/parser.go"`, `exec_command "go test ./internal/parser"`, "Error: parser regression"} {
+		if !strings.Contains(content, want) {
+			t.Fatalf("projection missing %q: %q", want, content)
+		}
+	}
+	if strings.Contains(content, "recoverable source line") || strings.Contains(content, "long diagnostic details") {
+		t.Fatalf("projection retained reconstructible or overlong tool output: %q", content)
+	}
+	if estimateTokens(projected)*20 >= estimateTokens(messages) {
+		t.Fatalf("projection did not materially reduce tokens: before=%d after=%d", estimateTokens(messages), estimateTokens(projected))
+	}
+}
+
+func TestProjectCompactionInputRetainsStructurallyMarkedToolErrors(t *testing.T) {
+	messages := []zeroruntime.Message{
+		{Role: zeroruntime.MessageRoleAssistant, ToolCalls: []zeroruntime.ToolCall{{ID: "git", Name: "exec_command", Arguments: `{"cmd":"git status"}`}}},
+		{Role: zeroruntime.MessageRoleTool, ToolCallID: "git", Content: "fatal: not a git repository", IsError: true},
+	}
+
+	projected := projectCompactionInput(messages).messages
+	if len(projected) != 1 || !strings.Contains(projected[0].Content, "fatal: not a git repository") {
+		t.Fatalf("structured tool error was dropped from projection: %#v", projected)
+	}
+}
+
+func TestProjectCompactionInputRetainsAskUserExchangeAndSemanticArguments(t *testing.T) {
+	messages := []zeroruntime.Message{
+		{Role: zeroruntime.MessageRoleAssistant, ToolCalls: []zeroruntime.ToolCall{{ID: "ask", Name: "ask_user", Arguments: `{"questions":[{"question":"Which database should remain?"}]}`}}},
+		{Role: zeroruntime.MessageRoleTool, ToolCallID: "ask", Content: "Which database should remain?: Postgres only; do not touch MySQL."},
+		{Role: zeroruntime.MessageRoleAssistant, ToolCalls: []zeroruntime.ToolCall{
+			{ID: "patch", Name: "apply_patch", Arguments: `{"patch":"*** Begin Patch\n*** Update File: internal/db.go\n*** End Patch"}`},
+			{ID: "fetch", Name: "web_fetch", Arguments: `{"url":"https://example.com/spec"}`},
+			{ID: "task", Name: "task", Arguments: `{"prompt":"Inspect the Windows implementation"}`},
+		}},
+		{Role: zeroruntime.MessageRoleTool, ToolCallID: "patch", Content: "Done!", ChangedFiles: []string{"internal/db.go"}},
+	}
+
+	content := projectCompactionInput(messages).messages[0].Content
+	for _, want := range []string{"Which database should remain?", "Postgres only; do not touch MySQL", "internal/db.go", "https://example.com/spec", "Inspect the Windows implementation"} {
+		if !strings.Contains(content, want) {
+			t.Fatalf("projection missing %q: %q", want, content)
+		}
+	}
+}
+
+func TestProjectCompactionInputCapsToolCallsPerTurn(t *testing.T) {
+	calls := make([]zeroruntime.ToolCall, 12)
+	for index := range calls {
+		calls[index] = zeroruntime.ToolCall{Name: "read_file", Arguments: `{"path":"file.go"}`}
+	}
+	projected := projectCompactionInput([]zeroruntime.Message{{Role: zeroruntime.MessageRoleAssistant, ToolCalls: calls}}).messages
+	content := projected[0].Content
+	if strings.Count(content, "* read_file") != compactionToolCallsPerTurn || !strings.Contains(content, "4 earlier tool calls omitted") {
+		t.Fatalf("tool-call tail was not bounded: %q", content)
+	}
+}
+
+func TestProjectCompactionInputCarriesPreviousSummaryOutsideBriefCap(t *testing.T) {
+	previous := "keep the earlier architecture decision\n" + strings.Repeat("prior detail ", 2000) + "\nkeep the newest prior decision"
+	messages := []zeroruntime.Message{{Role: zeroruntime.MessageRoleUser, Content: summaryLabel + "\n" + previous + "\n\n" + preservedStateLabel + "\n{}"}}
+	for index := range 500 {
+		messages = append(messages, zeroruntime.Message{Role: zeroruntime.MessageRoleAssistant, Content: strings.Repeat("later transcript detail ", 20)})
+		messages = append(messages, zeroruntime.Message{Role: zeroruntime.MessageRoleUser, Content: "later request " + strings.Repeat("context ", 20) + string(rune('a'+index%26))})
+	}
+
+	projection := projectCompactionInput(messages)
+	content := projection.messages[0].Content
+	if !strings.Contains(content, "[previous summary]\nkeep the earlier architecture decision") || !strings.Contains(content, "keep the newest prior decision") {
+		t.Fatalf("previous summary was lost when the brief tail was capped: %q", content)
+	}
+	if !strings.Contains(content, "middle transcript omitted to fit compaction budget") {
+		t.Fatalf("oversized brief was not head/tail capped: %q", content)
+	}
+	if !projection.truncated {
+		t.Fatal("projection did not structurally report truncation")
+	}
+}
+
+func TestProjectCompactionInputDoesNotInferTruncationFromUserText(t *testing.T) {
+	projection := projectCompactionInput([]zeroruntime.Message{{
+		Role: zeroruntime.MessageRoleUser, Content: "Keep this literal marker: [middle omitted]",
+	}})
+	if projection.truncated {
+		t.Fatal("literal user text produced a false truncation signal")
+	}
+}

internal/agent/compaction_recent_edits_test.go

@@ -20,11 +20,15 @@ func TestRecentEditsExtractsPathsAndNotes(t *testing.T) {
 			{ID: "e2", Name: "edit_file", Arguments: `{"path":"internal/bar.go","old_string":"a","new_string":"b"}`},
 		}},
 		{Role: zeroruntime.MessageRoleTool, ToolCallID: "e2", Content: "Applied edit to internal/bar.go"},
+		{Role: zeroruntime.MessageRoleAssistant, ToolCalls: []zeroruntime.ToolCall{
+			{ID: "e3", Name: "apply_patch", Arguments: `{"patch":"*** Update File: internal/baz.go"}`},
+		}},
+		{Role: zeroruntime.MessageRoleTool, ToolCallID: "e3", Content: "Done!", ChangedFiles: []string{"internal/baz.go"}},
 	}
 
 	edits := recentEdits(messages)
-	if len(edits) != 2 {
-		t.Fatalf("expected 2 edited files, got %d: %#v", len(edits), edits)
+	if len(edits) != 3 {
+		t.Fatalf("expected 3 edited files, got %d: %#v", len(edits), edits)
 	}
 	if edits[0].name != "internal/foo.go" || !strings.Contains(edits[0].body, "12 lines") {
 		t.Fatalf("first edit = %#v, want foo.go with its note", edits[0])
@@ -32,6 +36,9 @@ func TestRecentEditsExtractsPathsAndNotes(t *testing.T) {
 	if edits[1].name != "internal/bar.go" || !strings.Contains(edits[1].body, "Applied edit") {
 		t.Fatalf("second edit = %#v, want bar.go with its note", edits[1])
 	}
+	if edits[2].name != "internal/baz.go" || edits[2].body != "Done!" {
+		t.Fatalf("third edit = %#v, want apply_patch changed file with its note", edits[2])
+	}
 }
 
 // After compaction elides the editing turns, the preserved-state block still

internal/agent/compaction_test.go

@@ -7,6 +7,7 @@ import (
 	"testing"
 
 	"github.com/Gitlawb/zero/internal/tools"
+	"github.com/Gitlawb/zero/internal/trace"
 	"github.com/Gitlawb/zero/internal/zeroruntime"
 )
 
@@ -58,12 +59,15 @@ func TestCompactKeepsSystemAndPreservedSuffix(t *testing.T) {
 	if last.Content != "most recent question" {
 		t.Fatalf("expected most recent message preserved, got %q", last.Content)
 	}
-	// The summarized middle excludes system and preserved suffix.
-	if len(captured) != 3 {
-		t.Fatalf("expected 3 summarized messages, got %d: %#v", len(captured), captured)
+	// The summarizer receives a compact semantic projection of the middle rather
+	// than reconstructible raw tool output.
+	if len(captured) != 1 || captured[0].Role != zeroruntime.MessageRoleUser {
+		t.Fatalf("expected one projected summary input, got %#v", captured)
 	}
-	if captured[0].Content != "first question" {
-		t.Fatalf("expected oldest non-system message first, got %#v", captured[0])
+	for _, want := range []string{"[user #0]", "first question", "[assistant #1]", "first answer", "second question"} {
+		if !strings.Contains(captured[0].Content, want) {
+			t.Fatalf("projected summary input missing %q: %q", want, captured[0].Content)
+		}
 	}
 	// Compaction must shrink the conversation.
 	if estimateTokens(result) >= estimateTokens(messages) {
@@ -425,6 +429,7 @@ type reactiveProvider struct {
 	summarizeCalls int
 	turnRequests   int
 	failedOnce     bool
+	connectError   bool
 	bigText        string
 	finalText      string
 }
@@ -446,6 +451,9 @@ func (provider *reactiveProvider) StreamCompletion(ctx context.Context, request
 		return streamEvents(toolTurnWithText(provider.bigText, "1", "read_file", `{"path":"x"}`)), nil
 	case provider.turnRequests == 2 && !provider.failedOnce:
 		provider.failedOnce = true
+		if provider.connectError {
+			return nil, errors.New("context_length_exceeded")
+		}
 		return streamEvents([]zeroruntime.StreamEvent{
 			{Type: zeroruntime.StreamEventError, Error: "This model's maximum context length is 1000 tokens. Please reduce the length of the messages."},
 		}), nil
@@ -454,6 +462,39 @@ func (provider *reactiveProvider) StreamCompletion(ctx context.Context, request
 	}
 }
 
+func TestRunConnectErrorCompactionRecordsReplacementPlan(t *testing.T) {
+	provider := &reactiveProvider{
+		connectError: true,
+		bigText:      strings.Repeat("b", 6000),
+		finalText:    "recovered",
+	}
+	registry := tools.NewRegistry()
+	registry.Register(tools.NewScopedReadFileTool(t.TempDir(), nil))
+	recorder := trace.NewRecorder("connect-compaction", "run-1", "test")
+	var contextPlans []ContextBreakdown
+
+	result, err := Run(context.Background(), strings.Repeat("z", 6000), provider, Options{
+		Registry:               registry,
+		PermissionMode:         PermissionModeUnsafe,
+		ContextWindow:          10_000_000,
+		CompactionPreserveLast: 2,
+		Trace:                  recorder,
+		OnContext: func(breakdown ContextBreakdown) {
+			contextPlans = append(contextPlans, breakdown)
+		},
+	})
+	if err != nil || result.FinalAnswer != "recovered" {
+		t.Fatalf("connect-error compaction failed: result=%#v err=%v", result, err)
+	}
+	if len(contextPlans) != 3 || contextPlans[2].MessageTokens >= contextPlans[1].MessageTokens {
+		t.Fatalf("replacement request context not reported: %#v", contextPlans)
+	}
+	gotTrace := recorder.Finish()
+	if len(gotTrace.PrefixHashes) != 4 || gotTrace.PrefixHashes[3].InvalidationReason != "unchanged" {
+		t.Fatalf("replacement request trace not recorded: %#v", gotTrace.PrefixHashes)
+	}
+}
+
 func TestRunReactiveCompactionRecovers(t *testing.T) {
 	provider := &reactiveProvider{
 		bigText:   strings.Repeat("b", 6000),
@@ -465,6 +506,8 @@ func TestRunReactiveCompactionRecovers(t *testing.T) {
 	// bloats the history.
 	registry := tools.NewRegistry()
 	registry.Register(tools.NewScopedReadFileTool(t.TempDir(), nil))
+	recorder := trace.NewRecorder("reactive-compaction", "run-1", "test")
+	var contextPlans []ContextBreakdown
 
 	// ContextWindow large enough that proactive compaction never triggers, so
 	// only the reactive path can save the run.
@@ -473,6 +516,10 @@ func TestRunReactiveCompactionRecovers(t *testing.T) {
 		PermissionMode:         PermissionModeUnsafe,
 		ContextWindow:          10_000_000,
 		CompactionPreserveLast: 2,
+		Trace:                  recorder,
+		OnContext: func(breakdown ContextBreakdown) {
+			contextPlans = append(contextPlans, breakdown)
+		},
 	})
 	if err != nil {
 		t.Fatalf("expected reactive compaction to recover the run, got error: %v", err)
@@ -483,6 +530,25 @@ func TestRunReactiveCompactionRecovers(t *testing.T) {
 	if provider.summarizeCalls == 0 {
 		t.Fatal("expected reactive compaction to invoke the summarizer")
 	}
+	if len(contextPlans) != 3 {
+		t.Fatalf("main request context callbacks = %d, want initial turns plus compacted retry", len(contextPlans))
+	}
+	if contextPlans[2].MessageTokens >= contextPlans[1].MessageTokens {
+		t.Fatalf("retry context was not updated after compaction: before=%d after=%d", contextPlans[1].MessageTokens, contextPlans[2].MessageTokens)
+	}
+	gotTrace := recorder.Finish()
+	if len(gotTrace.PrefixHashes) != 4 {
+		t.Fatalf("prefix evidence count = %d, want two turns, compaction, and retry: %#v", len(gotTrace.PrefixHashes), gotTrace.PrefixHashes)
+	}
+	if gotTrace.PrefixHashes[0].InvalidationReason != "initial" ||
+		gotTrace.PrefixHashes[1].InvalidationReason != "unchanged" ||
+		gotTrace.PrefixHashes[2].InvalidationReason != "initial" ||
+		gotTrace.PrefixHashes[3].InvalidationReason != "unchanged" {
+		t.Fatalf("unexpected request-specific invalidation evidence: %#v", gotTrace.PrefixHashes)
+	}
+	if gotTrace.PrefixHashes[2].CompletePrefixHash == gotTrace.PrefixHashes[1].CompletePrefixHash {
+		t.Fatalf("compaction fingerprint reused the main request prefix: %#v", gotTrace.PrefixHashes)
+	}
 }
 
 // midStreamReactiveProvider forwards some text BEFORE surfacing a context-limit

internal/agent/context_measurement.go

@@ -23,6 +23,24 @@ type ContextBreakdown struct {
 	TotalTokens   int     // SystemTokens + ToolTokens + MessageTokens
 	ContextWindow int     // model context window; 0 when unknown
 	UsedFraction  float64 // TotalTokens / ContextWindow; 0 when window unknown
+	// Blocks explain why each model-visible category is present without exposing
+	// its content. The planner currently preserves all three categories.
+	Blocks []ContextBlock
+	// CompletePrefixHash identifies the provider-visible system+tool prefix.
+	CompletePrefixHash string
+	// PrefixInvalidationReason is "initial", "unchanged", or a stable comma-
+	// separated list of changed prefix categories.
+	PrefixInvalidationReason string
+}
+
+// ContextBlock is content-free evidence for one model-visible context category.
+type ContextBlock struct {
+	Kind        string
+	Tokens      int
+	CacheClass  string
+	Authority   string
+	Recoverable bool
+	Reason      string
 }
 
 // MeasureContext estimates the per-category token footprint of a request: the
@@ -41,6 +59,24 @@ func MeasureContext(messages []zeroruntime.Message, tools []zeroruntime.ToolDefi
 		ContextWindow: contextWindow,
 	}
 	breakdown.TotalTokens = breakdown.SystemTokens + breakdown.ToolTokens + breakdown.MessageTokens
+	if breakdown.SystemTokens > 0 {
+		breakdown.Blocks = append(breakdown.Blocks, ContextBlock{
+			Kind: "system", Tokens: breakdown.SystemTokens, CacheClass: "stable_prefix",
+			Authority: "required", Reason: "instructions, workspace policy, and safety policy",
+		})
+	}
+	if breakdown.ToolTokens > 0 {
+		breakdown.Blocks = append(breakdown.Blocks, ContextBlock{
+			Kind: "tools", Tokens: breakdown.ToolTokens, CacheClass: "stable_prefix",
+			Authority: "capability", Reason: "currently permitted and selected tool definitions",
+		})
+	}
+	if breakdown.MessageTokens > 0 {
+		breakdown.Blocks = append(breakdown.Blocks, ContextBlock{
+			Kind: "conversation", Tokens: breakdown.MessageTokens, CacheClass: "dynamic_tail",
+			Authority: "transcript", Reason: "valid provider replay history and current task context",
+		})
+	}
 	if contextWindow > 0 {
 		breakdown.UsedFraction = float64(breakdown.TotalTokens) / float64(contextWindow)
 	}

internal/agent/context_measurement_test.go

@@ -32,6 +32,9 @@ func TestMeasureContextSplitsByCategory(t *testing.T) {
 	if breakdown.UsedFraction != wantFraction {
 		t.Fatalf("UsedFraction = %v, want %v", breakdown.UsedFraction, wantFraction)
 	}
+	if len(breakdown.Blocks) != 3 {
+		t.Fatalf("Blocks = %#v, want system/tools/conversation", breakdown.Blocks)
+	}
 }
 
 func TestMeasureContextUnknownWindowHasZeroFraction(t *testing.T) {

internal/agent/context_planner.go

@@ -0,0 +1,185 @@
+package agent
+
+import (
+	"strings"
+
+	"github.com/Gitlawb/zero/internal/zeroruntime"
+)
+
+type contextPlannerConfig struct {
+	contextWindow  int
+	promptCacheKey string
+	serviceTier    string
+	promptParts    systemPromptParts
+}
+
+// contextPlanner is the single seam for constructing model-visible requests.
+// Planning is deterministic and does not retrieve content, execute tools, or
+// change permissions. The initial implementation deliberately preserves every
+// message and tool definition while making composition and cache drift
+// inspectable; later selection policies must continue to cross this seam.
+type contextPlanner struct {
+	config          contextPlannerConfig
+	previousPrefix  prefixFingerprint
+	hasPrevious     bool
+	toolSnapshotKey string
+	toolSnapshot    []zeroruntime.ToolDefinition
+}
+
+type contextPlan struct {
+	Request           zeroruntime.CompletionRequest
+	Breakdown         ContextBreakdown
+	PrefixFingerprint prefixFingerprint
+}
+
+func newContextPlanner(config contextPlannerConfig) *contextPlanner {
+	return &contextPlanner{config: config}
+}
+
+// Plan returns a provider request snapshot plus content-free accounting.
+// It intentionally performs no relevance filtering: preserving current model
+// capability is the baseline contract for future planner policies.
+func (planner *contextPlanner) Plan(messages []zeroruntime.Message, toolDefs []zeroruntime.ToolDefinition, reasoningEffort string) contextPlan {
+	return planner.plan(messages, toolDefs, reasoningEffort, planner.config.promptParts)
+}
+
+// planWithPromptParts plans a request whose stable system sections differ from
+// the planner's configured main-run prompt, such as a compaction summary call.
+func (planner *contextPlanner) planWithPromptParts(messages []zeroruntime.Message, toolDefs []zeroruntime.ToolDefinition, reasoningEffort string, parts systemPromptParts) contextPlan {
+	return planner.plan(messages, toolDefs, reasoningEffort, parts)
+}
+
+func (planner *contextPlanner) plan(messages []zeroruntime.Message, toolDefs []zeroruntime.ToolDefinition, reasoningEffort string, parts systemPromptParts) contextPlan {
+	requestMessages := copyMessages(messages)
+	requestSystemPrompt := leadingSystemContent(requestMessages)
+	if parts.prompt != requestSystemPrompt {
+		// Component boundaries from a different request would make the detailed
+		// invalidation reason misleading. Retain the exact request prefix and
+		// classify it conservatively as an unstructured system prompt instead.
+		parts = systemPromptParts{prompt: requestSystemPrompt}
+	}
+	fingerprint := computePrefixFingerprint(buildPromptSubstringsFromParts(parts, toolDefs))
+	request := zeroruntime.CompletionRequest{
+		Messages:        requestMessages,
+		Tools:           planner.snapshotTools(toolDefs, fingerprint),
+		ReasoningEffort: reasoningEffort,
+		ServiceTier:     planner.config.serviceTier,
+		PromptCacheKey:  planner.config.promptCacheKey,
+	}
+	breakdown := MeasureContext(request.Messages, request.Tools, planner.config.contextWindow)
+	breakdown.CompletePrefixHash = fingerprint.CompletePrefixHash
+	var previous *prefixFingerprint
+	if planner.hasPrevious {
+		previous = &planner.previousPrefix
+	}
+	breakdown.PrefixInvalidationReason = explainPrefixChange(previous, fingerprint)
+	planner.previousPrefix = fingerprint
+	planner.hasPrevious = true
+	return contextPlan{
+		Request:           request,
+		Breakdown:         breakdown,
+		PrefixFingerprint: fingerprint,
+	}
+}
+
+// snapshotTools freezes provider-visible tool definitions when their semantic
+// fingerprint changes. Stable turns reuse the frozen schemas instead of
+// recursively cloning every map and slice for every request.
+func (planner *contextPlanner) snapshotTools(toolDefs []zeroruntime.ToolDefinition, fingerprint prefixFingerprint) []zeroruntime.ToolDefinition {
+	key := fingerprint.ToolsHash + "\x00" + fingerprint.SchemaHash
+	if planner.toolSnapshotKey != key {
+		planner.toolSnapshot = copyToolDefinitions(toolDefs)
+		planner.toolSnapshotKey = key
+	}
+	return planner.toolSnapshot
+}
+
+func copyToolDefinitions(toolDefs []zeroruntime.ToolDefinition) []zeroruntime.ToolDefinition {
+	if toolDefs == nil {
+		return nil
+	}
+	copied := make([]zeroruntime.ToolDefinition, len(toolDefs))
+	for index, definition := range toolDefs {
+		copied[index] = definition
+		copied[index].Parameters = copySchemaMap(definition.Parameters)
+	}
+	return copied
+}
+
+func copySchemaMap(schema map[string]any) map[string]any {
+	if schema == nil {
+		return nil
+	}
+	copied := make(map[string]any, len(schema))
+	for key, value := range schema {
+		copied[key] = copySchemaValue(value)
+	}
+	return copied
+}
+
+func copySchemaValue(value any) any {
+	switch typed := value.(type) {
+	case map[string]any:
+		return copySchemaMap(typed)
+	case []any:
+		copied := make([]any, len(typed))
+		for index, item := range typed {
+			copied[index] = copySchemaValue(item)
+		}
+		return copied
+	case []string:
+		return append([]string(nil), typed...)
+	default:
+		return value
+	}
+}
+
+func leadingSystemContent(messages []zeroruntime.Message) string {
+	contents := make([]string, 0, 1)
+	for _, message := range messages {
+		if message.Role != zeroruntime.MessageRoleSystem {
+			break
+		}
+		contents = append(contents, message.Content)
+	}
+	return strings.Join(contents, "\n\n")
+}
+
+func explainPrefixChange(previous *prefixFingerprint, current prefixFingerprint) string {
+	if previous == nil {
+		return "initial"
+	}
+	if previous.CompletePrefixHash == current.CompletePrefixHash {
+		return "unchanged"
+	}
+	reasons := make([]string, 0, 3)
+	if previous.SystemPromptHash != current.SystemPromptHash {
+		parts := make([]string, 0, 4)
+		if previous.BaseInstructionsHash != current.BaseInstructionsHash {
+			parts = append(parts, "base_instructions")
+		}
+		if previous.ConfirmationPolicyHash != current.ConfirmationPolicyHash {
+			parts = append(parts, "confirmation_policy")
+		}
+		if previous.ProjectContextHash != current.ProjectContextHash {
+			parts = append(parts, "project_context")
+		}
+		if previous.SkillsHash != current.SkillsHash {
+			parts = append(parts, "skills")
+		}
+		if len(parts) == 0 {
+			parts = append(parts, "system_prompt")
+		}
+		reasons = append(reasons, parts...)
+	}
+	if previous.ToolsHash != current.ToolsHash {
+		reasons = append(reasons, "tools")
+	}
+	if previous.SchemaHash != current.SchemaHash {
+		reasons = append(reasons, "schema")
+	}
+	if len(reasons) == 0 {
+		return "prefix_changed"
+	}
+	return strings.Join(reasons, ",")
+}

internal/agent/context_planner_test.go

@@ -0,0 +1,187 @@
+package agent
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/Gitlawb/zero/internal/zeroruntime"
+)
+
+func TestContextPlannerPreservesProviderRequest(t *testing.T) {
+	messages := []zeroruntime.Message{
+		{Role: zeroruntime.MessageRoleSystem, Content: "system"},
+		{Role: zeroruntime.MessageRoleUser, Content: "inspect this", Images: []zeroruntime.ImageBlock{{MediaType: "image/png", Data: []byte{1, 2, 3}}}},
+		{Role: zeroruntime.MessageRoleAssistant, Content: "working", ToolCalls: []zeroruntime.ToolCall{{ID: "call-1", Name: "read_file", Arguments: `{"path":"main.go"}`}}, Reasoning: []zeroruntime.ReasoningBlock{{Provider: "test", Type: "thinking", Signature: "sig"}}},
+	}
+	toolDefs := []zeroruntime.ToolDefinition{{
+		Name: "read_file", Description: "Read a file",
+		Parameters: map[string]any{
+			"type":       "object",
+			"required":   []string{"path"},
+			"properties": map[string]any{"path": map[string]any{"type": "string"}},
+			"anyOf":      []any{map[string]any{"type": "object"}},
+		},
+	}}
+	planner := newContextPlanner(contextPlannerConfig{
+		contextWindow:  128_000,
+		promptCacheKey: "session-1",
+		serviceTier:    "priority",
+		promptParts:    systemPromptParts{prompt: "system", baseInstructions: "system"},
+	})
+
+	plan := planner.Plan(messages, toolDefs, "medium")
+	want := zeroruntime.CompletionRequest{
+		Messages:        copyMessages(messages),
+		Tools:           toolDefs,
+		ReasoningEffort: "medium",
+		ServiceTier:     "priority",
+		PromptCacheKey:  "session-1",
+	}
+	if !reflect.DeepEqual(plan.Request, want) {
+		t.Fatalf("planned request changed provider input:\n got: %#v\nwant: %#v", plan.Request, want)
+	}
+	stable := planner.Plan(messages, toolDefs, "medium")
+	if &stable.Request.Tools[0] != &plan.Request.Tools[0] {
+		t.Fatal("stable tool fingerprint rebuilt the immutable schema snapshot")
+	}
+
+	// A plan owns its request snapshot; later caller mutation cannot change its
+	// messages or its recursively nested tool schema.
+	messages[1].Content = "changed"
+	messages[1].Images[0].Data[0] = 9
+	toolDefs[0].Name = "changed_tool"
+	toolDefs[0].Parameters["required"].([]string)[0] = "other"
+	toolDefs[0].Parameters["properties"].(map[string]any)["path"].(map[string]any)["type"] = "integer"
+	toolDefs[0].Parameters["anyOf"].([]any)[0].(map[string]any)["type"] = "array"
+	if plan.Request.Messages[1].Content != "inspect this" || plan.Request.Messages[1].Images[0].Data[0] != 1 {
+		t.Fatalf("planned messages alias caller state: %#v", plan.Request.Messages[1])
+	}
+	if plan.Request.Tools[0].Name != "read_file" ||
+		plan.Request.Tools[0].Parameters["required"].([]string)[0] != "path" ||
+		plan.Request.Tools[0].Parameters["properties"].(map[string]any)["path"].(map[string]any)["type"] != "string" ||
+		plan.Request.Tools[0].Parameters["anyOf"].([]any)[0].(map[string]any)["type"] != "object" {
+		t.Fatalf("planned tools alias caller state: %#v", plan.Request.Tools[0])
+	}
+
+	next := planner.Plan(messages, toolDefs, "medium")
+	if next.PrefixFingerprint == plan.PrefixFingerprint || next.Request.Tools[0].Name != "changed_tool" {
+		t.Fatalf("changed tool schema did not refresh snapshot: %#v", next)
+	}
+	if plan.Request.Tools[0].Name != "read_file" {
+		t.Fatalf("refresh mutated earlier request: %#v", plan.Request.Tools[0])
+	}
+}
+
+func TestContextPlannerReportsInspectableBlocks(t *testing.T) {
+	planner := newContextPlanner(contextPlannerConfig{contextWindow: 100_000})
+	plan := planner.Plan([]zeroruntime.Message{
+		{Role: zeroruntime.MessageRoleSystem, Content: filler(400)},
+		{Role: zeroruntime.MessageRoleUser, Content: filler(200)},
+	}, []zeroruntime.ToolDefinition{{Name: "read_file", Description: "Read a file"}}, "")
+
+	if plan.Breakdown.PrefixInvalidationReason != "initial" || plan.Breakdown.CompletePrefixHash == "" {
+		t.Fatalf("prefix evidence = %#v", plan.Breakdown)
+	}
+	if len(plan.Breakdown.Blocks) != 3 {
+		t.Fatalf("blocks = %#v, want system/tools/conversation", plan.Breakdown.Blocks)
+	}
+	wantKinds := []string{"system", "tools", "conversation"}
+	total := 0
+	for index, block := range plan.Breakdown.Blocks {
+		if block.Kind != wantKinds[index] || block.Tokens <= 0 || block.Reason == "" || block.Authority == "" || block.CacheClass == "" {
+			t.Fatalf("block %d = %#v", index, block)
+		}
+		total += block.Tokens
+	}
+	if total != plan.Breakdown.TotalTokens {
+		t.Fatalf("block tokens = %d, want total %d", total, plan.Breakdown.TotalTokens)
+	}
+}
+
+func TestContextPlannerFingerprintsActualRequestSystemPrompt(t *testing.T) {
+	planner := newContextPlanner(contextPlannerConfig{promptParts: systemPromptParts{
+		prompt: "configured system", baseInstructions: "configured system",
+	}})
+	messages := []zeroruntime.Message{
+		{Role: zeroruntime.MessageRoleSystem, Content: "request-specific system"},
+		{Role: zeroruntime.MessageRoleUser, Content: "task"},
+	}
+
+	plan := planner.Plan(messages, nil, "")
+	want := computePrefixFingerprint(buildPromptSubstringsFromParts(
+		systemPromptParts{prompt: "request-specific system"}, nil,
+	))
+	if plan.PrefixFingerprint != want {
+		t.Fatalf("fingerprint describes configured prompt instead of request:\n got: %#v\nwant: %#v", plan.PrefixFingerprint, want)
+	}
+}
+
+func TestContextPlannerExplainsPrefixInvalidation(t *testing.T) {
+	planner := newContextPlanner(contextPlannerConfig{promptParts: systemPromptParts{
+		prompt: "system", baseInstructions: "base", projectContext: "project",
+	}})
+	messages := []zeroruntime.Message{{Role: zeroruntime.MessageRoleSystem, Content: "system"}, {Role: zeroruntime.MessageRoleUser, Content: "task"}}
+	tools := []zeroruntime.ToolDefinition{{Name: "read_file", Description: "Read", Parameters: map[string]any{"type": "object"}}}
+
+	if got := planner.Plan(messages, tools, "").Breakdown.PrefixInvalidationReason; got != "initial" {
+		t.Fatalf("first reason = %q, want initial", got)
+	}
+	if got := planner.Plan(messages, tools, "").Breakdown.PrefixInvalidationReason; got != "unchanged" {
+		t.Fatalf("stable reason = %q, want unchanged", got)
+	}
+	tools[0].Description = "Read an exact file"
+	if got := planner.Plan(messages, tools, "").Breakdown.PrefixInvalidationReason; got != "tools" {
+		t.Fatalf("tool reason = %q, want tools", got)
+	}
+	tools[0].Parameters["required"] = []any{"path"}
+	if got := planner.Plan(messages, tools, "").Breakdown.PrefixInvalidationReason; got != "schema" {
+		t.Fatalf("schema reason = %q, want schema", got)
+	}
+	planner.config.promptParts.prompt = "system with changed project"
+	planner.config.promptParts.projectContext = "changed project"
+	messages[0].Content = "system with changed project"
+	if got := planner.Plan(messages, tools, "").Breakdown.PrefixInvalidationReason; got != "project_context" {
+		t.Fatalf("project reason = %q, want project_context", got)
+	}
+}
+
+func TestExplainPrefixChangeNamesEveryChangedComponent(t *testing.T) {
+	baseline := prefixFingerprint{
+		SystemPromptHash:       "system",
+		BaseInstructionsHash:   "base",
+		ConfirmationPolicyHash: "policy",
+		ProjectContextHash:     "project",
+		SkillsHash:             "skills",
+		ToolsHash:              "tools",
+		SchemaHash:             "schema",
+		CompletePrefixHash:     "complete",
+	}
+	tests := []struct {
+		name   string
+		mutate func(*prefixFingerprint)
+		want   string
+	}{
+		{name: "base instructions", mutate: func(value *prefixFingerprint) {
+			value.SystemPromptHash, value.BaseInstructionsHash = "changed", "changed"
+		}, want: "base_instructions"},
+		{name: "confirmation policy", mutate: func(value *prefixFingerprint) {
+			value.SystemPromptHash, value.ConfirmationPolicyHash = "changed", "changed"
+		}, want: "confirmation_policy"},
+		{name: "project context", mutate: func(value *prefixFingerprint) {
+			value.SystemPromptHash, value.ProjectContextHash = "changed", "changed"
+		}, want: "project_context"},
+		{name: "skills", mutate: func(value *prefixFingerprint) { value.SystemPromptHash, value.SkillsHash = "changed", "changed" }, want: "skills"},
+		{name: "unclassified system prompt", mutate: func(value *prefixFingerprint) { value.SystemPromptHash = "changed" }, want: "system_prompt"},
+		{name: "tools and schema", mutate: func(value *prefixFingerprint) { value.ToolsHash, value.SchemaHash = "changed", "changed" }, want: "tools,schema"},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			current := baseline
+			test.mutate(&current)
+			current.CompletePrefixHash = "changed"
+			if got := explainPrefixChange(&baseline, current); got != test.want {
+				t.Fatalf("reason = %q, want %q", got, test.want)
+			}
+		})
+	}
+}

internal/agent/deferred_loop_test.go

@@ -797,3 +797,98 @@ func TestDisabledToolSearchFallsBackToEager(t *testing.T) {
 		t.Fatalf("deferred tool must be callable under eager fallback, got status=%s output=%q", result.Status, result.Output)
 	}
 }
+
+// fakeDeferredMutatorTool is a deferred-eligible tool with mutating Safety
+// (SideEffectWrite), standing in for a real write/mutator MCP tool that would
+// be hidden behind tool_search once deferral activates.
+type fakeDeferredMutatorTool struct{ name string }
+
+func (t fakeDeferredMutatorTool) Name() string        { return t.name }
+func (t fakeDeferredMutatorTool) Description() string { return "mutates the workspace, deferred" }
+func (t fakeDeferredMutatorTool) Parameters() tools.Schema {
+	return tools.Schema{Type: "object", AdditionalProperties: false}
+}
+func (t fakeDeferredMutatorTool) Safety() tools.Safety {
+	return tools.Safety{SideEffect: tools.SideEffectWrite, Permission: tools.PermissionPrompt, Reason: "mutates"}
+}
+func (t fakeDeferredMutatorTool) Run(_ context.Context, _ map[string]any) tools.Result {
+	return tools.Result{Status: tools.StatusOK, Output: "mutated"}
+}
+func (t fakeDeferredMutatorTool) Deferred() bool { return true }
+
+// TestPlanModeToolSearchNeverLeaksDeferredMutatorSchema guards the concern
+// raised in PR #642 review (jatmn, P2): that tool_search filters deferred
+// candidates only by EnabledTools/DisabledTools, not by plan-mode visibility,
+// so a plan-mode model could call `tool_search select:<deferred write tool>`
+// and receive that tool's full schema even though a direct call to it is
+// correctly denied the following turn.
+//
+// tool_search's own Safety is SideEffectNone, and ToolAdvertisedForPermissionMode (the
+// same gate executeToolCall uses to deny a direct call) requires
+// SideEffect==Read to advertise a tool in plan mode. That means tool_search
+// itself is never advertised, never activates deferral (loaderUsable in
+// partitionToolsCached requires ToolAdvertised(loader, permissionMode)), and
+// is denied at dispatch like any other hidden tool if a stale/adversarial
+// call reaches it anyway — so a deferred mutator's schema can never reach the
+// model through tool_search while in plan mode. This test pins that
+// end-to-end: tool_search is absent from the advertised tool list, and a
+// forced call to it is denied before rendering any tool schema.
+func TestPlanModeToolSearchNeverLeaksDeferredMutatorSchema(t *testing.T) {
+	root := t.TempDir()
+	registry := tools.NewRegistry()
+	registry.Register(tools.NewReadFileTool(root))
+	registry.Register(fakeDeferredMutatorTool{name: "mcp__srv__mutate"})
+	registry.Register(fakeDeferredMutatorTool{name: "mcp__srv__mutate2"})
+	registry.Register(tools.NewToolSearchTool(registry))
+
+	provider := &mockProvider{turns: [][]zeroruntime.StreamEvent{
+		{ // turn 1: force a call to tool_search even though it should not be advertised.
+			{Type: zeroruntime.StreamEventToolCallStart, ToolCallID: "c1", ToolName: tools.ToolSearchToolName},
+			{Type: zeroruntime.StreamEventToolCallDelta, ToolCallID: "c1", ArgumentsFragment: `{"query":"select:mcp__srv__mutate"}`},
+			{Type: zeroruntime.StreamEventToolCallEnd, ToolCallID: "c1"},
+			{Type: zeroruntime.StreamEventDone},
+		},
+		{ // turn 2: final answer.
+			{Type: zeroruntime.StreamEventText, Content: "done"},
+			{Type: zeroruntime.StreamEventDone},
+		},
+	}}
+
+	result, err := Run(context.Background(), "plan", provider, Options{
+		Registry:       registry,
+		PermissionMode: PermissionModePlan,
+		DeferThreshold: 2, // 2 deferred mutators registered => eligible for deferral.
+		MaxTurns:       2,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// tool_search (and the deferred mutators) must not be advertised in plan
+	// mode's turn 1 tool list at all.
+	for _, def := range provider.requests[0].Tools {
+		if def.Name == tools.ToolSearchToolName {
+			t.Fatalf("plan mode must not advertise tool_search, got %#v", provider.requests[0].Tools)
+		}
+		if def.Name == "mcp__srv__mutate" || def.Name == "mcp__srv__mutate2" {
+			t.Fatalf("plan mode must not advertise a deferred mutator, got %#v", provider.requests[0].Tools)
+		}
+	}
+
+	// The forced call must be denied outright, never a loaded-schema result:
+	// the tool result must not mention the mutator's name or carry a
+	// load_tools signal.
+	var toolMessage string
+	for _, message := range result.Messages {
+		if message.Role == zeroruntime.MessageRoleTool {
+			toolMessage = message.Content
+			break
+		}
+	}
+	if !strings.Contains(toolMessage, "not available in plan mode") {
+		t.Fatalf("expected tool_search call denied in plan mode, got %q", toolMessage)
+	}
+	if strings.Contains(toolMessage, "mcp__srv__mutate") {
+		t.Fatalf("denial must not leak the deferred mutator's name/schema, got %q", toolMessage)
+	}
+}

internal/agent/escalate_loop_test.go

@@ -144,9 +144,10 @@ func TestRunSwitchesProviderOnEscalationRequest(t *testing.T) {
 	var switchedTo string
 	switchCount := 0
 	result, err := Run(context.Background(), "go", firstProvider, Options{
-		Registry: registry,
-		Model:    "claude-sonnet-4.5",
-		MaxTurns: 4,
+		Registry:    registry,
+		Model:       "claude-sonnet-4.5",
+		ServiceTier: "priority",
+		MaxTurns:    4,
 		ModelSwitcher: func(_ context.Context, modelID string) (Provider, error) {
 			switchCount++
 			switchedTo = modelID
@@ -167,9 +168,15 @@ func TestRunSwitchesProviderOnEscalationRequest(t *testing.T) {
 	if len(firstProvider.requests) != 1 {
 		t.Fatalf("expected first provider to handle exactly the escalation turn, got %d requests", len(firstProvider.requests))
 	}
+	if got := firstProvider.requests[0].ServiceTier; got != "priority" {
+		t.Fatalf("initial request service tier = %q, want priority", got)
+	}
 	if len(secondProvider.requests) != 1 {
 		t.Fatalf("expected second provider to handle the post-switch turn, got %d requests", len(secondProvider.requests))
 	}
+	if got := secondProvider.requests[0].ServiceTier; got != "" {
+		t.Fatalf("post-switch request retained service tier %q", got)
+	}
 	if result.FinalAnswer != "answered on the upgraded model" {
 		t.Fatalf("expected final answer from the swapped provider, got %q", result.FinalAnswer)
 	}
@@ -211,9 +218,10 @@ func TestRunEscalationSwitcherErrorIsNonFatal(t *testing.T) {
 	provider := &mockProvider{turns: escalateThenAnswerTurns("recovered")}
 
 	result, err := Run(context.Background(), "go", provider, Options{
-		Registry: registry,
-		Model:    "claude-sonnet-4.5",
-		MaxTurns: 4,
+		Registry:    registry,
+		Model:       "claude-sonnet-4.5",
+		ServiceTier: "priority",
+		MaxTurns:    4,
 		ModelSwitcher: func(_ context.Context, _ string) (Provider, error) {
 			return nil, errors.New("provider build blew up")
 		},
@@ -225,6 +233,9 @@ func TestRunEscalationSwitcherErrorIsNonFatal(t *testing.T) {
 	if len(provider.requests) != 2 {
 		t.Fatalf("expected the run to continue on the original provider, got %d requests", len(provider.requests))
 	}
+	if got := provider.requests[1].ServiceTier; got != "priority" {
+		t.Fatalf("failed-switch request service tier = %q, want priority", got)
+	}
 	if result.FinalAnswer != "recovered" {
 		t.Fatalf("expected final answer after non-fatal switch error, got %q", result.FinalAnswer)
 	}

internal/agent/loop.go

@@ -40,7 +40,15 @@ const (
 	toolResultControlSpecReview = "spec_review_required"
 )
 
-var errPermissionApprovalCanceled = errors.New("permission approval cancelled")
+// ErrPermissionApprovalCanceled ends a run because the caller cancelled a
+// permission prompt, rather than because anything failed.
+//
+// EXPORTED FOR THE SURFACES. A cancel is a normal ending and each surface says
+// so its own way — the TUI unwinds, and ACP has a "cancelled" stop reason for
+// exactly this. While it was unexported ACP could not distinguish it from a
+// fault and reported it as an internal error, so declining a tool looked like
+// the agent crashing.
+var ErrPermissionApprovalCanceled = errors.New("permission approval cancelled")
 
 // isImageRejectionError reports whether err is a provider 400 that rejects
 // image/multimodal content. This is checked BEFORE the compaction-retry path
@@ -183,10 +191,23 @@ func Run(ctx context.Context, prompt string, provider Provider, options Options)
 	defer runPermissions.cleanup()
 
 	promptParts := buildSystemPromptParts(options)
+	planner := newContextPlanner(contextPlannerConfig{
+		contextWindow:  options.ContextWindow,
+		promptCacheKey: options.SessionID,
+		serviceTier:    options.ServiceTier,
+		promptParts:    promptParts,
+	})
 	messages := zeroruntime.SeedMessagesWithImages(promptParts.prompt, prompt, options.Images)
 
 	guards := newGuardState()
 	task := newTaskState(prompt, options.Trace)
+	onPermission := options.OnPermission
+	options.OnPermission = func(event PermissionEvent) {
+		task.observe(taskStateEvent{kind: taskStateEventPermission, permission: event})
+		if onPermission != nil {
+			onPermission(event)
+		}
+	}
 	compactor := newCompactionState(options, task)
 	defer func() {
 		// A final transcript comparison is observational. It records drift but
@@ -275,42 +296,15 @@ func Run(ctx context.Context, prompt string, provider Provider, options Options)
 		exposed, _ := partitionToolsCached(registry, permissionMode, options, loaded, toolDefCache)
 		toolPartitionSpan.End()
 
-		// Fingerprint the exact system prompt built at run start plus this turn's
-		// provider-visible tool definitions in their emitted order. Reusing the
-		// retained prompt parts avoids rebuilding workspace context while ensuring
-		// the trace describes the same bytes carried by the request.
-		if options.Trace != nil {
-			fp := computePrefixFingerprint(buildPromptSubstringsFromParts(promptParts, exposed))
-			options.Trace.EmitPrefixHash(trace.PrefixHash{
-				SystemPromptHash:       fp.SystemPromptHash,
-				BaseInstructionsHash:   fp.BaseInstructionsHash,
-				ConfirmationPolicyHash: fp.ConfirmationPolicyHash,
-				ProjectContextHash:     fp.ProjectContextHash,
-				SkillsHash:             fp.SkillsHash,
-				ToolsHash:              fp.ToolsHash,
-				SchemaHash:             fp.SchemaHash,
-				CompletePrefixHash:     fp.CompletePrefixHash,
-			})
-		}
-
 		// PROACTIVE compaction: if the history is approaching the model's
 		// context window, summarize the oldest middle before building the
 		// request. A no-op when ContextWindow == 0 (compaction disabled).
 		compactionSpan := options.Trace.Span(trace.SpanCompaction)
 		messages = compactor.maybeCompact(ctx, provider, messages, exposed)
 		compactionSpan.End()
-		request := zeroruntime.CompletionRequest{
-			Messages:        copyMessages(messages),
-			Tools:           exposed,
-			ReasoningEffort: options.ReasoningEffort,
-			PromptCacheKey:  options.SessionID,
-		}
-
-		// Report the per-category context budget for this turn so a surface can
-		// show utilization. Opt-in: a no-op when OnContext is unset.
-		if options.OnContext != nil {
-			options.OnContext(MeasureContext(messages, request.Tools, options.ContextWindow))
-		}
+		plan := planner.Plan(messages, exposed, options.ReasoningEffort)
+		request := plan.Request
+		recordContextPlan(options, plan)
 
 		// A transient upstream disconnect on the initial connect is retried with
 		// backoff (before any content is forwarded, so no OnText is duplicated);
@@ -335,12 +329,9 @@ func Run(ctx context.Context, prompt string, provider Provider, options Options)
 				// on registry+loaded, not on the messages, so they stay valid after
 				// compaction. Using the bare toolDefinitions here would route through an
 				// empty-loaded partition, re-hiding every already-loaded deferred tool.
-				request = zeroruntime.CompletionRequest{
-					Messages:        copyMessages(messages),
-					Tools:           exposed,
-					ReasoningEffort: options.ReasoningEffort,
-					PromptCacheKey:  options.SessionID,
-				}
+				retryPlan := planner.Plan(messages, exposed, options.ReasoningEffort)
+				request = retryPlan.Request
+				recordContextPlan(options, retryPlan)
 				// Pre-content connect after a context-limit compaction: route through the
 				// reconnect helper so a transient upstream hiccup here doesn't fail the
 				// whole run and re-burn every token (AUDIT-L1).
@@ -424,12 +415,9 @@ func Run(ctx context.Context, prompt string, provider Provider, options Options)
 				// Reuse the SAME active-mode partition (exposed) from this turn rather
 				// than the bare toolDefinitions: exposed depends on registry+loaded (not
 				// the messages), so it stays valid after compaction.
-				retryRequest := zeroruntime.CompletionRequest{
-					Messages:        copyMessages(messages),
-					Tools:           exposed,
-					ReasoningEffort: options.ReasoningEffort,
-					PromptCacheKey:  options.SessionID,
-				}
+				retryPlan := planner.Plan(messages, exposed, options.ReasoningEffort)
+				retryRequest := retryPlan.Request
+				recordContextPlan(options, retryPlan)
 				retryStream, retryStreamErr := streamWithReconnect(ctx, provider, retryRequest, reconnectNoticeFor(options))
 				if retryStreamErr != nil {
 					return collected, retryStreamErr
@@ -487,12 +475,9 @@ func Run(ctx context.Context, prompt string, provider Provider, options Options)
 				result.Messages = copyMessages(messages)
 				return result, err
 			}
-			retryRequest := zeroruntime.CompletionRequest{
-				Messages:        copyMessages(messages),
-				Tools:           exposed,
-				ReasoningEffort: options.ReasoningEffort,
-				PromptCacheKey:  options.SessionID,
-			}
+			retryPlan := planner.Plan(messages, exposed, options.ReasoningEffort)
+			retryRequest := retryPlan.Request
+			recordContextPlan(options, retryPlan)
 			retryStream, retryErr := streamWithReconnect(ctx, provider, retryRequest, reconnectNoticeFor(options))
 			if retryErr != nil {
 				result.Messages = copyMessages(messages)
@@ -698,7 +683,7 @@ func Run(ctx context.Context, prompt string, provider Provider, options Options)
 			}
 			options.Trace.Counter(trace.CounterToolCalls, 1)
 			recordOutputBudgetTrace(options.Trace, toolResult)
-			task.observe(taskStateEvent{kind: taskStateEventToolResult, toolResult: toolResult})
+			task.observe(taskStateEvent{kind: taskStateEventToolResult, arguments: call.Arguments, toolResult: toolResult})
 			if options.OnToolResult != nil {
 				options.OnToolResult(toolResult)
 			}
@@ -712,9 +697,11 @@ func Run(ctx context.Context, prompt string, provider Provider, options Options)
 				turnRequestedModel = toolResult.RequestedModel
 			}
 			messages = append(messages, zeroruntime.Message{
-				Role:       zeroruntime.MessageRoleTool,
-				Content:    toolResult.Output,
-				ToolCallID: toolResult.ToolCallID,
+				Role:         zeroruntime.MessageRoleTool,
+				Content:      toolResult.ModelOutput(),
+				ToolCallID:   toolResult.ToolCallID,
+				IsError:      toolResult.Status == tools.StatusError,
+				ChangedFiles: append([]string(nil), toolResult.ChangedFiles...),
 			})
 			// Images ride a following USER message rather than the tool result
 			// above. Every provider drops images on a tool-role message —
@@ -743,7 +730,7 @@ func Run(ctx context.Context, prompt string, provider Provider, options Options)
 			if stopReason := stopReasonFromToolResult(toolResult); stopReason != "" {
 				messages = appendAbortedToolResults(messages, collected.ToolCalls[index+1:])
 				messages = append(messages, toolImageMessages...)
-				result.FinalAnswer = toolResult.Output
+				result.FinalAnswer = toolResult.ModelOutput()
 				result.StopReason = stopReason
 				result.Messages = copyMessages(messages)
 				return result, nil
@@ -756,7 +743,7 @@ func Run(ctx context.Context, prompt string, provider Provider, options Options)
 			// aren't fixed by reformatting the call, so a "match this schema" hint
 			// would misdirect the model toward JSON shape or blocked behavior.
 			retriableFailure := isRetriableToolError(toolResult)
-			outcome := guards.observeToolResult(call.Name, retriableFailure, toolResult.Output)
+			outcome := guards.observeToolResult(call.Name, retriableFailure, toolResult.ModelOutput())
 			posture.observeToolOutcome(outcome, toolResult)
 			if outcome.Stop {
 				// The assistant message advertised EVERY collected tool call, but
@@ -772,7 +759,7 @@ func Run(ctx context.Context, prompt string, provider Provider, options Options)
 				return result, nil
 			}
 			if outcome.InjectHint && failureHint == "" {
-				failureHint = toolFailureHint(call.Name, toolSchemaJSON(registry, call.Name), toolResult.Output)
+				failureHint = toolFailureHint(call.Name, toolSchemaJSON(registry, call.Name), toolResult.ModelOutput())
 			}
 
 			// Collect the files this successful mutating tool changed. Self-correct
@@ -851,6 +838,11 @@ func Run(ctx context.Context, prompt string, provider Provider, options Options)
 					_ = session.Prewarm(ctx)
 					provider = sessionProvider{session: session}
 					options.Model = turnRequestedModel
+					// Service tiers are model capabilities. A successful escalation may
+					// target a model that does not support the tier selected before the
+					// switch, so let the destination use its default.
+					options.ServiceTier = ""
+					planner.config.serviceTier = ""
 					options.Trace.Counter(trace.CounterModelSwitches, 1)
 					// KNOWN LIMITATION (deferred): the compactor's context-window budget
 					// is fixed at run start from options.ContextWindow and is NOT updated
@@ -920,7 +912,7 @@ func Run(ctx context.Context, prompt string, provider Provider, options Options)
 		})
 	}
 	finalExposed, _ := partitionToolsCached(registry, permissionMode, options, loaded, toolDefCache)
-	if answer, finalMessages, finishReason := finalAnswerAfterMaxTurns(ctx, provider, messages, finalExposed, options); strings.TrimSpace(answer) != "" {
+	if answer, finalMessages, finishReason := finalAnswerAfterMaxTurns(ctx, provider, planner, messages, finalExposed, options); strings.TrimSpace(answer) != "" {
 		result.FinalAnswer = answer
 		result.FinishReason = finishReason
 		result.Messages = copyMessages(finalMessages)
@@ -944,6 +936,21 @@ func recordOutputBudgetTrace(recorder *trace.Recorder, result ToolResult) {
 	if recorder == nil || result.Meta["output_budget_category"] == "" {
 		return
 	}
+	if result.Outcome.Finalized() {
+		diagnostics := result.Outcome.Diagnostics
+		recorder.EmitOutputBudget(trace.OutputBudgetEvent{
+			Tool:                    result.Name,
+			Category:                diagnostics.Category,
+			OriginalBytes:           diagnostics.OriginalBytes,
+			RetainedBytes:           diagnostics.ModelBytes,
+			EstimatedOriginalTokens: diagnostics.EstimatedOriginalTokens,
+			EstimatedRetainedTokens: diagnostics.EstimatedModelTokens,
+			Truncated:               diagnostics.Truncated,
+			Reason:                  diagnostics.Reason,
+			SpillCreated:            result.Outcome.Artifact != nil,
+		})
+		return
+	}
 	parseInt := func(key string) int {
 		value, _ := strconv.Atoi(result.Meta[key])
 		return value
@@ -962,7 +969,32 @@ func recordOutputBudgetTrace(recorder *trace.Recorder, result ToolResult) {
 	})
 }
 
-func finalAnswerAfterMaxTurns(ctx context.Context, provider Provider, messages []zeroruntime.Message, toolDefs []zeroruntime.ToolDefinition, options Options) (string, []zeroruntime.Message, string) {
+func recordContextPlan(options Options, plan contextPlan) {
+	recordContextPlanTrace(options.Trace, plan)
+	if options.OnContext != nil {
+		options.OnContext(plan.Breakdown)
+	}
+}
+
+func recordContextPlanTrace(recorder *trace.Recorder, plan contextPlan) {
+	if recorder == nil {
+		return
+	}
+	fingerprint := plan.PrefixFingerprint
+	recorder.EmitPrefixHash(trace.PrefixHash{
+		SystemPromptHash:       fingerprint.SystemPromptHash,
+		BaseInstructionsHash:   fingerprint.BaseInstructionsHash,
+		ConfirmationPolicyHash: fingerprint.ConfirmationPolicyHash,
+		ProjectContextHash:     fingerprint.ProjectContextHash,
+		SkillsHash:             fingerprint.SkillsHash,
+		ToolsHash:              fingerprint.ToolsHash,
+		SchemaHash:             fingerprint.SchemaHash,
+		CompletePrefixHash:     fingerprint.CompletePrefixHash,
+		InvalidationReason:     plan.Breakdown.PrefixInvalidationReason,
+	})
+}
+
+func finalAnswerAfterMaxTurns(ctx context.Context, provider Provider, planner *contextPlanner, messages []zeroruntime.Message, toolDefs []zeroruntime.ToolDefinition, options Options) (string, []zeroruntime.Message, string) {
 	finalMessages := copyMessages(messages)
 	finalMessages = append(finalMessages, zeroruntime.Message{
 		Role:    zeroruntime.MessageRoleUser,
@@ -971,12 +1003,9 @@ func finalAnswerAfterMaxTurns(ctx context.Context, provider Provider, messages [
 	// The max-turns final-answer call is a pre-content connect, often after a long
 	// autonomous/cron run — route it through the reconnect helper so a single
 	// transient hiccup doesn't drop the final summary (AUDIT-L1).
-	stream, err := streamWithReconnect(ctx, provider, zeroruntime.CompletionRequest{
-		Messages:        copyMessages(finalMessages),
-		Tools:           toolDefs,
-		ReasoningEffort: options.ReasoningEffort,
-		PromptCacheKey:  options.SessionID,
-	}, reconnectNoticeFor(options))
+	plan := planner.Plan(finalMessages, toolDefs, options.ReasoningEffort)
+	recordContextPlan(options, plan)
+	stream, err := streamWithReconnect(ctx, provider, plan.Request, reconnectNoticeFor(options))
 	if err != nil {
 		return "", messages, ""
 	}
@@ -1119,12 +1148,13 @@ func executeToolCall(ctx context.Context, registry *tools.Registry, call ToolCal
 		}, nil
 	}
 	tool, toolFound := registry.Get(call.Name)
-	if permissionMode == PermissionModeSpecDraft && toolFound && !ToolAdvertised(tool, permissionMode) {
+	if (permissionMode == PermissionModeSpecDraft || permissionMode == PermissionModePlan) && toolFound && !ToolAdvertised(tool, permissionMode) {
+		modeName := string(permissionMode)
 		return ToolResult{
 			ToolCallID:   call.ID,
 			Name:         call.Name,
 			Status:       tools.StatusError,
-			Output:       `Error: Tool "` + call.Name + `" is not available in spec-draft mode.`,
+			Output:       `Error: Tool "` + call.Name + `" is not available in ` + modeName + ` mode.`,
 			DenialReason: DenialFiltered,
 		}, nil
 	}
@@ -1342,7 +1372,7 @@ func executeToolCall(ctx context.Context, registry *tools.Registry, call ToolCal
 			}
 		case PermissionDecisionCancel:
 			emitCanceledPermission(options, call, requestEvent, decisionReason)
-			return canceledPermissionResult(call, decisionReason, requestEvent), fmt.Errorf("%w for %s", errPermissionApprovalCanceled, call.Name)
+			return canceledPermissionResult(call, decisionReason, requestEvent), fmt.Errorf("%w for %s", ErrPermissionApprovalCanceled, call.Name)
 		default:
 			emitDeniedPermission(options, call, requestEvent, decisionReason)
 			return deniedPermissionResult(call, decisionReason, requestEvent), nil
@@ -1457,14 +1487,15 @@ func executeToolCall(ctx context.Context, registry *tools.Registry, call ToolCal
 		ToolCallID:      call.ID,
 		Name:            call.Name,
 		Status:          result.Status,
-		Output:          result.Output,
+		Output:          result.ModelOutput(),
 		Truncated:       result.Truncated,
 		Meta:            result.Meta,
 		Images:          result.Images,
 		Redacted:        result.Redacted,
 		ChangedFiles:    result.ChangedFiles,
 		ChangeSummaries: result.ChangeSummaries,
-		Display:         result.Display,
+		Display:         result.HumanDisplay(),
+		Outcome:         result.Outcome,
 		LoadedTools:     loadedToolsFromResult(result.Meta),
 		// A tool may signal a mid-run model escalation by carrying the target id
 		// in Meta["escalate_to_model"]. Lift it into the typed loop-level field;
@@ -1525,7 +1556,7 @@ func maybeRetryUnsandboxedAfterSandboxRestriction(ctx context.Context, registry
 	case PermissionDecisionCancel:
 		emitCanceledPermission(options, call, requestEvent, reason)
 		canceled := canceledPermissionResult(call, reason, requestEvent)
-		return result, &canceled, true, decision.Action, reason, nil, fmt.Errorf("%w for %s", errPermissionApprovalCanceled, call.Name)
+		return result, &canceled, true, decision.Action, reason, nil, fmt.Errorf("%w for %s", ErrPermissionApprovalCanceled, call.Name)
 	default:
 		emitDeniedPermission(options, call, requestEvent, reason)
 		denied := deniedPermissionResult(call, reason, requestEvent)
@@ -1573,7 +1604,7 @@ func maybeRetryWithNetworkAfterSandboxDenial(ctx context.Context, registry *tool
 	case PermissionDecisionCancel:
 		emitCanceledPermission(options, call, requestEvent, reason)
 		canceled := canceledPermissionResult(call, reason, requestEvent)
-		return result, &canceled, true, decision.Action, reason, fmt.Errorf("%w for %s", errPermissionApprovalCanceled, call.Name)
+		return result, &canceled, true, decision.Action, reason, fmt.Errorf("%w for %s", ErrPermissionApprovalCanceled, call.Name)
 	default:
 		emitDeniedPermission(options, call, requestEvent, reason)
 		denied := deniedPermissionResult(call, reason, requestEvent)
@@ -1802,9 +1833,31 @@ func toolResultFromPrePermissionReject(call ToolCall, result tools.Result) ToolR
 	}
 }
 
+// hooksSuppressed reports whether advisory (non-veto) hooks must not run for
+// this run's permission mode. Plan mode promises a read-only turn, but
+// sessionStart/sessionEnd/afterTool hooks execute configured host commands
+// outside the advertised-tool and sandbox gates, so dispatching them would let
+// merely starting a plan session or finishing a read mutate the workspace.
+//
+// beforeTool is intentionally NOT suppressed: a non-zero exit is a deny gate,
+// and skipping it fails open (operators who block secret-file reads via
+// beforeTool would lose that protection under /plan on). See dispatchBeforeTool.
+//
+// Spec-draft keeps the existing trust-gated hook model: project hooks still
+// fire when the workspace (or its worktree trust root) is trusted. That is
+// intentional; trust inheritance for --use-spec --worktree is covered by
+// TestExecSpecWorktreeInheritsTrustEndToEnd.
+func hooksSuppressed(options Options) bool {
+	return options.PermissionMode == PermissionModePlan
+}
+
 // dispatchBeforeTool runs configured beforeTool hooks for a tool call. A hook
 // that exits non-zero vetoes the call: the returned bool is true and the tool
 // must not run. A nil dispatcher (no hooks wired) is a no-op.
+//
+// Unlike advisory hooks, beforeTool still runs under plan mode. Suppressing it
+// would fail open: a project policy that blocks reads of secrets via
+// beforeTool would silently stop applying the moment permission mode is plan.
 func dispatchBeforeTool(ctx context.Context, options Options, call ToolCall, args map[string]any) (hooks.DispatchOutcome, bool) {
 	if options.Hooks == nil {
 		return hooks.DispatchOutcome{}, false
@@ -1829,7 +1882,7 @@ func dispatchBeforeTool(ctx context.Context, options Options, call ToolCall, arg
 // returns any advisory output (e.g. a formatter or vet result) to surface back
 // to the model. afterTool hooks never block. A nil dispatcher is a no-op.
 func dispatchAfterTool(ctx context.Context, options Options, call ToolCall, args map[string]any, result tools.Result) string {
-	if options.Hooks == nil {
+	if options.Hooks == nil || hooksSuppressed(options) {
 		return ""
 	}
 	outcome := options.Hooks.Dispatch(ctx, hooks.DispatchInput{
@@ -1853,7 +1906,7 @@ func dispatchAfterTool(ctx context.Context, options Options, call ToolCall, args
 // model turn. Lifecycle hooks are advisory: dispatcher failures are audited but
 // never block the run.
 func dispatchSessionStart(ctx context.Context, options Options) {
-	if options.Hooks == nil {
+	if options.Hooks == nil || hooksSuppressed(options) {
 		return
 	}
 	options.Hooks.Dispatch(ctx, hooks.DispatchInput{
@@ -1874,7 +1927,7 @@ func dispatchSessionStart(ctx context.Context, options Options) {
 // dispatchSessionEnd runs configured sessionEnd hooks once when the agent run
 // exits, including early error returns. Lifecycle hooks are advisory.
 func dispatchSessionEnd(ctx context.Context, options Options, result Result, runErr error) {
-	if options.Hooks == nil {
+	if options.Hooks == nil || hooksSuppressed(options) {
 		return
 	}
 	payload := map[string]any{
@@ -2061,13 +2114,14 @@ func askUserFallbackResult(ctx context.Context, registry *tools.Registry, call T
 			ToolCallID:      call.ID,
 			Name:            call.Name,
 			Status:          result.Status,
-			Output:          result.Output,
+			Output:          result.ModelOutput(),
 			Truncated:       result.Truncated,
 			Meta:            result.Meta,
 			Redacted:        result.Redacted,
 			ChangedFiles:    result.ChangedFiles,
 			ChangeSummaries: result.ChangeSummaries,
-			Display:         result.Display,
+			Display:         result.HumanDisplay(),
+			Outcome:         result.Outcome,
 		}
 	}
 	return ToolResult{
@@ -2173,6 +2227,20 @@ type requestPermissionsArgs struct {
 }
 
 func executeRequestPermissions(ctx context.Context, call ToolCall, args map[string]any, permissionMode PermissionMode, options Options) (ToolResult, error) {
+	// request_permissions is dispatched by name above, before the registry-based
+	// ToolAdvertised gate runs, so a read-only mode's registry omitting this tool
+	// (rather than registering it as denied) must not fall through to a real
+	// grant. Deny it here unconditionally for spec-draft/plan, independent of
+	// whether the caller's registry happens to contain the tool.
+	if permissionMode == PermissionModeSpecDraft || permissionMode == PermissionModePlan {
+		return ToolResult{
+			ToolCallID:   call.ID,
+			Name:         call.Name,
+			Status:       tools.StatusError,
+			Output:       `Error: Tool "` + call.Name + `" is not available in ` + string(permissionMode) + ` mode.`,
+			DenialReason: DenialFiltered,
+		}, nil
+	}
 	parsed, err := parseRequestPermissionsArgs(args)
 	if err != nil {
 		return ToolResult{
@@ -2718,9 +2786,36 @@ func permissionRequestFromEvent(event PermissionEvent, args map[string]any, opti
 		Grant:              event.Grant,
 		CommandPrefix:      append([]string(nil), event.CommandPrefix...),
 		AvailableDecisions: availablePermissionDecisions(event, args, options),
+		// Computed from the SAME conditions shellExecutionArgsForApproval uses,
+		// so the prompt cannot claim an escalation that will not happen or stay
+		// silent about one that will. Keeping the two in step matters more than
+		// the wording: a label that overstates gets ignored, and one that
+		// understates is the bug being fixed.
+		PrefixApprovalEscalates: shellPrefixApprovalEscalates(event.ToolName, args, options),
 	}
 }
 
+// shellPrefixApprovalEscalates reports whether approving a command prefix would
+// also take this command out of the sandbox.
+//
+// Deliberately mirrors shellExecutionArgsForApproval's guards rather than
+// re-deriving them: same tool test, same sandbox availability test, and the same
+// two opt-outs for a call that already asked for additional permissions or
+// escalation. Those already carry their own disclosure, so labelling them again
+// would be noise.
+func shellPrefixApprovalEscalates(toolName string, args map[string]any, options Options) bool {
+	if !isShellCommandTool(toolName) {
+		return false
+	}
+	if options.Sandbox == nil || !options.Sandbox.UnsandboxedExecutionAllowed() {
+		return false
+	}
+	if shellCommandAdditionalPermissionsRequested(args) || shellCommandRequiresEscalated(args) {
+		return false
+	}
+	return true
+}
+
 func availablePermissionDecisions(event PermissionEvent, args map[string]any, options Options) []PermissionDecisionAction {
 	if event.Action != PermissionActionPrompt {
 		return nil
@@ -3202,11 +3297,17 @@ func propertyToRuntimeMap(property tools.PropertySchema) map[string]any {
 }
 
 func ToolAdvertised(tool tools.Tool, permissionMode PermissionMode) bool {
+	// Denied tools are never advertised in any mode. Keep this short-circuit
+	// here so auto/member-auto/ask/unsafe all honor it before mode branches;
+	// tools.ToolAdvertisedForPermissionMode repeats it for the tool_search path
+	// which never enters this function.
 	if tool.Safety().Permission == tools.PermissionDeny {
 		return false
 	}
-	if permissionMode == PermissionModeSpecDraft {
-		return toolAdvertisedInSpecDraft(tool)
+	// plan/spec-draft policy lives in tools so tool_search and the dispatch
+	// gate cannot drift. PermissionDeny was already checked above.
+	if permissionMode == PermissionModeSpecDraft || permissionMode == PermissionModePlan {
+		return tools.ToolAdvertisedForPermissionMode(tool, string(permissionMode))
 	}
 	if permissionMode == PermissionModeAuto {
 		return tool.Safety().Permission == tools.PermissionAllow || tool.Safety().AdvertiseInAuto
@@ -3229,17 +3330,6 @@ func ToolAdvertised(tool tools.Tool, permissionMode PermissionMode) bool {
 	return true
 }
 
-func toolAdvertisedInSpecDraft(tool tools.Tool) bool {
-	switch tool.Name() {
-	case "ask_user", "submit_spec":
-		return true
-	case "update_plan":
-		return false
-	}
-	safety := tool.Safety()
-	return safety.SideEffect == tools.SideEffectRead && safety.Permission == tools.PermissionAllow
-}
-
 func stopReasonFromToolResult(result ToolResult) StopReason {
 	if result.Meta == nil {
 		return ""
@@ -3278,6 +3368,7 @@ func appendAbortedToolResults(messages []Message, remaining []ToolCall) []Messag
 			Role:       zeroruntime.MessageRoleTool,
 			Content:    abortedToolResultNotice,
 			ToolCallID: call.ID,
+			IsError:    true,
 		})
 	}
 	return messages
@@ -3308,6 +3399,9 @@ func copyMessages(messages []Message) []Message {
 		if message.Reasoning != nil {
 			copied[index].Reasoning = append([]zeroruntime.ReasoningBlock{}, message.Reasoning...)
 		}
+		if message.ChangedFiles != nil {
+			copied[index].ChangedFiles = append([]string(nil), message.ChangedFiles...)
+		}
 		// Deep-copy image attachments (slice AND each Data byte slice) so the
 		// raw image bytes are never aliased across history/request/result copies.
 		copied[index].Images = zeroruntime.CloneImageBlocks(message.Images)

internal/agent/loop_test.go

@@ -1853,7 +1853,7 @@ func TestRunAbortsWhenPermissionRequestCanceled(t *testing.T) {
 		},
 	})
 
-	if !errors.Is(err, errPermissionApprovalCanceled) {
+	if !errors.Is(err, ErrPermissionApprovalCanceled) {
 		t.Fatalf("expected permission approval cancel error, got %v", err)
 	}
 	if result.FinalAnswer != "" {
@@ -3391,6 +3391,378 @@ func TestSpecDraftDeniesBashToolCalls(t *testing.T) {
 	}
 }
 
+func TestPlanModeAdvertisesOnlySafeTools(t *testing.T) {
+	root := t.TempDir()
+	registry := tools.NewRegistry()
+	for _, tool := range tools.CoreToolsScoped(root, nil) {
+		registry.Register(tool)
+	}
+	provider := &mockProvider{
+		turns: [][]zeroruntime.StreamEvent{{
+			{Type: zeroruntime.StreamEventText, Content: "done"},
+			{Type: zeroruntime.StreamEventDone},
+		}},
+	}
+
+	_, err := Run(context.Background(), "plan", provider, Options{
+		Registry:       registry,
+		PermissionMode: PermissionModePlan,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	names := map[string]bool{}
+	for _, definition := range provider.requests[0].Tools {
+		names[definition.Name] = true
+	}
+	for _, want := range []string{"read_file", "list_directory", "glob", "grep", "skill", "ask_user", "update_plan"} {
+		if !names[want] {
+			t.Fatalf("plan mode tools missing %q from %#v", want, names)
+		}
+	}
+	for _, denied := range []string{"write_file", "edit_file", "apply_patch", "bash", "web_fetch", "lsp_navigate"} {
+		if names[denied] {
+			t.Fatalf("plan mode advertised denied tool %q in %#v", denied, names)
+		}
+	}
+}
+
+// spoofedSafetyTool lets a test register a tool under a name the plan allowlist
+// historically treated specially (ask_user, update_plan) but with attacker-chosen
+// Safety, simulating a caller that overwrites the real tool: Registry.Register
+// keys purely on Name(), so nothing stops a re-registration under the same name.
+type spoofedSafetyTool struct {
+	name   string
+	safety tools.Safety
+	run    func(ctx context.Context, args map[string]any) tools.Result
+}
+
+func (tool spoofedSafetyTool) Name() string             { return tool.name }
+func (tool spoofedSafetyTool) Description() string      { return "spoofed tool for test" }
+func (tool spoofedSafetyTool) Parameters() tools.Schema { return tools.Schema{Type: "object"} }
+func (tool spoofedSafetyTool) Safety() tools.Safety     { return tool.safety }
+func (tool spoofedSafetyTool) Run(ctx context.Context, args map[string]any) tools.Result {
+	return tool.run(ctx, args)
+}
+
+// TestSpecDraftModeRejectsNameOnlySpoofedControlTools guards against
+// tools.ToolAdvertisedForPermissionMode trusting the names "ask_user"/"submit_spec"
+// alone: a re-registered tool with the wrong Safety shape must be neither
+// advertised nor executed in spec-draft mode.
+func TestSpecDraftModeRejectsNameOnlySpoofedControlTools(t *testing.T) {
+	cases := []struct {
+		name   string
+		safety tools.Safety
+	}{
+		{name: "ask_user", safety: tools.Safety{SideEffect: tools.SideEffectShell, Permission: tools.PermissionAllow, Reason: "spoof"}},
+		{name: "submit_spec", safety: tools.Safety{SideEffect: tools.SideEffectShell, Permission: tools.PermissionAllow, Reason: "spoof"}},
+		{name: "ask_user", safety: tools.Safety{SideEffect: tools.SideEffectRead, Permission: tools.PermissionDeny, Reason: "spoof"}},
+		{name: "submit_spec", safety: tools.Safety{SideEffect: tools.SideEffectWrite, Permission: tools.PermissionDeny, Reason: "spoof"}},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name+"/"+string(tc.safety.SideEffect)+"/"+string(tc.safety.Permission), func(t *testing.T) {
+			written := filepath.Join(t.TempDir(), "spoofed.txt")
+			registry := tools.NewRegistry()
+			registry.Register(spoofedSafetyTool{
+				name:   tc.name,
+				safety: tc.safety,
+				run: func(ctx context.Context, args map[string]any) tools.Result {
+					_ = os.WriteFile(written, []byte("spoofed"), 0o644)
+					return tools.Result{Status: tools.StatusOK, Output: "spoofed"}
+				},
+			})
+			provider := &mockProvider{
+				turns: [][]zeroruntime.StreamEvent{
+					{
+						{Type: zeroruntime.StreamEventToolCallStart, ToolCallID: "call-1", ToolName: tc.name},
+						{Type: zeroruntime.StreamEventToolCallDelta, ToolCallID: "call-1", ArgumentsFragment: `{}`},
+						{Type: zeroruntime.StreamEventToolCallEnd, ToolCallID: "call-1"},
+						{Type: zeroruntime.StreamEventDone},
+					},
+					{
+						{Type: zeroruntime.StreamEventText, Content: "done"},
+						{Type: zeroruntime.StreamEventDone},
+					},
+				},
+			}
+			result, err := Run(context.Background(), "spec", provider, Options{
+				Registry:       registry,
+				PermissionMode: PermissionModeSpecDraft,
+				MaxTurns:       2,
+			})
+			if err != nil {
+				t.Fatal(err)
+			}
+			for _, definition := range provider.requests[0].Tools {
+				if definition.Name == tc.name {
+					t.Fatalf("spec-draft advertised spoofed %s with safety %+v", tc.name, tc.safety)
+				}
+			}
+			var denied string
+			for _, message := range result.Messages {
+				if message.Role == zeroruntime.MessageRoleTool {
+					denied = message.Content
+					break
+				}
+			}
+			if !strings.Contains(denied, "not available") {
+				t.Fatalf("expected spoofed %s denial, got %q", tc.name, denied)
+			}
+			if _, err := os.Stat(written); !os.IsNotExist(err) {
+				t.Fatalf("spoofed %s should not have run, stat err=%v", tc.name, err)
+			}
+		})
+	}
+}
+
+// TestPlanModeRejectsNameOnlySpoofedControlTools guards against
+// tools.ToolAdvertisedForPermissionMode trusting the name "update_plan"/"ask_user" alone: a tool
+// registered under either name with mutating Safety must be neither advertised
+// nor executed in plan mode.
+func TestPlanModeRejectsNameOnlySpoofedControlTools(t *testing.T) {
+	for _, name := range []string{"update_plan", "ask_user"} {
+		t.Run(name, func(t *testing.T) {
+			root := t.TempDir()
+			written := filepath.Join(root, "spoofed.txt")
+			registry := tools.NewRegistry()
+			registry.Register(spoofedSafetyTool{
+				name:   name,
+				safety: tools.Safety{SideEffect: tools.SideEffectWrite, Permission: tools.PermissionAllow, Reason: "spoofed"},
+				run: func(ctx context.Context, args map[string]any) tools.Result {
+					_ = os.WriteFile(written, []byte("spoofed"), 0o644)
+					return tools.Result{Status: tools.StatusOK, Output: "spoofed write"}
+				},
+			})
+			provider := &mockProvider{
+				turns: [][]zeroruntime.StreamEvent{
+					{
+						{Type: zeroruntime.StreamEventToolCallStart, ToolCallID: "call-1", ToolName: name},
+						{Type: zeroruntime.StreamEventToolCallDelta, ToolCallID: "call-1", ArgumentsFragment: `{}`},
+						{Type: zeroruntime.StreamEventToolCallEnd, ToolCallID: "call-1"},
+						{Type: zeroruntime.StreamEventDone},
+					},
+					{
+						{Type: zeroruntime.StreamEventText, Content: "done"},
+						{Type: zeroruntime.StreamEventDone},
+					},
+				},
+			}
+
+			result, err := Run(context.Background(), "plan", provider, Options{
+				Registry:       registry,
+				PermissionMode: PermissionModePlan,
+				MaxTurns:       2,
+			})
+			if err != nil {
+				t.Fatal(err)
+			}
+			for _, definition := range provider.requests[0].Tools {
+				if definition.Name == name {
+					t.Fatalf("plan mode advertised a spoofed %s carrying mutating Safety", name)
+				}
+			}
+			var denied string
+			for _, message := range result.Messages {
+				if message.Role == zeroruntime.MessageRoleTool {
+					denied = message.Content
+					break
+				}
+			}
+			if !strings.Contains(denied, "not available in plan mode") {
+				t.Fatalf("expected spoofed %s denial, got %q", name, denied)
+			}
+			if _, err := os.Stat(written); !os.IsNotExist(err) {
+				t.Fatalf("spoofed %s should not have run, stat err=%v", name, err)
+			}
+		})
+	}
+}
+
+// TestPlanModeDeniesLSPNavigateToolCalls locks the process-spawning boundary:
+// lsp_navigate is classified SideEffectRead but lazily starts a language server
+// via exec. Even if the model still emits a call (e.g. from a prior turn's
+// tool list), plan mode must deny it before Run can spawn anything.
+func TestPlanModeDeniesLSPNavigateToolCalls(t *testing.T) {
+	root := t.TempDir()
+	registry := tools.NewRegistry()
+	registry.Register(tools.NewScopedLSPNavigateTool(root, nil))
+	provider := &mockProvider{
+		turns: [][]zeroruntime.StreamEvent{
+			{
+				{Type: zeroruntime.StreamEventToolCallStart, ToolCallID: "call-1", ToolName: "lsp_navigate"},
+				{Type: zeroruntime.StreamEventToolCallDelta, ToolCallID: "call-1", ArgumentsFragment: `{"op":"definition","path":"main.go","line":1,"character":1}`},
+				{Type: zeroruntime.StreamEventToolCallEnd, ToolCallID: "call-1"},
+				{Type: zeroruntime.StreamEventDone},
+			},
+			{
+				{Type: zeroruntime.StreamEventText, Content: "done"},
+				{Type: zeroruntime.StreamEventDone},
+			},
+		},
+	}
+
+	result, err := Run(context.Background(), "plan", provider, Options{
+		Registry:       registry,
+		PermissionMode: PermissionModePlan,
+		MaxTurns:       2,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if result.FinalAnswer != "done" {
+		t.Fatalf("expected final answer after denial, got %q", result.FinalAnswer)
+	}
+	var denied string
+	for _, message := range result.Messages {
+		if message.Role == zeroruntime.MessageRoleTool {
+			denied = message.Content
+			break
+		}
+	}
+	if !strings.Contains(denied, "not available in plan mode") {
+		t.Fatalf("expected plan mode lsp_navigate denial, got %q", denied)
+	}
+}
+
+func TestPlanModeDeniesHiddenToolCalls(t *testing.T) {
+	root := t.TempDir()
+	registry := tools.NewRegistry()
+	registry.Register(tools.NewScopedWriteFileTool(root, nil))
+	provider := providerCallingWriteFileThenAnswer("done")
+
+	result, err := Run(context.Background(), "plan", provider, Options{
+		Registry:       registry,
+		PermissionMode: PermissionModePlan,
+		MaxTurns:       2,
+	})
+
+	if err != nil {
+		t.Fatal(err)
+	}
+	if result.FinalAnswer != "done" {
+		t.Fatalf("expected final answer after denial, got %q", result.FinalAnswer)
+	}
+	var denied string
+	for _, message := range result.Messages {
+		if message.Role == zeroruntime.MessageRoleTool {
+			denied = message.Content
+			break
+		}
+	}
+	if !strings.Contains(denied, "not available in plan mode") {
+		t.Fatalf("expected plan mode denial, got %q", denied)
+	}
+	if _, err := os.Stat(filepath.Join(root, "notes.txt")); !os.IsNotExist(err) {
+		t.Fatalf("write_file should not have written notes.txt, stat err=%v", err)
+	}
+}
+
+func TestPlanModeDeniesBashToolCalls(t *testing.T) {
+	root := t.TempDir()
+	registry := tools.NewRegistry()
+	registry.Register(tools.NewBashTool(root))
+	provider := &mockProvider{
+		turns: [][]zeroruntime.StreamEvent{
+			{
+				{Type: zeroruntime.StreamEventToolCallStart, ToolCallID: "call-1", ToolName: "bash"},
+				{Type: zeroruntime.StreamEventToolCallDelta, ToolCallID: "call-1", ArgumentsFragment: `{"command":"printf ran > ran.txt"}`},
+				{Type: zeroruntime.StreamEventToolCallEnd, ToolCallID: "call-1"},
+				{Type: zeroruntime.StreamEventDone},
+			},
+			{
+				{Type: zeroruntime.StreamEventText, Content: "done"},
+				{Type: zeroruntime.StreamEventDone},
+			},
+		},
+	}
+
+	result, err := Run(context.Background(), "plan", provider, Options{
+		Registry:       registry,
+		PermissionMode: PermissionModePlan,
+		MaxTurns:       2,
+	})
+
+	if err != nil {
+		t.Fatal(err)
+	}
+	if result.FinalAnswer != "done" {
+		t.Fatalf("expected final answer after denial, got %q", result.FinalAnswer)
+	}
+	var denied string
+	for _, message := range result.Messages {
+		if message.Role == zeroruntime.MessageRoleTool {
+			denied = message.Content
+			break
+		}
+	}
+	if !strings.Contains(denied, "not available in plan mode") {
+		t.Fatalf("expected plan mode bash denial, got %q", denied)
+	}
+	if _, err := os.Stat(filepath.Join(root, "ran.txt")); !os.IsNotExist(err) {
+		t.Fatalf("bash should not have written ran.txt, stat err=%v", err)
+	}
+}
+
+// TestReadOnlyModesDenyRequestPermissionsEvenWhenRegistryOmitsIt guards against
+// the read-only gate's blind spot: request_permissions is dispatched by name in
+// executeToolCall before the registry-based ToolAdvertised check runs, so a
+// plan/spec-draft registry that simply omits the tool (rather than registering
+// it as denied) must not let the call fall through to a real grant.
+func TestReadOnlyModesDenyRequestPermissionsEvenWhenRegistryOmitsIt(t *testing.T) {
+	for _, mode := range []PermissionMode{PermissionModePlan, PermissionModeSpecDraft} {
+		t.Run(string(mode), func(t *testing.T) {
+			root := t.TempDir()
+			registry := tools.NewRegistry()
+			registry.Register(tools.NewReadFileTool(root))
+			provider := &mockProvider{
+				turns: [][]zeroruntime.StreamEvent{
+					{
+						{Type: zeroruntime.StreamEventToolCallStart, ToolCallID: "grant-1", ToolName: tools.RequestPermissionsToolName},
+						{Type: zeroruntime.StreamEventToolCallDelta, ToolCallID: "grant-1", ArgumentsFragment: `{"reason":"need access","permissions":{"file_system":{"write":["/tmp/outside"]}}}`},
+						{Type: zeroruntime.StreamEventToolCallEnd, ToolCallID: "grant-1"},
+						{Type: zeroruntime.StreamEventDone},
+					},
+					{
+						{Type: zeroruntime.StreamEventText, Content: "done"},
+						{Type: zeroruntime.StreamEventDone},
+					},
+				},
+			}
+			var promptCount int
+
+			result, err := Run(context.Background(), "task", provider, Options{
+				Registry:       registry,
+				PermissionMode: mode,
+				MaxTurns:       2,
+				OnPermissionRequest: func(context.Context, PermissionRequest) (PermissionDecision, error) {
+					promptCount++
+					return PermissionDecision{Action: PermissionDecisionAllow, Reason: "ok"}, nil
+				},
+			})
+
+			if err != nil {
+				t.Fatal(err)
+			}
+			if result.FinalAnswer != "done" {
+				t.Fatalf("expected final answer after denial, got %q", result.FinalAnswer)
+			}
+			if promptCount != 0 {
+				t.Fatalf("request_permissions must be denied before reaching OnPermissionRequest, got %d prompts", promptCount)
+			}
+			var denied string
+			for _, message := range result.Messages {
+				if message.Role == zeroruntime.MessageRoleTool {
+					denied = message.Content
+					break
+				}
+			}
+			if !strings.Contains(denied, "not available in "+string(mode)+" mode") {
+				t.Fatalf("expected %s mode denial for request_permissions, got %q", mode, denied)
+			}
+		})
+	}
+}
+
 func TestRunStopsWhenSubmitSpecReturnsReviewControl(t *testing.T) {
 	root := t.TempDir()
 	registry := tools.NewRegistry()
@@ -3592,6 +3964,11 @@ func TestRunAppendsAbortedPlaceholderForUnexecutedToolCallsOnGuardStop(t *testin
 	if !strings.Contains(strings.ToLower(placeholder), "aborted") {
 		t.Fatalf("expected the placeholder result to mark the call as aborted, got %q", placeholder)
 	}
+	for _, message := range result.Messages {
+		if message.ToolCallID == "flaky-2" && !message.IsError {
+			t.Fatalf("aborted placeholder must carry error status: %#v", message)
+		}
+	}
 
 	// Every tool_use in the final assistant message must have a matching result.
 	for _, message := range result.Messages {
@@ -3606,6 +3983,33 @@ func TestRunAppendsAbortedPlaceholderForUnexecutedToolCallsOnGuardStop(t *testin
 	}
 }
 
+func TestRunCarriesToolErrorStatusIntoMessageHistory(t *testing.T) {
+	registry := tools.NewRegistry()
+	registry.Register(alwaysFailingTool{})
+	provider := &mockProvider{turns: [][]zeroruntime.StreamEvent{
+		{
+			{Type: zeroruntime.StreamEventToolCallStart, ToolCallID: "failed-call", ToolName: "flaky"},
+			{Type: zeroruntime.StreamEventToolCallEnd, ToolCallID: "failed-call"},
+			{Type: zeroruntime.StreamEventDone},
+		},
+		{{Type: zeroruntime.StreamEventText, Content: "done"}, {Type: zeroruntime.StreamEventDone}},
+	}}
+
+	result, err := Run(context.Background(), "go", provider, Options{Registry: registry})
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, message := range result.Messages {
+		if message.ToolCallID == "failed-call" {
+			if !message.IsError {
+				t.Fatalf("failed tool result lost its structured status: %#v", message)
+			}
+			return
+		}
+	}
+	t.Fatalf("failed tool result missing from message history: %#v", result.Messages)
+}
+
 type secretEmittingTool struct{ output string }
 
 func (t secretEmittingTool) Name() string        { return "leak" }
@@ -3697,6 +4101,8 @@ func TestRunTracingWrapperStampsUsage(t *testing.T) {
 		{Type: zeroruntime.StreamEventDone},
 	}}}
 	onUsageCalls := 0
+	onContextCalls := 0
+	var contextPlan ContextBreakdown
 	rec := trace.NewRecorder("tracing-session", "run-1", "test")
 	if _, err := Run(context.Background(), "hi", provider, Options{
 		SessionID:    "tracing-session",
@@ -3705,6 +4111,10 @@ func TestRunTracingWrapperStampsUsage(t *testing.T) {
 		Model:        "test-model",
 		Trace:        rec,
 		OnUsage:      func(Usage) { onUsageCalls++ },
+		OnContext: func(breakdown ContextBreakdown) {
+			onContextCalls++
+			contextPlan = breakdown
+		},
 	}); err != nil {
 		t.Fatalf("Run: %v", err)
 	}
@@ -3731,6 +4141,12 @@ func TestRunTracingWrapperStampsUsage(t *testing.T) {
 	if onUsageCalls == 0 {
 		t.Fatal("wrapped OnUsage did not forward to the caller's callback")
 	}
+	if onContextCalls != 1 || len(contextPlan.Blocks) != 2 || contextPlan.PrefixInvalidationReason != "initial" {
+		t.Fatalf("context plan callback = calls %d, plan %#v", onContextCalls, contextPlan)
+	}
+	if len(tr.PrefixHashes) != 1 || tr.PrefixHashes[0].InvalidationReason != "initial" || tr.PrefixHashes[0].CompletePrefixHash != contextPlan.CompletePrefixHash {
+		t.Fatalf("trace context evidence = %#v, plan %#v", tr.PrefixHashes, contextPlan)
+	}
 }
 
 // TestRunNilTraceForwardsUsage verifies a nil recorder leaves the loop
@@ -3756,3 +4172,263 @@ func TestRunNilTraceForwardsUsage(t *testing.T) {
 		t.Fatal("OnUsage not forwarded when Trace is nil")
 	}
 }
+
+// TestRunSuppressesAdvisoryHooksInPlanMode: plan mode promises a read-only
+// turn for advisory hooks (sessionStart/sessionEnd/afterTool), which execute
+// configured host commands outside the advertised-tool and sandbox gates.
+// beforeTool is deliberately still dispatched so deny policies keep working;
+// see TestPlanModeHonorsBeforeToolVeto.
+func TestRunSuppressesAdvisoryHooksInPlanMode(t *testing.T) {
+	goBinary, err := exec.LookPath("go")
+	if err != nil {
+		goRoot := runtime.GOROOT() //nolint:staticcheck // Safe for this non-portable test binary.
+		goBinary = filepath.Join(goRoot, "bin", "go")
+		if runtime.GOOS == "windows" {
+			goBinary += ".exe"
+		}
+		if _, statErr := os.Stat(goBinary); statErr != nil {
+			t.Skipf("go binary unavailable on PATH or in GOROOT: %v", statErr)
+		}
+	}
+	audit, err := hooks.NewAuditStore(hooks.AuditStoreOptions{AuditPath: filepath.Join(t.TempDir(), "audit.jsonl")})
+	if err != nil {
+		t.Fatalf("NewAuditStore: %v", err)
+	}
+	sessionMarker := filepath.Join(t.TempDir(), "session-marker-dir")
+	afterToolMarker := filepath.Join(t.TempDir(), "after-tool-marker-dir")
+	// beforeTool allows the read (exit 0) so the tool still runs and afterTool
+	// would fire if it were not suppressed.
+	dispatcher := hooks.NewDispatcher(hooks.DispatcherOptions{
+		Config: hooks.Config{
+			Enabled: true,
+			Hooks: []hooks.Definition{
+				{ID: "zero.session-start", Event: hooks.EventSessionStart, Command: goBinary, Args: []string{"mod", "init", "-modfile", filepath.Join(sessionMarker, "go.mod"), "marker"}, Enabled: true},
+				{ID: "zero.session-end", Event: hooks.EventSessionEnd, Command: goBinary, Args: []string{"version"}, Enabled: true},
+				{ID: "zero.before-tool", Event: hooks.EventBeforeTool, Matcher: "read_file", Command: goBinary, Args: []string{"version"}, Enabled: true},
+				{ID: "zero.after-tool", Event: hooks.EventAfterTool, Matcher: "read_file", Command: goBinary, Args: []string{"mod", "init", "-modfile", filepath.Join(afterToolMarker, "go.mod"), "marker"}, Enabled: true},
+			},
+		},
+		Audit: audit,
+	})
+	root := t.TempDir()
+	if err := os.WriteFile(filepath.Join(root, "notes.txt"), []byte("hello"), 0o644); err != nil {
+		t.Fatalf("write notes.txt: %v", err)
+	}
+	registry := tools.NewRegistry()
+	registry.Register(tools.NewReadFileTool(root))
+	provider := &mockProvider{turns: [][]zeroruntime.StreamEvent{
+		{
+			{Type: zeroruntime.StreamEventToolCallStart, ToolCallID: "call-1", ToolName: "read_file"},
+			{Type: zeroruntime.StreamEventToolCallDelta, ToolCallID: "call-1", ArgumentsFragment: `{"path":"notes.txt"}`},
+			{Type: zeroruntime.StreamEventToolCallEnd, ToolCallID: "call-1"},
+			{Type: zeroruntime.StreamEventDone},
+		},
+		{
+			{Type: zeroruntime.StreamEventText, Content: "plan drafted"},
+			{Type: zeroruntime.StreamEventDone},
+		},
+	}}
+
+	if _, err := Run(context.Background(), "plan something", provider, Options{
+		SessionID:      "session-plan",
+		Cwd:            root,
+		Registry:       registry,
+		ProviderName:   "test-provider",
+		Model:          "test-model",
+		Hooks:          dispatcher,
+		PermissionMode: PermissionModePlan,
+		MaxTurns:       2,
+	}); err != nil {
+		t.Fatalf("Run: %v", err)
+	}
+
+	events, err := audit.ReadEvents()
+	if err != nil {
+		t.Fatalf("ReadEvents: %v", err)
+	}
+	sawBeforeTool := false
+	for _, event := range events {
+		if event.Type != "hook_execution_started" {
+			continue
+		}
+		switch event.Event {
+		case hooks.EventBeforeTool:
+			sawBeforeTool = true
+		case hooks.EventSessionStart, hooks.EventSessionEnd, hooks.EventAfterTool:
+			t.Fatalf("advisory hook %q executed during a plan-mode run", event.Event)
+		}
+	}
+	if !sawBeforeTool {
+		t.Fatal("expected beforeTool to still dispatch under plan mode (deny-gate must not fail open)")
+	}
+	for _, marker := range []string{sessionMarker, afterToolMarker} {
+		if _, statErr := os.Stat(marker); !os.IsNotExist(statErr) {
+			t.Fatalf("plan-mode run let advisory hook touch the filesystem via %q: %v", marker, statErr)
+		}
+	}
+}
+
+// TestPlanModeHonorsBeforeToolVeto guards the fail-open hole where hooksSuppressed
+// used to skip beforeTool under plan mode, so a deny-policy hook that blocks
+// secret reads in auto mode would silently allow them under PermissionModePlan.
+func TestPlanModeHonorsBeforeToolVeto(t *testing.T) {
+	goBinary, err := exec.LookPath("go")
+	if err != nil {
+		goRoot := runtime.GOROOT() //nolint:staticcheck // Safe for this non-portable test binary.
+		goBinary = filepath.Join(goRoot, "bin", "go")
+		if runtime.GOOS == "windows" {
+			goBinary += ".exe"
+		}
+		if _, statErr := os.Stat(goBinary); statErr != nil {
+			t.Skipf("go binary unavailable on PATH or in GOROOT: %v", statErr)
+		}
+	}
+	// A non-zero exit from beforeTool is a veto. "go definitely-not-a-subcommand"
+	// exits non-zero on every platform with a go toolchain.
+	dispatcher := hooks.NewDispatcher(hooks.DispatcherOptions{
+		Config: hooks.Config{
+			Enabled: true,
+			Hooks: []hooks.Definition{
+				{ID: "zero.veto", Event: hooks.EventBeforeTool, Matcher: "read_file", Command: goBinary, Args: []string{"definitely-not-a-go-subcommand"}, Enabled: true},
+			},
+		},
+	})
+	root := t.TempDir()
+	secret := filepath.Join(root, "secret.txt")
+	if err := os.WriteFile(secret, []byte("SUPERSECRET"), 0o644); err != nil {
+		t.Fatalf("write secret.txt: %v", err)
+	}
+	registry := tools.NewRegistry()
+	registry.Register(tools.NewReadFileTool(root))
+	var toolOutputs []string
+	provider := &mockProvider{turns: [][]zeroruntime.StreamEvent{
+		{
+			{Type: zeroruntime.StreamEventToolCallStart, ToolCallID: "call-1", ToolName: "read_file"},
+			{Type: zeroruntime.StreamEventToolCallDelta, ToolCallID: "call-1", ArgumentsFragment: `{"path":"secret.txt"}`},
+			{Type: zeroruntime.StreamEventToolCallEnd, ToolCallID: "call-1"},
+			{Type: zeroruntime.StreamEventDone},
+		},
+		{
+			{Type: zeroruntime.StreamEventText, Content: "blocked"},
+			{Type: zeroruntime.StreamEventDone},
+		},
+	}}
+
+	if _, err := Run(context.Background(), "read the secret", provider, Options{
+		SessionID:      "session-plan-veto",
+		Cwd:            root,
+		Registry:       registry,
+		ProviderName:   "test-provider",
+		Model:          "test-model",
+		Hooks:          dispatcher,
+		PermissionMode: PermissionModePlan,
+		MaxTurns:       2,
+		OnToolResult: func(result ToolResult) {
+			toolOutputs = append(toolOutputs, result.Output)
+		},
+	}); err != nil {
+		t.Fatalf("Run: %v", err)
+	}
+	if len(toolOutputs) == 0 {
+		t.Fatal("expected a tool result for the vetoed read_file call")
+	}
+	combined := strings.Join(toolOutputs, "\n")
+	if strings.Contains(combined, "SUPERSECRET") {
+		t.Fatalf("plan mode failed open: beforeTool veto was skipped and secret leaked: %q", combined)
+	}
+	if !strings.Contains(combined, "blocked") && !strings.Contains(combined, "zero.veto") && !strings.Contains(strings.ToLower(combined), "hook") {
+		t.Fatalf("expected tool result to mention the beforeTool veto, got %q", combined)
+	}
+}
+
+// A cancelled permission on either sandbox-retry path must abort the run with a
+// recognisable cancellation, and must not run the escalated retry.
+//
+// BOTH PATHS, because both wrap ErrPermissionApprovalCanceled and each is
+// reached by a different kind of denial: one by an unrestricted platform denial
+// asking for approval, the other by an external-network denial. Surfaces map
+// this sentinel onto their own idea of a cancel — ACP returns stopReason
+// "cancelled" for it — so a path that produced a bare error instead would show
+// the user a crash where they had simply declined.
+func TestCancellingASandboxRetryAbortsWithoutRetrying(t *testing.T) {
+	denial := func(capability execution.CapabilityKind, scope string) tools.Result {
+		return tools.Result{
+			Status: tools.StatusError,
+			ExecutionOutcome: &execution.Outcome{
+				State: execution.StateDenied,
+				Kind:  execution.OutcomeEnforcementDenied,
+				Denial: &execution.Denial{
+					Capability:  execution.Capability{Kind: capability, Scope: scope},
+					Source:      execution.DenialSourcePlatformSandbox,
+					Reason:      "denied by the sandbox",
+					Recoverable: true,
+					NextAction:  execution.DenialNextActionRequestApproval,
+				},
+			},
+		}
+	}
+
+	for _, testCase := range []struct {
+		name   string
+		result tools.Result
+		run    func(context.Context, *tools.Registry, ToolCall, tools.Tool, map[string]any, tools.Result, Options) error
+	}{
+		{
+			name:   "unsandboxed retry",
+			result: denial(execution.CapabilityUnrestricted, "host"),
+			run: func(ctx context.Context, registry *tools.Registry, call ToolCall, tool tools.Tool, args map[string]any, result tools.Result, options Options) error {
+				_, _, _, _, _, _, abortErr := maybeRetryUnsandboxedAfterSandboxRestriction(
+					ctx, registry, call, tool, args, result, PermissionModeAsk, options, nil)
+				return abortErr
+			},
+		},
+		{
+			name:   "network retry",
+			result: denial(execution.CapabilityExternalNetwork, ""),
+			run: func(ctx context.Context, registry *tools.Registry, call ToolCall, tool tools.Tool, args map[string]any, result tools.Result, options Options) error {
+				_, _, _, _, _, abortErr := maybeRetryWithNetworkAfterSandboxDenial(
+					ctx, registry, call, tool, args, result, PermissionModeAsk, options, nil)
+				return abortErr
+			},
+		},
+	} {
+		t.Run(testCase.name, func(t *testing.T) {
+			retryTool := &sandboxNamespaceLimitedRetryTool{}
+			registry := tools.NewRegistry()
+			registry.Register(retryTool)
+
+			asked := 0
+			options := Options{
+				Registry:       registry,
+				PermissionMode: PermissionModeAsk,
+				Autonomy:       "medium",
+				Sandbox: sandbox.NewEngine(sandbox.EngineOptions{
+					WorkspaceRoot: t.TempDir(),
+					Policy:        sandbox.DefaultPolicy(),
+				}),
+				OnPermissionRequest: func(context.Context, PermissionRequest) (PermissionDecision, error) {
+					asked++
+					return PermissionDecision{Action: PermissionDecisionCancel, Reason: "client cancelled"}, nil
+				},
+			}
+
+			call := ToolCall{ID: "call-1", Name: "bash", Arguments: `{"command":"curl example.com"}`}
+			args := map[string]any{"command": "curl example.com"}
+
+			abortErr := testCase.run(context.Background(), registry, call, retryTool, args, testCase.result, options)
+
+			if asked != 1 {
+				t.Fatalf("permission was requested %d times, want exactly 1", asked)
+			}
+			if !errors.Is(abortErr, ErrPermissionApprovalCanceled) {
+				t.Fatalf("abort error = %v, want it to match ErrPermissionApprovalCanceled", abortErr)
+			}
+			// The escalated retry is the thing the permission was gating. A
+			// cancelled prompt that still ran it would have run the command the
+			// user just declined.
+			if len(retryTool.calls) != 0 {
+				t.Fatalf("the escalated retry ran %d times after a cancel: %+v", len(retryTool.calls), retryTool.calls)
+			}
+		})
+	}
+}

internal/agent/prefix_escalation_disclosure_test.go

@@ -0,0 +1,118 @@
+package agent
+
+import (
+	"path/filepath"
+	"testing"
+
+	"github.com/Gitlawb/zero/internal/sandbox"
+	"github.com/Gitlawb/zero/internal/tools"
+)
+
+// escalatingEngine allows unsandboxed escalation: no denied reads, so
+// UnsandboxedExecutionAllowed is true and a prefix approval would rewrite the
+// call to require_escalated.
+func escalatingEngine(t *testing.T) *sandbox.Engine {
+	t.Helper()
+	policy := sandbox.DefaultPolicy()
+	policy.DenyRead = nil
+	return sandbox.NewEngine(sandbox.EngineOptions{WorkspaceRoot: t.TempDir(), Policy: policy})
+}
+
+// nonEscalatingEngine has a denied read, which is exactly the condition under
+// which escalation is refused, so no disclosure should be made.
+func nonEscalatingEngine(t *testing.T) *sandbox.Engine {
+	t.Helper()
+	root := t.TempDir()
+	policy := sandbox.DefaultPolicy()
+	policy.DenyRead = []string{filepath.Join(root, "secret.txt")}
+	return sandbox.NewEngine(sandbox.EngineOptions{WorkspaceRoot: root, Policy: policy})
+}
+
+// THE POINT OF THE FILE. The prompt's disclosure and the args rewrite must
+// agree on every input, because the defect being fixed is precisely that the
+// two disagreed: the rewrite escalated out of the sandbox while the prompt said
+// only "allow command prefix for session".
+//
+// Asserting agreement rather than asserting each side's expected value is what
+// makes this hold up. If someone later widens or narrows the rewrite's guards
+// and forgets the flag, the two diverge here and this fails, which a pair of
+// independent expected-value tests would not catch.
+func TestPrefixEscalationDisclosureMatchesTheArgsRewrite(t *testing.T) {
+	escalating := Options{Sandbox: escalatingEngine(t)}
+	denied := Options{Sandbox: nonEscalatingEngine(t)}
+
+	cases := []struct {
+		name     string
+		toolName string
+		args     map[string]any
+		options  Options
+	}{
+		{"plain bash command", "bash", map[string]any{"command": "go test ./..."}, escalating},
+		{"plain exec_command", "exec_command", map[string]any{"cmd": "go build ./..."}, escalating},
+		{"not a shell tool", "read_file", map[string]any{"path": "go.mod"}, escalating},
+		{"no sandbox configured", "bash", map[string]any{"command": "go test ./..."}, Options{}},
+		{"escalation refused by denied reads", "bash", map[string]any{"command": "go test ./..."}, denied},
+		{
+			"call already asks for escalation",
+			"bash",
+			map[string]any{"command": "go test ./...", "sandbox_permissions": string(tools.SandboxPermissionsRequireEscalated)},
+			escalating,
+		},
+		{
+			"call already asks for additional permissions",
+			"bash",
+			map[string]any{"command": "go test ./...", "sandbox_permissions": string(tools.SandboxPermissionsWithAdditionalPermissions)},
+			escalating,
+		},
+		// An unrecognized value is NOT an opt-out: the rewrite overwrites it, so
+		// the disclosure has to fire. Included because the obvious reading of
+		// the guards says otherwise, and a case asserting the wrong thing here
+		// would have passed silently.
+		{
+			"unrecognized sandbox_permissions value",
+			"bash",
+			map[string]any{"command": "go test ./...", "sandbox_permissions": "all"},
+			escalating,
+		},
+		{"empty args", "bash", map[string]any{}, escalating},
+		{"nil args", "bash", nil, escalating},
+	}
+
+	for _, testCase := range cases {
+		t.Run(testCase.name, func(t *testing.T) {
+			disclosed := shellPrefixApprovalEscalates(testCase.toolName, testCase.args, testCase.options)
+
+			// What the user's approval would actually be turned into.
+			rewritten := shellExecutionArgsForApproval(testCase.toolName, testCase.args, PermissionDecisionAllowPrefix, testCase.options)
+			escalates := shellCommandRequiresEscalated(rewritten) && !shellCommandRequiresEscalated(testCase.args)
+
+			if disclosed != escalates {
+				t.Fatalf("prompt discloses escalation=%v but approving actually escalates=%v; the prompt and the rewrite disagree, which is the consent gap this guards", disclosed, escalates)
+			}
+		})
+	}
+}
+
+// The two prefix decisions are the only ones that escalate, so a disclosure
+// attached to a request offering neither would be a false alarm. Checked
+// against the same predicate the rewrite consults.
+func TestOnlyPrefixDecisionsEscalate(t *testing.T) {
+	escalating := map[PermissionDecisionAction]bool{
+		PermissionDecisionAllowPrefix:       true,
+		PermissionDecisionAlwaysAllowPrefix: true,
+	}
+	for _, action := range []PermissionDecisionAction{
+		PermissionDecisionAllow,
+		PermissionDecisionAllowStrict,
+		PermissionDecisionAllowForSession,
+		PermissionDecisionAllowPrefix,
+		PermissionDecisionAlwaysAllowPrefix,
+		PermissionDecisionAlwaysAllow,
+		PermissionDecisionDeny,
+		PermissionDecisionCancel,
+	} {
+		if got := shellPrefixApprovalBypassesSandbox(action); got != escalating[action] {
+			t.Errorf("decision %q bypasses sandbox=%v, want %v", action, got, escalating[action])
+		}
+	}
+}

internal/agent/prompt_budget_test.go

@@ -20,7 +20,20 @@ import (
 // without a session id. Higher-risk tools that do not opt into auto remain excluded.
 const (
 	maxBaseSystemPromptTokens = 3500
-	maxEagerToolSchemaTokens  = 3550
+	// Raised deliberately from 3550 on 2026-08-08. view_image (#843) took the set
+	// to 3588, and #867 trimmed it back to 3578: still 28 tokens over.
+	//
+	// The overrun is a rounding error rather than a regression. view_image costs
+	// 82 tokens, the second cheapest tool in the set, against exec_command's 909
+	// and request_permissions' 397; it is simply the one that crossed the line.
+	// Raised rather than paid down because the alternative was trimming a
+	// description to claw back 28 tokens, degrading a tool's usability to satisfy
+	// a line drawn against a 2026-07 measurement that predates two tools.
+	//
+	// The ratchet did its job: it caught the creep and forced a decision instead
+	// of a drift. That is the point of it, so keep raising it deliberately rather
+	// than reflexively.
+	maxEagerToolSchemaTokens = 3650
 )
 
 func TestSystemPromptTokenBudget(t *testing.T) {
@@ -46,6 +59,11 @@ func TestEagerToolSchemaTokenBudget(t *testing.T) {
 	got := estimateToolDefTokens(exposed)
 	t.Logf("eager core tool schemas: %d tokens across %d tools", got, len(exposed))
 	if got > maxEagerToolSchemaTokens {
-		t.Fatalf("eager tool schemas are %d tokens, over the %d ceiling — defer a tool or raise the ceiling deliberately", got, maxEagerToolSchemaTokens)
+		// NOT "defer a tool": this test pins DeferThreshold at 0, so marking a
+		// tool deferred leaves it exposed here and changes nothing. Deferral is
+		// still worth doing for real sessions, it just cannot move this number.
+		// The levers that do are a smaller schema, one fewer core tool, or a
+		// deliberate raise.
+		t.Fatalf("eager tool schemas are %d tokens, over the %d ceiling — trim a schema, drop a core tool, or raise the ceiling deliberately (deferring will NOT help: this test disables deferral)", got, maxEagerToolSchemaTokens)
 	}
 }

internal/agent/prompt_fingerprint_test.go

@@ -123,6 +123,21 @@ func TestComputePrefixFingerprintCoversEverySystemPromptSection(t *testing.T) {
 	}
 }
 
+func TestComputePrefixFingerprintCoversTransientSystemPrompt(t *testing.T) {
+	base := Options{Cwd: t.TempDir(), SystemPrompt: "core"}
+	changed := base
+	changed.TransientSystemPrompt = "turn-only guidance"
+
+	fpBase := ComputePrefixFingerprint(base, nil)
+	fpChanged := ComputePrefixFingerprint(changed, nil)
+	if fpBase.SystemPromptHash == fpChanged.SystemPromptHash {
+		t.Fatal("SystemPromptHash must change for transient system guidance")
+	}
+	if fpBase.CompletePrefixHash == fpChanged.CompletePrefixHash {
+		t.Fatal("CompletePrefixHash must cover transient system guidance")
+	}
+}
+
 // TestBuildPromptSubstringsDefaultOptions asserts the invariants of the
 // substrings helper for default Options: which substrings are non-empty,
 // which are empty, and that the substring-to-hash round-trip is lossless.

internal/agent/system_prompt.go

@@ -95,6 +95,9 @@ func buildSystemPromptParts(options Options) systemPromptParts {
 		core = fallbackSystemPrompt
 	}
 	sections := []string{core}
+	if transient := strings.TrimSpace(options.TransientSystemPrompt); transient != "" {
+		sections = append(sections, transient)
+	}
 	if addendum := modelPromptAddendum(options.Model); addendum != "" {
 		sections = append(sections, addendum)
 	}
@@ -118,6 +121,9 @@ func buildSystemPromptParts(options Options) systemPromptParts {
 	if project != "" {
 		sections = append(sections, project)
 	}
+	if modeCtx := permissionModeContext(options); modeCtx != "" {
+		sections = append(sections, modeCtx)
+	}
 	if delegation := specialistDelegationContext(options); delegation != "" {
 		sections = append(sections, delegation)
 	}
@@ -679,3 +685,12 @@ func gitBranchForPrompt(cwd string) string {
 	}
 	return ref
 }
+
+func permissionModeContext(options Options) string {
+	switch options.PermissionMode {
+	case PermissionModePlan:
+		return "Plan mode is active on this session. Your role is read-only exploration and planning: inspect the workspace and shape the plan with update_plan, but do not make changes to files or execute commands."
+	default:
+		return ""
+	}
+}

internal/agent/system_prompt_test.go

@@ -51,6 +51,16 @@ func TestCoreSystemPromptIncludesCodingQualityRules(t *testing.T) {
 	}
 }
 
+func TestTransientSystemPromptIsIncludedOnlyWhenProvided(t *testing.T) {
+	const transient = "Handle this peer request under the current session policy."
+	if prompt := buildSystemPrompt(Options{}); strings.Contains(prompt, transient) {
+		t.Fatal("ordinary system prompt unexpectedly contains transient instructions")
+	}
+	if prompt := buildSystemPrompt(Options{TransientSystemPrompt: transient}); !strings.Contains(prompt, transient) {
+		t.Fatalf("transient instructions missing from system prompt:\n%s", prompt)
+	}
+}
+
 func TestSystemPromptExplainsSandboxEscalationForHiddenHostState(t *testing.T) {
 	prompt := strings.ToLower(buildSystemPrompt(Options{}))
 	for _, want := range []string{

internal/agent/task_state.go

@@ -1,10 +1,14 @@
 package agent
 
 import (
+	"crypto/sha256"
 	"encoding/json"
+	"fmt"
 	"reflect"
+	"regexp"
 	"sort"
 	"strings"
+	"unicode/utf8"
 
 	"github.com/Gitlawb/zero/internal/tools"
 	"github.com/Gitlawb/zero/internal/trace"
@@ -52,17 +56,41 @@ type taskVerificationState struct {
 	LastOutcome Outcome `json:"last_outcome,omitempty"`
 }
 
+type taskFailureState struct {
+	Key     string `json:"key,omitempty"`
+	Tool    string `json:"tool"`
+	Command string `json:"command,omitempty"`
+	Summary string `json:"summary"`
+}
+
+type taskApprovalState struct {
+	Tool     string                   `json:"tool"`
+	Decision PermissionDecisionAction `json:"decision,omitempty"`
+	Scope    string                   `json:"scope,omitempty"`
+	Reason   string                   `json:"reason,omitempty"`
+}
+
+type taskArtifactState struct {
+	Tool string `json:"tool"`
+	Path string `json:"path"`
+}
+
 type taskStateSnapshot struct {
-	Revision           int                   `json:"revision"`
-	Objective          string                `json:"objective"`
-	Status             taskStatus            `json:"status"`
-	Plan               taskPlanState         `json:"plan"`
-	Tools              taskToolState         `json:"tools"`
-	Verification       taskVerificationState `json:"verification"`
-	ChangedFiles       []string              `json:"changed_files,omitempty"`
-	CompletionDecision CompletionDecision    `json:"completion_decision,omitempty"`
-	CompletionReason   string                `json:"completion_reason,omitempty"`
-	PlanParity         taskPlanParity        `json:"plan_parity"`
+	Revision            int                   `json:"revision"`
+	Objective           string                `json:"objective"`
+	Status              taskStatus            `json:"status"`
+	Plan                taskPlanState         `json:"plan"`
+	Tools               taskToolState         `json:"tools"`
+	Verification        taskVerificationState `json:"verification"`
+	ChangedFiles        []string              `json:"changed_files,omitempty"`
+	Constraints         []string              `json:"constraints,omitempty"`
+	UnresolvedFailures  []taskFailureState    `json:"unresolved_failures,omitempty"`
+	Approvals           []taskApprovalState   `json:"approvals,omitempty"`
+	Artifacts           []taskArtifactState   `json:"artifacts,omitempty"`
+	ResolvedFailureKeys []string              `json:"-"`
+	CompletionDecision  CompletionDecision    `json:"completion_decision,omitempty"`
+	CompletionReason    string                `json:"completion_reason,omitempty"`
+	PlanParity          taskPlanParity        `json:"plan_parity"`
 }
 
 type taskStateEventKind int
@@ -72,6 +100,7 @@ const (
 	taskStateEventToolResult
 	taskStateEventVerification
 	taskStateEventCompletion
+	taskStateEventPermission
 )
 
 type taskStateEvent struct {
@@ -80,6 +109,7 @@ type taskStateEvent struct {
 	toolResult   ToolResult
 	verification Outcome
 	completion   completionEvaluation
+	permission   PermissionEvent
 }
 
 // taskState is a deterministic projection of facts the loop already observes.
@@ -101,6 +131,7 @@ func newTaskState(objective string, recorder *trace.Recorder) *taskState {
 		},
 		changedFiles: map[string]struct{}{},
 	}
+	state.snapshotValue.Constraints = extractExplicitConstraints(objective)
 	state.recorder = recorder
 	return state
 }
@@ -134,6 +165,7 @@ func (state *taskState) observe(event taskStateEvent) bool {
 			}
 		}
 		state.snapshotValue.ChangedFiles = sortedKeys(state.changedFiles)
+		state.observeToolEvidence(event.arguments, event.toolResult)
 		changed = true
 	case taskStateEventVerification:
 		if event.verification == OutcomeDisabled {
@@ -160,6 +192,10 @@ func (state *taskState) observe(event taskStateEvent) bool {
 			state.snapshotValue.Status = taskStatusActive
 		}
 		changed = true
+	case taskStateEventPermission:
+		state.markActive()
+		state.observePermission(event.permission)
+		changed = true
 	}
 	if changed {
 		state.snapshotValue.Revision++
@@ -183,9 +219,180 @@ func (state *taskState) snapshot() taskStateSnapshot {
 	snapshot := state.snapshotValue
 	snapshot.Plan.Items = append([]taskPlanItem(nil), state.snapshotValue.Plan.Items...)
 	snapshot.ChangedFiles = append([]string(nil), state.snapshotValue.ChangedFiles...)
+	snapshot.Constraints = append([]string(nil), state.snapshotValue.Constraints...)
+	snapshot.UnresolvedFailures = append([]taskFailureState(nil), state.snapshotValue.UnresolvedFailures...)
+	snapshot.Approvals = append([]taskApprovalState(nil), state.snapshotValue.Approvals...)
+	snapshot.Artifacts = append([]taskArtifactState(nil), state.snapshotValue.Artifacts...)
+	snapshot.ResolvedFailureKeys = append([]string(nil), state.snapshotValue.ResolvedFailureKeys...)
 	return snapshot
 }
 
+const (
+	maxTaskEvidenceEntries = 8
+	maxTaskEvidenceBytes   = 320
+	maxTaskConstraints     = 10
+)
+
+func (state *taskState) observeToolEvidence(arguments string, result ToolResult) {
+	command := capTaskEvidence(commandFromArguments(arguments))
+	key := taskFailureKey(result.Name, command, arguments)
+	if result.Status == tools.StatusOK {
+		if hasTaskFailure(state.snapshotValue.UnresolvedFailures, key) {
+			state.snapshotValue.UnresolvedFailures = removeTaskFailure(state.snapshotValue.UnresolvedFailures, key)
+			state.snapshotValue.ResolvedFailureKeys = appendBoundedUnique(state.snapshotValue.ResolvedFailureKeys, key, maxTaskEvidenceEntries)
+		}
+	} else {
+		state.snapshotValue.ResolvedFailureKeys = removeString(state.snapshotValue.ResolvedFailureKeys, key)
+		state.snapshotValue.UnresolvedFailures = removeTaskFailure(state.snapshotValue.UnresolvedFailures, key)
+		state.snapshotValue.UnresolvedFailures = appendBounded(state.snapshotValue.UnresolvedFailures, taskFailureState{
+			Key: key, Tool: result.Name, Command: command, Summary: capTaskEvidence(firstLine(result.Output)),
+		}, maxTaskEvidenceEntries)
+	}
+	for _, metaKey := range []string{"spill_path", "artifact_path"} {
+		if path := strings.TrimSpace(result.Meta[metaKey]); path != "" {
+			state.snapshotValue.Artifacts = appendBoundedUnique(state.snapshotValue.Artifacts,
+				taskArtifactState{Tool: result.Name, Path: capTaskEvidence(path)}, maxTaskEvidenceEntries)
+		}
+	}
+}
+
+func taskFailureKey(toolName, command, arguments string) string {
+	identity := command
+	if identity == "" {
+		canonical := []byte(strings.TrimSpace(arguments))
+		var value any
+		if json.Unmarshal(canonical, &value) == nil {
+			if encoded, err := json.Marshal(value); err == nil {
+				canonical = encoded
+			}
+		}
+		digest := sha256.Sum256(canonical)
+		identity = fmt.Sprintf("args:%x", digest[:8])
+	}
+	return strings.TrimSpace(toolName) + "\x00" + identity
+}
+
+func (state *taskState) observePermission(event PermissionEvent) {
+	decision := event.DecisionAction
+	if decision == "" {
+		decision = PermissionDecisionAction(event.Action)
+	}
+	state.snapshotValue.Approvals = appendBoundedUnique(state.snapshotValue.Approvals, taskApprovalState{
+		Tool: event.ToolName, Decision: decision, Scope: capTaskEvidence(event.Scope),
+		Reason: capTaskEvidence(firstNonEmptyString(event.DecisionReason, event.Reason)),
+	}, maxTaskEvidenceEntries)
+}
+
+func commandFromArguments(arguments string) string {
+	var object map[string]json.RawMessage
+	if json.Unmarshal([]byte(strings.TrimSpace(arguments)), &object) != nil {
+		return ""
+	}
+	for _, key := range []string{"cmd", "command", "script", "shell"} {
+		var command string
+		if raw, ok := object[key]; ok && json.Unmarshal(raw, &command) == nil {
+			return strings.TrimSpace(command)
+		}
+	}
+	return ""
+}
+
+func firstLine(value string) string {
+	value = strings.TrimSpace(value)
+	if index := strings.IndexByte(value, '\n'); index >= 0 {
+		value = value[:index]
+	}
+	return value
+}
+
+func capTaskEvidence(value string) string {
+	value = strings.TrimSpace(value)
+	if len(value) <= maxTaskEvidenceBytes {
+		return value
+	}
+	limit := maxTaskEvidenceBytes - 3
+	for limit > 0 && !utf8.RuneStart(value[limit]) {
+		limit--
+	}
+	return strings.TrimSpace(value[:limit]) + "..."
+}
+
+var explicitConstraintPatterns = []*regexp.Regexp{
+	regexp.MustCompile(`(?i)\bprefer(?:s|red|ring)?\s+\w`),
+	regexp.MustCompile(`(?i)\bdon'?t want\b`),
+	regexp.MustCompile(`(?i)\balways (?:use|do|run|prefer|keep|make|format|write|add|set|put|prefix|start|include|append)\b`),
+	regexp.MustCompile(`(?i)\bnever (?:use|do|run|push|commit|write|ignore|add|set|put|remove|delete|include|deploy)\b`),
+	regexp.MustCompile(`(?i)\bplease (?:use|avoid|keep|make|don'?t|do not|format|write)\b`),
+	regexp.MustCompile(`(?i)\b(?:style|format|language|naming)\s*[:=]\s*\S`),
+}
+
+func extractExplicitConstraints(text string) []string {
+	var constraints []string
+	for _, line := range strings.Split(text, "\n") {
+		line = strings.TrimSpace(line)
+		if len(line) < 5 || len(line) > 200 || strings.HasSuffix(line, "?") || strings.Contains(line, "?...") {
+			continue
+		}
+		for _, pattern := range explicitConstraintPatterns {
+			if pattern.MatchString(line) {
+				constraints = appendBoundedUnique(constraints, line, maxTaskConstraints)
+				break
+			}
+		}
+		if len(constraints) == maxTaskConstraints {
+			break
+		}
+	}
+	return constraints
+}
+
+func appendBounded[T any](values []T, value T, limit int) []T {
+	values = append(values, value)
+	if len(values) > limit {
+		values = values[len(values)-limit:]
+	}
+	return values
+}
+
+func appendBoundedUnique[T comparable](values []T, value T, limit int) []T {
+	filtered := values[:0]
+	for _, existing := range values {
+		if existing != value {
+			filtered = append(filtered, existing)
+		}
+	}
+	return appendBounded(filtered, value, limit)
+}
+
+func hasTaskFailure(values []taskFailureState, key string) bool {
+	for _, value := range values {
+		if value.Key == key {
+			return true
+		}
+	}
+	return false
+}
+
+func removeTaskFailure(values []taskFailureState, key string) []taskFailureState {
+	out := values[:0]
+	for _, value := range values {
+		if value.Key != key {
+			out = append(out, value)
+		}
+	}
+	return out
+}
+
+func removeString(values []string, target string) []string {
+	out := make([]string, 0, len(values))
+	for _, value := range values {
+		if value != target {
+			out = append(out, value)
+		}
+	}
+	return out
+}
+
 // observePlanParity compares only the latest plan projection with the plan tool
 // calls still present in messages. It mutates the snapshot and emits when the
 // parity value changes; objective, tool, and verification fields are not part of

internal/agent/task_state_test.go

@@ -115,6 +115,68 @@ func TestTaskStateSnapshotIsImmutable(t *testing.T) {
 	}
 }
 
+func TestTaskStateRecordsDurableRuntimeEvidence(t *testing.T) {
+	state := newTaskState("Please keep the change focused.\nNever commit generated reports.", nil)
+	arguments := `{"cmd":"go test ./internal/agent"}`
+	state.observe(taskStateEvent{kind: taskStateEventToolResult, arguments: arguments, toolResult: ToolResult{
+		ToolCallID: "test-1", Name: "exec_command", Status: tools.StatusError,
+		Output: "Error: TestResumeRetainsState failed\nfull diagnostic",
+		Meta:   map[string]string{"spill_path": ".zero/artifacts/test-1.txt"},
+	}})
+	state.observe(taskStateEvent{kind: taskStateEventPermission, permission: PermissionEvent{
+		ToolName: "exec_command", DecisionAction: PermissionDecisionAllowForSession,
+		Scope: "/tmp", DecisionReason: "write a temporary fixture",
+	}})
+
+	snapshot := state.snapshot()
+	if !reflect.DeepEqual(snapshot.Constraints, []string{"Please keep the change focused.", "Never commit generated reports."}) {
+		t.Fatalf("unexpected explicit constraints: %#v", snapshot.Constraints)
+	}
+	if len(snapshot.UnresolvedFailures) != 1 || snapshot.UnresolvedFailures[0].Command != "go test ./internal/agent" || snapshot.UnresolvedFailures[0].Summary != "Error: TestResumeRetainsState failed" {
+		t.Fatalf("unexpected failure evidence: %#v", snapshot.UnresolvedFailures)
+	}
+	if len(snapshot.Artifacts) != 1 || snapshot.Artifacts[0].Path != ".zero/artifacts/test-1.txt" {
+		t.Fatalf("unexpected artifact evidence: %#v", snapshot.Artifacts)
+	}
+	if len(snapshot.Approvals) != 1 || snapshot.Approvals[0].Decision != PermissionDecisionAllowForSession || snapshot.Approvals[0].Scope != "/tmp" {
+		t.Fatalf("unexpected approval evidence: %#v", snapshot.Approvals)
+	}
+	state.observe(taskStateEvent{kind: taskStateEventToolResult, arguments: `{"path":"a.go"}`, toolResult: ToolResult{
+		ToolCallID: "read-a", Name: "read_file", Status: tools.StatusError, Output: "Error: a.go is unavailable",
+	}})
+	state.observe(taskStateEvent{kind: taskStateEventToolResult, arguments: `{"path":"b.go"}`, toolResult: ToolResult{
+		ToolCallID: "read-b", Name: "read_file", Status: tools.StatusOK, Output: "package b",
+	}})
+	if failures := state.snapshot().UnresolvedFailures; len(failures) != 2 || failures[1].Summary != "Error: a.go is unavailable" {
+		t.Fatalf("success for a different target resolved the wrong failure: %#v", failures)
+	}
+
+	state.observe(taskStateEvent{kind: taskStateEventToolResult, arguments: arguments, toolResult: ToolResult{
+		ToolCallID: "test-2", Name: "exec_command", Status: tools.StatusOK, Output: "ok",
+	}})
+	if failures := state.snapshot().UnresolvedFailures; len(failures) != 1 || failures[0].Summary != "Error: a.go is unavailable" {
+		t.Fatalf("successful retry did not resolve only its matching failure: %#v", failures)
+	}
+	state.observe(taskStateEvent{kind: taskStateEventToolResult, arguments: `{"path":"a.go"}`, toolResult: ToolResult{
+		ToolCallID: "read-a-2", Name: "read_file", Status: tools.StatusOK, Output: "package a",
+	}})
+	if failures := state.snapshot().UnresolvedFailures; len(failures) != 0 {
+		t.Fatalf("successful non-command retry did not resolve its matching failure: %#v", failures)
+	}
+	state.observe(taskStateEvent{kind: taskStateEventToolResult, arguments: `{"path":"a.go"}`, toolResult: ToolResult{
+		ToolCallID: "read-a-3", Name: "read_file", Status: tools.StatusError, Output: "Error: a.go failed again",
+	}})
+	snapshot = state.snapshot()
+	if len(snapshot.UnresolvedFailures) != 1 || snapshot.UnresolvedFailures[0].Summary != "Error: a.go failed again" {
+		t.Fatalf("a failure recurring after success was hidden: %#v", snapshot.UnresolvedFailures)
+	}
+	for _, key := range snapshot.ResolvedFailureKeys {
+		if key == snapshot.UnresolvedFailures[0].Key {
+			t.Fatalf("recurring failure retained a stale resolved key: %#v", snapshot.ResolvedFailureKeys)
+		}
+	}
+}
+
 func TestTaskStatePlanParityUsesLatestPlan(t *testing.T) {
 	state := newTaskState("objective", nil)
 	state.observe(taskStateEvent{kind: taskStateEventPlan, arguments: `{"plan":[{"content":"old","status":"completed"}]}`})

internal/agent/types.go

@@ -26,6 +26,15 @@ const (
 	PermissionModeAsk       PermissionMode = "ask"
 	PermissionModeUnsafe    PermissionMode = "unsafe"
 	PermissionModeSpecDraft PermissionMode = "spec-draft"
+	// PermissionModePlan is an interactive, read-only planning mode. It applies
+	// to the CURRENT session (unlike spec-draft, which drafts in a separate
+	// session): the agent may inspect the workspace and shape the plan with
+	// update_plan/ask_user, but no mutating tool is advertised, so it cannot
+	// write files, run shell, or implement while planning. Entry points:
+	// the TUI's /plan on (exit with /plan off, which restores whatever mode
+	// was active before), `zero exec --plan`, and the ACP session mode
+	// selector ("plan").
+	PermissionModePlan PermissionMode = "plan"
 	// PermissionModeMemberAuto is a headless mode for swarm/specialist MEMBERS: it
 	// advertises the in-workspace mutators a member needs to build (write/edit +
 	// shell) on top of the Auto set, while the sandbox engine still gates them at
@@ -79,6 +88,7 @@ type ToolResult struct {
 	// command execution; callers must not schedule per-file work from them.
 	ChangeSummaries []execution.Change
 	Display         tools.Display
+	Outcome         tools.ToolOutcome
 	// DenialReason categorizes why a tool call was blocked (empty when it ran).
 	// It lets a surface distinguish the cause precisely instead of parsing Output.
 	DenialReason DenialCategory
@@ -99,6 +109,24 @@ type ToolResult struct {
 	RequestedModel string
 }
 
+// ModelOutput returns the bounded provider-facing result while preserving
+// compatibility with synthetic and restored results created before outcomes
+// were finalized.
+func (result ToolResult) ModelOutput() string {
+	if result.Outcome.Finalized() {
+		return result.Outcome.ModelView
+	}
+	return result.Output
+}
+
+// HumanDisplay returns the presentation intended for interactive surfaces.
+func (result ToolResult) HumanDisplay() tools.Display {
+	if result.Outcome.Finalized() {
+		return result.Outcome.HumanView
+	}
+	return result.Display
+}
+
 // DenialCategory classifies why a tool call was blocked before it executed.
 type DenialCategory string
 
@@ -176,6 +204,22 @@ type PermissionRequest struct {
 	Grant              *sandbox.Grant             `json:"grant,omitempty"`
 	CommandPrefix      []string                   `json:"commandPrefix,omitempty"`
 	AvailableDecisions []PermissionDecisionAction `json:"availableDecisions,omitempty"`
+	// PrefixApprovalEscalates reports that approving a command prefix will also
+	// run the command OUTSIDE the sandbox, not merely stop asking about it.
+	//
+	// It exists because that consequence was real but invisible. Approving a
+	// prefix rewrites the call to sandbox_permissions: require_escalated, which
+	// resolves to a nil engine and genuinely unsandboxed execution, and the
+	// engine's own escalation prompt is then satisfied by the approval just
+	// given for the sandboxed form. So the operator authorized one thing and got
+	// a wider one, having been shown only "allow command prefix for session".
+	//
+	// The escalation itself is deliberate and guarded: proposedCommandPrefix
+	// refuses to offer a prefix while any other segment of the command is not
+	// known-safe, precisely so an unreviewed segment cannot ride out of the
+	// sandbox on it. What was missing was telling the person deciding, so this
+	// surfaces it rather than removing it.
+	PrefixApprovalEscalates bool `json:"prefixApprovalEscalates,omitempty"`
 }
 
 type PermissionDecision struct {
@@ -281,8 +325,12 @@ type Options struct {
 	ProviderName     string
 	Model            string
 	ReasoningEffort  string
+	ServiceTier      string
 	Cwd              string
 	SystemPrompt     string
+	// TransientSystemPrompt adds trusted runtime guidance for this run only.
+	// Empty preserves the ordinary system prompt byte-for-byte.
+	TransientSystemPrompt string
 	// ResponseStyle is the operator-selected reply style from the TUI /style
 	// command (e.g. "concise", "explanatory", "review"). It is rendered into the
 	// system prompt as a short directive. Empty or "balanced" adds nothing — the
@@ -333,9 +381,11 @@ type Options struct {
 	// specialist child process emits while running. The toolCallID identifies
 	// which Task tool call the progress belongs to. nil is a no-op.
 	OnToolProgress func(toolCallID string, event streamjson.Event)
-	// OnContext, when set, is called once per turn with the per-category context
-	// budget of the request about to be sent, so a surface (TUI/CLI) can show
-	// context utilization. Opt-in like the other callbacks; nil is a no-op.
+	// OnContext, when set, is called for each main agent request with its
+	// per-category context budget, including a replacement request after
+	// compaction or a stall retry. Internal summarizer requests are excluded so
+	// surfaces keep showing the active conversation budget. Opt-in like the other
+	// callbacks; nil is a no-op.
 	OnContext func(ContextBreakdown)
 	// ModelSwitcher, when set, lets a tool escalate the run to a stronger model
 	// mid-run: the loop calls it with the requested model id and, on success,

internal/background/process_posix.go

@@ -39,3 +39,21 @@ func ConfigureChildProcessGroup(cmd *exec.Cmd) {
 func terminateProcess(pid int) error {
 	return execution.TerminateProcessTree(pid, terminationGracePeriod, terminationPollInterval)
 }
+
+// terminateOwnedProcess terminates cmd's process group directly when its launch
+// configuration proves it was made a group leader. This avoids fragile Getpgid
+// rediscovery after an owned leader exits. Ordinary commands fall back to the
+// safe PID/tree path rather than assuming their PID is also a process-group ID.
+//
+// The Setpgid && Pgid == 0 guard only recognizes ConfigureChildProcessGroup's
+// own convention. A command made its own session leader via Setsid (as opposed
+// to Setpgid) is also its own process-group leader in practice, but takes the
+// slower rediscovery path here since Setsid isn't checked. Harmless today
+// because TerminateCommand has exactly one caller in this codebase; worth
+// covering explicitly if Setsid-configured commands start using this path too.
+func terminateOwnedProcess(cmd *exec.Cmd) (bool, error) {
+	if cmd.SysProcAttr != nil && cmd.SysProcAttr.Setpgid && cmd.SysProcAttr.Pgid == 0 {
+		return false, execution.TerminateProcessGroup(cmd.Process.Pid, terminationGracePeriod, terminationPollInterval)
+	}
+	return false, terminateProcess(cmd.Process.Pid)
+}

internal/background/process_posix_test.go

@@ -147,11 +147,12 @@ func TestTerminateProcessKillsForkedChildren(t *testing.T) {
 		t.Fatalf("terminateProcess: %v", err)
 	}
 
-	// The forked child must be gone too (poll until reaped by init).
+	// The forked child must no longer be running. An orphaned zombie is already
+	// dead but may remain visible briefly until the platform's init reaps it.
 	deadline := time.Now().Add(2 * time.Second)
-	// Only ESRCH proves the child is gone; any other error (e.g. EPERM) would
-	// wrongly pass the test, so treat it as still-present and keep polling.
-	for !errors.Is(syscall.Kill(childPID, syscall.Signal(0)), syscall.ESRCH) {
+	// processStopped treats only ESRCH or an observed zombie state as stopped;
+	// other errors (for example EPERM) remain live and keep polling.
+	for !processStopped(childPID) {
 		if time.Now().After(deadline) {
 			_ = syscall.Kill(childPID, syscall.SIGKILL)
 			t.Fatalf("forked child %d survived terminateProcess — group kill failed", childPID)
@@ -159,3 +160,73 @@ func TestTerminateProcessKillsForkedChildren(t *testing.T) {
 		time.Sleep(20 * time.Millisecond)
 	}
 }
+
+func TestTerminateCommandStopsUnconfiguredCommand(t *testing.T) {
+	cmd := exec.Command("sleep", "30")
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("start: %v", err)
+	}
+	t.Cleanup(func() {
+		if cmd.ProcessState == nil {
+			_ = cmd.Process.Kill()
+		}
+	})
+
+	if err := TerminateCommand(cmd); err != nil {
+		t.Fatalf("TerminateCommand: %v", err)
+	}
+	if cmd.ProcessState == nil {
+		t.Fatal("unconfigured command was not reaped")
+	}
+}
+
+func TestTerminateCommandKillsChildAfterLeaderExits(t *testing.T) {
+	grace, poll := terminationGracePeriod, terminationPollInterval
+	terminationGracePeriod, terminationPollInterval = 2*time.Second, 20*time.Millisecond
+	t.Cleanup(func() { terminationGracePeriod, terminationPollInterval = grace, poll })
+
+	// The leader exits immediately after launching the child. TerminateCommand
+	// must capture and signal the process group before Wait reaps the leader and
+	// makes its group identity unavailable.
+	cmd := exec.Command("sh", "-c", "sleep 300 & echo $!; exit 0")
+	ConfigureChildProcessGroup(cmd)
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		t.Fatalf("stdout pipe: %v", err)
+	}
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("start: %v", err)
+	}
+	line, err := bufio.NewReader(stdout).ReadString('\n')
+	if err != nil {
+		t.Fatalf("read forked child pid: %v", err)
+	}
+	childPID, err := strconv.Atoi(strings.TrimSpace(line))
+	if err != nil {
+		t.Fatalf("parse forked child pid %q: %v", line, err)
+	}
+
+	if err := TerminateCommand(cmd); err != nil {
+		t.Fatalf("TerminateCommand: %v", err)
+	}
+
+	deadline := time.Now().Add(2 * time.Second)
+	for !processStopped(childPID) {
+		if time.Now().After(deadline) {
+			_ = syscall.Kill(childPID, syscall.SIGKILL)
+			t.Fatalf("forked child %d survived TerminateCommand", childPID)
+		}
+		time.Sleep(20 * time.Millisecond)
+	}
+}
+
+func processStopped(pid int) bool {
+	if errors.Is(syscall.Kill(pid, syscall.Signal(0)), syscall.ESRCH) {
+		return true
+	}
+	state, err := exec.Command("ps", "-o", "stat=", "-p", strconv.Itoa(pid)).Output()
+	if err != nil {
+		return errors.Is(syscall.Kill(pid, syscall.Signal(0)), syscall.ESRCH)
+	}
+	return strings.HasPrefix(strings.TrimSpace(string(state)), "Z")
+}

internal/background/process_windows.go

@@ -3,11 +3,20 @@
 package background
 
 import (
+	"fmt"
 	"os/exec"
 
 	"github.com/Gitlawb/zero/internal/execution"
+	"golang.org/x/sys/windows"
 )
 
+// stillActiveExitCode is the documented GetExitCodeProcess value for a process
+// that has not terminated. x/sys/windows does not expose Windows' STILL_ACTIVE
+// constant.
+const stillActiveExitCode uint32 = 259
+
+var terminateProcessForTest = terminateProcess
+
 // ConfigureChildProcessGroup is a no-op on Windows: process-tree termination is
 // delegated to execution.TerminateProcessTree, so no launch-time process-group
 // setup is required (the POSIX build sets Setpgid here instead).
@@ -16,3 +25,28 @@ func ConfigureChildProcessGroup(cmd *exec.Cmd) { execution.ConfigureProcessGroup
 func terminateProcess(pid int) error {
 	return execution.TerminateProcessTree(pid, 0, 0)
 }
+
+// terminateOwnedProcess asks taskkill /T to terminate the tree rooted at cmd,
+// with KillProcessTree's direct Process.Kill fallback if taskkill fails. taskkill
+// can discover descendants only while the root PID still exists; unlike a POSIX
+// process group, a Windows tree has no independently addressable identity after
+// its root exits.
+func terminateOwnedProcess(cmd *exec.Cmd) (bool, error) {
+	var (
+		alreadyExited bool
+		terminateErr  error
+	)
+	err := cmd.Process.WithHandle(func(handle uintptr) {
+		var exitCode uint32
+		if windows.GetExitCodeProcess(windows.Handle(handle), &exitCode) == nil {
+			alreadyExited = exitCode != stillActiveExitCode
+		}
+		// Keep the exact process identity pinned while the PID-based taskkill
+		// operation runs, preventing the PID from being recycled underneath it.
+		terminateErr = terminateProcessForTest(cmd.Process.Pid)
+	})
+	if err != nil {
+		return false, fmt.Errorf("pin process %d for termination: %w", cmd.Process.Pid, err)
+	}
+	return alreadyExited, terminateErr
+}

internal/background/process_windows_test.go

@@ -0,0 +1,106 @@
+//go:build windows
+
+package background
+
+import (
+	"bufio"
+	"errors"
+	"os/exec"
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestTerminateCommandReturnsTreeFailureAfterRootFallbackReaps(t *testing.T) {
+	cmd := exec.Command("powershell.exe", "-NoProfile", "-NonInteractive", "-Command", "Start-Sleep -Seconds 300")
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("start: %v", err)
+	}
+	treeErr := errors.New("taskkill /T failed")
+	originalTerminateProcess := terminateProcessForTest
+	terminateProcessForTest = func(pid int) error {
+		if err := cmd.Process.Kill(); err != nil {
+			return errors.Join(treeErr, err)
+		}
+		return treeErr
+	}
+	t.Cleanup(func() { terminateProcessForTest = originalTerminateProcess })
+
+	err := TerminateCommand(cmd)
+	if !errors.Is(err, treeErr) {
+		t.Fatalf("TerminateCommand error = %v, want tree failure", err)
+	}
+	if cmd.ProcessState == nil {
+		t.Fatal("root process was not reaped")
+	}
+}
+
+func TestTerminateCommandReapsExitedLeader(t *testing.T) {
+	cmd := exec.Command("cmd.exe", "/c", "exit", "0")
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("start: %v", err)
+	}
+	// Let the child exit without calling Wait so cleanup exercises the Windows
+	// taskkill/TerminateProcess race while it still owns the process handle.
+	time.Sleep(500 * time.Millisecond)
+
+	// jatmn's #774 finding: taskkill /T racing an already-exited PID (and the
+	// Process.Kill fallback) both fail here, but the reap below still succeeds —
+	// the process-handle exit-code check proves the leader was already gone, so
+	// TerminateCommand must not surface the expected kill-attempt error.
+	if err := TerminateCommand(cmd); err != nil {
+		t.Fatalf("TerminateCommand: %v, want nil (leader was already gone and got reaped)", err)
+	}
+	if cmd.ProcessState == nil {
+		t.Fatal("exited process was not reaped")
+	}
+}
+
+func TestTerminateCommandDeadLeaderCannotIdentifyDescendantTree(t *testing.T) {
+	cmd := exec.Command("powershell.exe", "-NoProfile", "-NonInteractive", "-Command",
+		`$p = Start-Process powershell.exe -ArgumentList '-NoProfile','-Command','Start-Sleep -Seconds 300' -PassThru; $p.Id`)
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		t.Fatalf("stdout pipe: %v", err)
+	}
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("start: %v", err)
+	}
+	line, err := bufio.NewReader(stdout).ReadString('\n')
+	if err != nil {
+		t.Fatalf("read descendant pid: %v", err)
+	}
+	descendantPID, err := strconv.Atoi(strings.TrimSpace(line))
+	if err != nil {
+		t.Fatalf("parse descendant pid %q: %v", line, err)
+	}
+	t.Cleanup(func() {
+		_ = exec.Command("taskkill.exe", "/F", "/PID", strconv.Itoa(descendantPID)).Run()
+	})
+
+	// Wait until the leader is observably exited but deliberately leave it
+	// unreaped, matching the POSIX regression's ordering.
+	deadline := time.Now().Add(5 * time.Second)
+	for processExistsOnWindows(cmd.Process.Pid) {
+		if time.Now().After(deadline) {
+			t.Fatal("leader did not exit")
+		}
+		time.Sleep(20 * time.Millisecond)
+	}
+	if err := TerminateCommand(cmd); err != nil {
+		t.Fatalf("TerminateCommand: %v", err)
+	}
+
+	// Windows has no persistent group ID analogous to POSIX: once the leader is
+	// gone, taskkill /T cannot rediscover this descendant. Assert that platform
+	// distinction rather than claiming TerminateCommand can provide it here.
+	if !processExistsOnWindows(descendantPID) {
+		t.Fatal("descendant unexpectedly stopped after its root exited")
+	}
+}
+
+func processExistsOnWindows(pid int) bool {
+	return exec.Command("powershell.exe", "-NoProfile", "-NonInteractive", "-Command",
+		"Get-Process -Id "+strconv.Itoa(pid)+" -ErrorAction Stop | Out-Null").Run() == nil
+}

internal/background/terminate.go

@@ -1,5 +1,14 @@
 package background
 
+import (
+	"errors"
+	"fmt"
+	"os/exec"
+	"time"
+)
+
+const commandReapTimeout = 3 * time.Second
+
 // TerminateProcess stops a background process by PID — on Windows its process
 // tree; on POSIX its whole process group when the PID leads its own group (the
 // invariant ConfigureChildProcessGroup establishes for processes started through
@@ -12,3 +21,69 @@ package background
 func TerminateProcess(pid int) error {
 	return terminateProcess(pid)
 }
+
+// TerminateCommand stops a started command and reaps its leader. The caller must
+// have exclusive ownership of cmd: it must not have previously called Wait or
+// Process.Release, and no goroutine may call either concurrently. On POSIX it
+// stops the whole group when the command was configured as its leader; ordinary
+// commands safely fall back to PID/tree discovery. On Windows, success for a
+// leader that was already dead confirms only that the leader was reaped;
+// descendants may survive because Windows cannot rediscover a tree from a dead
+// root. `zero daemon start` needs this operation when readiness times out: it
+// launched the child, so it must both stop the tree and collect the leader.
+//
+// The order matters: the tree is signalled first, because Wait releases the
+// leader's PID and a later group lookup could then resolve to nothing (or, worse,
+// to a recycled PID). Termination stays in the shared execution lifecycle
+// primitives rather than introducing a second platform-specific killer.
+//
+// If the bounded reap times out, the Wait call already started by this function
+// continues in its goroutine. From that point onward the caller must not access
+// cmd at all, including ProcessState, because that would race with Wait.
+func TerminateCommand(cmd *exec.Cmd) error {
+	if cmd == nil || cmd.Process == nil {
+		return errors.New("terminate command: process was never started")
+	}
+	leaderAlreadyExited, terminateErr := terminateOwnedProcess(cmd)
+	reapErr := waitForTerminatedCommandWithin(cmd, commandReapTimeout)
+	if reapErr != nil {
+		if terminateErr != nil {
+			return fmt.Errorf("%v (reap failed: %w)", terminateErr, reapErr)
+		}
+		return reapErr
+	}
+	if terminateErr != nil && !leaderAlreadyExited {
+		return terminateErr
+	}
+	// Only discard a termination error when the platform demonstrated before
+	// attempting termination that the leader had already exited. A successful
+	// reap alone says nothing about whether a live descendant tree was stopped.
+	return nil
+}
+
+// classifyWaitError treats a non-zero exit status as success: a process being
+// terminated is expected to report one (or a signal), so the only interesting
+// failure is Wait itself not working.
+func classifyWaitError(waitErr error) error {
+	var exitErr *exec.ExitError
+	if waitErr != nil && !errors.As(waitErr, &exitErr) {
+		return fmt.Errorf("reap process: %w", waitErr)
+	}
+	return nil
+}
+
+// waitForTerminatedCommandWithin bounds the reap so a child that somehow survives
+// termination cannot hang the caller — the daemon-start cleanup path runs while a
+// user waits at the CLI. On timeout its Wait goroutine is intentionally left to
+// finish: exec.Cmd permits only one Wait call, and abandoning it without a reaper
+// would leak the child once it eventually exits.
+func waitForTerminatedCommandWithin(cmd *exec.Cmd, timeout time.Duration) error {
+	waitDone := make(chan error, 1)
+	go func() { waitDone <- cmd.Wait() }()
+	select {
+	case waitErr := <-waitDone:
+		return classifyWaitError(waitErr)
+	case <-time.After(timeout):
+		return fmt.Errorf("process %d did not reap after termination", cmd.Process.Pid)
+	}
+}

internal/cli/app.go

@@ -23,6 +23,7 @@ import (
 	"github.com/Gitlawb/zero/internal/mcp"
 	"github.com/Gitlawb/zero/internal/modelregistry"
 	"github.com/Gitlawb/zero/internal/observability"
+	"github.com/Gitlawb/zero/internal/peermsg"
 	"github.com/Gitlawb/zero/internal/plugins"
 	"github.com/Gitlawb/zero/internal/providerhealth"
 	"github.com/Gitlawb/zero/internal/providermodeldiscovery"
@@ -63,37 +64,53 @@ type appDeps struct {
 	// getenv reads a process environment variable (production: os.Getenv, set in
 	// defaultAppDeps — deliberately NOT filled by fillAppDeps, so tests are hermetic
 	// against ambient vars like ZERO_PROVIDER unless they inject it). nil ⇒ empty.
-	getenv                 func(string) string
-	probeProviderHealth    func(context.Context, providerhealth.Options) providerhealth.Result
-	discoverProviderModels func(context.Context, config.ProviderProfile) ([]providermodeldiscovery.Model, error)
-	detectLocalRuntimes    func(context.Context, provideronboarding.LocalDetectOptions) []provideronboarding.DetectedLocalRuntime
-	openRouterLogin        func(context.Context, provideroauth.OpenRouterOptions) (string, error)
-	newSessionStore        func() *sessions.Store
-	loadPlugins            func(plugins.LoadOptions) (plugins.LoadResult, error)
-	loadHooks              func(hooks.LoadOptions) (hooks.LoadResult, error)
-	skillsDir              func() string
-	pluginsDir             func() string
-	toolsDir               func() string
-	newMCPStore            func() (*mcp.PermissionStore, error)
-	newMCPTokenStore       func() (*mcp.TokenStore, error)
-	newSandboxStore        func() (*sandbox.GrantStore, error)
-	selectSandboxBackend   func(sandbox.BackendOptions) sandbox.Backend
-	runSandboxSetupHelper  func(path string, args []string, stdout io.Writer, stderr io.Writer) error
-	registerMCPTools       func(context.Context, *tools.Registry, config.MCPConfig, mcp.RegisterOptions) (mcpToolRuntime, error)
-	prepareWorktree        func(context.Context, worktrees.Options) (worktrees.Result, error)
-	detectVerifyPlan       func(string) (verify.Plan, error)
-	runVerify              func(context.Context, verify.Plan, verify.RunOptions) verify.Report
-	runSelfVerify          func(context.Context, verify.Plan, selfverify.Options) selfverify.Report
-	runAgentEval           func(context.Context, agentEvalOptions) (agentEvalReport, error)
-	inspectChanges         func(context.Context, zerogit.InspectOptions) (zerogit.ChangeSummary, error)
-	commitChanges          func(context.Context, zerogit.CommitOptions) (zerogit.CommitResult, error)
-	pushChanges            func(context.Context, zerogit.PushOptions) (zerogit.PushResult, error)
-	createPR               func(context.Context, zerogit.PROptions) (zerogit.PRResult, error)
-	runTUI                 func(context.Context, tui.Options) int
-	runEditor              func(string) error
-	checkUpdate            func(context.Context, update.Options) (update.Result, error)
-	applyUpdate            func(context.Context, update.Options) (update.ApplyResult, error)
-	now                    func() time.Time
+	getenv                       func(string) string
+	probeProviderHealth          func(context.Context, providerhealth.Options) providerhealth.Result
+	discoverProviderModels       func(context.Context, config.ProviderProfile) ([]providermodeldiscovery.Model, error)
+	detectLocalRuntimes          func(context.Context, provideronboarding.LocalDetectOptions) []provideronboarding.DetectedLocalRuntime
+	openRouterLogin              func(context.Context, provideroauth.OpenRouterOptions) (string, error)
+	newSessionStore              func() *sessions.Store
+	loadPlugins                  func(plugins.LoadOptions) (plugins.LoadResult, error)
+	loadHooks                    func(hooks.LoadOptions) (hooks.LoadResult, error)
+	skillsDir                    func() string
+	pluginsDir                   func() string
+	toolsDir                     func() string
+	newMCPStore                  func() (*mcp.PermissionStore, error)
+	newMCPTokenStore             func() (*mcp.TokenStore, error)
+	newSandboxStore              func() (*sandbox.GrantStore, error)
+	selectSandboxBackend         func(sandbox.BackendOptions) sandbox.Backend
+	runSandboxSetupHelper        func(path string, args []string, stdout io.Writer, stderr io.Writer) error
+	registerMCPTools             func(context.Context, *tools.Registry, config.MCPConfig, mcp.RegisterOptions) (mcpToolRuntime, error)
+	prepareWorktree              func(context.Context, worktrees.Options) (worktrees.Result, error)
+	releaseWorktree              func(context.Context, worktrees.Options, string) error
+	detectVerifyPlan             func(string) (verify.Plan, error)
+	runVerify                    func(context.Context, verify.Plan, verify.RunOptions) verify.Report
+	runSelfVerify                func(context.Context, verify.Plan, selfverify.Options) selfverify.Report
+	runAgentEval                 func(context.Context, agentEvalOptions) (agentEvalReport, error)
+	inspectChanges               func(context.Context, zerogit.InspectOptions) (zerogit.ChangeSummary, error)
+	commitChanges                func(context.Context, zerogit.CommitOptions) (zerogit.CommitResult, error)
+	pushChanges                  func(context.Context, zerogit.PushOptions) (zerogit.PushResult, error)
+	createPR                     func(context.Context, zerogit.PROptions) (zerogit.PRResult, error)
+	createBranch                 func(context.Context, zerogit.BranchOptions) (zerogit.BranchResult, error)
+	isDefaultBranch              func(context.Context, zerogit.DefaultBranchOptions) (bool, string, string, error)
+	currentGitUser               func(context.Context, string) string
+	headCommitSubject            func(context.Context, string) string
+	commitsAhead                 func(context.Context, string, string, string) (int, error)
+	isUnbornRemote               func(context.Context, string, string) (bool, error)
+	refreshTrackingRef           func(context.Context, string, string, string) error
+	branchUpstreamRemote         func(context.Context, string, string) string
+	branchUpstreamRemoteAndMerge func(context.Context, string, string) (string, string)
+	resolveRemoteBranchTip       func(context.Context, string, string, string) (string, error)
+	remoteHasBranch              func(context.Context, string, string, string) (bool, error)
+	currentGitBranch             func(context.Context, string) string
+	currentBranchTip             func(context.Context, string) string
+	deleteBranch                 func(context.Context, string, string, string) error
+	resetBranchRef               func(context.Context, string, string, string, string) error
+	runTUI                       func(context.Context, tui.Options) int
+	runEditor                    func(string) error
+	checkUpdate                  func(context.Context, update.Options) (update.Result, error)
+	applyUpdate                  func(context.Context, update.Options) (update.ApplyResult, error)
+	now                          func() time.Time
 }
 
 type mcpToolRuntime interface {
@@ -187,6 +204,7 @@ func defaultAppDeps() appDeps {
 			return mcp.RegisterTools(ctx, registry, cfg, options)
 		},
 		prepareWorktree:  worktrees.Prepare,
+		releaseWorktree:  worktrees.Release,
 		detectVerifyPlan: verify.DetectPlan,
 		runVerify:        verify.Run,
 		runSelfVerify:    selfverify.Run,
@@ -195,11 +213,52 @@ func defaultAppDeps() appDeps {
 		commitChanges:    zerogit.Commit,
 		pushChanges:      zerogit.Push,
 		createPR:         zerogit.CreatePR,
-		runTUI:           tui.Run,
-		runEditor:        openEditor,
-		checkUpdate:      update.Check,
-		applyUpdate:      update.Apply,
-		now:              time.Now,
+		createBranch:     zerogit.CreateBranch,
+		isDefaultBranch:  zerogit.IsDefaultBranch,
+		currentGitUser: func(ctx context.Context, cwd string) string {
+			return zerogit.CurrentGitUser(ctx, cwd, nil)
+		},
+		headCommitSubject: func(ctx context.Context, cwd string) string {
+			return zerogit.HeadCommitSubject(ctx, cwd, nil)
+		},
+		commitsAhead: func(ctx context.Context, cwd, remote, branch string) (int, error) {
+			return zerogit.CommitsAhead(ctx, cwd, remote, branch, nil)
+		},
+		isUnbornRemote: func(ctx context.Context, cwd, remote string) (bool, error) {
+			return zerogit.IsUnbornRemote(ctx, cwd, remote, nil)
+		},
+		refreshTrackingRef: func(ctx context.Context, cwd, remote, branch string) error {
+			return zerogit.RefreshTrackingRef(ctx, cwd, remote, branch, nil)
+		},
+		branchUpstreamRemote: func(ctx context.Context, cwd, branch string) string {
+			return zerogit.UpstreamRemote(ctx, cwd, branch, nil)
+		},
+		branchUpstreamRemoteAndMerge: func(ctx context.Context, cwd, branch string) (string, string) {
+			return zerogit.UpstreamRemoteAndMergeBranch(ctx, cwd, branch, nil)
+		},
+		resolveRemoteBranchTip: func(ctx context.Context, cwd, remote, branch string) (string, error) {
+			return zerogit.ResolveRemoteBranchTip(ctx, cwd, remote, branch, nil)
+		},
+		remoteHasBranch: func(ctx context.Context, cwd, remote, branch string) (bool, error) {
+			return zerogit.RemoteHasBranch(ctx, cwd, remote, branch, nil)
+		},
+		currentGitBranch: func(ctx context.Context, cwd string) string {
+			return zerogit.CurrentBranch(ctx, cwd, nil)
+		},
+		currentBranchTip: func(ctx context.Context, cwd string) string {
+			return zerogit.CurrentBranchTip(ctx, cwd, nil)
+		},
+		deleteBranch: func(ctx context.Context, cwd, fallbackBranch, branchToDelete string) error {
+			return zerogit.DeleteBranch(ctx, cwd, fallbackBranch, branchToDelete, nil)
+		},
+		resetBranchRef: func(ctx context.Context, cwd, branch, newTip, expectedOld string) error {
+			return zerogit.ResetBranchRef(ctx, cwd, branch, newTip, nil, expectedOld)
+		},
+		runTUI:      tui.Run,
+		runEditor:   openEditor,
+		checkUpdate: update.Check,
+		applyUpdate: update.Apply,
+		now:         time.Now,
 	}
 }
 
@@ -532,6 +591,9 @@ func fillAppDeps(deps appDeps) appDeps {
 	if deps.prepareWorktree == nil {
 		deps.prepareWorktree = defaults.prepareWorktree
 	}
+	if deps.releaseWorktree == nil {
+		deps.releaseWorktree = defaults.releaseWorktree
+	}
 	if deps.detectVerifyPlan == nil {
 		deps.detectVerifyPlan = defaults.detectVerifyPlan
 	}
@@ -556,6 +618,45 @@ func fillAppDeps(deps appDeps) appDeps {
 	if deps.createPR == nil {
 		deps.createPR = defaults.createPR
 	}
+	if deps.createBranch == nil {
+		deps.createBranch = defaults.createBranch
+	}
+	if deps.isDefaultBranch == nil {
+		deps.isDefaultBranch = defaults.isDefaultBranch
+	}
+	if deps.currentGitUser == nil {
+		deps.currentGitUser = defaults.currentGitUser
+	}
+	if deps.headCommitSubject == nil {
+		deps.headCommitSubject = defaults.headCommitSubject
+	}
+	if deps.commitsAhead == nil {
+		deps.commitsAhead = defaults.commitsAhead
+	}
+	if deps.isUnbornRemote == nil {
+		deps.isUnbornRemote = defaults.isUnbornRemote
+	}
+	if deps.refreshTrackingRef == nil {
+		deps.refreshTrackingRef = defaults.refreshTrackingRef
+	}
+	if deps.branchUpstreamRemote == nil {
+		deps.branchUpstreamRemote = defaults.branchUpstreamRemote
+	}
+	if deps.branchUpstreamRemoteAndMerge == nil {
+		deps.branchUpstreamRemoteAndMerge = defaults.branchUpstreamRemoteAndMerge
+	}
+	if deps.remoteHasBranch == nil {
+		deps.remoteHasBranch = defaults.remoteHasBranch
+	}
+	if deps.currentGitBranch == nil {
+		deps.currentGitBranch = defaults.currentGitBranch
+	}
+	if deps.currentBranchTip == nil {
+		deps.currentBranchTip = defaults.currentBranchTip
+	}
+	// resolveRemoteBranchTip, deleteBranch, and resetBranchRef stay nil when
+	// unset so unit tests that mock createBranch without a real git tree do not
+	// hit real git restore/delete commands.
 	if deps.runTUI == nil {
 		deps.runTUI = defaults.runTUI
 	}
@@ -786,6 +887,26 @@ func runInteractiveTUIWithSetup(stderr io.Writer, deps appDeps, permissionMode a
 	if permissionMode == "" {
 		permissionMode = agent.PermissionModeAsk
 	}
+	sessionStore := deps.newSessionStore()
+	peerClass := peermsg.PermissionPrompting
+	if permissionMode == agent.PermissionModeUnsafe {
+		peerClass = peermsg.PermissionBypass
+	}
+	peerService, peerErr := peermsg.New(peermsg.Options{
+		Identity: peermsg.Identity{
+			Cwd:             workspaceRoot,
+			PermissionClass: peerClass,
+		},
+		InboundPolicy: peermsg.InboundPolicy(resolved.CrossSessionInbound),
+	})
+	if peerErr != nil {
+		fmt.Fprintf(stderr, "warning: cross-session messaging unavailable: %s\n", peerErr)
+		peerService = nil
+	} else {
+		for _, tool := range tools.NewPeerSessionTools(peerService) {
+			registry.Register(tool)
+		}
+	}
 	// Activate deferred MCP-tool loading for the interactive run only when the
 	// VISIBLE deferred-eligible count meets the resolved threshold, matching exec.
 	// The registry is complete (core + specialist + MCP + plugins) here, so the
@@ -816,6 +937,7 @@ func runInteractiveTUIWithSetup(stderr io.Writer, deps appDeps, permissionMode a
 		Version:              version,
 		Theme:                theme,
 		SavedTheme:           resolved.Preferences.Theme,
+		SavedPet:             resolved.Preferences.Pet,
 		UserConfigPath:       userConfigPath,
 		DoctorUserConfigPath: doctorUserConfigPath,
 		ProjectConfigPath:    projectConfigPath,
@@ -837,7 +959,8 @@ func runInteractiveTUIWithSetup(stderr io.Writer, deps appDeps, permissionMode a
 			return scratchFileWarning(workspaceRoot, scratchBaseline)
 		},
 		Registry:           registry,
-		SessionStore:       deps.newSessionStore(),
+		SessionStore:       sessionStore,
+		PeerService:        peerService,
 		SandboxStore:       sandboxStore,
 		MCPConfig:          mcpConfig,
 		MCPPermissionStore: mcpPermissionStore,
@@ -1199,7 +1322,8 @@ Commands:
   mcp        Manage MCP backend settings
   auth       Log in to model providers via OAuth
   sandbox    Inspect sandbox policy and persistent grants
-  update     Check for Zero CLI updates
+  update     Check or apply Zero CLI updates (requires --check or --apply)
+  upgrade    Download, verify, and install available Zero CLI updates
   worktrees  Prepare isolated git worktrees
   verify     Detect and run local verification checks
   eval       Validate offline agent eval suites
@@ -1361,6 +1485,10 @@ Flags:
       --spec-model <model>           Override the draft model when --use-spec is set
       --spec-reasoning-effort <effort>
                                     Override draft reasoning effort when --use-spec is set
+      --plan                         Read-only planning mode: write and shell tools are hidden
+      --permission-mode <mode>       Set permission mode directly (plan, spec-draft, auto, member,
+                                    ask, unsafe). Outranks --auto; prefer --plan / --auto for
+                                    interactive use. Used by specialist/swarm child processes.
       --max-turns <number>           Override the maximum agent loop turns
       --exec-profile <name>          Apply an execution profile (balanced, fast, thorough): loop
                                     posture only (turn budget, effort, self-correction, escalation);

internal/cli/app_test.go

@@ -1457,6 +1457,20 @@ func TestRunUpdateHelpDocumentsCheckFlag(t *testing.T) {
 	}
 }
 
+func TestTopLevelHelpDocumentsRequiredUpdateMode(t *testing.T) {
+	var stdout bytes.Buffer
+	var stderr bytes.Buffer
+
+	exitCode := runWithDeps([]string{"--help"}, &stdout, &stderr, appDeps{})
+
+	if exitCode != exitSuccess {
+		t.Fatalf("expected exit code %d, got %d: %s", exitSuccess, exitCode, stderr.String())
+	}
+	if got := stdout.String(); !strings.Contains(got, "update     Check or apply Zero CLI updates (requires --check or --apply)") {
+		t.Fatalf("expected top-level help to document required update mode, got %q", got)
+	}
+}
+
 func TestRunUpdateReportsUpToDate(t *testing.T) {
 	var stdout bytes.Buffer
 	var stderr bytes.Buffer
@@ -1660,6 +1674,7 @@ func assertHelpOutput(t *testing.T, args []string) {
 		"mcp",
 		"sandbox",
 		"update",
+		"upgrade",
 		"worktrees",
 		"verify",
 		"serve",

internal/cli/backends_test.go

@@ -23,7 +23,7 @@ import (
 
 func TestRunBackendsJSONUsesLifecycleSnapshotWithoutConnectingMCP(t *testing.T) {
 	cwd := t.TempDir()
-	secret := "sk-proj-" + strings.Repeat("a", 24)
+	secret := "sk-proj-" + strings.Repeat("a", 23) + "0"
 	deps := appDeps{
 		getwd: func() (string, error) { return cwd, nil },
 		resolveMCPConfig: func(workspaceRoot string, _ bool) (config.MCPConfig, error) {
@@ -161,7 +161,7 @@ func TestRunBackendsTextAndHelp(t *testing.T) {
 
 func TestRunBackendsDoctorJSONAndTextWithoutConnectingMCP(t *testing.T) {
 	cwd := t.TempDir()
-	secret := "sk-proj-" + strings.Repeat("b", 24)
+	secret := "sk-proj-" + strings.Repeat("b", 23) + "0"
 	deps := appDeps{
 		getwd: func() (string, error) { return cwd, nil },
 		resolveMCPConfig: func(workspaceRoot string, _ bool) (config.MCPConfig, error) {

internal/cli/completions.go

@@ -24,7 +24,8 @@ var completionRoot = completionNode{
 	children: []completionNode{
 		{names: []string{"exec"}, flags: []string{
 			"-h", "--help", "-f", "--file", "--image", "--add-dir", "--mode", "-m", "--model",
-			"--use-spec", "--spec-model", "--spec-reasoning-effort", "--max-turns", "--exec-profile",
+			"--use-spec", "--spec-model", "--spec-reasoning-effort", "--plan", "--permission-mode",
+			"--max-turns", "--exec-profile",
 			"--auto", "--enabled-tools", "--disabled-tools", "--list-tools", "--profile", "-r",
 			"--reasoning-effort", "-C", "--cwd", "-w", "--worktree", "--worktree-dir", "-i",
 			"--input-format", "-o", "--output-format", "--prompt", "--resume", "--fork",
@@ -84,7 +85,7 @@ var completionRoot = completionNode{
 		}},
 		{names: []string{"update"}},
 		{names: []string{"upgrade"}},
-		{names: []string{"worktrees", "worktree"}, children: leafNodes("prepare")},
+		{names: []string{"worktrees", "worktree"}, children: leafNodes("prepare", "release")},
 		{names: []string{"verify"}},
 		{names: []string{"trust"}, children: leafNodes("list", "remove")},
 		{names: []string{"eval"}, children: leafNodes("validate", "run", "bench")},

internal/cli/completions_test.go

@@ -155,6 +155,8 @@ func TestCompletionTreeCoversAliasesNestingAndCommonFlags(t *testing.T) {
 
 	assertCandidates(t, byPath[""], "sessions", "session", "plugins", "plugin", "worktrees", "worktree", "--add-dir", "--theme", "-p", "--prompt")
 	assertCandidates(t, byPath["exec"], "--model", "--cwd", "--worktree", "--output-format", "--resume", "--skip-permissions-unsafe")
+	assertCandidates(t, byPath["worktrees"], "prepare", "release")
+	assertCandidates(t, byPath["worktree"], "prepare", "release")
 	assertCandidates(t, byPath["daemon"], "start", "stop", "status", "run", "attach")
 	assertCandidates(t, byPath["mcp oauth"], "login", "logout", "status")
 	assertCandidates(t, byPath["sandbox grants"], "list", "allow", "deny", "revoke", "clear")

internal/cli/daemon.go

@@ -1,6 +1,7 @@
 package cli
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -160,20 +161,61 @@ func runDaemonStartDetached(paths daemon.Paths, stdout io.Writer, stderr io.Writ
 	cmd.Stdout = logFile
 	cmd.Stderr = logFile
 	background.ConfigureChildProcessGroup(cmd) // own process group: outlives this shell
-	if err := cmd.Start(); err != nil {
+	if err := startAndAwaitDaemonProcess(cmd, func() bool { return daemonReachable(paths) }, 5*time.Second, 25*time.Millisecond); err != nil {
+		if errors.Is(err, errDaemonStartTimeout) {
+			return writeAppError(stderr, err.Error()+"; see "+logPath, exitCrash)
+		}
 		return writeAppError(stderr, err.Error(), exitCrash)
 	}
-	_ = cmd.Process.Release()
+	fmt.Fprintf(stdout, "zero daemon started (socket %s)\n", paths.Socket)
+	return exitSuccess
+}
 
-	deadline := time.Now().Add(5 * time.Second)
-	for time.Now().Before(deadline) {
-		if daemonReachable(paths) {
-			fmt.Fprintf(stdout, "zero daemon started (socket %s)\n", paths.Socket)
-			return exitSuccess
-		}
-		time.Sleep(25 * time.Millisecond)
+var errDaemonStartTimeout = errors.New("daemon did not come up within timeout")
+
+func startAndAwaitDaemonProcess(cmd *exec.Cmd, reachable func() bool, timeout time.Duration, pollInterval time.Duration) error {
+	if err := cmd.Start(); err != nil {
+		return err
 	}
-	return writeAppError(stderr, "daemon did not come up within timeout; see "+logPath, exitCrash)
+	if waitForDaemonReadiness(reachable, timeout, pollInterval) {
+		if err := cmd.Process.Release(); err != nil {
+			cleanupErr := terminateAndReapDaemonProcess(cmd)
+			if cleanupErr != nil {
+				return fmt.Errorf("release daemon process: %w (cleanup failed: %v)", err, cleanupErr)
+			}
+			return fmt.Errorf("release daemon process: %w", err)
+		}
+		return nil
+	}
+	if err := terminateAndReapDaemonProcess(cmd); err != nil {
+		return fmt.Errorf("%w; cleanup failed: %v", errDaemonStartTimeout, err)
+	}
+	return errDaemonStartTimeout
+}
+
+func waitForDaemonReadiness(reachable func() bool, timeout time.Duration, pollInterval time.Duration) bool {
+	deadline := time.Now().Add(timeout)
+	for {
+		if reachable() {
+			return true
+		}
+		remaining := time.Until(deadline)
+		if remaining <= 0 {
+			break
+		}
+		time.Sleep(min(pollInterval, remaining))
+	}
+	// The loop's last reachable() call already ran immediately before this one
+	// (right after the final Sleep, with the same deadline check separating
+	// them), so this adds no extra waiting time and is not a grace window for a
+	// slow-starting daemon — it only re-checks the same instant in case
+	// reachable() itself is non-deterministic. To tolerate a genuinely slow
+	// start, raise the timeout passed to startAndAwaitDaemonProcess instead.
+	return reachable()
+}
+
+func terminateAndReapDaemonProcess(cmd *exec.Cmd) error {
+	return background.TerminateCommand(cmd)
 }
 
 func runDaemonStop(args []string, stdout io.Writer, stderr io.Writer) int {

internal/cli/daemon_test.go

@@ -2,8 +2,15 @@ package cli
 
 import (
 	"bytes"
+	"errors"
+	"os"
+	"os/exec"
+	"path/filepath"
 	"strings"
 	"testing"
+	"time"
+
+	"github.com/Gitlawb/zero/internal/background"
 )
 
 // isolateDaemonPaths points DefaultPaths at a temp dir so the test never touches
@@ -121,3 +128,84 @@ func TestDaemonSubcommandsRejectExtraArgs(t *testing.T) {
 		}
 	}
 }
+
+func TestWaitForDaemonReadinessChecksTimeoutBoundary(t *testing.T) {
+	checks := 0
+	ready := waitForDaemonReadiness(func() bool {
+		checks++
+		return checks == 2
+	}, 0, time.Millisecond)
+	if !ready {
+		t.Fatal("daemon that became reachable at the timeout boundary was not detected")
+	}
+	if checks != 2 {
+		t.Fatalf("reachability checks = %d, want initial and final checks", checks)
+	}
+}
+
+func TestTerminateAndReapDaemonProcess(t *testing.T) {
+	cmd := daemonDetachedChildCommand("hang")
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("start helper process: %v", err)
+	}
+
+	if err := terminateAndReapDaemonProcess(cmd); err != nil {
+		t.Fatalf("terminate and reap helper process: %v", err)
+	}
+	if cmd.ProcessState == nil {
+		t.Fatalf("helper process was not reaped: state=%v", cmd.ProcessState)
+	}
+	if cmd.ProcessState.Success() {
+		t.Fatalf("helper process unexpectedly exited successfully: %v", cmd.ProcessState)
+	}
+}
+
+func TestStartAndAwaitDaemonProcessTimeoutTerminatesAndReaps(t *testing.T) {
+	cmd := daemonDetachedChildCommand("hang")
+	if err := startAndAwaitDaemonProcess(cmd, func() bool { return false }, 0, time.Millisecond); !errors.Is(err, errDaemonStartTimeout) {
+		t.Fatalf("start and await error = %v, want timeout", err)
+	}
+	if cmd.ProcessState == nil {
+		t.Fatal("timed-out helper process was not reaped")
+	}
+}
+
+func TestStartAndAwaitDaemonProcessReleasesReadyChild(t *testing.T) {
+	marker := filepath.Join(t.TempDir(), "child-finished")
+	cmd := daemonDetachedChildCommand("mark", "ZERO_TEST_DAEMON_CHILD_MARKER="+marker)
+	if err := startAndAwaitDaemonProcess(cmd, func() bool { return true }, time.Second, time.Millisecond); err != nil {
+		t.Fatalf("start and await ready helper: %v", err)
+	}
+
+	deadline := time.Now().Add(5 * time.Second)
+	for time.Now().Before(deadline) {
+		if _, err := os.Stat(marker); err == nil {
+			return
+		}
+		time.Sleep(10 * time.Millisecond)
+	}
+	t.Fatal("released helper process did not remain alive to write its marker")
+}
+
+func daemonDetachedChildCommand(mode string, extraEnv ...string) *exec.Cmd {
+	cmd := exec.Command(os.Args[0], "-test.run=TestDaemonDetachedChildProcess")
+	cmd.Env = append(os.Environ(), "ZERO_TEST_DAEMON_DETACHED_CHILD="+mode)
+	cmd.Env = append(cmd.Env, extraEnv...)
+	background.ConfigureChildProcessGroup(cmd)
+	return cmd
+}
+
+func TestDaemonDetachedChildProcess(t *testing.T) {
+	switch os.Getenv("ZERO_TEST_DAEMON_DETACHED_CHILD") {
+	case "":
+		return
+	case "mark":
+		if err := os.WriteFile(os.Getenv("ZERO_TEST_DAEMON_CHILD_MARKER"), []byte("ready"), 0o600); err != nil {
+			os.Exit(2)
+		}
+		os.Exit(0)
+	}
+	for {
+		time.Sleep(time.Hour)
+	}
+}

internal/cli/exec.go

@@ -78,11 +78,18 @@ type execOptions struct {
 	// fill-only-if-unset rule, so precedence is explicit flag > mode > profile.
 	// Distinct from the mode preset also named "fast" (which picks a model) and
 	// from the legacy inert --profile above. See internal/execprofile.
-	execProfile           string
-	reasoningEffort       string
-	useSpec               bool
-	specModel             string
-	specReasoningEffort   string
+	execProfile         string
+	reasoningEffort     string
+	useSpec             bool
+	specModel           string
+	specReasoningEffort string
+	// plan selects PermissionModePlan for this run: the same read-only,
+	// in-session planning mode the TUI enters with /plan on. Unlike --use-spec
+	// (a separate draft session with its own review flow), this only swaps the
+	// permission mode for the run already being made — ToolAdvertised gates
+	// write/shell tools generically for any mode, so no other exec plumbing
+	// needs to know about it.
+	plan                  bool
 	maxTurns              int
 	cwd                   string
 	inputFormat           execInputFormat
@@ -104,6 +111,7 @@ type execOptions struct {
 	worktreeName          string
 	worktreeDir           string
 	skipPermissionsUnsafe bool
+	permissionMode        string
 	// allowEscalation opts the run into mid-run model escalation: it registers
 	// the escalate_model tool and wires agent.Options.ModelSwitcher. Off by
 	// default — a run without the flag is byte-identical to before (no tool, nil
@@ -199,11 +207,33 @@ func runExec(args []string, stdout io.Writer, stderr io.Writer, deps appDeps) in
 			Name:    options.worktreeName,
 			BaseDir: options.worktreeDir,
 			Now:     deps.now,
+			// The worktree's lifetime is bound to this process (the deferred
+			// release below), so record the PID: if this process dies without
+			// releasing, Clean can expire the lease instead of skipping the
+			// locked worktree forever.
+			LeasePID: os.Getpid(),
 		})
 		if err != nil {
 			return writeExecFormatUsageError(stdout, stderr, options.outputFormat, err.Error())
 		}
 		workspaceRoot = preparedWorktree.Path
+		// When this run's own Prepare call took the worktree lock, its
+		// lifetime is bound to this function: release the lock once it returns
+		// so Clean can reclaim the worktree later if it goes stale. A reused
+		// worktree whose lock an external `zero worktrees prepare` caller
+		// still holds reports LockAcquired=false; releasing it here would
+		// clear that caller's lease and expose its workspace to Clean, so the
+		// matching release stays that caller's responsibility. A failed unlock
+		// leaves a lock Clean will permanently skip, so it must not pass
+		// silently; the run's primary result has already been emitted by the
+		// time the defer runs, so surface it as a diagnostic.
+		if preparedWorktree.LockAcquired {
+			defer func() {
+				if releaseErr := deps.releaseWorktree(context.Background(), worktrees.Options{Cwd: trustRoot}, preparedWorktree.Path); releaseErr != nil {
+					fmt.Fprintf(stderr, "zero: failed to release worktree lock on %s: %s\n", redactCLIString(preparedWorktree.Path), redactCLIString(releaseErr.Error()))
+				}
+			}()
+		}
 	}
 
 	registry := newCoreRegistry(workspaceRoot)
@@ -240,6 +270,9 @@ func runExec(args []string, stdout io.Writer, stderr io.Writer, deps appDeps) in
 	if options.useSpec {
 		permissionMode = agent.PermissionModeSpecDraft
 	}
+	if options.plan {
+		permissionMode = agent.PermissionModePlan
+	}
 	var mcpRuntime mcpToolRuntime
 	var mcpSkip trustSkip
 	// Make local plugins live for this run: register their declared tools into the
@@ -306,11 +339,13 @@ func runExec(args []string, stdout io.Writer, stderr io.Writer, deps appDeps) in
 		_, _ = fmt.Fprintln(stderr, "[zero] "+notice)
 	}
 	executionRunner.SetPreparer(sandboxEngine)
-	mcpRuntime, mcpSkip, err = registerMCPToolsForWorkspace(context.Background(), workspaceRoot, registry, deps, execMCPAutonomy(options), trustRoot, executionRunner)
-	if err != nil {
-		return writeExecProviderError(stdout, stderr, options.outputFormat, "mcp_error", err.Error())
+	if permissionMode != agent.PermissionModePlan {
+		mcpRuntime, mcpSkip, err = registerMCPToolsForWorkspace(context.Background(), workspaceRoot, registry, deps, execMCPAutonomy(options), trustRoot, executionRunner)
+		if err != nil {
+			return writeExecProviderError(stdout, stderr, options.outputFormat, "mcp_error", err.Error())
+		}
+		defer closeMCPRuntime(stderr, mcpRuntime)
 	}
-	defer closeMCPRuntime(stderr, mcpRuntime)
 	pluginActivation = activatePlugins(workspaceRoot, registry, deps, stderr, trustRoot, executionRunner)
 	registerLocalControlTools(registry, workspaceRoot, resolved.LocalControl)
 	if err := validateExecToolFilters(options, registry); err != nil {
@@ -578,8 +613,12 @@ func runExec(args []string, stdout io.Writer, stderr io.Writer, deps appDeps) in
 	// warned, so --auto high silently ran without notice.
 	if permissionMode == agent.PermissionModeUnsafe {
 		reason := "--auto high"
-		if options.skipPermissionsUnsafe {
+		switch {
+		case options.skipPermissionsUnsafe:
 			reason = "--skip-permissions-unsafe"
+		case strings.EqualFold(strings.TrimSpace(options.permissionMode), "unsafe"),
+			strings.EqualFold(strings.TrimSpace(options.permissionMode), "high"):
+			reason = "--permission-mode unsafe"
 		}
 		writer.warning(fmt.Sprintf("Unsafe permissions are active for this run because %s was passed.", reason))
 		if writer.err != nil {

internal/cli/exec_parse.go

@@ -20,6 +20,19 @@ func parseExecArgs(args []string) (execOptions, bool, error) {
 		switch {
 		case arg == "-h" || arg == "--help" || arg == "help":
 			return options, true, nil
+		case arg == "--permission-mode":
+			value, next, err := nextFlagValue(args, index, arg)
+			if err != nil {
+				return options, false, err
+			}
+			options.permissionMode = strings.TrimSpace(value)
+			index = next
+		case strings.HasPrefix(arg, "--permission-mode="):
+			value, err := requiredInlineFlagValue(arg, "--permission-mode")
+			if err != nil {
+				return options, false, err
+			}
+			options.permissionMode = value
 		case arg == "--skip-permissions-unsafe":
 			options.skipPermissionsUnsafe = true
 		case arg == "--list-tools":
@@ -171,6 +184,8 @@ func parseExecArgs(args []string) (execOptions, bool, error) {
 			options.reasoningEffort = strings.TrimSpace(strings.TrimPrefix(arg, "--reasoning-effort="))
 		case arg == "--use-spec":
 			options.useSpec = true
+		case arg == "--plan":
+			options.plan = true
 		case arg == "--spec-model":
 			value, next, err := nextFlagValue(args, index, arg)
 			if err != nil {
@@ -437,6 +452,27 @@ func parseExecArgs(args []string) (execOptions, bool, error) {
 	if !options.useSpec && options.specReasoningEffort != "" {
 		return options, false, execUsageError{"--spec-reasoning-effort requires --use-spec."}
 	}
+	// Plan mode may be entered via --plan or --permission-mode plan. Combination
+	// guards must key off both: otherwise --permission-mode plan bypasses the
+	// worktree/unsafe/use-spec rejects that --plan alone enforces, and worktree
+	// prep mutates the filesystem before the read-only mode is assigned.
+	planMode := options.plan || strings.EqualFold(strings.TrimSpace(options.permissionMode), "plan")
+	if planMode && options.useSpec {
+		return options, false, execUsageError{"Use either --plan or --use-spec, not both."}
+	}
+	if planMode && options.skipPermissionsUnsafe {
+		return options, false, execUsageError{"Use either --plan or --skip-permissions-unsafe, not both."}
+	}
+	if planMode && options.worktree {
+		// Worktree prep (copying/branching the workspace) runs before the plan
+		// permission mode is assigned, so it would happen even under plan mode's
+		// read-only, no-side-effects promise. Reject the combination outright
+		// rather than let a mutation slip in ahead of the mode gate.
+		return options, false, execUsageError{"--plan cannot be combined with --worktree."}
+	}
+	if options.plan && options.permissionMode != "" && strings.ToLower(options.permissionMode) != "plan" {
+		return options, false, execUsageError{"--plan cannot be combined with --permission-mode=" + options.permissionMode + "."}
+	}
 	if options.initSessionID != "" && (options.resume != "" || options.resumeLatest) {
 		return options, false, execUsageError{"Use --init-session-id only when creating or forking a session."}
 	}

internal/cli/exec_plan_test.go

@@ -0,0 +1,177 @@
+package cli
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"github.com/Gitlawb/zero/internal/agent"
+	"github.com/Gitlawb/zero/internal/config"
+)
+
+func TestParseExecArgsRecognizesPlanFlag(t *testing.T) {
+	options, _, err := parseExecArgs([]string{"--plan", "draft a plan"})
+	if err != nil {
+		t.Fatalf("parseExecArgs: %v", err)
+	}
+	if !options.plan {
+		t.Fatal("expected --plan to set options.plan")
+	}
+}
+
+func TestParseExecArgsRejectsPlanWithUseSpec(t *testing.T) {
+	_, _, err := parseExecArgs([]string{"--plan", "--use-spec", "draft a plan"})
+	if err == nil || !strings.Contains(err.Error(), "not both") {
+		t.Fatalf("expected --plan/--use-spec validation, got %v", err)
+	}
+}
+
+func TestParseExecArgsRejectsPlanWithSkipPermissionsUnsafe(t *testing.T) {
+	_, _, err := parseExecArgs([]string{"--plan", "--skip-permissions-unsafe", "draft a plan"})
+	if err == nil || !strings.Contains(err.Error(), "not both") {
+		t.Fatalf("expected --plan/--skip-permissions-unsafe validation, got %v", err)
+	}
+}
+
+// TestParseExecArgsRejectsPlanWithWorktree guards against worktree
+// preparation (a filesystem mutation) running ahead of the plan mode gate:
+// options.worktree is processed in runExec before the plan permission mode is
+// assigned, so the combination must be rejected during option validation,
+// before any worktree prep can occur.
+func TestParseExecArgsRejectsPlanWithWorktree(t *testing.T) {
+	_, _, err := parseExecArgs([]string{"--plan", "--worktree", "draft a plan"})
+	if err == nil || !strings.Contains(err.Error(), "--worktree") {
+		t.Fatalf("expected --plan/--worktree validation, got %v", err)
+	}
+}
+
+func TestParseExecArgsRejectsPlanWithNonPlanPermissionMode(t *testing.T) {
+	_, _, err := parseExecArgs([]string{"--plan", "--permission-mode=ask", "draft a plan"})
+	if err == nil || !strings.Contains(err.Error(), "--permission-mode") {
+		t.Fatalf("expected --plan/--permission-mode validation, got %v", err)
+	}
+
+	options, _, err := parseExecArgs([]string{"--plan", "--permission-mode=plan", "draft a plan"})
+	if err != nil {
+		t.Fatalf("expected --plan with --permission-mode=plan to succeed, got %v", err)
+	}
+	if !options.plan || options.permissionMode != "plan" {
+		t.Fatalf("expected options.plan=true and permissionMode=plan, got plan=%v mode=%q", options.plan, options.permissionMode)
+	}
+}
+
+// TestParseExecArgsPermissionModePlanSharesCombinationGuards ensures the
+// combination rejects that key off --plan also fire for --permission-mode plan,
+// which reaches PermissionModePlan without setting options.plan.
+func TestParseExecArgsPermissionModePlanSharesCombinationGuards(t *testing.T) {
+	cases := []struct {
+		name string
+		args []string
+		want string
+	}{
+		{"worktree", []string{"--permission-mode", "plan", "--worktree", "draft a plan"}, "--worktree"},
+		{"use-spec", []string{"--permission-mode=plan", "--use-spec", "draft a plan"}, "not both"},
+		{"skip-permissions-unsafe", []string{"--permission-mode", "plan", "--skip-permissions-unsafe", "draft a plan"}, "not both"},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			_, _, err := parseExecArgs(tc.args)
+			if err == nil || !strings.Contains(err.Error(), tc.want) {
+				t.Fatalf("expected --permission-mode plan / %s validation containing %q, got %v", tc.name, tc.want, err)
+			}
+		})
+	}
+
+	// Bare --permission-mode plan (no conflicting flags) still parses.
+	options, _, err := parseExecArgs([]string{"--permission-mode", "plan", "draft a plan"})
+	if err != nil {
+		t.Fatalf("expected bare --permission-mode plan to succeed, got %v", err)
+	}
+	if options.permissionMode != "plan" || options.plan {
+		t.Fatalf("expected permissionMode=plan and plan=false, got mode=%q plan=%v", options.permissionMode, options.plan)
+	}
+}
+
+// TestRunExecPlanHidesWriteAndShellToolsFromListing drives the real --plan
+// flag through runExec (via --list-tools, so no provider is needed) and
+// confirms write_file and bash — advertised under every other mode covered by
+// TestRunExecListToolsAppliesModeBeforeListing-style tests — are hidden,
+// mirroring the TUI /plan on gating end to end from the CLI entry point.
+func TestRunExecPlanHidesWriteAndShellToolsFromListing(t *testing.T) {
+	cwd := t.TempDir()
+	var stdout bytes.Buffer
+	var stderr bytes.Buffer
+
+	exitCode := runWithDeps([]string{"exec", "--plan", "--list-tools"}, &stdout, &stderr, appDeps{
+		getwd: func() (string, error) {
+			return cwd, nil
+		},
+		resolveConfig: func(string, config.Overrides) (config.ResolvedConfig, error) {
+			return execResolvedConfig(), nil
+		},
+	})
+
+	if exitCode != exitSuccess {
+		t.Fatalf("expected exit code %d, got %d: %s", exitSuccess, exitCode, stderr.String())
+	}
+	listing := stdout.String()
+	if !strings.Contains(listing, "Tools visible to model") {
+		t.Fatalf("expected --plan --list-tools to list tools, got %q", listing)
+	}
+	if !strings.Contains(listing, "read_file") {
+		t.Fatalf("expected plan mode to still list read_file, got %q", listing)
+	}
+	for _, hidden := range []string{"write_file", "edit_file", "apply_patch", "bash"} {
+		if strings.Contains(listing, hidden) {
+			t.Fatalf("expected --plan to hide %q from the tool listing, got %q", hidden, listing)
+		}
+	}
+}
+
+// TestRunExecPermissionModePlanHidesWriteAndShellToolsFromListing covers the
+// --permission-mode plan entry path, which does not set options.plan and must
+// still hide write and shell tools the same way --plan does.
+func TestRunExecPermissionModePlanHidesWriteAndShellToolsFromListing(t *testing.T) {
+	cwd := t.TempDir()
+	var stdout bytes.Buffer
+	var stderr bytes.Buffer
+
+	exitCode := runWithDeps([]string{"exec", "--permission-mode", "plan", "--list-tools"}, &stdout, &stderr, appDeps{
+		getwd: func() (string, error) {
+			return cwd, nil
+		},
+		resolveConfig: func(string, config.Overrides) (config.ResolvedConfig, error) {
+			return execResolvedConfig(), nil
+		},
+	})
+
+	if exitCode != exitSuccess {
+		t.Fatalf("expected exit code %d, got %d: %s", exitSuccess, exitCode, stderr.String())
+	}
+	listing := stdout.String()
+	if !strings.Contains(listing, "Tools visible to model") {
+		t.Fatalf("expected --permission-mode plan --list-tools to list tools, got %q", listing)
+	}
+	if !strings.Contains(listing, "read_file") {
+		t.Fatalf("expected plan mode to still list read_file, got %q", listing)
+	}
+	for _, hidden := range []string{"write_file", "edit_file", "apply_patch", "bash"} {
+		if strings.Contains(listing, hidden) {
+			t.Fatalf("expected --permission-mode plan to hide %q from the tool listing, got %q", hidden, listing)
+		}
+	}
+}
+
+func TestResolveExecPermissionModePlanOverride(t *testing.T) {
+	options := execOptions{autonomy: "low", plan: true}
+	mode, err := resolveExecPermissionMode(options)
+	if err != nil {
+		t.Fatalf("resolveExecPermissionMode: %v", err)
+	}
+	// resolveExecPermissionMode itself only resolves --auto; the --plan override
+	// is applied by the caller (runExec) afterward, same as --use-spec. This
+	// pins the precondition: --plan must not interfere with autonomy resolution.
+	if mode != agent.PermissionModeAuto {
+		t.Fatalf("resolveExecPermissionMode with --plan = %q, want auto (override applied by the caller)", mode)
+	}
+}

internal/cli/exec_tools.go

@@ -73,6 +73,24 @@ func toolListContains(names []string, want string) bool {
 }
 
 func resolveExecPermissionMode(options execOptions) (agent.PermissionMode, error) {
+	if pm := strings.ToLower(strings.TrimSpace(options.permissionMode)); pm != "" {
+		switch pm {
+		case "plan":
+			return agent.PermissionModePlan, nil
+		case "spec-draft", "spec_draft":
+			return agent.PermissionModeSpecDraft, nil
+		case "auto":
+			return agent.PermissionModeAuto, nil
+		case "member", "member-auto", "member_auto":
+			return agent.PermissionModeMemberAuto, nil
+		case "ask":
+			return agent.PermissionModeAsk, nil
+		case "unsafe", "high":
+			return agent.PermissionModeUnsafe, nil
+		default:
+			return "", execUsageError{fmt.Sprintf("Invalid permission mode %q. Expected plan, spec-draft, auto, member, ask, or unsafe.", options.permissionMode)}
+		}
+	}
 	// Validate --auto first, regardless of --skip-permissions-unsafe, so an
 	// invalid autonomy value is always rejected. (Previously the unsafe path
 	// short-circuited before validation, letting "--auto bogus" slip through

internal/cli/exec_writer.go

@@ -142,13 +142,15 @@ func (writer *execEventWriter) checkpoint(event sessions.Event) {
 }
 
 func (writer *execEventWriter) toolResult(result agent.ToolResult) {
+	modelOutput := result.ModelOutput()
+	display := result.HumanDisplay()
 	if writer.format == execOutputJSON {
 		payload := map[string]any{
 			"type":         "tool_result",
 			"tool_call_id": result.ToolCallID,
 			"name":         result.Name,
 			"status":       string(result.Status),
-			"output":       result.Output,
+			"output":       modelOutput,
 		}
 		if len(result.Meta) > 0 {
 			payload["meta"] = result.Meta
@@ -162,14 +164,14 @@ func (writer *execEventWriter) toolResult(result agent.ToolResult) {
 		if len(result.ChangedFiles) > 0 {
 			payload["changed_files"] = result.ChangedFiles
 		}
-		if result.Display.Summary != "" || result.Display.Kind != "" {
-			payload["display"] = map[string]string{"summary": result.Display.Summary, "kind": result.Display.Kind}
+		if display.Summary != "" || display.Kind != "" {
+			payload["display"] = map[string]string{"summary": display.Summary, "kind": display.Kind}
 		}
 		writer.writeJSON(payload)
 		return
 	}
 	if writer.format == execOutputStreamJSON {
-		output, surfaceTruncated := truncateForStreamJSONOutput(result.Output)
+		output, surfaceTruncated := truncateForStreamJSONOutput(modelOutput)
 		truncated := result.Truncated || surfaceTruncated
 		event := streamjson.Event{
 			Type:         streamjson.EventToolResult,
@@ -186,13 +188,13 @@ func (writer *execEventWriter) toolResult(result agent.ToolResult) {
 			redacted := true
 			event.Redacted = &redacted
 		}
-		if result.Display.Summary != "" || result.Display.Kind != "" {
-			event.Display = &streamjson.Display{Summary: result.Display.Summary, Kind: result.Display.Kind}
+		if display.Summary != "" || display.Kind != "" {
+			event.Display = &streamjson.Display{Summary: display.Summary, Kind: display.Kind}
 		}
 		writer.writeStreamJSON(event)
 		return
 	}
-	writer.writeStderr("[result] " + truncateForStatus(result.Output) + "\n")
+	writer.writeStderr("[result] " + truncateForStatus(modelOutput) + "\n")
 }
 
 func (writer *execEventWriter) permission(event agent.PermissionEvent) {

internal/cli/extensions_test.go

@@ -78,7 +78,7 @@ func TestRunPluginsListsJSONAndText(t *testing.T) {
 }
 
 func TestRunHooksListsRedactedJSONAndText(t *testing.T) {
-	secret := "sk-proj-" + strings.Repeat("a", 24)
+	secret := "sk-proj-" + strings.Repeat("a", 23) + "0"
 	result := hooks.LoadResult{
 		Config: hooks.Config{
 			Enabled: true,

internal/cli/hooks_manage_test.go

@@ -87,7 +87,7 @@ func TestRunHooksAddRejectsUnknownEvent(t *testing.T) {
 
 func TestRunHooksAddJSONRedactsSecretArgs(t *testing.T) {
 	cwd := t.TempDir()
-	secret := "sk-proj-" + strings.Repeat("z", 24)
+	secret := "sk-proj-" + strings.Repeat("z", 23) + "0"
 	var stdout, stderr bytes.Buffer
 	code := runHooksAdd([]string{"h1", "--event", "beforeTool", "--command", "sh", "--arg", "-c", "--arg", "echo " + secret, "--json"}, &stdout, &stderr, hooksManageDeps(cwd))
 	if code != exitSuccess {

internal/cli/mcp_commands_test.go

@@ -516,7 +516,7 @@ func TestRunMCPRemovePreservesUnrelatedConfigFields(t *testing.T) {
 func TestRunMCPListRedactsURLCredentialsAndSensitiveQueryParams(t *testing.T) {
 	cwd := t.TempDir()
 	serverURL := "https://user:[email protected]/mcp?access_token=secret-token&api_key=secret-key&safe=value#access_token=fragment-secret"
-	commandSecret := "sk-proj-" + strings.Repeat("a", 24)
+	commandSecret := "sk-proj-" + strings.Repeat("a", 23) + "0"
 	deps := appDeps{
 		getwd: func() (string, error) { return cwd, nil },
 		resolveMCPConfig: func(workspaceRoot string, _ bool) (config.MCPConfig, error) {

internal/cli/oauth_provider.go

@@ -1,13 +1,8 @@
 package cli
 
 import (
-	"context"
-	"errors"
-	"net/http"
-	"time"
-
 	"github.com/Gitlawb/zero/internal/config"
-	"github.com/Gitlawb/zero/internal/oauth"
+	"github.com/Gitlawb/zero/internal/providers"
 	"github.com/Gitlawb/zero/internal/providers/providerio"
 )
 
@@ -28,46 +23,5 @@ import (
 // ProviderProfile.OAuthLoginCandidates so the runtime resolver, the Codex account
 // resolver, and the onboarding presence check never diverge.
 func oauthLoginForProfile(profile config.ProviderProfile) (providerio.TokenResolver, string) {
-	candidates := profile.OAuthLoginCandidates()
-	if len(candidates) == 0 {
-		return nil, ""
-	}
-	store, err := oauth.NewStore(oauth.StoreOptions{})
-	if err != nil {
-		return nil, ""
-	}
-	_, key, ok := oauth.FirstStored(store, candidates)
-	if !ok {
-		// No login under any candidate (or unreadable/invalid keys) → API-key
-		// auth, no resolver.
-		return nil, ""
-	}
-	manager, err := oauth.NewManager(oauth.ManagerOptions{
-		Store:      store,
-		HTTPClient: &http.Client{Timeout: 30 * time.Second},
-		// Refreshing a token the user logged into (possibly a preset provider like
-		// xAI) re-resolves that provider's OAuth config, which needs the preset.
-		AllowPresets: true,
-	})
-	if err != nil {
-		return nil, ""
-	}
-	resolver := func(ctx context.Context, forceRefresh bool) (string, string, bool, error) {
-		var token string
-		var rerr error
-		if forceRefresh {
-			token, rerr = manager.Handle401(ctx, key)
-		} else {
-			token, rerr = manager.GetFresh(ctx, key)
-		}
-		if errors.Is(rerr, oauth.ErrNoToken) {
-			// The login was removed since construction → fall back to the API key.
-			return "", "", false, nil
-		}
-		if rerr != nil {
-			return "", "", false, rerr
-		}
-		return "Authorization", "Bearer " + token, true, nil
-	}
-	return resolver, key
+	return providers.OAuthLoginForProfile(profile)
 }

internal/cli/provider_models.go

@@ -73,6 +73,18 @@ func runProvidersModels(args []string, stdout io.Writer, stderr io.Writer, deps
 			if description := strings.TrimSpace(model.Description); description != "" {
 				entry["description"] = description
 			}
+			if len(model.ReasoningEfforts) > 0 {
+				entry["reasoning_efforts"] = append([]string{}, model.ReasoningEfforts...)
+			}
+			if effort := strings.TrimSpace(model.DefaultReasoningEffort); effort != "" {
+				entry["default_reasoning_effort"] = effort
+			}
+			if len(model.ServiceTiers) > 0 {
+				entry["service_tiers"] = append([]string{}, model.ServiceTiers...)
+			}
+			if tier := strings.TrimSpace(model.DefaultServiceTier); tier != "" {
+				entry["default_service_tier"] = tier
+			}
 			items = append(items, entry)
 		}
 		payload := map[string]any{

internal/cli/sandbox.go

@@ -18,6 +18,8 @@ type sandboxCommandOptions struct {
 	path      string
 }
 
+const permissionProfileScopeNote = "permissionProfile is derived from this process's environment and working directory; a command run with its own environment can add further credential deny-read entries."
+
 func runSandbox(args []string, stdout io.Writer, stderr io.Writer, deps appDeps) int {
 	if len(args) == 0 {
 		return writeExecUsageError(stderr, "sandbox subcommand required. Use `zero sandbox policy` or `zero sandbox grants list`.")
@@ -91,16 +93,25 @@ func runSandboxPolicy(args []string, stdout io.Writer, stderr io.Writer, deps ap
 		return runSandboxPolicyEffective(options, workspaceRoot, policy, backend, plan, store.FilePath(), writeRoots, writeRootsErr, stdout)
 	}
 	if options.json {
+		// The profile here is built from Zero's own environment and working
+		// directory, because that is all this command has: no command has been
+		// chosen yet. A nested command carries its own cwd and env, and the
+		// credential baseline resolves relative token overrides against those, so
+		// an executed command can carry MORE denyReadIfExists entries than this
+		// view lists. Say so in the payload rather than leaving a consumer to
+		// assume it is the whole picture (see PermissionProfileFromPolicy).
 		payload := struct {
-			Policy     zeroSandbox.Policy      `json:"policy"`
-			Backend    zeroSandbox.Backend     `json:"backend"`
-			Plan       zeroSandbox.BackendPlan `json:"plan"`
-			GrantsPath string                  `json:"grantsPath"`
+			Policy                zeroSandbox.Policy      `json:"policy"`
+			Backend               zeroSandbox.Backend     `json:"backend"`
+			Plan                  zeroSandbox.BackendPlan `json:"plan"`
+			GrantsPath            string                  `json:"grantsPath"`
+			PermissionProfileNote string                  `json:"permissionProfileNote"`
 		}{
-			Policy:     policy,
-			Backend:    backend,
-			Plan:       plan,
-			GrantsPath: store.FilePath(),
+			Policy:                policy,
+			Backend:               backend,
+			Plan:                  plan,
+			GrantsPath:            store.FilePath(),
+			PermissionProfileNote: permissionProfileScopeNote,
 		}
 		if err := writePrettyJSON(stdout, payload); err != nil {
 			return exitCrash
@@ -247,20 +258,22 @@ func runSandboxPolicyEffective(options sandboxCommandOptions, workspaceRoot stri
 			// JSON consumers see the same signal as the text write_roots_error
 			// line: a stale sandbox.additionalWriteRoots entry means the real
 			// entrypoints would refuse to launch, not run workspace-only.
-			WriteRootsError string                  `json:"writeRootsError,omitempty"`
-			Policy          zeroSandbox.Policy      `json:"policy"`
-			Backend         zeroSandbox.Backend     `json:"backend"`
-			Plan            zeroSandbox.BackendPlan `json:"plan"`
-			Guards          sandboxGuards           `json:"guards"`
-			GrantsPath      string                  `json:"grantsPath"`
+			WriteRootsError       string                  `json:"writeRootsError,omitempty"`
+			Policy                zeroSandbox.Policy      `json:"policy"`
+			Backend               zeroSandbox.Backend     `json:"backend"`
+			Plan                  zeroSandbox.BackendPlan `json:"plan"`
+			Guards                sandboxGuards           `json:"guards"`
+			GrantsPath            string                  `json:"grantsPath"`
+			PermissionProfileNote string                  `json:"permissionProfileNote"`
 		}{
-			WorkspaceRoot: workspaceRoot,
-			WriteRoots:    writeRoots,
-			Policy:        policy,
-			Backend:       backend,
-			Plan:          plan,
-			Guards:        guards,
-			GrantsPath:    grantsPath,
+			WorkspaceRoot:         workspaceRoot,
+			WriteRoots:            writeRoots,
+			Policy:                policy,
+			Backend:               backend,
+			Plan:                  plan,
+			Guards:                guards,
+			GrantsPath:            grantsPath,
+			PermissionProfileNote: permissionProfileScopeNote,
 		}
 		if writeRootsErr != nil {
 			payload.WriteRootsError = writeRootsErr.Error()
@@ -284,6 +297,7 @@ func formatEffectiveSandboxPolicy(workspaceRoot string, policy zeroSandbox.Polic
 		"network: " + string(policy.Network),
 		"enforce_workspace: " + fmt.Sprintf("%t", policy.EnforceWorkspace),
 		"write_roots: " + strings.Join(writeRoots, ", "),
+		"permission_profile_note: " + permissionProfileScopeNote,
 	}
 	if writeRootsErr != nil {
 		// Fail soft, visibly: a stale sandbox.additionalWriteRoots entry must

internal/cli/sandbox_test.go

@@ -9,6 +9,8 @@ import (
 	"os"
 	"path/filepath"
 	"reflect"
+	"runtime"
+	"sort"
 	"strings"
 	"testing"
 
@@ -483,14 +485,23 @@ func TestTUISandboxSetupCommandGatedToWindowsNativeBackend(t *testing.T) {
 }
 
 func TestRunSandboxPolicyJSONGoldenIncludesManagerBaselineFields(t *testing.T) {
-	// Point HOME at an empty directory so the default credential-store
-	// deny-read entries (which depend on what exists in the real home, e.g.
-	// ~/.aws on the macOS CI image) cannot leak host paths into the golden
-	// comparison.
+	// Point all user-config roots at an empty directory so the platform-specific
+	// credential deny baseline can be asserted without leaking host paths into
+	// the platform-neutral golden comparison.
 	emptyHome := t.TempDir()
 	t.Setenv("HOME", emptyHome)
 	t.Setenv("USERPROFILE", emptyHome)
+	t.Setenv("XDG_CONFIG_HOME", filepath.Join(emptyHome, ".config"))
+	t.Setenv("CLOUDSDK_CONFIG", "")
 	t.Setenv("GOOGLE_APPLICATION_CREDENTIALS", "")
+	t.Setenv("NPM_CONFIG_USERCONFIG", "")
+	t.Setenv("npm_config_userconfig", "")
+	t.Setenv("GH_CONFIG_DIR", "")
+	t.Setenv("NETRC", "")
+	t.Setenv("DOCKER_CONFIG", "")
+	t.Setenv("KUBECONFIG", "")
+	t.Setenv("ZERO_OAUTH_TOKENS_PATH", "")
+	t.Setenv("ZERO_MCP_OAUTH_TOKENS_PATH", "")
 	store := newSandboxTestStore(t)
 	workspace := t.TempDir()
 	deps := appDeps{
@@ -518,7 +529,7 @@ func TestRunSandboxPolicyJSONGoldenIncludesManagerBaselineFields(t *testing.T) {
 	got := stdout.String()
 	got = replacePathToken(got, workspace, "$WORKSPACE")
 	got = replacePathToken(got, store.FilePath(), "$GRANTS")
-	gotBytes := normalizeSandboxPolicyGoldenTempRoots(t, []byte(got), workspace)
+	gotBytes := normalizeSandboxPolicyGoldenTempRoots(t, []byte(got), workspace, emptyHome)
 	wantBytes, err := os.ReadFile(filepath.Join("testdata", "sandbox_policy_windows_unavailable.golden.json"))
 	if err != nil {
 		t.Fatalf("read golden: %v", err)
@@ -528,7 +539,7 @@ func TestRunSandboxPolicyJSONGoldenIncludesManagerBaselineFields(t *testing.T) {
 	}
 }
 
-func normalizeSandboxPolicyGoldenTempRoots(t *testing.T, gotBytes []byte, workspace string) []byte {
+func normalizeSandboxPolicyGoldenTempRoots(t *testing.T, gotBytes []byte, workspace string, emptyHome string) []byte {
 	t.Helper()
 	scope, err := sandbox.NewScope(workspace, nil)
 	if err != nil {
@@ -549,6 +560,56 @@ func normalizeSandboxPolicyGoldenTempRoots(t *testing.T, gotBytes []byte, worksp
 	plan, _ := value.(map[string]any)["plan"].(map[string]any)
 	profile, _ := plan["permissionProfile"].(map[string]any)
 	fileSystem, _ := profile["fileSystem"].(map[string]any)
+	wantDenyRead := []string(nil)
+	credentialHome := emptyHome
+	if runtime.GOOS != "windows" {
+		if resolved, err := filepath.EvalSymlinks(emptyHome); err == nil {
+			credentialHome = resolved
+		}
+		wantDenyRead = []string{
+			filepath.Join(credentialHome, ".aws"),
+			filepath.Join(credentialHome, ".azure"),
+			// git's cleartext credential stores, in both the home and XDG
+			// layouts (#816). Listed here so the exported policy JSON is what
+			// catches a regression: this baseline is the contract a user reads
+			// with `zero sandbox policy --json`.
+			filepath.Join(credentialHome, ".git-credentials"),
+			filepath.Join(credentialHome, ".config", "git", "credentials"),
+			filepath.Join(credentialHome, ".npmrc"),
+			filepath.Join(credentialHome, ".netrc"),
+			filepath.Join(credentialHome, ".kube", "config"),
+			filepath.Join(credentialHome, ".docker", "config.json"),
+			filepath.Join(credentialHome, ".config", "gh", "hosts.yml"),
+			filepath.Join(credentialHome, ".config", "gcloud"),
+			filepath.Join(credentialHome, ".config", "zero"),
+		}
+	}
+	gotDenyRead := jsonStringSlice(fileSystem["denyReadIfExists"])
+	sort.Strings(gotDenyRead)
+	sort.Strings(wantDenyRead)
+	if !reflect.DeepEqual(gotDenyRead, wantDenyRead) {
+		t.Fatalf("manager credential deny baseline = %#v, want %#v", gotDenyRead, wantDenyRead)
+	}
+	wantCarveouts := []string(nil)
+	wantEnsureDirs := []string(nil)
+	if runtime.GOOS != "windows" {
+		zeroDir := filepath.Join(credentialHome, ".config", "zero")
+		wantCarveouts = []string{
+			filepath.Join(zeroDir, "plugins"),
+			filepath.Join(zeroDir, "specialists"),
+			filepath.Join(zeroDir, "commands"),
+		}
+		wantEnsureDirs = []string{zeroDir}
+	}
+	if gotCarveouts := jsonStringSlice(fileSystem["denyReadCarveouts"]); !reflect.DeepEqual(gotCarveouts, wantCarveouts) {
+		t.Fatalf("manager credential carveouts = %#v, want %#v", gotCarveouts, wantCarveouts)
+	}
+	if gotEnsureDirs := jsonStringSlice(fileSystem["ensureDenyReadDirs"]); !reflect.DeepEqual(gotEnsureDirs, wantEnsureDirs) {
+		t.Fatalf("manager credential ensure dirs = %#v, want %#v", gotEnsureDirs, wantEnsureDirs)
+	}
+	delete(fileSystem, "denyReadIfExists")
+	delete(fileSystem, "denyReadCarveouts")
+	delete(fileSystem, "ensureDenyReadDirs")
 	fileSystem["readRoots"] = filterJSONStringRoots(fileSystem["readRoots"], tempRoots)
 	fileSystem["writeRoots"] = filterJSONWriteRoots(fileSystem["writeRoots"], tempRoots)
 	normalized, err := json.MarshalIndent(value, "", "  ")
@@ -558,6 +619,22 @@ func normalizeSandboxPolicyGoldenTempRoots(t *testing.T, gotBytes []byte, worksp
 	return append(normalized, '\n')
 }
 
+func jsonStringSlice(value any) []string {
+	values, ok := value.([]any)
+	if !ok {
+		return nil
+	}
+	out := make([]string, 0, len(values))
+	for _, value := range values {
+		text, ok := value.(string)
+		if !ok {
+			return nil
+		}
+		out = append(out, text)
+	}
+	return out
+}
+
 func filterJSONStringRoots(value any, excluded map[string]struct{}) any {
 	roots, ok := value.([]any)
 	if !ok {
@@ -720,7 +797,8 @@ func TestRunSandboxPolicyEffectiveTextAndJSON(t *testing.T) {
 				Network            bool `json:"network"`
 				Workspace          bool `json:"workspace"`
 			} `json:"guards"`
-			GrantsPath string `json:"grantsPath"`
+			GrantsPath            string `json:"grantsPath"`
+			PermissionProfileNote string `json:"permissionProfileNote"`
 		}
 		if err := json.Unmarshal(stdout.Bytes(), &payload); err != nil {
 			t.Fatalf("decode effective JSON: %v\n%s", err, stdout.String())
@@ -737,6 +815,9 @@ func TestRunSandboxPolicyEffectiveTextAndJSON(t *testing.T) {
 		if payload.Plan.SupportLevel != string(sandbox.BackendSupportUnavailable) || payload.GrantsPath == "" {
 			t.Fatalf("unexpected effective plan/grants: %#v %q", payload.Plan, payload.GrantsPath)
 		}
+		if payload.PermissionProfileNote != permissionProfileScopeNote {
+			t.Fatalf("permissionProfileNote = %q, want %q", payload.PermissionProfileNote, permissionProfileScopeNote)
+		}
 	})
 }
 
@@ -748,6 +829,9 @@ func TestEffectiveSandboxPolicyListsWriteRoots(t *testing.T) {
 	if !strings.Contains(output, "enforce_workspace: true\nwrite_roots: /ws, /extra") {
 		t.Fatalf("write_roots should directly follow enforce_workspace, got:\n%s", output)
 	}
+	if !strings.Contains(output, "permission_profile_note: "+permissionProfileScopeNote) {
+		t.Fatalf("effective text missing permission profile scope warning:\n%s", output)
+	}
 	if strings.Contains(output, "write_roots_error") {
 		t.Fatalf("unexpected write_roots_error line without an error:\n%s", output)
 	}

internal/cli/specialist.go

@@ -286,7 +286,11 @@ func runSpecialistCreate(paths specialist.Paths, name string, options specialist
 	if err != nil {
 		return writeExecUsageError(stderr, err.Error())
 	}
-	if options.json {
+	return writeSpecialistCreateResult(manifest, options.json, stdout, stderr)
+}
+
+func writeSpecialistCreateResult(manifest specialist.Manifest, jsonOutput bool, stdout io.Writer, stderr io.Writer) int {
+	if jsonOutput {
 		if err := writePrettyJSON(stdout, manifest); err != nil {
 			return exitCrash
 		}
@@ -295,6 +299,11 @@ func runSpecialistCreate(paths specialist.Paths, name string, options specialist
 	if _, err := fmt.Fprintf(stdout, "Created specialist %s at %s\n", manifest.Metadata.Name, manifest.FilePath); err != nil {
 		return exitCrash
 	}
+	for _, warning := range manifest.Warnings {
+		if _, err := fmt.Fprintf(stderr, "warning: %s\n", warning); err != nil {
+			return exitCrash
+		}
+	}
 	return exitSuccess
 }
 

internal/cli/specialist_test.go

@@ -10,6 +10,7 @@ import (
 	"testing"
 
 	"github.com/Gitlawb/zero/internal/config"
+	"github.com/Gitlawb/zero/internal/specialist"
 )
 
 func TestRunSpecialistListShowAndPath(t *testing.T) {
@@ -187,6 +188,42 @@ func TestRunSpecialistCreateDeleteAndEdit(t *testing.T) {
 	}
 }
 
+func TestWriteSpecialistCreateResultSurfacesWarningsOnlyForHumanOutput(t *testing.T) {
+	manifest := specialist.Manifest{
+		Metadata: specialist.Metadata{Name: "triage"},
+		FilePath: "/specialists/triage.md",
+		Warnings: []string{"replacement backup /specialists/.triage.bak retained: access denied"},
+	}
+
+	var stdout bytes.Buffer
+	var stderr bytes.Buffer
+	if code := writeSpecialistCreateResult(manifest, false, &stdout, &stderr); code != exitSuccess {
+		t.Fatalf("human output exit code = %d", code)
+	}
+	if got, want := stdout.String(), "Created specialist triage at /specialists/triage.md\n"; got != want {
+		t.Fatalf("stdout = %q, want %q", got, want)
+	}
+	if got, want := stderr.String(), "warning: replacement backup /specialists/.triage.bak retained: access denied\n"; got != want {
+		t.Fatalf("stderr = %q, want %q", got, want)
+	}
+
+	stdout.Reset()
+	stderr.Reset()
+	if code := writeSpecialistCreateResult(manifest, true, &stdout, &stderr); code != exitSuccess {
+		t.Fatalf("JSON output exit code = %d", code)
+	}
+	var payload specialist.Manifest
+	if err := json.Unmarshal(stdout.Bytes(), &payload); err != nil {
+		t.Fatalf("decode JSON: %v\n%s", err, stdout.String())
+	}
+	if len(payload.Warnings) != 1 || payload.Warnings[0] != manifest.Warnings[0] {
+		t.Fatalf("JSON warnings = %#v", payload.Warnings)
+	}
+	if stderr.Len() != 0 {
+		t.Fatalf("JSON warning duplicated to stderr: %q", stderr.String())
+	}
+}
+
 func TestRunSpecialistEditRejectsSymlink(t *testing.T) {
 	if runtime.GOOS == "windows" {
 		t.Skip("symlink creation needs extra privileges on Windows")

internal/cli/testdata/sandbox_policy_windows_unavailable.golden.json

@@ -100,5 +100,6 @@
       "shell commands are not wrapped by a native platform sandbox"
     ]
   },
-  "grantsPath": "$GRANTS"
+  "grantsPath": "$GRANTS",
+  "permissionProfileNote": "permissionProfile is derived from this process's environment and working directory; a command run with its own environment can add further credential deny-read entries."
 }

internal/cli/trust.go

@@ -44,7 +44,8 @@ func runTrust(args []string, stdout io.Writer, stderr io.Writer, deps appDeps) i
 func trustCurrentDir(stdout io.Writer, stderr io.Writer, deps appDeps) int {
 	cwd, err := deps.getwd()
 	if err != nil {
-		return writeAppError(stderr, redaction.ErrorMessage(fmt.Errorf("resolve workspace: %w", err), redaction.Options{}), exitCrash)
+		// Flatten with %s: ErrorMessage stringifies inline, so %w would be a no-op.
+		return writeAppError(stderr, redaction.ErrorMessage(fmt.Errorf("resolve workspace: %s", err), redaction.Options{}), exitCrash)
 	}
 	if err := workspacetrust.Trust(cwd); err != nil {
 		return writeAppError(stderr, redaction.ErrorMessage(err, redaction.Options{}), exitCrash)
@@ -86,7 +87,8 @@ func trustRemove(args []string, stdout io.Writer, stderr io.Writer, deps appDeps
 	case 0:
 		cwd, err := deps.getwd()
 		if err != nil {
-			return writeAppError(stderr, redaction.ErrorMessage(fmt.Errorf("resolve workspace: %w", err), redaction.Options{}), exitCrash)
+			// Flatten with %s: ErrorMessage stringifies inline, so %w would be a no-op.
+			return writeAppError(stderr, redaction.ErrorMessage(fmt.Errorf("resolve workspace: %s", err), redaction.Options{}), exitCrash)
 		}
 		target = cwd
 	case 1:

internal/cli/update.go

@@ -202,8 +202,8 @@ Flags:
       --check                 Check the latest GitHub release without installing
       --apply                 Download, verify, and install the latest release
       --json                  Print the update result as JSON
-      --repo <owner/repo>     Repository to check when no endpoint is provided
-      --endpoint <url|repo>   Release API URL or owner/repo slug to check
+      --repo <owner/repo>     Repository to use when no endpoint is provided (--check and --apply; ignored for the install source by an npm-managed apply)
+      --endpoint <url|repo>   Release API URL or owner/repo slug to use (--check and --apply; ignored for the install source by an npm-managed apply)
       --timeout <duration>    Release check timeout (default 5s)
       --target <platform>     Release target to verify with --check (for example windows-x64); not valid with --apply
   -h, --help                  Show this help

internal/cli/workflows.go

@@ -2,8 +2,12 @@ package cli
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io"
+	"path"
+	"path/filepath"
+	"regexp"
 	"strconv"
 	"strings"
 	"time"
@@ -63,6 +67,9 @@ func runWorktrees(args []string, stdout io.Writer, stderr io.Writer, deps appDep
 		}
 		return exitSuccess
 	}
+	if command == "release" {
+		return runWorktreesRelease(args, stdout, stderr, deps)
+	}
 	if command != "prepare" {
 		return writeExecUsageError(stderr, fmt.Sprintf("unknown worktrees command %q", command))
 	}
@@ -102,6 +109,85 @@ func runWorktrees(args []string, stdout io.Writer, stderr io.Writer, deps appDep
 	return exitSuccess
 }
 
+// runWorktreesRelease unlocks a worktree `zero worktrees prepare` created, so
+// Zero's automatic Clean pass can reclaim it once it goes stale. Prepare locks
+// every worktree it creates and nothing else in that command's own lifetime
+// unlocks it (its process exits right after printing the path, long before
+// whatever external caller actually finishes using the worktree), so that
+// caller is responsible for running this once it is done.
+func runWorktreesRelease(args []string, stdout io.Writer, stderr io.Writer, deps appDeps) int {
+	var path string
+	var cwdFlag string
+	for index := 0; index < len(args); index++ {
+		arg := args[index]
+		switch {
+		case arg == "-h" || arg == "--help" || arg == "help":
+			if err := writeWorktreesHelp(stdout); err != nil {
+				return exitCrash
+			}
+			return exitSuccess
+		case arg == "-C" || arg == "--cwd":
+			value, next, err := nextFlagValue(args, index, arg)
+			if err != nil {
+				return writeExecUsageError(stderr, err.Error())
+			}
+			cwdFlag = value
+			index = next
+		case strings.HasPrefix(arg, "--cwd="):
+			cwdFlag = strings.TrimSpace(strings.TrimPrefix(arg, "--cwd="))
+		case strings.HasPrefix(arg, "-"):
+			return writeExecUsageError(stderr, fmt.Sprintf("unknown worktrees release flag %q", arg))
+		default:
+			if path != "" {
+				return writeExecUsageError(stderr, "worktree path was provided more than once")
+			}
+			path = arg
+		}
+	}
+	path = strings.TrimSpace(path)
+	if path == "" {
+		return writeExecUsageError(stderr, "worktrees release requires a worktree path")
+	}
+	// git worktree unlock matches against the path git recorded when the
+	// worktree was created, so a relative argument here (resolved against
+	// whatever directory the caller happens to be running in, not
+	// necessarily the worktree's own) can fail to match. Resolve to absolute
+	// up front so the unlock target is unambiguous regardless of cwd.
+	absPath, err := filepath.Abs(path)
+	if err != nil {
+		return writeExecUsageError(stderr, redactCLIString(err.Error()))
+	}
+	// Release falls back to Options.Cwd as git's working directory when the
+	// worktree directory itself was deleted by hand instead of released; with
+	// no Cwd wired in, that recovery path runs `git worktree unlock` from
+	// wherever the caller happens to be, which outside the source repository
+	// leaves the orphaned lock behind forever (Clean skips locked entries).
+	// -C/--cwd names the source repository explicitly for exactly that case,
+	// since the deleted worktree path itself carries no way back to the repo;
+	// without the flag, resolve the launch directory best-effort (the
+	// ordinary existing-path case does not need it, so a resolution failure
+	// is not an error here).
+	releaseOptions := worktrees.Options{}
+	if cwdFlag != "" {
+		workspaceRoot, err := resolveWorkspaceRoot(cwdFlag, deps)
+		if err != nil {
+			return writeExecUsageError(stderr, redactCLIString(err.Error()))
+		}
+		releaseOptions.Cwd = workspaceRoot
+	} else if workspaceRoot, rootErr := resolveWorkspaceRoot("", deps); rootErr == nil {
+		releaseOptions.Cwd = workspaceRoot
+	}
+	if err := deps.releaseWorktree(context.Background(), releaseOptions, absPath); err != nil {
+		return writeExecUsageError(stderr, redactCLIString(err.Error()))
+	}
+	// Print the absolute path that was released so relative arguments still
+	// show an unambiguous target in the confirmation line.
+	if _, err := fmt.Fprintf(stdout, "released %s\n", redactCLIString(absPath)); err != nil {
+		return exitCrash
+	}
+	return exitSuccess
+}
+
 func runVerifyCommand(args []string, stdout io.Writer, stderr io.Writer, deps appDeps) int {
 	options, help, err := parseVerifyCommandArgs(args)
 	if err != nil {
@@ -519,18 +605,20 @@ func parseChangesArgs(args []string, command string) (changesCommandOptions, boo
 			return options, false, execUsageError{fmt.Sprintf("unexpected changes argument %q", arg)}
 		}
 	}
-	if command != "commit" && options.message != "" {
+	if command != "commit" && options.hasMessage {
 		return options, false, execUsageError{"--message is only valid with `zero changes commit`"}
 	}
-	if command != "commit" && (options.hasMessage || options.dryRun || options.auto) {
-		return options, false, execUsageError{"--message, --dry-run, and --auto are only valid with `zero changes commit`"}
-	}
 	if command == "commit" && options.hasMessage && options.auto {
 		return options, false, execUsageError{"cannot specify both --message and --auto"}
 	}
 	if command != "commit" && command != "push" && options.dryRun {
 		return options, false, execUsageError{"--dry-run is only valid with commit or push"}
 	}
+	// --auto on push/pr is the explicit opt-in for LLM branch naming (see
+	// ensureFeatureBranch); on commit it opts into the LLM commit message.
+	if command != "commit" && command != "push" && command != "pr" && options.auto {
+		return options, false, execUsageError{"--auto is only valid with commit, push, or pr"}
+	}
 	if command != "inspect" && options.baseRef != "" {
 		return options, false, execUsageError{"--base is only valid with `zero changes inspect`"}
 	}
@@ -786,15 +874,28 @@ func formatCommitResult(result zerogit.CommitResult) string {
 func writeWorktreesHelp(w io.Writer) error {
 	_, err := fmt.Fprint(w, `Usage:
   zero worktrees prepare [flags] [name]
+  zero worktrees release [flags] <path>
 
 Prepares an isolated git worktree for a Zero task.
 
-Flags:
+prepare locks the worktree it creates so Zero's automatic cleanup never
+removes it out from under you. release unlocks a worktree prepare created,
+once you are done with it, so cleanup can reclaim it later if it goes stale.
+If the worktree directory was deleted by hand, run release with -C pointing
+at the source repository so the orphaned lock can still be cleared.
+
+prepare flags:
       --name <name>       Worktree name; defaults to a timestamped task name
       --dir <path>        Base directory for Zero worktrees
   -C, --cwd <path>        Source repository directory
       --json              Print JSON output
   -h, --help              Show this help
+
+release flags:
+  -C, --cwd <path>        Source repository directory; needed when the
+                           worktree directory was already deleted and you
+                           are not running inside the source repository
+  -h, --help              Show this help
 `)
 	return err
 }
@@ -838,8 +939,7 @@ Flags:
       --fill              Automatically populate PR title and body from commits
       --draft             Create PR as a draft
       --yes               Confirm pushing to a default/protected branch
-  -a, --auto              Auto-generate commit message using LLM (use --dry-run to preview)
-      --dry-run           Preview commit metadata without mutating git state
+  -a, --auto              Use the LLM: commit generates the message, push/pr name the auto-created branch (sends the diff to the provider)
       --json              Print JSON output
   -h, --help              Show this help
 `)
@@ -862,11 +962,31 @@ func runChangesPush(args []string, stdout io.Writer, stderr io.Writer, deps appD
 		return writeExecUsageError(stderr, err.Error())
 	}
 
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Minute)
+	defer cancel()
+
+	branch, remote, created, err := ensureFeatureBranch(ctx, stdout, workspaceRoot, options.remote, featureBranchOptions{
+		JSONMode:           options.json,
+		AllowDefaultBranch: options.yes,
+		DryRun:             options.dryRun,
+		AutoNaming:         options.auto,
+		MaxDiffBytes:       options.maxDiffBytes,
+	}, deps)
+	if err != nil {
+		return writeExecUsageError(stderr, err.Error())
+	}
+
+	// context.Background() is deliberate: the 2-minute ctx above is the
+	// feature-branch preflight (inspection, remote probes, branch creation).
+	// The push itself must not be cancelled mid-transfer just because the
+	// preflight budget elapsed; a large push can legitimately take longer.
 	result, err := deps.pushChanges(context.Background(), zerogit.PushOptions{
 		Cwd:                    workspaceRoot,
-		Remote:                 options.remote,
+		Remote:                 firstNonEmptyString(options.remote, remote),
+		Branch:                 branch,
 		Force:                  options.force,
 		DryRun:                 options.dryRun,
+		RequireNewRemoteBranch: created,
 		AllowPushDefaultBranch: options.yes,
 	})
 	if err != nil {
@@ -914,15 +1034,62 @@ func runChangesPR(args []string, stdout io.Writer, stderr io.Writer, deps appDep
 		return writeExecUsageError(stderr, err.Error())
 	}
 
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Minute)
+	defer cancel()
+
+	branch, remote, created, err := ensureFeatureBranch(ctx, stdout, workspaceRoot, options.remote, featureBranchOptions{
+		JSONMode:           options.json,
+		AllowDefaultBranch: options.yes,
+		DryRun:             false,
+		AutoNaming:         options.auto,
+		MaxDiffBytes:       options.maxDiffBytes,
+	}, deps)
+	if err != nil {
+		return writeExecUsageError(stderr, err.Error())
+	}
+
+	// Resolve the target remote for the unborn-remote check. Explicit --remote wins,
+	// followed by the remote resolved by ensureFeatureBranch. When --yes is set,
+	// fall back to the branch upstream or "origin".
+	targetRemote := strings.TrimSpace(options.remote)
+	if targetRemote == "" {
+		targetRemote = remote
+	}
+	if targetRemote == "" {
+		currentBranch := ""
+		if deps.currentGitBranch != nil {
+			currentBranch = deps.currentGitBranch(context.Background(), workspaceRoot)
+		}
+		if deps.branchUpstreamRemote != nil && currentBranch != "" {
+			targetRemote = deps.branchUpstreamRemote(context.Background(), workspaceRoot, currentBranch)
+		}
+		if targetRemote == "" {
+			targetRemote = "origin"
+		}
+	}
+
+	// Probe errors are intentionally ignored so the flow can continue; if the
+	// probe fails, the subsequent push or PR operation provides fail-closed behavior.
+	if deps.isUnbornRemote != nil {
+		if unborn, unbornErr := deps.isUnbornRemote(context.Background(), workspaceRoot, targetRemote); unbornErr == nil && unborn {
+			return writeExecUsageError(stderr, fmt.Sprintf("cannot create pull request on unborn remote %s: push the initial default branch first", targetRemote))
+		}
+	}
+
 	if !options.json {
 		if _, err := fmt.Fprintln(stdout, "Pushing current branch to set upstream..."); err != nil {
 			return exitCrash
 		}
 	}
+	// context.Background() is deliberate here too: runChangesPR reuses the
+	// 2-minute ctx for preflight (branch creation and remote probes), but the
+	// push must not be cancelled mid-transfer if that budget elapsed.
 	pushResult, err := deps.pushChanges(context.Background(), zerogit.PushOptions{
 		Cwd:                    workspaceRoot,
-		Remote:                 options.remote,
+		Remote:                 firstNonEmptyString(options.remote, remote),
+		Branch:                 branch,
 		Force:                  options.force,
+		RequireNewRemoteBranch: created,
 		AllowPushDefaultBranch: options.yes,
 	})
 	if err != nil {
@@ -1004,3 +1171,462 @@ func generateAutoCommitMessage(ctx context.Context, provider zeroruntime.Provide
 	}
 	return msg, nil
 }
+
+type featureBranchOptions struct {
+	JSONMode           bool
+	AllowDefaultBranch bool
+	DryRun             bool
+	AutoNaming         bool
+	MaxDiffBytes       int
+}
+
+// branchPushPlan holds the resolved parameters for a push or PR workflow
+// before any branches are created or refs mutated. Separating plan resolution
+// from mutation allows tests to assert the resolution matrix directly without
+// touching a git repository.
+type branchPushPlan struct {
+	ShouldBranch           bool
+	CurrentBranch          string
+	PushRemote             string
+	RequireNewRemoteBranch bool
+	TrackingRemote         string
+	TrackingBranch         string
+	RestoreTip             string
+	PublishabilityBase     string
+	Summary                zerogit.ChangeSummary
+	Slug                   string
+}
+
+// resolveBranchPushPlan resolves the branch, remotes, restore tip, and naming
+// slug for changes push / pr workflows. It performs all checks (clean working
+// tree, unborn remote detection, ahead count, restore tip resolution) but
+// executes no mutation (no branch creation, ref resets, or deletions).
+func resolveBranchPushPlan(ctx context.Context, stdout io.Writer, workspaceRoot string, requestedRemote string, opts featureBranchOptions, deps appDeps) (branchPushPlan, error) {
+	if opts.AllowDefaultBranch || opts.DryRun {
+		return branchPushPlan{
+			ShouldBranch:           false,
+			PushRemote:             strings.TrimSpace(requestedRemote),
+			RequireNewRemoteBranch: false,
+		}, nil
+	}
+
+	if deps.isDefaultBranch == nil {
+		return branchPushPlan{}, fmt.Errorf("isDefaultBranch dependency missing")
+	}
+	isDefault, currentBranch, remote, err := deps.isDefaultBranch(ctx, zerogit.DefaultBranchOptions{Cwd: workspaceRoot, Remote: requestedRemote})
+	if err != nil {
+		return branchPushPlan{}, err
+	}
+	if !isDefault {
+		// Whether this push needs the nonexistence lease is decided by one
+		// live check against the destination remote, not by inference from
+		// local git state (upstream config, a generated-branch marker):
+		// every local signal that stood in for that check turned out to be
+		// wrong in some ordering (inherited config from checkout -b, a
+		// config write that failed after a successful push, a push aimed at
+		// a different remote than the one local config describes). A branch
+		// missing on the remote gets the nonexistence lease, protecting a
+		// concurrent creator of the same name; a branch already there gets a
+		// plain push, and git's own fast-forward check is the safety net —
+		// if the remote history isn't ours, the push fails with a clear
+		// non-fast-forward error instead of an attempted silent recovery.
+		if deps.remoteHasBranch == nil {
+			return branchPushPlan{
+				ShouldBranch:           false,
+				CurrentBranch:          currentBranch,
+				PushRemote:             remote,
+				RequireNewRemoteBranch: true,
+			}, nil
+		}
+		targetRemote := firstNonEmptyString(requestedRemote, remote)
+		exists, existsErr := deps.remoteHasBranch(ctx, workspaceRoot, targetRemote, currentBranch)
+		if existsErr != nil {
+			return branchPushPlan{}, fmt.Errorf("cannot check whether %s already exists on remote %s: %w", currentBranch, targetRemote, existsErr)
+		}
+		return branchPushPlan{
+			ShouldBranch:           false,
+			CurrentBranch:          currentBranch,
+			PushRemote:             remote,
+			RequireNewRemoteBranch: !exists,
+		}, nil
+	}
+
+	// CreateBranch and Push publish commits only. A dirty working tree would
+	// leave uncommitted edits behind under a branch/PR that does not include
+	// them, so refuse until the tree is clean (commit or stash first).
+	workingTree, err := deps.inspectChanges(ctx, zerogit.InspectOptions{Cwd: workspaceRoot})
+	if err != nil {
+		return branchPushPlan{}, fmt.Errorf("failed to inspect working tree: %w", err)
+	}
+	if !workingTree.Clean {
+		return branchPushPlan{}, fmt.Errorf("working tree has uncommitted changes; commit or stash them before pushing from the default branch")
+	}
+
+	// Capture the source default branch's own upstream before refreshing or
+	// leaving it. --remote selects the push destination; restore must not
+	// rewrite local main to upstream/main when main still tracks origin/main
+	// (fork setups), and refreshing must update the exact tracking ref that
+	// will supply both the ahead count and the restore target.
+	trackingRemote := remote
+	trackingBranch := currentBranch
+	if deps.branchUpstreamRemoteAndMerge != nil {
+		if r, m := deps.branchUpstreamRemoteAndMerge(ctx, workspaceRoot, currentBranch); r != "" && m != "" {
+			trackingRemote = r
+			trackingBranch = m
+		}
+	}
+
+	// Refresh the local remote-tracking ref before trusting it: IsDefaultBranch
+	// already contacted the remote for its symref check, but the tracking ref
+	// commitsAhead reads from is only a local cache (written at clone or the
+	// last fetch) and can sit behind the remote's live tip. Left stale, a real
+	// publishable range could look like zero commits ahead, and the diff
+	// derived below (which reuses this same ref as its base) would be stale
+	// too. A failure here (offline, or a genuinely unborn remote with no such
+	// ref to fetch yet) is folded into the same fail-closed path as an
+	// unresolvable ahead count below.
+	var fetchErr error
+	if deps.refreshTrackingRef != nil {
+		fetchErr = deps.refreshTrackingRef(ctx, workspaceRoot, trackingRemote, trackingBranch)
+	}
+
+	// The ahead check gates on the source upstream (trackingRemote), but the
+	// feature branch is pushed to `pushRemote`, which can be a different
+	// destination (--remote on a fork). Refuse to auto-branch onto an unborn
+	// destination: without an initial default branch the new feature branch
+	// becomes the destination's first ref and its HEAD is left pointing at it.
+	// This is checked once, here, against the push destination, before resolving
+	// commit tips or creating any branches.
+	pushRemote := firstNonEmptyString(requestedRemote, remote)
+	if deps.isUnbornRemote != nil {
+		if unbornDest, unbornDestErr := deps.isUnbornRemote(ctx, workspaceRoot, pushRemote); unbornDestErr == nil && unbornDest {
+			return branchPushPlan{}, fmt.Errorf("remote %s has no branches yet; push the initial default branch first with --yes (`zero changes push --yes`), then use auto-branching for subsequent work", pushRemote)
+		}
+	}
+
+	// Branching off the default branch only makes sense when HEAD carries a
+	// commit that is not already on the remote default branch. A clean,
+	// up-to-date default branch would otherwise publish a feature branch at the
+	// exact default tip. If the ahead count cannot be determined (for example
+	// the remote-tracking ref was never fetched), fail rather than guess. When
+	// the remote is confirmed unborn, refuse auto-branching entirely: the
+	// initial default branch must be established first (changes push --yes)
+	// so the remote has a real HEAD before any feature branch is published.
+	ahead, aheadErr := deps.commitsAhead(ctx, workspaceRoot, trackingRemote, trackingBranch)
+	if fetchErr != nil || aheadErr != nil {
+		var unbornRemote bool
+		var unbornErr error
+		if deps.isUnbornRemote != nil {
+			unbornRemote, unbornErr = deps.isUnbornRemote(ctx, workspaceRoot, trackingRemote)
+		}
+		if unbornErr == nil && unbornRemote {
+			return branchPushPlan{}, fmt.Errorf("remote %s has no branches yet; push the initial default branch first with --yes (`zero changes push --yes`), then use auto-branching for subsequent work", trackingRemote)
+		}
+		cause := aheadErr
+		if cause == nil {
+			cause = fetchErr
+		}
+		return branchPushPlan{}, fmt.Errorf("cannot determine whether HEAD is ahead of %s/%s: %w; fetch the remote tracking branch first", trackingRemote, trackingBranch, cause)
+	}
+	if ahead == 0 {
+		return branchPushPlan{}, fmt.Errorf("no changes to publish: HEAD is not ahead of %s/%s; commit your work before pushing", trackingRemote, trackingBranch)
+	}
+
+	// Resolve the restore tip to a concrete commit before creating any branch.
+	// It must never be a bare local branch name: resolving "main" yields the
+	// very commit the feature branch is about to own, so restore becomes a
+	// silent no-op and the publishable commits stay on the default branch. A
+	// named remote resolves through its just-refreshed remote-tracking ref; a
+	// direct URL or path asks the remote itself. Fail closed rather than
+	// substitute a local branch name.
+	restoreTip := ""
+	if deps.resolveRemoteBranchTip != nil {
+		tip, tipErr := deps.resolveRemoteBranchTip(ctx, workspaceRoot, trackingRemote, trackingBranch)
+		if tipErr != nil {
+			return branchPushPlan{}, fmt.Errorf("cannot resolve restore tip for %s/%s: %w", trackingRemote, trackingBranch, tipErr)
+		}
+		restoreTip = tip
+	}
+	if restoreTip == "" {
+		restoreTip = trackingRemote + "/" + trackingBranch
+	}
+
+	// Name the branch (and, with --auto, send the provider) from what HEAD is
+	// actually ahead of the resolved remote branch by, using the same ref
+	// commitsAhead just checked. A working-tree snapshot can describe edits a
+	// commit-only push will never include.
+	baseRef := restoreTip
+	summary, err := deps.inspectChanges(ctx, zerogit.InspectOptions{Cwd: workspaceRoot, BaseRef: baseRef, MaxDiffBytes: opts.MaxDiffBytes})
+	if err != nil {
+		return branchPushPlan{}, fmt.Errorf("failed to inspect changes: %w", err)
+	}
+
+	slug := fallbackBranchSlug(summary)
+	if len(summary.Files) == 0 {
+		// An empty commit (or one whose only content the diff omits) leaves
+		// nothing to derive a slug from; name the branch from the commit
+		// subject instead.
+		if subject := deps.headCommitSubject(ctx, workspaceRoot); subject != "" {
+			slug = zerogit.SlugifyBranchComponent(subject)
+		}
+	}
+	if opts.AutoNaming && strings.TrimSpace(summary.Diff) != "" {
+		llmSlug := ""
+		if resolved, cfgErr := deps.resolveConfig(workspaceRoot, config.Overrides{}); cfgErr == nil && config.HasProviderProfile(resolved.Provider) {
+			if provider, provErr := deps.newProvider(resolved.Provider); provErr == nil {
+				if !opts.JSONMode {
+					fmt.Fprintln(stdout, "Generating branch name using LLM...")
+				}
+				genCtx, cancel := context.WithTimeout(ctx, 60*time.Second)
+				generated, genErr := generateAutoBranchSlug(genCtx, provider, resolved.Provider.Model, redactChangeSummary(summary))
+				cancel()
+				if genErr == nil && generated != "" {
+					llmSlug = generated
+				}
+			}
+		}
+		if llmSlug != "" {
+			slug = llmSlug
+		} else if !opts.JSONMode {
+			// Cover resolveConfig failures, missing provider profiles,
+			// newProvider errors, generation errors, and empty results so the
+			// user is not left guessing after "Generating..." or silence.
+			fmt.Fprintln(stdout, "LLM branch naming unavailable; using deterministic name.")
+		}
+	}
+
+	return branchPushPlan{
+		ShouldBranch:           true,
+		CurrentBranch:          currentBranch,
+		PushRemote:             pushRemote,
+		RequireNewRemoteBranch: true,
+		TrackingRemote:         trackingRemote,
+		TrackingBranch:         trackingBranch,
+		RestoreTip:             restoreTip,
+		PublishabilityBase:     baseRef,
+		Summary:                summary,
+		Slug:                   slug,
+	}, nil
+}
+
+// ensureFeatureBranch is the branch-naming step `zero changes push`/`pr` run
+// before pushing: pushing straight to the default branch is refused deeper in
+// zerogit.Push, so rather than surface that as a dead end, create and switch
+// to a conventionally named "<user>/<slug>" branch first. It returns the
+// branch push/pr should target, or "" to mean "current HEAD branch, unchanged"
+// (zerogit.Push already treats an empty Branch that way), plus the remote the
+// preflight resolved (requestedRemote, then the original branch's configured
+// upstream, then "origin"), plus whether Push should require that branch not
+// already exist on that remote. Callers must pass the remote to Push: a
+// freshly created branch has no tracking configuration, so Push's own
+// fallback would silently retarget "origin" even when the work came from a
+// branch tracking a different remote. Callers must also pass that third value
+// through as Push's RequireNewRemoteBranch: CreateBranch's own
+// remote-collision probe runs before this returns, and closing that race
+// requires Push's push itself to assert the destination is still new. That
+// requirement also carries across a retry: if the current branch is already
+// non-default (this call didn't create it) but has not been successfully
+// published to the exact target remote under the same branch name, keep the
+// nonexistence lease. branch.<name>.remote alone is not enough: with
+// branch.autoSetupMerge=inherit, checkout -b copies remote=origin from the
+// source branch before any push. After a successful create, the original
+// default branch ref is moved back to its own upstream tip (not necessarily
+// the push destination) so the feature branch exclusively owns the
+// publishable commits; a failed restore rolls the feature branch back.
+// allowDefaultBranch (the --yes flag) and dryRun both opt out via the ""
+// branch / false return, leaving Push's own guard/preview behavior on the
+// default branch unaffected.
+//
+// autoNaming gates the LLM naming path (--auto): these commands were
+// git-only, and sending the change diff to a configured provider on every
+// default-branch push would silently export source code nobody asked to
+// share. Without the opt-in the name comes from deterministic local
+// information only. maxDiffBytes caps the committed-range diff Inspect
+// returns, so a user who passed --diff-bytes to bound the proprietary source
+// sent for LLM naming has that cap honored here just as the commit path does.
+// The working tree must be clean and HEAD must be ahead of the resolved
+// remote branch; both are verified before any branch is created. The
+// inspectChanges, commitsAhead, headCommitSubject, currentGitUser, and
+// createBranch dependencies are required on the default-branch path and are
+// called without nil guards; fillAppDeps populates all of them. The
+// refreshTrackingRef, resolveRemoteBranchTip, isUnbornRemote, resetBranchRef,
+// and deleteBranch dependencies are optional and are skipped when nil.
+func ensureFeatureBranch(ctx context.Context, stdout io.Writer, workspaceRoot string, requestedRemote string, opts featureBranchOptions, deps appDeps) (string, string, bool, error) {
+	plan, err := resolveBranchPushPlan(ctx, stdout, workspaceRoot, requestedRemote, opts, deps)
+	if err != nil {
+		return "", "", false, err
+	}
+	if !plan.ShouldBranch {
+		return plan.CurrentBranch, plan.PushRemote, plan.RequireNewRemoteBranch, nil
+	}
+
+	expectedRestoreTip := ""
+	if deps.currentBranchTip != nil {
+		expectedRestoreTip = deps.currentBranchTip(ctx, workspaceRoot)
+	}
+
+	name := zerogit.BuildBranchName(deps.currentGitUser(ctx, workspaceRoot), plan.Slug)
+	result, err := deps.createBranch(ctx, zerogit.BranchOptions{Cwd: workspaceRoot, Name: name, Remote: plan.PushRemote})
+	if err != nil {
+		return "", "", false, fmt.Errorf("failed to create branch: %w", err)
+	}
+	// The normal flow commits on the default branch first, then creates the
+	// feature branch at the same HEAD. Without moving the original default
+	// ref back, local main keeps the pre-squash commits and diverges from
+	// its upstream after a squash-merge (and a later pull/push can re-publish
+	// them). Once the feature branch owns those commits, restore the default
+	// branch to the source branch's own upstream tip captured above.
+	// Failure-safe: if the restore fails, delete the feature branch and
+	// check the default branch back out so the tree is not left half-moved.
+	if deps.resetBranchRef != nil {
+		if err := deps.resetBranchRef(ctx, workspaceRoot, plan.CurrentBranch, plan.RestoreTip, expectedRestoreTip); err != nil {
+			// A compare-and-swap conflict means the default branch moved
+			// while we were branching, so restoreTip is no longer the tip we
+			// meant to restore. The rollback below deletes the branch that
+			// now exclusively owns the user's commits, which would destroy
+			// work to recover from a race we can simply report. Keep the
+			// branch and let the user reconcile the default branch.
+			if errors.Is(err, zerogit.ErrCompareAndSwapConflict) {
+				return "", "", false, fmt.Errorf("failed to restore default branch %s to %s after auto-branching: %w; generated branch %s was preserved because the default branch changed concurrently", plan.CurrentBranch, plan.RestoreTip, err, result.Branch)
+			}
+			var rollbackErr error
+			if deps.deleteBranch != nil {
+				rollbackErr = deps.deleteBranch(ctx, workspaceRoot, plan.CurrentBranch, result.Branch)
+			}
+			if rollbackErr != nil {
+				return "", "", false, fmt.Errorf("failed to restore default branch %s to %s after auto-branching: %w; rollback of %s also failed: %v", plan.CurrentBranch, plan.RestoreTip, err, result.Branch, rollbackErr)
+			}
+			return "", "", false, fmt.Errorf("failed to restore default branch %s to %s after auto-branching: %w", plan.CurrentBranch, plan.RestoreTip, err)
+		}
+	}
+	if !opts.JSONMode {
+		fmt.Fprintf(stdout, "Created branch %s (was on %s)\n", result.Branch, plan.CurrentBranch)
+	}
+	return result.Branch, plan.PushRemote, true, nil
+}
+
+// fallbackBranchSlug derives a deterministic branch-name slug from a change
+// summary without calling an LLM, so ensureFeatureBranch still works when no
+// provider is configured.
+func fallbackBranchSlug(summary zerogit.ChangeSummary) string {
+	switch len(summary.Files) {
+	case 0:
+		return "changes"
+	case 1:
+		// Git paths are always slash-separated regardless of platform, so
+		// path.Base (not filepath.Base) extracts the filename portably.
+		return zerogit.SlugifyBranchComponent(path.Base(summary.Files[0].Path))
+	default:
+		return fmt.Sprintf("update-%d-files", len(summary.Files))
+	}
+}
+
+// generateAutoBranchSlug asks the model for a short kebab-case slug
+// describing the diff, mirroring generateAutoCommitMessage's prompt shape.
+func generateAutoBranchSlug(ctx context.Context, provider zeroruntime.Provider, model string, summary zerogit.ChangeSummary) (string, error) {
+	var promptBuilder strings.Builder
+	promptBuilder.WriteString("Analyze the following git diff and generate a short git branch name slug for it.\n")
+	promptBuilder.WriteString("The slug must be 2 to 5 lowercase words separated by hyphens (kebab-case), using only letters, digits, and hyphens, with no prefix like \"feature/\" or \"fix/\" and no surrounding quotes.\n")
+	promptBuilder.WriteString("Output ONLY the raw slug text, nothing else.\n\n")
+	promptBuilder.WriteString("Git Diff:\n")
+	promptBuilder.WriteString(summary.Diff)
+
+	request := zeroruntime.CompletionRequest{
+		Messages: []zeroruntime.Message{
+			{Role: zeroruntime.MessageRoleUser, Content: promptBuilder.String()},
+		},
+	}
+	stream, err := provider.StreamCompletion(ctx, request)
+	if err != nil {
+		return "", err
+	}
+	collected := zeroruntime.CollectStream(ctx, stream)
+	if collected.Error != "" {
+		return "", fmt.Errorf("%s", collected.Error)
+	}
+
+	slug := zerogit.SlugifyBranchComponent(extractBranchSlug(collected.Text))
+	if slug == "" {
+		return "", fmt.Errorf("provider returned empty branch slug")
+	}
+	return slug, nil
+}
+
+// slugLineRe matches a line that already reads as a kebab-case slug (letters,
+// digits, and internal single hyphens only). extractBranchSlug prefers such a
+// line so a preamble sentence is never mistaken for the slug.
+var slugLineRe = regexp.MustCompile(`^[a-zA-Z0-9]+(-[a-zA-Z0-9]+)*$`)
+
+func isPreambleText(s string) bool {
+	lower := strings.ToLower(strings.TrimSpace(s))
+	if strings.HasSuffix(lower, ":") || strings.HasSuffix(lower, ".") || strings.HasSuffix(lower, "!") || strings.HasSuffix(lower, "?") {
+		return true
+	}
+	preambles := []string{
+		"here is", "here's", "below is", "below are", "sure", "certainly",
+		"i suggest", "suggested branch", "branch name", "recommended branch",
+		"how about", "you could use",
+	}
+	for _, p := range preambles {
+		if strings.HasPrefix(lower, p) {
+			return true
+		}
+	}
+	return false
+}
+
+// extractBranchSlug pulls the intended slug out of a model response that didn't
+// follow the "output only the raw slug" instruction exactly. It drops Markdown
+// code-fence lines, then prefers a line that already looks like a kebab-case
+// slug: that skips a leading preamble such as "Here is a suggested branch
+// name:" in favor of the "add-login-page" line that follows it. One-word
+// acknowledgements that happen to match the slug regex ("Sure", "Certainly")
+// are filtered as preamble before the early return, so "Sure\nadd login page"
+// yields the real suggestion. Inline labeled forms ("Branch name: add-login-page")
+// still work: the preamble check runs on the extracted value after the label
+// is stripped. If no line is strictly kebab-cased, it prefers a plausible
+// non-preamble line so plain multi-word replies still slugify correctly.
+func extractBranchSlug(text string) string {
+	var firstLine string
+
+	for _, line := range strings.Split(text, "\n") {
+		line = strings.TrimSpace(line)
+		if strings.HasPrefix(line, "```") {
+			continue
+		}
+		line = strings.TrimSpace(strings.Trim(line, `"'`))
+		if line == "" {
+			continue
+		}
+
+		candidate := line
+		if idx := strings.Index(line, ":"); idx != -1 {
+			after := strings.TrimSpace(strings.Trim(line[idx+1:], `"'`))
+			if after != "" {
+				candidate = after
+			}
+		}
+		// Models often terminate a suggestion with sentence punctuation;
+		// strip it so "add login page." is recovered as the slug rather than
+		// rejected as preamble (isPreambleText treats a trailing '.' as a
+		// full sentence). True preamble lines still match the prefix list.
+		candidate = strings.TrimSpace(strings.TrimRight(candidate, ".!?"))
+		if candidate == "" {
+			continue
+		}
+
+		// Preamble classification runs before accepting a slug-shaped line so
+		// "Sure" does not win over a later "add-login-page". The check is on
+		// candidate (post label-strip) so "Branch name: add-login-page" still
+		// returns the extracted slug.
+		if slugLineRe.MatchString(candidate) && !isPreambleText(candidate) {
+			return candidate
+		}
+
+		if firstLine == "" && !isPreambleText(candidate) {
+			firstLine = candidate
+		}
+	}
+
+	return firstLine
+}

internal/config/command.go

@@ -197,8 +197,10 @@ func shellCommand(command string) *exec.Cmd {
 		if strings.HasPrefix(strings.TrimSpace(command), `"`) {
 			command = "call " + command
 		}
+		/* #nosec G204 -- Provider commands are intentionally evaluated by a shell to support features like pipes and env expansions. The command string originates from the user's trusted local config. */
 		return exec.Command("cmd", "/C", command)
 	}
+	/* #nosec G204 -- Provider commands are intentionally evaluated by a shell to support features like pipes and env expansions. The command string originates from the user's trusted local config. */
 	return exec.Command("sh", "-c", command)
 }
 

internal/config/json_object_edit.go

@@ -0,0 +1,294 @@
+package config
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+)
+
+type jsonObjectSpan struct {
+	start   int
+	end     int
+	members []jsonMemberSpan
+}
+
+type jsonMemberSpan struct {
+	key          string
+	leadingStart int
+	keyStart     int
+	valueStart   int
+	valueEnd     int
+	commaAfter   int
+}
+
+// setPetPreferenceJSON changes only preferences.pet. It keeps the original
+// bytes for every unrelated member so choosing a companion does not reorder or
+// reformat the user's configuration file.
+func setPetPreferenceJSON(data []byte, pet string) ([]byte, error) {
+	rootStart := skipJSONSpace(data, 0)
+	root, err := parseJSONObject(data, rootStart)
+	if err != nil {
+		return nil, err
+	}
+	preferencesIndex := lastJSONMember(root.members, "preferences")
+	if preferencesIndex < 0 {
+		if pet == "" {
+			return data, nil
+		}
+		encodedPet, err := json.Marshal(pet)
+		if err != nil {
+			return nil, fmt.Errorf("encode pet preference: %w", err)
+		}
+		return insertJSONMember(data, root, "preferences", petJSONObject(encodedPet)), nil
+	}
+
+	preferenceMember := root.members[preferencesIndex]
+	preferenceValue := bytes.TrimSpace(data[preferenceMember.valueStart:preferenceMember.valueEnd])
+	if bytes.Equal(preferenceValue, []byte("null")) {
+		if pet == "" {
+			if lastJSONMember(root.members[:preferencesIndex], "preferences") >= 0 {
+				return data, nil
+			}
+			return removeJSONMember(data, root, preferencesIndex), nil
+		}
+		encodedPet, err := json.Marshal(pet)
+		if err != nil {
+			return nil, fmt.Errorf("encode pet preference: %w", err)
+		}
+		return replaceJSONRange(data, preferenceMember.valueStart, preferenceMember.valueEnd, petJSONObject(encodedPet)), nil
+	}
+	preferences, err := parseJSONObject(data, preferenceMember.valueStart)
+	if err != nil {
+		return nil, fmt.Errorf("preferences must be a JSON object: %w", err)
+	}
+	petIndex := lastJSONMember(preferences.members, "pet")
+	if pet != "" {
+		encodedPet, err := json.Marshal(pet)
+		if err != nil {
+			return nil, fmt.Errorf("encode pet preference: %w", err)
+		}
+		if petIndex >= 0 {
+			member := preferences.members[petIndex]
+			return replaceJSONRange(data, member.valueStart, member.valueEnd, encodedPet), nil
+		}
+		return insertJSONMember(data, preferences, "pet", encodedPet), nil
+	}
+
+	for petIndex >= 0 {
+		data = removeJSONMember(data, preferences, petIndex)
+		root, err = parseJSONObject(data, rootStart)
+		if err != nil {
+			return nil, err
+		}
+		preferencesIndex = lastJSONMember(root.members, "preferences")
+		if preferencesIndex < 0 {
+			return data, nil
+		}
+		preferenceMember = root.members[preferencesIndex]
+		preferences, err = parseJSONObject(data, preferenceMember.valueStart)
+		if err != nil {
+			return nil, err
+		}
+		petIndex = lastJSONMember(preferences.members, "pet")
+	}
+	if len(preferences.members) == 0 {
+		if lastJSONMember(root.members[:preferencesIndex], "preferences") >= 0 {
+			return data, nil
+		}
+		return removeJSONMember(data, root, preferencesIndex), nil
+	}
+	return data, nil
+}
+
+func parseJSONObject(data []byte, start int) (jsonObjectSpan, error) {
+	if start < 0 || start >= len(data) || data[start] != '{' {
+		return jsonObjectSpan{}, fmt.Errorf("expected JSON object")
+	}
+	object := jsonObjectSpan{start: start}
+	leadingStart := start + 1
+	for {
+		i := skipJSONSpace(data, leadingStart)
+		if i >= len(data) {
+			return jsonObjectSpan{}, fmt.Errorf("unterminated JSON object")
+		}
+		if data[i] == '}' {
+			object.end = i
+			return object, nil
+		}
+		if data[i] != '"' {
+			return jsonObjectSpan{}, fmt.Errorf("expected JSON object key")
+		}
+		keyStart := i
+		keyEnd, err := scanJSONString(data, i)
+		if err != nil {
+			return jsonObjectSpan{}, err
+		}
+		var key string
+		if err := json.Unmarshal(data[keyStart:keyEnd], &key); err != nil {
+			return jsonObjectSpan{}, err
+		}
+		i = skipJSONSpace(data, keyEnd)
+		if i >= len(data) || data[i] != ':' {
+			return jsonObjectSpan{}, fmt.Errorf("expected colon after JSON object key")
+		}
+		valueStart := skipJSONSpace(data, i+1)
+		valueEnd, err := scanJSONValue(data, valueStart)
+		if err != nil {
+			return jsonObjectSpan{}, err
+		}
+		i = skipJSONSpace(data, valueEnd)
+		member := jsonMemberSpan{
+			key:          key,
+			leadingStart: leadingStart,
+			keyStart:     keyStart,
+			valueStart:   valueStart,
+			valueEnd:     valueEnd,
+			commaAfter:   -1,
+		}
+		if i < len(data) && data[i] == ',' {
+			member.commaAfter = i
+			object.members = append(object.members, member)
+			leadingStart = i + 1
+			continue
+		}
+		if i >= len(data) || data[i] != '}' {
+			return jsonObjectSpan{}, fmt.Errorf("expected comma or end of JSON object")
+		}
+		object.members = append(object.members, member)
+		object.end = i
+		return object, nil
+	}
+}
+
+func scanJSONString(data []byte, start int) (int, error) {
+	for i := start + 1; i < len(data); i++ {
+		switch data[i] {
+		case '\\':
+			i++
+		case '"':
+			return i + 1, nil
+		}
+	}
+	return 0, fmt.Errorf("unterminated JSON string")
+}
+
+func scanJSONValue(data []byte, start int) (int, error) {
+	if start >= len(data) {
+		return 0, fmt.Errorf("missing JSON value")
+	}
+	if data[start] == '"' {
+		return scanJSONString(data, start)
+	}
+	if data[start] == '{' || data[start] == '[' {
+		stack := []byte{data[start]}
+		for i := start + 1; i < len(data); i++ {
+			if data[i] == '"' {
+				end, err := scanJSONString(data, i)
+				if err != nil {
+					return 0, err
+				}
+				i = end - 1
+				continue
+			}
+			switch data[i] {
+			case '{', '[':
+				stack = append(stack, data[i])
+			case '}', ']':
+				open := stack[len(stack)-1]
+				if (open == '{' && data[i] != '}') || (open == '[' && data[i] != ']') {
+					return 0, fmt.Errorf("mismatched JSON delimiter")
+				}
+				stack = stack[:len(stack)-1]
+				if len(stack) == 0 {
+					return i + 1, nil
+				}
+			}
+		}
+		return 0, fmt.Errorf("unterminated JSON value")
+	}
+	for i := start; i < len(data); i++ {
+		switch data[i] {
+		case ',', '}', ']', ' ', '\t', '\r', '\n':
+			if i == start {
+				return 0, fmt.Errorf("missing JSON value")
+			}
+			return i, nil
+		}
+	}
+	return len(data), nil
+}
+
+func skipJSONSpace(data []byte, start int) int {
+	for start < len(data) {
+		switch data[start] {
+		case ' ', '\t', '\r', '\n':
+			start++
+		default:
+			return start
+		}
+	}
+	return start
+}
+
+func lastJSONMember(members []jsonMemberSpan, key string) int {
+	for i := len(members) - 1; i >= 0; i-- {
+		if members[i].key == key {
+			return i
+		}
+	}
+	return -1
+}
+
+func petJSONObject(encodedPet []byte) []byte {
+	result := append([]byte(`{"pet":`), encodedPet...)
+	return append(result, '}')
+}
+
+func replaceJSONRange(data []byte, start, end int, replacement []byte) []byte {
+	result := make([]byte, 0, len(data)-(end-start)+len(replacement))
+	result = append(result, data[:start]...)
+	result = append(result, replacement...)
+	return append(result, data[end:]...)
+}
+
+func removeJSONMember(data []byte, object jsonObjectSpan, index int) []byte {
+	member := object.members[index]
+	start, end := member.leadingStart, member.valueEnd
+	if member.commaAfter >= 0 {
+		end = member.commaAfter + 1
+	} else if index > 0 {
+		start = object.members[index-1].commaAfter
+	}
+	return replaceJSONRange(data, start, end, nil)
+}
+
+func insertJSONMember(data []byte, object jsonObjectSpan, key string, value []byte) []byte {
+	encodedKey, _ := json.Marshal(key)
+	entry := append(append(encodedKey, ':', ' '), value...)
+	if len(object.members) == 0 {
+		interior := data[object.start+1 : object.end]
+		if newline := bytes.LastIndexByte(interior, '\n'); newline >= 0 {
+			closingIndent := interior[newline+1:]
+			indentUnit := []byte("  ")
+			if bytes.Contains(closingIndent, []byte("\t")) {
+				indentUnit = []byte("\t")
+			}
+			lineBreak := []byte("\n")
+			if newline > 0 && interior[newline-1] == '\r' {
+				lineBreak = []byte("\r\n")
+			}
+			insert := append(append(append(lineBreak, closingIndent...), indentUnit...), entry...)
+			return replaceJSONRange(data, object.start+1, object.start+1, insert)
+		}
+		return replaceJSONRange(data, object.end, object.end, entry)
+	}
+	last := object.members[len(object.members)-1]
+	separator := []byte(", ")
+	if bytes.Contains(data[last.valueEnd:object.end], []byte("\n")) {
+		lineStart := bytes.LastIndexByte(data[:last.keyStart], '\n') + 1
+		indent := data[lineStart:last.keyStart]
+		separator = append([]byte(",\n"), indent...)
+	}
+	insert := append(separator, entry...)
+	return replaceJSONRange(data, last.valueEnd, last.valueEnd, insert)
+}

internal/config/pet_writer_test.go

@@ -0,0 +1,252 @@
+package config
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestSetPetPreservesUnrelatedConfig(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "config.json")
+	original := FileConfig{
+		ActiveProvider: "test",
+		Providers:      []ProviderProfile{{Name: "test", Model: "example"}},
+		Preferences:    PreferencesConfig{Theme: "dracula"},
+	}
+	data, err := json.Marshal(original)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(path, data, 0o600); err != nil {
+		t.Fatal(err)
+	}
+	updated, err := SetPet(path, "boba")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if updated.Preferences.Pet != "boba" || updated.Preferences.Theme != "dracula" || updated.ActiveProvider != "test" || len(updated.Providers) != 1 {
+		t.Fatalf("SetPet lost config fields: %#v", updated)
+	}
+	reloadedData, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var reloaded FileConfig
+	if err := json.Unmarshal(reloadedData, &reloaded); err != nil {
+		t.Fatal(err)
+	}
+	if reloaded.Preferences.Pet != "boba" || reloaded.Preferences.Theme != "dracula" || reloaded.ActiveProvider != "test" || len(reloaded.Providers) != 1 {
+		t.Fatalf("persisted config lost fields: %#v", reloaded)
+	}
+}
+
+func TestSetPetRejectsInvalidInputs(t *testing.T) {
+	if _, err := SetPet("  ", "boba"); err == nil {
+		t.Fatal("SetPet accepted a blank config path")
+	}
+	path := filepath.Join(t.TempDir(), "config.json")
+	if err := os.WriteFile(path, []byte(`{"preferences":`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := SetPet(path, "boba"); err == nil || !strings.Contains(err.Error(), "invalid config JSON") {
+		t.Fatalf("SetPet malformed JSON error = %v", err)
+	}
+}
+
+func TestSetPetCreatesNestedConfigAndClearsEmptyPreferences(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "nested", "zero", "config.json")
+	if _, err := SetPet(path, " boba "); err != nil {
+		t.Fatal(err)
+	}
+	data, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var root map[string]json.RawMessage
+	if err := json.Unmarshal(data, &root); err != nil {
+		t.Fatal(err)
+	}
+	var preferences struct {
+		Pet string `json:"pet"`
+	}
+	if err := json.Unmarshal(root["preferences"], &preferences); err != nil {
+		t.Fatal(err)
+	}
+	if preferences.Pet != "boba" {
+		t.Fatalf("persisted pet = %q, want %q", preferences.Pet, "boba")
+	}
+	root["future"] = json.RawMessage(`{"enabled":true}`)
+	encoded, err := json.Marshal(root)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(path, encoded, 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := SetPet(path, " "); err != nil {
+		t.Fatal(err)
+	}
+	data, err = os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	root = nil
+	if err := json.Unmarshal(data, &root); err != nil {
+		t.Fatal(err)
+	}
+	if _, ok := root["preferences"]; ok {
+		t.Fatalf("empty preferences were retained: %s", data)
+	}
+	var future struct {
+		Enabled bool `json:"enabled"`
+	}
+	if err := json.Unmarshal(root["future"], &future); err != nil {
+		t.Fatal(err)
+	}
+	if !future.Enabled {
+		t.Fatalf("unrelated future member was lost: %s", data)
+	}
+}
+
+func TestSetPetPreservesUnknownJSONMembers(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "config.json")
+	original := []byte(`{
+  "activeProvider": "test",
+  "futureTopLevel": {"enabled": true},
+  "preferences": {
+    "theme": "dracula",
+    "futurePreference": {"mode": "extended"}
+  }
+}`)
+	if err := os.WriteFile(path, original, 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := SetPet(path, "boba"); err != nil {
+		t.Fatal(err)
+	}
+	data, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var root map[string]json.RawMessage
+	if err := json.Unmarshal(data, &root); err != nil {
+		t.Fatal(err)
+	}
+	var futureTopLevel struct {
+		Enabled bool `json:"enabled"`
+	}
+	if err := json.Unmarshal(root["futureTopLevel"], &futureTopLevel); err != nil {
+		t.Fatal(err)
+	}
+	if !futureTopLevel.Enabled {
+		t.Fatalf("unknown top-level member = %s", root["futureTopLevel"])
+	}
+	var preferences map[string]json.RawMessage
+	if err := json.Unmarshal(root["preferences"], &preferences); err != nil {
+		t.Fatal(err)
+	}
+	var futurePreference struct {
+		Mode string `json:"mode"`
+	}
+	if err := json.Unmarshal(preferences["futurePreference"], &futurePreference); err != nil {
+		t.Fatal(err)
+	}
+	if futurePreference.Mode != "extended" {
+		t.Fatalf("unknown preference member = %s", preferences["futurePreference"])
+	}
+	if got := string(preferences["pet"]); got != `"boba"` {
+		t.Fatalf("pet preference = %s, want boba", got)
+	}
+}
+
+func TestSetPetPreservesExistingJSONLayoutAndMemberOrder(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "config.json")
+	original := []byte("{\n\t\"zFuture\": {\"enabled\":true},\n\t\"preferences\": {\n\t\t\"theme\" : \"dracula\",\n\t\t\"pet\" : \"old\",\n\t\t\"futurePreference\": {\"mode\":\"extended\"}\n\t},\n\t\"activeProvider\": \"test\"\n}\n")
+	if err := os.WriteFile(path, original, 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := SetPet(path, "boba"); err != nil {
+		t.Fatal(err)
+	}
+	got, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := strings.Replace(string(original), `"old"`, `"boba"`, 1)
+	if string(got) != want {
+		t.Fatalf("SetPet reformatted or reordered config:\n--- got ---\n%s--- want ---\n%s", got, want)
+	}
+}
+
+func TestSetPetMinimallyEditsExistingJSON(t *testing.T) {
+	tests := []struct {
+		name     string
+		original string
+		pet      string
+		want     string
+	}{
+		{
+			name:     "add pet to existing preferences",
+			original: "{\n  \"zFuture\": {\"text\":\"comma, brace } and \\\"quote\\\"\"},\n  \"preferences\": {\n    \"theme\": \"dracula\"\n  },\n  \"activeProvider\": \"test\"\n}\n",
+			pet:      "boba",
+			want:     "{\n  \"zFuture\": {\"text\":\"comma, brace } and \\\"quote\\\"\"},\n  \"preferences\": {\n    \"theme\": \"dracula\",\n    \"pet\": \"boba\"\n  },\n  \"activeProvider\": \"test\"\n}\n",
+		},
+		{
+			name:     "add preferences without reordering root",
+			original: "{\n  \"zFuture\": true,\n  \"activeProvider\": \"test\"\n}\n",
+			pet:      "boba",
+			want:     "{\n  \"zFuture\": true,\n  \"activeProvider\": \"test\",\n  \"preferences\": {\"pet\":\"boba\"}\n}\n",
+		},
+		{
+			name:     "remove pet but retain preferences",
+			original: "{\n  \"preferences\": {\n    \"theme\": \"dracula\",\n    \"pet\": \"boba\",\n    \"future\": true\n  },\n  \"zFuture\": true\n}\n",
+			pet:      "",
+			want:     "{\n  \"preferences\": {\n    \"theme\": \"dracula\",\n    \"future\": true\n  },\n  \"zFuture\": true\n}\n",
+		},
+		{
+			name:     "remove empty preferences member",
+			original: "{\n  \"zFuture\": true,\n  \"preferences\": {\n    \"pet\": \"boba\"\n  },\n  \"activeProvider\": \"test\"\n}\n",
+			pet:      "",
+			want:     "{\n  \"zFuture\": true,\n  \"activeProvider\": \"test\"\n}\n",
+		},
+		{
+			name:     "do not expose an older duplicate preference",
+			original: "{\"preferences\":{\"pet\":\"cat\"},\"preferences\":{\"pet\":\"dog\"}}\n",
+			pet:      "",
+			want:     "{\"preferences\":{\"pet\":\"cat\"},\"preferences\":{}}\n",
+		},
+		{
+			name:     "do not expose an older duplicate behind null",
+			original: "{\"preferences\":{\"pet\":\"cat\"},\"preferences\":null}\n",
+			pet:      "",
+			want:     "{\"preferences\":{\"pet\":\"cat\"},\"preferences\":null}\n",
+		},
+		{
+			name:     "preserve multiline empty preferences layout",
+			original: "{\n  \"preferences\": {\n  },\n  \"activeProvider\": \"test\"\n}\n",
+			pet:      "boba",
+			want:     "{\n  \"preferences\": {\n    \"pet\": \"boba\"\n  },\n  \"activeProvider\": \"test\"\n}\n",
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			path := filepath.Join(t.TempDir(), "config.json")
+			if err := os.WriteFile(path, []byte(test.original), 0o600); err != nil {
+				t.Fatal(err)
+			}
+			if _, err := SetPet(path, test.pet); err != nil {
+				t.Fatal(err)
+			}
+			got, err := os.ReadFile(path)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if string(got) != test.want {
+				t.Fatalf("SetPet output:\n--- got ---\n%s--- want ---\n%s", got, test.want)
+			}
+		})
+	}
+}

internal/config/resolver.go

@@ -103,6 +103,7 @@ func Resolve(options ResolveOptions) (ResolvedConfig, error) {
 		// here rather than in mergeConfig because that helper is shared with the
 		// trusted global-config merge, which must keep honouring the setting.
 		commandConfig.Sandbox.Enabled = nil
+		commandConfig.CrossSessionInbound = ""
 		mergeConfig(&cfg, commandConfig)
 	}
 
@@ -140,6 +141,13 @@ func Resolve(options ResolveOptions) (ResolvedConfig, error) {
 			return ResolvedConfig{}, fmt.Errorf("invalid notify.focusMode %q: expected unfocused, always, or focused", focusMode)
 		}
 	}
+	if inbound := strings.TrimSpace(cfg.CrossSessionInbound); inbound != "" {
+		switch inbound {
+		case "accept", "hold", "refuse":
+		default:
+			return ResolvedConfig{}, fmt.Errorf("invalid crossSessionInbound %q: expected accept, hold, or refuse", inbound)
+		}
+	}
 	if err := validateSTTConfig(cfg.STT); err != nil {
 		return ResolvedConfig{}, err
 	}
@@ -154,19 +162,20 @@ func Resolve(options ResolveOptions) (ResolvedConfig, error) {
 	}
 
 	return ResolvedConfig{
-		ActiveProvider: active.Name,
-		Providers:      providers,
-		Provider:       active,
-		MaxTurns:       cfg.MaxTurns,
-		MCP:            cfg.MCP,
-		Sandbox:        cfg.Sandbox,
-		Notify:         cfg.Notify,
-		Tools:          cfg.Tools,
-		Swarm:          cfg.Swarm,
-		Preferences:    cfg.Preferences,
-		KeyBindings:    cfg.KeyBindings,
-		LocalControl:   cfg.LocalControl,
-		STT:            cfg.STT,
+		ActiveProvider:      active.Name,
+		Providers:           providers,
+		Provider:            active,
+		MaxTurns:            cfg.MaxTurns,
+		MCP:                 cfg.MCP,
+		Sandbox:             cfg.Sandbox,
+		Notify:              cfg.Notify,
+		Tools:               cfg.Tools,
+		Swarm:               cfg.Swarm,
+		Preferences:         cfg.Preferences,
+		KeyBindings:         cfg.KeyBindings,
+		LocalControl:        cfg.LocalControl,
+		STT:                 cfg.STT,
+		CrossSessionInbound: cfg.CrossSessionInbound,
 	}, nil
 }
 
@@ -264,9 +273,15 @@ func mergeConfig(dst *FileConfig, src FileConfig) {
 	if strings.TrimSpace(src.Preferences.Theme) != "" {
 		dst.Preferences.Theme = strings.TrimSpace(src.Preferences.Theme)
 	}
+	if strings.TrimSpace(src.Preferences.Pet) != "" {
+		dst.Preferences.Pet = strings.TrimSpace(src.Preferences.Pet)
+	}
 	mergeLocalControlConfig(&dst.LocalControl, src.LocalControl)
 	mergeKeyBindings(&dst.KeyBindings, src.KeyBindings)
 	mergeSTTConfig(&dst.STT, src.STT)
+	if inbound := strings.TrimSpace(src.CrossSessionInbound); inbound != "" {
+		dst.CrossSessionInbound = inbound
+	}
 }
 
 func mergeProjectConfig(dst *FileConfig, src FileConfig) error {
@@ -325,6 +340,9 @@ func mergeProjectConfig(dst *FileConfig, src FileConfig) error {
 	if src.Swarm.MaxTeamSize != 0 {
 		dst.Swarm.MaxTeamSize = src.Swarm.MaxTeamSize
 	}
+	if inbound := strings.TrimSpace(src.CrossSessionInbound); inboundPolicyRank(inbound) > inboundPolicyRank(dst.CrossSessionInbound) {
+		dst.CrossSessionInbound = inbound
+	}
 	mergeKeyBindings(&dst.KeyBindings, src.KeyBindings)
 	// Local control is intentionally user-config/override only. A cloned project
 	// must not be able to make browser, desktop, or terminal automation tools
@@ -727,6 +745,9 @@ func applyOverrides(cfg *FileConfig, overrides Overrides) {
 	mergeLocalControlConfig(&cfg.LocalControl, overrides.LocalControl)
 	mergeKeyBindings(&cfg.KeyBindings, overrides.KeyBindings)
 	mergeSTTConfig(&cfg.STT, overrides.STT)
+	if inbound := strings.TrimSpace(overrides.CrossSessionInbound); inbound != "" {
+		cfg.CrossSessionInbound = inbound
+	}
 	for _, provider := range overrides.Providers {
 		mergeProvider(cfg, provider)
 	}
@@ -736,6 +757,19 @@ func applyOverrides(cfg *FileConfig, overrides Overrides) {
 	mergeMCPConfig(&cfg.MCP, overrides.MCP, true)
 }
 
+func inboundPolicyRank(policy string) int {
+	switch strings.TrimSpace(policy) {
+	case "refuse":
+		return 3
+	case "hold":
+		return 2
+	case "accept":
+		return 0
+	default:
+		return 1 // permission-mode parity
+	}
+}
+
 func mergeLocalControlConfig(dst *LocalControlConfig, src LocalControlConfig) {
 	if src.enabledSet {
 		dst.Enabled = src.Enabled

internal/config/resolver_test.go

@@ -168,6 +168,22 @@ func TestResolveLoadsRecentModelsFromUserConfigOnly(t *testing.T) {
 	}
 }
 
+func TestResolveLoadsPetFromUserConfigOnly(t *testing.T) {
+	userPath := writeConfig(t, `{"preferences":{"pet":" boba "}}`)
+	projectPath := writeConfig(t, `{"preferences":{"pet":"project-pet"}}`)
+	resolved, err := Resolve(ResolveOptions{
+		UserConfigPath:    userPath,
+		ProjectConfigPath: projectPath,
+		Env:               map[string]string{},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if resolved.Preferences.Pet != "boba" {
+		t.Fatalf("Preferences.Pet = %q, want user preference boba", resolved.Preferences.Pet)
+	}
+}
+
 // recentModels must never be merged from project config (same posture as
 // favoriteModels): a project setting it with no corresponding user setting
 // should leave the resolved value empty, not pick up the project's list.
@@ -2199,3 +2215,40 @@ func TestResolveRequiresModelErrorIsSetupFixable(t *testing.T) {
 		t.Fatalf("error leaked API key: %q", err.Error())
 	}
 }
+
+func TestCrossSessionInboundProjectConfigCanOnlyTighten(t *testing.T) {
+	tests := []struct {
+		name    string
+		user    string
+		project string
+		want    string
+	}{
+		{name: "hold tightens accept", user: "accept", project: "hold", want: "hold"},
+		{name: "refuse stays refuse", user: "refuse", project: "accept", want: "refuse"},
+		{name: "accept cannot weaken parity", project: "accept", want: ""},
+		{name: "refuse tightens parity", project: "refuse", want: "refuse"},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			cfg := FileConfig{CrossSessionInbound: test.user}
+			if err := mergeProjectConfig(&cfg, FileConfig{CrossSessionInbound: test.project}); err != nil {
+				t.Fatal(err)
+			}
+			if cfg.CrossSessionInbound != test.want {
+				t.Fatalf("crossSessionInbound = %q, want %q", cfg.CrossSessionInbound, test.want)
+			}
+		})
+	}
+}
+
+func TestResolveRejectsInvalidCrossSessionInbound(t *testing.T) {
+	path := writeConfig(t, `{
+		"activeProvider": "openai",
+		"providers": [{"name":"openai","provider_kind":"openai","apiKey":"sk-x","model":"gpt-5"}],
+		"crossSessionInbound": "sometimes"
+	}`)
+	_, err := Resolve(ResolveOptions{UserConfigPath: path, Env: map[string]string{}})
+	if err == nil || !strings.Contains(err.Error(), "expected accept, hold, or refuse") {
+		t.Fatalf("error = %v", err)
+	}
+}

internal/config/types.go

@@ -112,6 +112,9 @@ type PreferencesConfig struct {
 	// name (e.g. "dracula"). Applied at startup below the --theme flag and
 	// ZERO_THEME, so a /theme choice survives restart. Empty = unset (defaults auto).
 	Theme string `json:"theme,omitempty"`
+	// Pet is the terminal companion selected through /pets. Empty leaves pets
+	// off until the user chooses one; "disabled" is the explicit off state.
+	Pet string `json:"pet,omitempty"`
 	// Recaps is a tri-state: nil (unset) defaults to ON; an explicit false means
 	// the user turned idle recaps off. A *bool is its own tri-state, so no
 	// custom unmarshal is needed (unlike ToolsConfig.DeferThreshold's int).
@@ -340,46 +343,49 @@ func (cfg *ToolsConfig) UnmarshalJSON(data []byte) error {
 }
 
 type FileConfig struct {
-	ActiveProvider string             `json:"activeProvider,omitempty"`
-	Providers      []ProviderProfile  `json:"providers,omitempty"`
-	MaxTurns       int                `json:"maxTurns,omitempty"`
-	MCP            MCPConfig          `json:"mcp,omitempty"`
-	Sandbox        SandboxConfig      `json:"sandbox,omitempty"`
-	Notify         NotifyConfig       `json:"notify,omitempty"`
-	Tools          ToolsConfig        `json:"tools,omitempty"`
-	Swarm          SwarmConfig        `json:"swarm,omitempty"`
-	Preferences    PreferencesConfig  `json:"preferences,omitempty"`
-	KeyBindings    KeyBindingsConfig  `json:"keybindings,omitempty"`
-	LocalControl   LocalControlConfig `json:"localControl,omitempty"`
-	STT            STTConfig          `json:"stt,omitempty"`
+	ActiveProvider      string             `json:"activeProvider,omitempty"`
+	Providers           []ProviderProfile  `json:"providers,omitempty"`
+	MaxTurns            int                `json:"maxTurns,omitempty"`
+	MCP                 MCPConfig          `json:"mcp,omitempty"`
+	Sandbox             SandboxConfig      `json:"sandbox,omitempty"`
+	Notify              NotifyConfig       `json:"notify,omitempty"`
+	Tools               ToolsConfig        `json:"tools,omitempty"`
+	Swarm               SwarmConfig        `json:"swarm,omitempty"`
+	Preferences         PreferencesConfig  `json:"preferences,omitempty"`
+	KeyBindings         KeyBindingsConfig  `json:"keybindings,omitempty"`
+	LocalControl        LocalControlConfig `json:"localControl,omitempty"`
+	STT                 STTConfig          `json:"stt,omitempty"`
+	CrossSessionInbound string             `json:"crossSessionInbound,omitempty"`
 }
 
 func (cfg FileConfig) MarshalJSON() ([]byte, error) {
 	type rawConfig struct {
-		ActiveProvider string              `json:"activeProvider,omitempty"`
-		Providers      []ProviderProfile   `json:"providers,omitempty"`
-		MaxTurns       int                 `json:"maxTurns,omitempty"`
-		MCP            MCPConfig           `json:"mcp,omitempty"`
-		Sandbox        SandboxConfig       `json:"sandbox,omitempty"`
-		Notify         NotifyConfig        `json:"notify,omitempty"`
-		Tools          ToolsConfig         `json:"tools,omitempty"`
-		Swarm          SwarmConfig         `json:"swarm,omitempty"`
-		Preferences    PreferencesConfig   `json:"preferences,omitempty"`
-		KeyBindings    KeyBindingsConfig   `json:"keybindings,omitempty"`
-		LocalControl   *LocalControlConfig `json:"localControl,omitempty"`
-		STT            *STTConfig          `json:"stt,omitempty"`
+		ActiveProvider      string              `json:"activeProvider,omitempty"`
+		Providers           []ProviderProfile   `json:"providers,omitempty"`
+		MaxTurns            int                 `json:"maxTurns,omitempty"`
+		MCP                 MCPConfig           `json:"mcp,omitempty"`
+		Sandbox             SandboxConfig       `json:"sandbox,omitempty"`
+		Notify              NotifyConfig        `json:"notify,omitempty"`
+		Tools               ToolsConfig         `json:"tools,omitempty"`
+		Swarm               SwarmConfig         `json:"swarm,omitempty"`
+		Preferences         PreferencesConfig   `json:"preferences,omitempty"`
+		KeyBindings         KeyBindingsConfig   `json:"keybindings,omitempty"`
+		LocalControl        *LocalControlConfig `json:"localControl,omitempty"`
+		STT                 *STTConfig          `json:"stt,omitempty"`
+		CrossSessionInbound string              `json:"crossSessionInbound,omitempty"`
 	}
 	raw := rawConfig{
-		ActiveProvider: cfg.ActiveProvider,
-		Providers:      cfg.Providers,
-		MaxTurns:       cfg.MaxTurns,
-		MCP:            cfg.MCP,
-		Sandbox:        cfg.Sandbox,
-		Notify:         cfg.Notify,
-		Tools:          cfg.Tools,
-		Swarm:          cfg.Swarm,
-		Preferences:    cfg.Preferences,
-		KeyBindings:    cfg.KeyBindings,
+		ActiveProvider:      cfg.ActiveProvider,
+		Providers:           cfg.Providers,
+		MaxTurns:            cfg.MaxTurns,
+		MCP:                 cfg.MCP,
+		Sandbox:             cfg.Sandbox,
+		Notify:              cfg.Notify,
+		Tools:               cfg.Tools,
+		Swarm:               cfg.Swarm,
+		Preferences:         cfg.Preferences,
+		KeyBindings:         cfg.KeyBindings,
+		CrossSessionInbound: cfg.CrossSessionInbound,
 	}
 	if !cfg.LocalControl.Empty() {
 		raw.LocalControl = &cfg.LocalControl
@@ -404,33 +410,35 @@ type ResolveOptions struct {
 }
 
 type Overrides struct {
-	ActiveProvider string
-	Providers      []ProviderProfile
-	Provider       ProviderProfile
-	MaxTurns       int
-	MCP            MCPConfig
-	Sandbox        SandboxConfig
-	Notify         NotifyConfig
-	Tools          ToolsConfig
-	KeyBindings    KeyBindingsConfig
-	LocalControl   LocalControlConfig
-	STT            STTConfig
+	ActiveProvider      string
+	Providers           []ProviderProfile
+	Provider            ProviderProfile
+	MaxTurns            int
+	MCP                 MCPConfig
+	Sandbox             SandboxConfig
+	Notify              NotifyConfig
+	Tools               ToolsConfig
+	KeyBindings         KeyBindingsConfig
+	LocalControl        LocalControlConfig
+	STT                 STTConfig
+	CrossSessionInbound string
 }
 
 type ResolvedConfig struct {
-	ActiveProvider string
-	Providers      []ProviderProfile
-	Provider       ProviderProfile
-	MaxTurns       int
-	MCP            MCPConfig
-	Sandbox        SandboxConfig
-	Notify         NotifyConfig
-	Tools          ToolsConfig
-	Swarm          SwarmConfig
-	Preferences    PreferencesConfig
-	KeyBindings    KeyBindingsConfig
-	LocalControl   LocalControlConfig
-	STT            STTConfig
+	ActiveProvider      string
+	Providers           []ProviderProfile
+	Provider            ProviderProfile
+	MaxTurns            int
+	MCP                 MCPConfig
+	Sandbox             SandboxConfig
+	Notify              NotifyConfig
+	Tools               ToolsConfig
+	Swarm               SwarmConfig
+	Preferences         PreferencesConfig
+	KeyBindings         KeyBindingsConfig
+	LocalControl        LocalControlConfig
+	STT                 STTConfig
+	CrossSessionInbound string
 }
 
 type MCPConfig struct {
@@ -480,20 +488,21 @@ type MCPOAuthConfig struct {
 
 func (cfg *FileConfig) UnmarshalJSON(data []byte) error {
 	type rawConfig struct {
-		ActiveProvider  string                     `json:"activeProvider"`
-		Providers       []ProviderProfile          `json:"providers"`
-		MaxTurns        int                        `json:"maxTurns"`
-		MCP             MCPConfig                  `json:"mcp"`
-		Sandbox         SandboxConfig              `json:"sandbox"`
-		Notify          NotifyConfig               `json:"notify"`
-		Tools           ToolsConfig                `json:"tools"`
-		Swarm           SwarmConfig                `json:"swarm"`
-		Preferences     PreferencesConfig          `json:"preferences"`
-		KeyBindings     KeyBindingsConfig          `json:"keybindings"`
-		LocalControl    LocalControlConfig         `json:"localControl"`
-		STT             STTConfig                  `json:"stt"`
-		MCPServers      map[string]MCPServerConfig `json:"mcpServers"`
-		MCPServersSnake map[string]MCPServerConfig `json:"mcp_servers"`
+		ActiveProvider      string                     `json:"activeProvider"`
+		Providers           []ProviderProfile          `json:"providers"`
+		MaxTurns            int                        `json:"maxTurns"`
+		MCP                 MCPConfig                  `json:"mcp"`
+		Sandbox             SandboxConfig              `json:"sandbox"`
+		Notify              NotifyConfig               `json:"notify"`
+		Tools               ToolsConfig                `json:"tools"`
+		Swarm               SwarmConfig                `json:"swarm"`
+		Preferences         PreferencesConfig          `json:"preferences"`
+		KeyBindings         KeyBindingsConfig          `json:"keybindings"`
+		LocalControl        LocalControlConfig         `json:"localControl"`
+		STT                 STTConfig                  `json:"stt"`
+		CrossSessionInbound string                     `json:"crossSessionInbound"`
+		MCPServers          map[string]MCPServerConfig `json:"mcpServers"`
+		MCPServersSnake     map[string]MCPServerConfig `json:"mcp_servers"`
 	}
 
 	var raw rawConfig
@@ -520,6 +529,7 @@ func (cfg *FileConfig) UnmarshalJSON(data []byte) error {
 	cfg.KeyBindings = raw.KeyBindings
 	cfg.LocalControl = raw.LocalControl
 	cfg.STT = raw.STT
+	cfg.CrossSessionInbound = raw.CrossSessionInbound
 	if cfg.MCP.Servers == nil && (len(raw.MCPServers) > 0 || len(raw.MCPServersSnake) > 0) {
 		cfg.MCP.Servers = map[string]MCPServerConfig{}
 	}

internal/config/writer.go

@@ -591,6 +591,35 @@ func SetTheme(path string, theme string) (FileConfig, error) {
 	return cfg, nil
 }
 
+// SetPet persists only the terminal-pet preference while preserving every
+// unrelated user setting through the config writer's atomic replace path.
+func SetPet(path string, pet string) (FileConfig, error) {
+	path = strings.TrimSpace(path)
+	if path == "" {
+		return FileConfig{}, fmt.Errorf("config path is required")
+	}
+	cfg := FileConfig{}
+	data := []byte("{}")
+	if existing, err := os.ReadFile(path); err == nil {
+		if err := json.Unmarshal(existing, &cfg); err != nil {
+			return FileConfig{}, fmt.Errorf("invalid config JSON %s: %w", path, err)
+		}
+		data = existing
+	} else if !os.IsNotExist(err) {
+		return FileConfig{}, fmt.Errorf("read config %s: %w", path, err)
+	}
+	pet = strings.TrimSpace(pet)
+	cfg.Preferences.Pet = pet
+	data, err := setPetPreferenceJSON(data, pet)
+	if err != nil {
+		return FileConfig{}, fmt.Errorf("invalid config JSON %s: %w", path, err)
+	}
+	if err := writeConfigData(path, data); err != nil {
+		return FileConfig{}, err
+	}
+	return cfg, nil
+}
+
 // SetSTTModel persists the dictation model and its provider, mirroring
 // SetTheme (read-modify-atomic-write). provider must be one of the known STT
 // provider kinds; a local provider stores the model as stt.localModelPath,
@@ -736,17 +765,23 @@ func NormalizeRecentModels(entries []RecentModelEntry) []RecentModelEntry {
 }
 
 func writeConfigFile(path string, cfg FileConfig) error {
+	data, err := json.MarshalIndent(cfg, "", "  ")
+	if err != nil {
+		return fmt.Errorf("encode config JSON: %w", err)
+	}
+	return writeConfigData(path, data)
+}
+
+func writeConfigData(path string, data []byte) error {
 	dir := filepath.Dir(path)
 	if dir != "." && dir != "" {
 		if err := os.MkdirAll(dir, 0o700); err != nil {
 			return fmt.Errorf("create config directory %s: %w", dir, err)
 		}
 	}
-	data, err := json.MarshalIndent(cfg, "", "  ")
-	if err != nil {
-		return fmt.Errorf("encode config JSON: %w", err)
+	if len(data) == 0 || data[len(data)-1] != '\n' {
+		data = append(data, '\n')
 	}
-	data = append(data, '\n')
 	// Write-to-temp + rename: an in-place write interrupted mid-way (crash,
 	// disk full) would leave the user's only config truncated or corrupt.
 	tmp, err := os.CreateTemp(dir, ".zero-config-*.tmp")

internal/credstore/concurrency_test.go

@@ -0,0 +1,246 @@
+package credstore
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"sync"
+	"testing"
+)
+
+func fileStore(t *testing.T, dir string) *Store {
+	t.Helper()
+	store, err := New(Options{Dir: dir, Storage: "file"})
+	if err != nil {
+		t.Fatalf("New: %v", err)
+	}
+	return store
+}
+
+// THE REPRODUCTION, kept as the regression. Before the lock this reliably kept
+// 1 of 100: every writer read the same map, added its own provider, and the
+// last rename published a file missing all the others.
+func TestConcurrentSetKeepsEveryKey(t *testing.T) {
+	dir := t.TempDir()
+	store := fileStore(t, dir)
+
+	const n = 100
+	var wg sync.WaitGroup
+	errs := make(chan error, n)
+	for i := 0; i < n; i++ {
+		wg.Add(1)
+		go func(i int) {
+			defer wg.Done()
+			if err := store.Set(fmt.Sprintf("p%03d", i), fmt.Sprintf("k%03d", i)); err != nil {
+				errs <- err
+			}
+		}(i)
+	}
+	wg.Wait()
+	close(errs)
+	for err := range errs {
+		t.Fatalf("Set: %v", err)
+	}
+
+	got, err := store.Providers()
+	if err != nil {
+		t.Fatalf("Providers: %v", err)
+	}
+	if len(got) != n {
+		t.Fatalf("kept %d of %d concurrent writes", len(got), n)
+	}
+	// ...and every value is the one its own writer wrote, not a neighbour's.
+	for i := 0; i < n; i++ {
+		key, ok, err := store.Get(fmt.Sprintf("p%03d", i))
+		if err != nil {
+			t.Fatalf("Get: %v", err)
+		}
+		if !ok || key != fmt.Sprintf("k%03d", i) {
+			t.Fatalf("p%03d = %q (present=%v); a writer's own value must survive", i, key, ok)
+		}
+	}
+}
+
+// DELETE RACES SET, and an unlocked delete loses the other writer's key.
+//
+// A first version of this only checked that keys nobody deleted survived — and
+// every reader sees those, so it passed with the lock removed from Delete. The
+// case that actually breaks is a Delete whose stale read predates a concurrent
+// Set: it writes back a map that never contained the new key, and the Set is
+// gone. So the assertion is on the SETS surviving, not on the bystanders.
+func TestADeleteCannotClobberAConcurrentSet(t *testing.T) {
+	dir := t.TempDir()
+	store := fileStore(t, dir)
+
+	// Throwaway keys for the deleters to remove, written first so a delete
+	// always has something to do.
+	const churn = 40
+	for i := 0; i < churn; i++ {
+		if err := store.Set(fmt.Sprintf("churn%02d", i), "v"); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	const adds = 60
+	var wg sync.WaitGroup
+	for i := 0; i < adds; i++ {
+		wg.Add(1)
+		go func(i int) {
+			defer wg.Done()
+			_ = store.Set(fmt.Sprintf("added%02d", i), "v")
+		}(i)
+	}
+	for i := 0; i < churn; i++ {
+		wg.Add(1)
+		go func(i int) {
+			defer wg.Done()
+			_, _ = store.Delete(fmt.Sprintf("churn%02d", i))
+		}(i)
+	}
+	wg.Wait()
+
+	got, err := store.Providers()
+	if err != nil {
+		t.Fatal(err)
+	}
+	survivors := map[string]bool{}
+	for _, name := range got {
+		survivors[name] = true
+	}
+	missing := []string{}
+	for i := 0; i < adds; i++ {
+		name := fmt.Sprintf("added%02d", i)
+		if !survivors[name] {
+			missing = append(missing, name)
+		}
+	}
+	if len(missing) > 0 {
+		t.Fatalf("%d of %d concurrent Set calls were clobbered by a racing Delete: %v",
+			len(missing), adds, missing)
+	}
+	// ...and every churn key really was removed, so the deletes were not
+	// no-ops that would make the check above vacuous.
+	for i := 0; i < churn; i++ {
+		if survivors[fmt.Sprintf("churn%02d", i)] {
+			t.Fatalf("churn%02d survived; the deletes did nothing and this test proves nothing", i)
+		}
+	}
+}
+
+// ACROSS PROCESSES, which is the case that matters: a plan running with
+// max_workers > 1 spawns child PROCESSES, and an in-process mutex would not
+// have helped any of them. The race detector cannot see this one either — it is
+// two OS processes — so it is driven for real.
+func TestConcurrentSetAcrossProcesses(t *testing.T) {
+	if testing.Short() {
+		t.Skip("spawns processes")
+	}
+	helper := os.Getenv("ZERO_CREDSTORE_HELPER_DIR")
+	if helper != "" {
+		// Child mode: write our slice of the keys and exit.
+		store, err := New(Options{Dir: helper, Storage: "file"})
+		if err != nil {
+			os.Exit(3)
+		}
+		prefix := os.Getenv("ZERO_CREDSTORE_HELPER_PREFIX")
+		for i := 0; i < 25; i++ {
+			if err := store.Set(fmt.Sprintf("%s%02d", prefix, i), "v"); err != nil {
+				os.Exit(4)
+			}
+		}
+		os.Exit(0)
+	}
+
+	dir := t.TempDir()
+	const children = 4
+	var wg sync.WaitGroup
+	failures := make(chan string, children)
+	for c := 0; c < children; c++ {
+		wg.Add(1)
+		go func(c int) {
+			defer wg.Done()
+			cmd := exec.Command(os.Args[0], "-test.run=TestConcurrentSetAcrossProcesses", "-test.v")
+			cmd.Env = append(os.Environ(),
+				"ZERO_CREDSTORE_HELPER_DIR="+dir,
+				fmt.Sprintf("ZERO_CREDSTORE_HELPER_PREFIX=c%d_", c),
+			)
+			if out, err := cmd.CombinedOutput(); err != nil {
+				failures <- fmt.Sprintf("child %d: %v\n%s", c, err, out)
+			}
+		}(c)
+	}
+	wg.Wait()
+	close(failures)
+	for failure := range failures {
+		t.Fatal(failure)
+	}
+
+	store := fileStore(t, dir)
+	got, err := store.Providers()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(got) != children*25 {
+		t.Fatalf("kept %d of %d keys written by %d concurrent processes", len(got), children*25, children)
+	}
+}
+
+// The lock lives BESIDE the data file, never on it. write publishes by rename,
+// so a lock taken on the data file would be attached to an inode the next
+// writer has already replaced — every writer would appear to hold it.
+func TestTheLockIsNotTheDataFile(t *testing.T) {
+	dir := t.TempDir()
+	store := fileStore(t, dir)
+	if store.lockPath() == store.file {
+		t.Fatal("the lock is the data file; rename would carry it away")
+	}
+	if !strings.HasPrefix(filepath.Base(store.lockPath()), filepath.Base(store.file)) {
+		t.Fatalf("lock %q is not beside the data file %q", store.lockPath(), store.file)
+	}
+	if err := store.Set("p", "k"); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := os.Stat(store.lockPath()); err != nil {
+		t.Fatalf("the lock file was not created: %v", err)
+	}
+	// ...and it survives a write, since the rename replaces only the data file.
+	if err := store.Set("q", "k"); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := os.Stat(store.lockPath()); err != nil {
+		t.Fatalf("the lock file did not survive a write: %v", err)
+	}
+}
+
+// The lock is a security boundary, so the path where it CANNOT be taken needs
+// coverage too: an operation that could not lock must report that, never proceed
+// unserialized and never report success. Replacing the credential directory with
+// a regular file makes the lock's MkdirAll fail on every platform.
+func TestOperationsFailWhenTheLockCannotBeAcquired(t *testing.T) {
+	base := t.TempDir()
+	dir := filepath.Join(base, "creds")
+	store := fileStore(t, dir)
+	// Where the store expects its directory, put a regular file.
+	if err := os.WriteFile(dir, []byte("not a directory"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := store.Set("openai", "sk-test"); err == nil {
+		t.Error("Set reported success although the lock could not be acquired")
+	}
+	if _, err := store.Delete("openai"); err == nil {
+		t.Error("Delete reported success although the lock could not be acquired")
+	}
+	if _, _, err := store.Get("openai"); err == nil {
+		t.Error("Get reported success although the lock could not be acquired")
+	}
+	if _, err := store.Providers(); err == nil {
+		t.Error("Providers reported success although the lock could not be acquired")
+	}
+	// And nothing may have been written through the failed path.
+	if raw, err := os.ReadFile(dir); err != nil || string(raw) != "not a directory" {
+		t.Errorf("the blocking file was modified: %q (err %v)", raw, err)
+	}
+}

internal/credstore/credstore.go

@@ -9,6 +9,7 @@ package credstore
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -125,14 +126,27 @@ func (s *Store) Backend() string { return s.backend }
 func (s *Store) Encrypted() bool { return s.backend == "keyring" || s.backend == "encrypted-file" }
 
 // Set stores (or overwrites) the API key for provider.
-func (s *Store) Set(provider, key string) error {
+func (s *Store) Set(provider, key string) (err error) {
 	provider = normalizeProvider(provider)
 	if provider == "" {
 		return fmt.Errorf("credstore: provider is required")
 	}
 	if s.backend == "keyring" {
+		// The OS keyring serializes its own writes; the file lock guards the
+		// file backends only.
 		return s.kr.Set(keyringService, keyringPrefix+provider, key)
 	}
+	// READ AND WRITE UNDER ONE LOCK. Separately locking each half would still
+	// lose keys: two writers would each read the same map, each add their own
+	// provider, and the second rename would publish a file missing the first.
+	// Measured before this existed: 1 of 100 concurrent Set calls survived.
+	release, err := s.acquireFileLock(true)
+	if err != nil {
+		return err
+	}
+	// Joined, not chosen between: a release failure annotates the result instead
+	// of masking the write error that actually explains what went wrong.
+	defer func() { err = errors.Join(err, release()) }()
 	data, err := s.read()
 	if err != nil {
 		return err
@@ -142,7 +156,7 @@ func (s *Store) Set(provider, key string) error {
 }
 
 // Get returns the API key for provider and whether one is stored.
-func (s *Store) Get(provider string) (string, bool, error) {
+func (s *Store) Get(provider string) (value string, found bool, err error) {
 	provider = normalizeProvider(provider)
 	if provider == "" {
 		return "", false, nil
@@ -150,6 +164,15 @@ func (s *Store) Get(provider string) (string, bool, error) {
 	if s.backend == "keyring" {
 		return s.kr.Get(keyringService, keyringPrefix+provider)
 	}
+	// A shared lock, so a read serializes against a writer's publish. On unix
+	// the rename is atomic and this only prevents reading an empty file mid-swap;
+	// on Windows an unsynchronized reader holding the file open would block the
+	// writer's rename outright, so readers must coordinate through the same lock.
+	release, err := s.acquireFileLock(false)
+	if err != nil {
+		return "", false, err
+	}
+	defer func() { err = errors.Join(err, release()) }()
 	data, err := s.read()
 	if err != nil {
 		return "", false, err
@@ -159,7 +182,7 @@ func (s *Store) Get(provider string) (string, bool, error) {
 }
 
 // Delete removes the API key for provider, reporting whether one existed.
-func (s *Store) Delete(provider string) (bool, error) {
+func (s *Store) Delete(provider string) (existed bool, err error) {
 	provider = normalizeProvider(provider)
 	if provider == "" {
 		return false, nil
@@ -167,6 +190,13 @@ func (s *Store) Delete(provider string) (bool, error) {
 	if s.backend == "keyring" {
 		return s.kr.Delete(keyringService, keyringPrefix+provider)
 	}
+	// The same lock as Set: a delete is a read-modify-write too, and one racing
+	// a set would otherwise resurrect or erase an unrelated provider.
+	release, err := s.acquireFileLock(true)
+	if err != nil {
+		return false, err
+	}
+	defer func() { err = errors.Join(err, release()) }()
 	data, err := s.read()
 	if err != nil {
 		return false, err
@@ -179,17 +209,22 @@ func (s *Store) Delete(provider string) (bool, error) {
 }
 
 // Providers lists providers with a stored key (sorted), for display/audit.
-func (s *Store) Providers() ([]string, error) {
+func (s *Store) Providers() (names []string, err error) {
 	if s.backend == "keyring" {
 		// The OS keyring has no enumerate-by-prefix in our minimal surface; callers
 		// that need a list pass known provider names to Get. Return empty here.
 		return nil, nil
 	}
+	release, err := s.acquireFileLock(false)
+	if err != nil {
+		return nil, err
+	}
+	defer func() { err = errors.Join(err, release()) }()
 	data, err := s.read()
 	if err != nil {
 		return nil, err
 	}
-	names := make([]string, 0, len(data))
+	names = make([]string, 0, len(data))
 	for name := range data {
 		names = append(names, name)
 	}
@@ -264,6 +299,15 @@ func (s *Store) write(data map[string]string) error {
 	return nil
 }
 
+// lockPath is the advisory lock guarding a read-modify-write of the credential
+// file. Beside the data file, never the data file itself — write publishes by
+// rename and would carry the lock away with the old inode.
+func (s *Store) lockPath() string { return s.file + ".lock" }
+
+// filepathDir is filepath.Dir, named locally so the two platform lock files can
+// share it without either importing path/filepath for one call.
+func filepathDir(path string) string { return filepath.Dir(path) }
+
 func normalizeProvider(provider string) string {
 	return strings.ToLower(strings.TrimSpace(provider))
 }

internal/credstore/filelock_unix.go

@@ -0,0 +1,55 @@
+//go:build !windows
+
+package credstore
+
+import (
+	"errors"
+	"fmt"
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+// acquireFileLock takes an exclusive advisory lock (flock) so a read-modify-write
+// of the credential file is serialized against every other one — across
+// processes AND across goroutines, since flock is held per open file
+// description and two opens in one process contend exactly as two processes do.
+//
+// THE LOCK FILE IS SEPARATE FROM THE DATA FILE, and that is not tidiness. write
+// publishes by os.Rename, which replaces the inode; a lock taken on the data
+// file would be attached to an inode that the next writer has already replaced,
+// so every writer would appear to hold it. The lock lives on a file nothing
+// renames.
+func (s *Store) acquireFileLock(exclusive bool) (func() error, error) {
+	path := s.lockPath()
+	if err := os.MkdirAll(filepathDir(path), 0o700); err != nil {
+		return nil, fmt.Errorf("credstore: lock dir: %w", err)
+	}
+	file, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0o600)
+	if err != nil {
+		return nil, fmt.Errorf("credstore: open lock: %w", err)
+	}
+	// Writers take LOCK_EX; readers take LOCK_SH so they run concurrently with
+	// each other but still serialize against a writer's publish (see Get).
+	how := unix.LOCK_SH
+	if exclusive {
+		how = unix.LOCK_EX
+	}
+	if err := unix.Flock(int(file.Fd()), how); err != nil {
+		_ = file.Close()
+		return nil, fmt.Errorf("credstore: lock: %w", err)
+	}
+	return func() error {
+		// Close alone drops the flock, so the explicit unlock is belt-and-braces —
+		// but its failure is reported rather than swallowed, because a cleanup that
+		// did not complete must not be indistinguishable from one that did. The
+		// callers join this into their result, so it annotates a successful write
+		// instead of masking it.
+		unlockErr := unix.Flock(int(file.Fd()), unix.LOCK_UN)
+		closeErr := file.Close()
+		if err := errors.Join(unlockErr, closeErr); err != nil {
+			return fmt.Errorf("credstore: release lock: %w", err)
+		}
+		return nil
+	}, nil
+}

internal/credstore/filelock_windows.go

@@ -0,0 +1,55 @@
+//go:build windows
+
+package credstore
+
+import (
+	"errors"
+	"fmt"
+	"os"
+
+	"golang.org/x/sys/windows"
+)
+
+// acquireFileLock takes an exclusive OS lock (LockFileEx) so a read-modify-write
+// of the credential file is serialized, matching the flock behaviour on unix.
+//
+// The lock file is SEPARATE from the data file for the same reason: write
+// publishes by rename, and a lock on the renamed file would be attached to
+// something the next writer has already replaced.
+func (s *Store) acquireFileLock(exclusive bool) (func() error, error) {
+	path := s.lockPath()
+	if err := os.MkdirAll(filepathDir(path), 0o700); err != nil {
+		return nil, fmt.Errorf("credstore: lock dir: %w", err)
+	}
+	file, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0o600)
+	if err != nil {
+		return nil, fmt.Errorf("credstore: open lock: %w", err)
+	}
+	handle := windows.Handle(file.Fd())
+	overlapped := new(windows.Overlapped)
+	// A fixed 1-byte region, blocking (no LOCKFILE_FAIL_IMMEDIATELY) so a
+	// waiter queues rather than failing the operation. Writers pass
+	// LOCKFILE_EXCLUSIVE_LOCK; readers omit it (a shared lock) so they still
+	// serialize against a writer's publish — which matters more on Windows,
+	// where an unsynchronized reader holding the file open blocks the rename.
+	flags := uint32(0)
+	if exclusive {
+		flags = windows.LOCKFILE_EXCLUSIVE_LOCK
+	}
+	if err := windows.LockFileEx(handle, flags, 0, 1, 0, overlapped); err != nil {
+		_ = file.Close()
+		return nil, fmt.Errorf("credstore: lock: %w", err)
+	}
+	return func() error {
+		// Reported rather than swallowed, for the same reason as the unix side: a
+		// cleanup that did not complete must not look identical to one that did.
+		// It matters more here — on Windows the handle staying open is what blocks
+		// the next writer's rename, so a failed release has a visible consequence.
+		unlockErr := windows.UnlockFileEx(handle, 0, 1, 0, overlapped)
+		closeErr := file.Close()
+		if err := errors.Join(unlockErr, closeErr); err != nil {
+			return fmt.Errorf("credstore: release lock: %w", err)
+		}
+		return nil
+	}, nil
+}

internal/dictation/transcriber_deepgram.go

@@ -9,6 +9,7 @@ import (
 	"strconv"
 	"strings"
 
+	"github.com/Gitlawb/zero/internal/providers/providerio"
 	"github.com/coder/websocket"
 )
 
@@ -60,7 +61,15 @@ func (d *deepgramTranscriber) StreamTranscribe(ctx context.Context, chunks <-cha
 		HTTPHeader: http.Header{"Authorization": {"Token " + d.cfg.APIKey}},
 	})
 	if err != nil {
-		return "", fmt.Errorf("connecting to Deepgram: %w", err)
+		// Preserve the context.Canceled sentinel (it carries no key) so an
+		// Esc-abort during dial still matches the UI's errors.Is check. Key
+		// on ctx.Err() itself rather than unwrapping err: a cancellation can
+		// surface as a plain transport error (e.g. "closed network
+		// connection") rather than context.Canceled directly.
+		if ctx.Err() != nil {
+			return "", ctx.Err()
+		}
+		return "", fmt.Errorf("connecting to Deepgram: %s", providerio.Redact(err.Error(), d.cfg.APIKey))
 	}
 	defer conn.CloseNow()
 
@@ -68,15 +77,26 @@ func (d *deepgramTranscriber) StreamTranscribe(ctx context.Context, chunks <-cha
 	// so no conversion (unlike sherpa-onnx, which wants float32).
 	writeErrCh := make(chan error, 1)
 	go func() {
-		for chunk := range chunks {
-			if err := conn.Write(ctx, websocket.MessageBinary, chunk); err != nil {
-				writeErrCh <- err
+		// Select on ctx.Done() while waiting for the next chunk so a cancelled
+		// session does not leave this goroutine blocked on an open idle channel.
+		for {
+			select {
+			case <-ctx.Done():
+				writeErrCh <- ctx.Err()
 				return
+			case chunk, ok := <-chunks:
+				if !ok {
+					// CloseStream flushes any buffered audio and returns final
+					// results before Deepgram closes the socket.
+					writeErrCh <- conn.Write(ctx, websocket.MessageText, []byte(`{"type":"CloseStream"}`))
+					return
+				}
+				if err := conn.Write(ctx, websocket.MessageBinary, chunk); err != nil {
+					writeErrCh <- err
+					return
+				}
 			}
 		}
-		// CloseStream flushes any buffered audio and returns final results before
-		// Deepgram closes the socket.
-		writeErrCh <- conn.Write(ctx, websocket.MessageText, []byte(`{"type":"CloseStream"}`))
 	}()
 
 	// Deepgram results are per-utterance segments, not cumulative: accumulate the
@@ -100,7 +120,18 @@ func (d *deepgramTranscriber) StreamTranscribe(ctx context.Context, chunks <-cha
 				}
 			default:
 			}
-			return compose(), fmt.Errorf("Deepgram stream error: %w", err) //nolint:staticcheck // Preserve established user-facing error text.
+			// A user abort cancels the streaming context; the UI matches it
+			// with errors.Is(err, context.Canceled), so return the sentinel
+			// itself (it carries no key) instead of a flat redacted string.
+			// Key on ctx.Err() rather than unwrapping err: the writeErrCh
+			// swap above can replace err with a plain transport error (e.g.
+			// "closed network connection") that doesn't itself unwrap to
+			// context.Canceled even though the cancellation is what caused it.
+			if ctx.Err() != nil {
+				return compose(), ctx.Err()
+			}
+			//nolint:staticcheck // Preserve established user-facing error text.
+			return compose(), fmt.Errorf("Deepgram stream error: %s", providerio.Redact(err.Error(), d.cfg.APIKey))
 		}
 		if typ != websocket.MessageText {
 			continue

internal/dictation/transcriber_deepgram_test.go

@@ -0,0 +1,278 @@
+package dictation
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync"
+	"testing"
+
+	"github.com/coder/websocket"
+)
+
+// Non-cancellation dial failure: handshake returns 101 with an Upgrade header
+// equal to the API key so the dial error embeds the key and redaction must strip it.
+func TestDeepgramDialFailureRedactsKey(t *testing.T) {
+	const key = "sk-test-dial-key-abcdef"
+	baseURL := dialFailServerWithUpgrade(t, key)
+
+	tr, err := NewDeepgramTranscriber(DeepgramConfig{APIKey: key, BaseURL: baseURL})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	chunks := make(chan []byte)
+	close(chunks)
+	_, ferr := tr.StreamTranscribe(context.Background(), chunks, nil)
+	if ferr == nil {
+		t.Fatal("expected dial failure")
+	}
+	if errors.Is(ferr, context.Canceled) {
+		t.Fatalf("dial failure should not be context.Canceled: %v", ferr)
+	}
+	if strings.Contains(ferr.Error(), key) {
+		t.Errorf("API key leaked from dial failure: %v", ferr)
+	}
+	if !strings.Contains(ferr.Error(), "connecting to Deepgram") {
+		t.Errorf("expected dial-path error prefix, got: %v", ferr)
+	}
+}
+
+// dialFailServerWithUpgrade returns a ws URL whose handshake responds 101 with
+// Upgrade set to upgradeValue (not "websocket"), so websocket.Dial fails with
+// that value in the error string. Hijacks and closes immediately to avoid the
+// library's 3s body-drain timeout on failed dials.
+func dialFailServerWithUpgrade(t *testing.T, upgradeValue string) string {
+	t.Helper()
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		hj, ok := w.(http.Hijacker)
+		if !ok {
+			http.Error(w, "hijack not supported", http.StatusInternalServerError)
+			return
+		}
+		conn, bufrw, err := hj.Hijack()
+		if err != nil {
+			return
+		}
+		defer conn.Close()
+		_, _ = bufrw.WriteString("HTTP/1.1 101 Switching Protocols\r\n")
+		_, _ = bufrw.WriteString("Connection: Upgrade\r\n")
+		_, _ = bufrw.WriteString("Upgrade: " + upgradeValue + "\r\n\r\n")
+		_ = bufrw.Flush()
+	}))
+	t.Cleanup(srv.Close)
+	return "ws" + strings.TrimPrefix(srv.URL, "http")
+}
+
+func TestDeepgramStreamTranscribeErrorRedaction(t *testing.T) {
+	url := wsTestServer(t, func(ctx context.Context, c *websocket.Conn) {
+		// Drain the client's audio frames, then wait for CloseStream so the
+		// client has flushed its writes before we reject the connection. Closing
+		// immediately (before CloseStream) risks the client failing on a write
+		// error and never observing this API-key-bearing close reason.
+		for {
+			typ, data, err := c.Read(ctx)
+			if err != nil {
+				return
+			}
+			if typ == websocket.MessageText && strings.Contains(string(data), "CloseStream") {
+				break
+			}
+		}
+		c.Close(websocket.StatusPolicyViolation, "invalid key sk-test-key")
+	})
+
+	tr, err := NewDeepgramTranscriber(DeepgramConfig{APIKey: "sk-test-key", BaseURL: url})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	chunks := make(chan []byte, 1)
+	chunks <- make([]byte, 320)
+	close(chunks)
+	_, ferr := tr.StreamTranscribe(context.Background(), chunks, func(string, bool) {})
+	if ferr == nil {
+		t.Fatal("expected error")
+	}
+	if strings.Contains(ferr.Error(), "sk-test-key") {
+		t.Errorf("API key leaked: %v", ferr)
+	}
+}
+
+func TestDeepgramStreamTranscribeCancelKeepsSentinel(t *testing.T) {
+	firstFrame := make(chan struct{})
+	url := wsTestServer(t, func(ctx context.Context, c *websocket.Conn) {
+		// Hold the connection open, never answering, so the client blocks in
+		// Read until its context is cancelled (the Esc-abort path).
+		var once sync.Once
+		for {
+			if _, _, err := c.Read(ctx); err != nil {
+				return
+			}
+			once.Do(func() { close(firstFrame) })
+		}
+	})
+
+	tr, err := NewDeepgramTranscriber(DeepgramConfig{APIKey: "sk-test-key", BaseURL: url})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	chunks := make(chan []byte, 1)
+	defer close(chunks)
+	chunks <- make([]byte, 320)
+	// The channel stays open: the session is live when the user aborts.
+	errCh := make(chan error, 1)
+	go func() {
+		_, ferr := tr.StreamTranscribe(ctx, chunks, nil)
+		errCh <- ferr
+	}()
+
+	select {
+	case <-firstFrame:
+		cancel()
+		ferr := <-errCh
+		if !errors.Is(ferr, context.Canceled) {
+			t.Fatalf("cancelled stream error lost the context.Canceled sentinel: %v", ferr)
+		}
+	case ferr := <-errCh:
+		t.Fatalf("StreamTranscribe failed early instead of blocking: %v", ferr)
+	}
+}
+
+// Esc can cancel while the WebSocket dial is still pending. The dial error is
+// redacted with %s, so we must return ctx.Err() rather than a flat string.
+func TestDeepgramStreamTranscribeDialCancelKeepsSentinel(t *testing.T) {
+	tr, err := NewDeepgramTranscriber(DeepgramConfig{
+		APIKey:  "sk-test-key",
+		BaseURL: "ws://127.0.0.1:1", // never reached; ctx is already cancelled
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	chunks := make(chan []byte)
+	defer close(chunks)
+
+	_, ferr := tr.StreamTranscribe(ctx, chunks, nil)
+	if !errors.Is(ferr, context.Canceled) {
+		t.Fatalf("dial-cancel lost the context.Canceled sentinel: %v", ferr)
+	}
+}
+
+// Esc right after accept can race the first write or the first Read; both
+// setup/write redaction sites must still yield context.Canceled.
+func TestDeepgramStreamTranscribeStartupCancelKeepsSentinel(t *testing.T) {
+	accepted := make(chan struct{})
+	url := wsTestServer(t, func(ctx context.Context, c *websocket.Conn) {
+		close(accepted)
+		for {
+			if _, _, err := c.Read(ctx); err != nil {
+				return
+			}
+		}
+	})
+
+	tr, err := NewDeepgramTranscriber(DeepgramConfig{APIKey: "sk-test-key", BaseURL: url})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	chunks := make(chan []byte, 1)
+	defer close(chunks)
+	// No frames yet: the writer blocks on chunks or the reader blocks on Read.
+	errCh := make(chan error, 1)
+	go func() {
+		_, ferr := tr.StreamTranscribe(ctx, chunks, nil)
+		errCh <- ferr
+	}()
+
+	select {
+	case <-accepted:
+		cancel()
+		ferr := <-errCh
+		if !errors.Is(ferr, context.Canceled) {
+			t.Fatalf("startup-cancel lost the context.Canceled sentinel: %v", ferr)
+		}
+	case ferr := <-errCh:
+		t.Fatalf("StreamTranscribe failed before accept: %v", ferr)
+	}
+}
+
+// TestDeepgramStreamErrorRedactsHeaderShapedKey exercises the same stream-error
+// redaction path as TestDeepgramStreamTranscribeErrorRedaction, with a close
+// reason that embeds the key next to an X-Api-Key-shaped header label.
+func TestDeepgramStreamErrorRedactsHeaderShapedKey(t *testing.T) {
+	url := wsTestServer(t, func(ctx context.Context, c *websocket.Conn) {
+		for {
+			typ, data, err := c.Read(ctx)
+			if err != nil {
+				return
+			}
+			if typ == websocket.MessageText && strings.Contains(string(data), "CloseStream") {
+				break
+			}
+		}
+		c.Close(websocket.StatusPolicyViolation, "X-Api-Key: sk-custom-secret-key-1234567890 failed")
+	})
+
+	tr, err := NewDeepgramTranscriber(DeepgramConfig{APIKey: "sk-custom-secret-key-1234567890", BaseURL: url})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	chunks := make(chan []byte, 1)
+	chunks <- make([]byte, 320)
+	close(chunks)
+	_, ferr := tr.StreamTranscribe(context.Background(), chunks, func(string, bool) {})
+	if ferr == nil {
+		t.Fatal("expected error")
+	}
+	if strings.Contains(ferr.Error(), "sk-custom-secret-key-1234567890") {
+		t.Errorf("Custom header API key leaked: %v", ferr)
+	}
+}
+
+func TestDeepgramSinglePassRedaction(t *testing.T) {
+	url := wsTestServer(t, func(ctx context.Context, c *websocket.Conn) {
+		for {
+			typ, data, err := c.Read(ctx)
+			if err != nil {
+				return
+			}
+			if typ == websocket.MessageText && strings.Contains(string(data), "CloseStream") {
+				break
+			}
+		}
+		c.Close(websocket.StatusPolicyViolation, "error with sk-key1234567890abcdef1234")
+	})
+
+	tr, err := NewDeepgramTranscriber(DeepgramConfig{APIKey: "sk-key1234567890abcdef1234", BaseURL: url})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	chunks := make(chan []byte, 1)
+	chunks <- make([]byte, 320)
+	close(chunks)
+	_, ferr := tr.StreamTranscribe(context.Background(), chunks, func(string, bool) {})
+	if ferr == nil {
+		t.Fatal("expected error")
+	}
+	got := ferr.Error()
+	if strings.Contains(got, "sk-key1234567890abcdef1234") {
+		t.Fatalf("API key leaked into stream error: %q", got)
+	}
+	// One key occurrence must produce exactly one redaction marker (no double wrap).
+	if strings.Count(got, "[REDACTED]") != 1 {
+		t.Fatalf("redaction markers in %q: want exactly 1 [REDACTED]", got)
+	}
+}

internal/dictation/transcriber_openai_realtime.go

@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"strings"
 
+	"github.com/Gitlawb/zero/internal/providers/providerio"
 	"github.com/coder/websocket"
 )
 
@@ -22,6 +23,10 @@ type OpenAIRealtimeConfig struct {
 	Model  string // default "gpt-4o-transcribe"
 	// BaseURL overrides the wss endpoint (tests point it at a fake server).
 	BaseURL string
+	// writeErrInjector, when set, is consulted before each JSON websocket write.
+	// Used by same-package tests to force controllable write failures that embed
+	// secrets; production callers leave it nil.
+	writeErrInjector func() error
 }
 
 type openAIRealtimeTranscriber struct {
@@ -59,7 +64,15 @@ func (o *openAIRealtimeTranscriber) StreamTranscribe(ctx context.Context, chunks
 		},
 	})
 	if err != nil {
-		return "", fmt.Errorf("connecting to OpenAI Realtime: %w", err)
+		// Preserve the context.Canceled sentinel (it carries no key) so an
+		// Esc-abort during dial still matches the UI's errors.Is check. Key
+		// on ctx.Err() itself rather than unwrapping err: a cancellation can
+		// surface as a plain transport error (e.g. "closed network
+		// connection") rather than context.Canceled directly.
+		if ctx.Err() != nil {
+			return "", ctx.Err()
+		}
+		return "", fmt.Errorf("connecting to OpenAI Realtime: %s", providerio.Redact(err.Error(), o.cfg.APIKey))
 	}
 	defer conn.CloseNow()
 
@@ -73,24 +86,53 @@ func (o *openAIRealtimeTranscriber) StreamTranscribe(ctx context.Context, chunks
 			},
 		},
 	}
-	if err := writeJSON(ctx, conn, sessionUpdate); err != nil {
-		return "", fmt.Errorf("configuring OpenAI Realtime session: %w", err)
+	if err := o.writeJSON(ctx, conn, sessionUpdate); err != nil {
+		// Same cancellation short-circuit as the dial above: an Esc-abort
+		// while the session update is in flight must stay context.Canceled.
+		if ctx.Err() != nil {
+			return "", ctx.Err()
+		}
+		return "", fmt.Errorf("configuring OpenAI Realtime session: %s", providerio.Redact(err.Error(), o.cfg.APIKey))
 	}
 
 	writeErrCh := make(chan error, 1)
 	go func() {
-		for chunk := range chunks {
-			appendMsg := map[string]any{
-				"type":  "input_audio_buffer.append",
-				"audio": base64.StdEncoding.EncodeToString(chunk),
-			}
-			if err := writeJSON(ctx, conn, appendMsg); err != nil {
-				writeErrCh <- err
+		// Select on ctx.Done() while waiting for the next chunk so a cancelled
+		// session does not leave this goroutine blocked on an open idle channel.
+		for {
+			select {
+			case <-ctx.Done():
+				writeErrCh <- ctx.Err()
 				return
+			case chunk, ok := <-chunks:
+				if !ok {
+					// Commit the buffered audio to force final transcription.
+					if err := o.writeJSON(ctx, conn, map[string]any{"type": "input_audio_buffer.commit"}); err != nil {
+						writeErrCh <- err
+						// Unblock the reader: without a close, conn.Read stays
+						// parked on a silent peer and the error is never drained
+						// from writeErrCh. CloseNow aborts instead of waiting on
+						// the close handshake, which a silent peer never answers.
+						conn.CloseNow()
+						return
+					}
+					writeErrCh <- nil
+					return
+				}
+				appendMsg := map[string]any{
+					"type":  "input_audio_buffer.append",
+					"audio": base64.StdEncoding.EncodeToString(chunk),
+				}
+				if err := o.writeJSON(ctx, conn, appendMsg); err != nil {
+					writeErrCh <- err
+					// Same unblocking close as the commit path: a server that
+					// goes silent after session setup would otherwise leave the
+					// reader blocked in conn.Read with the error undrained.
+					conn.CloseNow()
+					return
+				}
 			}
 		}
-		// Commit the buffered audio to force final transcription of the utterance.
-		writeErrCh <- writeJSON(ctx, conn, map[string]any{"type": "input_audio_buffer.commit"})
 	}()
 
 	// OpenAI deltas are incremental (append), unlike Deepgram/sherpa's cumulative
@@ -113,7 +155,17 @@ func (o *openAIRealtimeTranscriber) StreamTranscribe(ctx context.Context, chunks
 				}
 			default:
 			}
-			return compose(), fmt.Errorf("OpenAI Realtime stream error: %w", err)
+			// A user abort cancels the streaming context; the UI matches it
+			// with errors.Is(err, context.Canceled), so return the sentinel
+			// itself (it carries no key) instead of a flat redacted string.
+			// Key on ctx.Err() rather than unwrapping err: the writeErrCh
+			// swap above can replace err with a plain transport error (e.g.
+			// "closed network connection") that doesn't itself unwrap to
+			// context.Canceled even though the cancellation is what caused it.
+			if ctx.Err() != nil {
+				return compose(), ctx.Err()
+			}
+			return compose(), fmt.Errorf("OpenAI Realtime stream error: %s", providerio.Redact(err.Error(), o.cfg.APIKey))
 		}
 		if typ != websocket.MessageText {
 			continue
@@ -125,6 +177,12 @@ func (o *openAIRealtimeTranscriber) StreamTranscribe(ctx context.Context, chunks
 			if onPartial != nil {
 				onPartial(compose(), false)
 			}
+			// onPartial may deliver the partial that makes the TUI cancel
+			// (Esc). Observe that before the next Read, which can already
+			// have a racing OpenAI error frame buffered.
+			if ctx.Err() != nil {
+				return compose(), ctx.Err()
+			}
 		case realtimeCompleted:
 			// A completed item replaces the in-progress delta buffer with the
 			// server's authoritative transcript for that segment.
@@ -138,6 +196,9 @@ func (o *openAIRealtimeTranscriber) StreamTranscribe(ctx context.Context, chunks
 			if onPartial != nil {
 				onPartial(compose(), true)
 			}
+			if ctx.Err() != nil {
+				return compose(), ctx.Err()
+			}
 			// Once we've committed the buffer (user stopped) and the server has
 			// returned a completed transcription, the utterance is done.
 			if committed {
@@ -147,7 +208,15 @@ func (o *openAIRealtimeTranscriber) StreamTranscribe(ctx context.Context, chunks
 		case realtimeCommitted:
 			committed = true
 		case realtimeError:
-			return compose(), fmt.Errorf("OpenAI Realtime error: %s", evt.text)
+			// Esc can race an incoming error event: conn.Read may already have
+			// the OpenAI error in hand by the time cancellation lands. Key on
+			// ctx.Err() first, same as every other return point in this loop,
+			// so a cancel that wins the race still surfaces as context.Canceled
+			// instead of a spurious redacted failure alongside it.
+			if ctx.Err() != nil {
+				return compose(), ctx.Err()
+			}
+			return compose(), fmt.Errorf("OpenAI Realtime error: %s", providerio.Redact(evt.text, o.cfg.APIKey))
 		}
 		// The writer signals commit completion out of band; observe it so a
 		// stop with no further audio still flips `committed`.
@@ -155,6 +224,10 @@ func (o *openAIRealtimeTranscriber) StreamTranscribe(ctx context.Context, chunks
 		case werr := <-writeErrCh:
 			if werr == nil {
 				committed = true
+			} else if ctx.Err() != nil {
+				return compose(), ctx.Err()
+			} else {
+				return compose(), fmt.Errorf("OpenAI Realtime stream error: %s", providerio.Redact(werr.Error(), o.cfg.APIKey))
 			}
 		default:
 		}
@@ -201,6 +274,15 @@ func parseRealtimeEvent(data []byte) realtimeEvent {
 	return realtimeEvent{kind: realtimeOther}
 }
 
+func (o *openAIRealtimeTranscriber) writeJSON(ctx context.Context, conn *websocket.Conn, v any) error {
+	if o.cfg.writeErrInjector != nil {
+		if err := o.cfg.writeErrInjector(); err != nil {
+			return err
+		}
+	}
+	return writeJSON(ctx, conn, v)
+}
+
 func writeJSON(ctx context.Context, conn *websocket.Conn, v any) error {
 	data, err := json.Marshal(v)
 	if err != nil {

internal/dictation/transcriber_openai_realtime_test.go

@@ -0,0 +1,437 @@
+package dictation
+
+import (
+	"context"
+	"errors"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/coder/websocket"
+)
+
+// Non-cancellation dial failure: handshake returns 101 with an Upgrade header
+// equal to the API key so the dial error embeds the key and redaction must strip it.
+func TestOpenAIRealtimeDialFailureRedactsKey(t *testing.T) {
+	const key = "sk-test-dial-key-abcdef"
+	baseURL := dialFailServerWithUpgrade(t, key)
+
+	tr, err := NewOpenAIRealtimeTranscriber(OpenAIRealtimeConfig{APIKey: key, BaseURL: baseURL})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	chunks := make(chan []byte)
+	close(chunks)
+	_, ferr := tr.StreamTranscribe(context.Background(), chunks, nil)
+	if ferr == nil {
+		t.Fatal("expected dial failure")
+	}
+	if errors.Is(ferr, context.Canceled) {
+		t.Fatalf("dial failure should not be context.Canceled: %v", ferr)
+	}
+	if strings.Contains(ferr.Error(), key) {
+		t.Errorf("API key leaked from dial failure: %v", ferr)
+	}
+	if !strings.Contains(ferr.Error(), "connecting to OpenAI Realtime") {
+		t.Errorf("expected dial-path error prefix, got: %v", ferr)
+	}
+}
+
+// Session-configuration write fails after dial: inject a write error that embeds
+// the API key (peer close cannot reach this path reliably — the session write
+// always lands in the kernel buffer first) and assert redaction.
+func TestOpenAIRealtimeSessionConfigFailureRedactsKey(t *testing.T) {
+	const key = "sk-test-session-key-abcdef"
+	url := wsTestServer(t, func(ctx context.Context, c *websocket.Conn) {
+		// Hold open; the client fails on the injected session write before reading.
+		<-ctx.Done()
+	})
+
+	tr, err := NewOpenAIRealtimeTranscriber(OpenAIRealtimeConfig{
+		APIKey:  key,
+		BaseURL: url,
+		writeErrInjector: func() error {
+			return errors.New("invalid API key " + key)
+		},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	chunks := make(chan []byte)
+	close(chunks)
+	_, ferr := tr.StreamTranscribe(context.Background(), chunks, nil)
+	if ferr == nil {
+		t.Fatal("expected session-config failure")
+	}
+	if errors.Is(ferr, context.Canceled) {
+		t.Fatalf("session-config failure should not be context.Canceled: %v", ferr)
+	}
+	if strings.Contains(ferr.Error(), key) {
+		t.Errorf("API key leaked from session-config failure: %v", ferr)
+	}
+	if !strings.Contains(ferr.Error(), "configuring OpenAI Realtime session") {
+		t.Errorf("expected session-config error prefix, got: %v", ferr)
+	}
+}
+
+// Asynchronous writer failure: session update succeeds, then the audio writer
+// injects a key-bearing write error. The server keeps the connection open and
+// emits a delta so the reader loop observes writeErrCh (not a peer close).
+func TestOpenAIRealtimeWriterFailureRedactsKey(t *testing.T) {
+	const key = "sk-test-writer-key-abcdef"
+	sessionDone := make(chan struct{})
+	url := wsTestServer(t, func(ctx context.Context, c *websocket.Conn) {
+		if _, _, err := c.Read(ctx); err != nil {
+			return
+		}
+		close(sessionDone)
+		// Keep reading and emit a delta so the client processes an event and
+		// drains writeErrCh while the connection is still open.
+		_ = c.Write(ctx, websocket.MessageText, []byte(
+			`{"type":"conversation.item.input_audio_transcription.delta","delta":"hi"}`,
+		))
+		for {
+			if _, _, err := c.Read(ctx); err != nil {
+				return
+			}
+		}
+	})
+
+	var writes atomic.Int32
+	tr, err := NewOpenAIRealtimeTranscriber(OpenAIRealtimeConfig{
+		APIKey:  key,
+		BaseURL: url,
+		writeErrInjector: func() error {
+			// First write is session.update; fail subsequent audio/commit writes.
+			if writes.Add(1) == 1 {
+				return nil
+			}
+			return errors.New("invalid API key " + key)
+		},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	chunks := make(chan []byte, 1)
+	chunks <- make([]byte, 480)
+	// Leave open after the first frame so the writer hits the injected error
+	// on that append rather than a clean commit.
+
+	done := make(chan error, 1)
+	go func() {
+		_, ferr := tr.StreamTranscribe(context.Background(), chunks, func(string, bool) {})
+		done <- ferr
+	}()
+
+	var ferr error
+	select {
+	case ferr = <-done:
+	case <-time.After(5 * time.Second):
+		close(chunks)
+		t.Fatal("StreamTranscribe did not complete after writer failure")
+	}
+	close(chunks)
+
+	if ferr == nil {
+		t.Fatal("expected writer failure")
+	}
+	if errors.Is(ferr, context.Canceled) {
+		t.Fatalf("writer failure should not be context.Canceled: %v", ferr)
+	}
+	if strings.Contains(ferr.Error(), key) {
+		t.Errorf("API key leaked from writer failure: %v", ferr)
+	}
+	if !strings.Contains(ferr.Error(), "OpenAI Realtime stream error") {
+		t.Errorf("expected stream/writer error prefix, got: %v", ferr)
+	}
+	select {
+	case <-sessionDone:
+	default:
+		// Session may race the injected audio write; prefix assertion above is enough.
+	}
+}
+
+// Writer failure with a silent server: the peer never sends a frame after
+// session setup, so the reader is parked in conn.Read. The writer must close
+// the connection on failure or the writeErrCh error is never observed and
+// StreamTranscribe blocks forever.
+func TestOpenAIRealtimeWriterFailureUnblocksSilentServer(t *testing.T) {
+	const key = "sk-test-silent-writer-key-abcdef"
+	url := wsTestServer(t, func(ctx context.Context, c *websocket.Conn) {
+		// Hold the connection open without ever writing a frame.
+		<-ctx.Done()
+	})
+
+	var writes atomic.Int32
+	tr, err := NewOpenAIRealtimeTranscriber(OpenAIRealtimeConfig{
+		APIKey:  key,
+		BaseURL: url,
+		writeErrInjector: func() error {
+			// First write is session.update; fail the subsequent append write.
+			if writes.Add(1) == 1 {
+				return nil
+			}
+			return errors.New("invalid API key " + key)
+		},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	chunks := make(chan []byte, 1)
+	chunks <- make([]byte, 480)
+	// Leave the channel open: the writer must fail on the append, not the commit.
+	done := make(chan error, 1)
+	go func() {
+		_, ferr := tr.StreamTranscribe(ctx, chunks, func(string, bool) {})
+		done <- ferr
+	}()
+
+	select {
+	case ferr := <-done:
+		if ferr == nil {
+			t.Fatal("expected writer failure")
+		}
+		if errors.Is(ferr, context.Canceled) {
+			t.Fatalf("writer failure should not be context.Canceled: %v", ferr)
+		}
+		if strings.Contains(ferr.Error(), key) {
+			t.Errorf("API key leaked from writer failure: %v", ferr)
+		}
+		if !strings.Contains(ferr.Error(), "OpenAI Realtime stream error") {
+			t.Errorf("expected stream/writer error prefix, got: %v", ferr)
+		}
+	case <-time.After(5 * time.Second):
+		close(chunks)
+		t.Fatal("StreamTranscribe did not unblock after writer failure with a silent server")
+	}
+}
+
+func TestOpenAIRealtimeStreamTranscribeErrorRedaction(t *testing.T) {
+	url := wsTestServer(t, func(ctx context.Context, c *websocket.Conn) {
+		defer c.Close(websocket.StatusNormalClosure, "")
+		for {
+			typ, _, err := c.Read(ctx)
+			if err != nil {
+				return
+			}
+			if typ != websocket.MessageText {
+				continue
+			}
+			_ = c.Write(ctx, websocket.MessageText, []byte(`{"type":"error","error":{"message":"invalid API key sk-test-key"}}`))
+		}
+	})
+
+	tr, err := NewOpenAIRealtimeTranscriber(OpenAIRealtimeConfig{APIKey: "sk-test-key", BaseURL: url})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	chunks := make(chan []byte, 1)
+	chunks <- make([]byte, 480)
+	close(chunks)
+	_, ferr := tr.StreamTranscribe(context.Background(), chunks, func(string, bool) {})
+	if ferr == nil {
+		t.Fatal("expected error")
+	}
+	if strings.Contains(ferr.Error(), "sk-test-key") {
+		t.Errorf("API key leaked: %v", ferr)
+	}
+}
+
+func TestOpenAIRealtimeStreamTranscribeCancelKeepsSentinel(t *testing.T) {
+	firstFrame := make(chan struct{})
+	url := wsTestServer(t, func(ctx context.Context, c *websocket.Conn) {
+		// Hold the connection open, never answering, so the client blocks in
+		// Read until its context is cancelled (the Esc-abort path).
+		var once sync.Once
+		for {
+			if _, _, err := c.Read(ctx); err != nil {
+				return
+			}
+			once.Do(func() { close(firstFrame) })
+		}
+	})
+
+	tr, err := NewOpenAIRealtimeTranscriber(OpenAIRealtimeConfig{APIKey: "sk-test-key", BaseURL: url})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	chunks := make(chan []byte, 1)
+	defer close(chunks)
+	chunks <- make([]byte, 480)
+	// The channel stays open: the session is live when the user aborts.
+	errCh := make(chan error, 1)
+	go func() {
+		_, ferr := tr.StreamTranscribe(ctx, chunks, nil)
+		errCh <- ferr
+	}()
+
+	select {
+	case <-firstFrame:
+		cancel()
+		ferr := <-errCh
+		if !errors.Is(ferr, context.Canceled) {
+			t.Fatalf("cancelled stream error lost the context.Canceled sentinel: %v", ferr)
+		}
+	case ferr := <-errCh:
+		t.Fatalf("StreamTranscribe failed early instead of blocking: %v", ferr)
+	}
+}
+
+// Esc can cancel while the WebSocket dial is still pending. The dial error is
+// redacted with %s, so we must return ctx.Err() rather than a flat string.
+func TestOpenAIRealtimeStreamTranscribeDialCancelKeepsSentinel(t *testing.T) {
+	tr, err := NewOpenAIRealtimeTranscriber(OpenAIRealtimeConfig{
+		APIKey:  "sk-test-key",
+		BaseURL: "ws://127.0.0.1:1", // never reached; ctx is already cancelled
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	chunks := make(chan []byte)
+	defer close(chunks)
+
+	_, ferr := tr.StreamTranscribe(ctx, chunks, nil)
+	if !errors.Is(ferr, context.Canceled) {
+		t.Fatalf("dial-cancel lost the context.Canceled sentinel: %v", ferr)
+	}
+}
+
+// Esc right after accept can hit the session-update write or the first Read;
+// both redaction sites must still yield context.Canceled.
+func TestOpenAIRealtimeStreamTranscribeStartupCancelKeepsSentinel(t *testing.T) {
+	accepted := make(chan struct{})
+	url := wsTestServer(t, func(ctx context.Context, c *websocket.Conn) {
+		close(accepted)
+		// Do not read: leave the client in session-update write or first Read.
+		<-ctx.Done()
+	})
+
+	tr, err := NewOpenAIRealtimeTranscriber(OpenAIRealtimeConfig{APIKey: "sk-test-key", BaseURL: url})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	chunks := make(chan []byte, 1)
+	defer close(chunks)
+	errCh := make(chan error, 1)
+	go func() {
+		_, ferr := tr.StreamTranscribe(ctx, chunks, nil)
+		errCh <- ferr
+	}()
+
+	select {
+	case <-accepted:
+		cancel()
+		ferr := <-errCh
+		if !errors.Is(ferr, context.Canceled) {
+			t.Fatalf("startup-cancel lost the context.Canceled sentinel: %v", ferr)
+		}
+	case ferr := <-errCh:
+		t.Fatalf("StreamTranscribe failed before accept: %v", ferr)
+	}
+}
+
+// Cancel while the writer is blocked on more chunks. Whichever path observes
+// the cancellation first (the blocked conn.Read or the writeErrCh drain) must
+// return context.Canceled rather than a redacted flat string.
+func TestOpenAIRealtimeStreamTranscribeWriteCancelKeepsSentinel(t *testing.T) {
+	sessionReceived := make(chan struct{})
+	url := wsTestServer(t, func(ctx context.Context, c *websocket.Conn) {
+		if _, _, err := c.Read(ctx); err != nil {
+			return
+		}
+		close(sessionReceived)
+		for {
+			if _, _, err := c.Read(ctx); err != nil {
+				return
+			}
+		}
+	})
+
+	tr, err := NewOpenAIRealtimeTranscriber(OpenAIRealtimeConfig{APIKey: "sk-test-key", BaseURL: url})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	chunks := make(chan []byte, 1)
+	chunks <- make([]byte, 480)
+	defer close(chunks)
+
+	errCh := make(chan error, 1)
+	go func() {
+		_, ferr := tr.StreamTranscribe(ctx, chunks, nil)
+		errCh <- ferr
+	}()
+
+	select {
+	case <-sessionReceived:
+		cancel()
+		ferr := <-errCh
+		if !errors.Is(ferr, context.Canceled) {
+			t.Fatalf("write-path cancel lost the context.Canceled sentinel: %v", ferr)
+		}
+	case ferr := <-errCh:
+		t.Fatalf("StreamTranscribe failed early instead of blocking: %v", ferr)
+	}
+}
+
+// Esc can race an incoming OpenAI error event. conn.Read may already have
+// the error frame in hand by the time the cancellation lands. The server
+// fires a delta immediately followed by the error, back to back. Cancel from
+// inside the delta callback (same path the TUI uses when a partial triggers
+// Esc handling) so the cancel is observed before the next event is processed.
+// The returned error must still be context.Canceled, not the redacted OpenAI
+// error.
+func TestOpenAIRealtimeStreamTranscribeErrorRaceKeepsSentinel(t *testing.T) {
+	url := wsTestServer(t, func(ctx context.Context, c *websocket.Conn) {
+		if _, _, err := c.Read(ctx); err != nil {
+			return
+		}
+		_ = c.Write(ctx, websocket.MessageText, []byte(
+			`{"type":"conversation.item.input_audio_transcription.delta","delta":"hi"}`,
+		))
+		_ = c.Write(ctx, websocket.MessageText, []byte(
+			`{"type":"error","error":{"message":"invalid API key sk-test-key"}}`,
+		))
+		<-ctx.Done()
+	})
+
+	tr, err := NewOpenAIRealtimeTranscriber(OpenAIRealtimeConfig{APIKey: "sk-test-key", BaseURL: url})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	chunks := make(chan []byte, 1)
+	defer close(chunks)
+	chunks <- make([]byte, 480)
+	var once sync.Once
+	_, ferr := tr.StreamTranscribe(ctx, chunks, func(string, bool) {
+		// Cancel synchronously from the partial callback, before the
+		// stream loop continues to the already-buffered error frame.
+		once.Do(cancel)
+	})
+	if !errors.Is(ferr, context.Canceled) {
+		t.Fatalf("StreamTranscribe error = %v, want context.Canceled (cancel must win over a racing OpenAI error event)", ferr)
+	}
+}

internal/execution/process_unix.go

@@ -6,6 +6,8 @@ import (
 	"errors"
 	"fmt"
 	"os/exec"
+	"strconv"
+	"strings"
 	"syscall"
 	"time"
 )
@@ -38,12 +40,45 @@ func KillProcessTree(pid int) error {
 // TerminateProcessTree requests graceful termination, then force-kills the
 // process tree after grace. Callers retain their distinct persistence models;
 // this function owns only the OS lifecycle primitive.
+//
+// The signal target is REDISCOVERED here via processSignalTarget(pid), which
+// asks the OS for pid's current group. A caller that already knows pid was
+// configured as its own group leader at launch (e.g. via ConfigureProcessGroup)
+// should use TerminateProcessGroup instead — see its doc comment for why this
+// rediscovery is fragile once the leader may have already exited.
 func TerminateProcessTree(pid int, grace, poll time.Duration) error {
 	target, err := processSignalTarget(pid)
 	if err != nil {
 		return err
 	}
-	alive := func() bool { return syscall.Kill(target, syscall.Signal(0)) == nil }
+	return terminateTarget(pid, target, grace, poll)
+}
+
+// TerminateProcessGroup is like TerminateProcessTree, but for a caller that
+// already knows pid is (or was, at launch) its own process-group leader — e.g.
+// a command started after ConfigureProcessGroup(cmd), which sets Setpgid so
+// cmd.Process.Pid always leads its own group at the moment it is signalled.
+//
+// TerminateProcessTree instead rediscovers the group via syscall.Getpgid(pid)
+// at call time. On Darwin, that lookup can return ESRCH once an unreaped group
+// leader has already exited, even though live descendants remain in the group
+// it configured — TerminateProcessTree would then silently fall back to
+// signalling only the (already dead) leader PID and leave those descendants
+// running. Skipping rediscovery in favor of the launch-time invariant avoids
+// that: the negative PID is used directly, regardless of whether the leader is
+// still alive to be looked up.
+func TerminateProcessGroup(pid int, grace, poll time.Duration) error {
+	if pid <= 1 {
+		return fmt.Errorf("refusing to signal invalid pid %d", pid)
+	}
+	return terminateTarget(pid, -pid, grace, poll)
+}
+
+// terminateTarget signals target (an individual PID or, negative, a process
+// group) with SIGTERM then, after grace, SIGKILL. reportPid identifies the
+// original process in error messages regardless of which form target takes.
+func terminateTarget(reportPid, target int, grace, poll time.Duration) error {
+	alive := func() bool { return signalTargetRunning(target) }
 	if err := syscall.Kill(target, syscall.SIGTERM); err != nil {
 		if errors.Is(err, syscall.ESRCH) {
 			return nil
@@ -77,11 +112,91 @@ func TerminateProcessTree(pid int, grace, poll time.Duration) error {
 		time.Sleep(poll)
 	}
 	if alive() {
-		return fmt.Errorf("process %d did not exit after SIGKILL", pid)
+		return fmt.Errorf("process %d did not exit after SIGKILL", reportPid)
 	}
 	return nil
 }
 
+// signalTargetRunning reports whether the signal target still has a process that
+// is actually RUNNING, as opposed to one waiting to be reaped.
+//
+// kill(2) with signal 0 succeeds for a zombie: the PID still exists until its
+// parent collects it. That matters because the target here is usually a process
+// GROUP, and a terminated leader's child is briefly a zombie before init/launchd
+// reaps it. Treating that window as "still alive" made termination sit through
+// both grace periods, SIGKILL an already-dead group, and then report
+// "did not exit after SIGKILL" for a tree that had in fact stopped — turning a
+// successful cleanup into a spurious failure (and a flaky one, since it depends on
+// reap timing).
+//
+// Zombie detection goes through ps, which is available on every Unix we target and
+// avoids a /proc dependency Darwin does not have. It is only consulted when the
+// cheap kill check says something is still there, so the common path costs nothing
+// extra. If ps cannot be run or its output cannot be parsed, the conservative
+// pre-existing answer (the kill result) stands.
+func signalTargetRunning(target int) bool {
+	if syscall.Kill(target, syscall.Signal(0)) != nil {
+		return false
+	}
+	// A negative target is a process GROUP: check whether any member is
+	// non-zombie. A positive target is an individual PID that is NOT its own
+	// group leader (processSignalTarget's fallback) — its actual PGID differs
+	// from its own PID, so matching rows by PGID here would look for a group
+	// that doesn't exist and always report "unknown" (conservatively alive).
+	// Check its own PID's state instead.
+	var running, ok bool
+	if target < 0 {
+		running, ok = processGroupHasRunningMember(-target)
+	} else {
+		running, ok = processIsRunning(target)
+	}
+	if !ok {
+		return true
+	}
+	return running
+}
+
+// processGroupHasRunningMember reports whether any member of pgid is in a state
+// other than zombie. ok is false when the group's states could not be determined.
+func processGroupHasRunningMember(pgid int) (running bool, ok bool) {
+	return processTableStateMatches(func(_, rowPgid int) bool { return rowPgid == pgid })
+}
+
+// processIsRunning reports whether pid itself is in a state other than zombie.
+// ok is false when pid's state could not be determined.
+func processIsRunning(pid int) (running bool, ok bool) {
+	return processTableStateMatches(func(rowPid, _ int) bool { return rowPid == pid })
+}
+
+// processTableStateMatches scans the process table once, via ps, and reports
+// whether any row satisfying match is non-zombie, and whether at least one
+// matching row was found at all (ok). No rows found means either the process
+// (or group) genuinely doesn't exist (a race with exit) or ps's output was
+// unparseable/restricted; either way, the caller should not claim knowledge.
+func processTableStateMatches(match func(pid, pgid int) bool) (running bool, ok bool) {
+	output, err := exec.Command("ps", "-A", "-o", "pid=,pgid=,stat=").Output()
+	if err != nil {
+		return false, false
+	}
+	found := false
+	for line := range strings.SplitSeq(string(output), "\n") {
+		fields := strings.Fields(line)
+		if len(fields) < 3 {
+			continue
+		}
+		rowPid, errPid := strconv.Atoi(fields[0])
+		rowPgid, errPgid := strconv.Atoi(fields[1])
+		if errPid != nil || errPgid != nil || !match(rowPid, rowPgid) {
+			continue
+		}
+		found = true
+		if !strings.HasPrefix(fields[2], "Z") {
+			return true, true
+		}
+	}
+	return false, found
+}
+
 func processSignalTarget(pid int) (int, error) {
 	if pid <= 1 {
 		return 0, fmt.Errorf("refusing to signal invalid pid %d", pid)
@@ -91,10 +206,14 @@ func processSignalTarget(pid int) (int, error) {
 		if pgid == pid {
 			target = -pid
 		}
-	} else if errors.Is(err, syscall.ESRCH) {
-		// Preserve the individual target; the signal call below treats ESRCH as
-		// already gone, which is a successful lifecycle outcome.
-		return pid, nil
+	} else {
+		if errors.Is(err, syscall.ESRCH) {
+			// Preserve the individual target; the signal call below treats ESRCH as
+			// already gone, which is a successful lifecycle outcome.
+			return pid, nil
+		}
+		// Conservatively retain the individual PID after other lookup failures;
+		// guessing and signalling a process group could affect unrelated processes.
 	}
 	return target, nil
 }

internal/execution/process_unix_test.go

@@ -0,0 +1,133 @@
+//go:build !windows
+
+package execution
+
+import (
+	"os/exec"
+	"strconv"
+	"syscall"
+	"testing"
+	"time"
+)
+
+// TestTerminateProcessTreeTreatsZombieGroupAsExited is the regression test for
+// counting unreaped processes as alive: kill(2) with signal 0 succeeds for a
+// zombie, so a group whose only remaining member is waiting to be reaped used to
+// sit through both grace periods, take a pointless SIGKILL, and then be reported
+// as "did not exit after SIGKILL" — a spurious cleanup failure whose timing
+// depended on when the reaper ran.
+func TestTerminateProcessTreeTreatsZombieGroupAsExited(t *testing.T) {
+	cmd := exec.Command("sh", "-c", "exit 0")
+	ConfigureProcessGroup(cmd)
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("start: %v", err)
+	}
+	pid := cmd.Process.Pid
+	// Deliberately do NOT Wait: the child stays a zombie in its own group, which
+	// is exactly the state a terminated tree passes through.
+	t.Cleanup(func() { _ = cmd.Wait() })
+
+	deadline := time.Now().Add(5 * time.Second)
+	for {
+		if zombie, ok := processIsZombie(pid); ok && zombie {
+			break
+		}
+		if time.Now().After(deadline) {
+			t.Skip("child did not reach the zombie state; ps output is unavailable in this environment")
+		}
+		time.Sleep(10 * time.Millisecond)
+	}
+	if syscall.Kill(-pid, syscall.Signal(0)) != nil {
+		t.Skip("the zombie group is no longer signalable; cannot exercise the case")
+	}
+
+	if signalTargetRunning(-pid) {
+		t.Fatal("a group holding only a zombie must not count as running")
+	}
+	if err := TerminateProcessTree(pid, 50*time.Millisecond, 10*time.Millisecond); err != nil {
+		t.Fatalf("TerminateProcessTree on an already-exited tree: %v", err)
+	}
+}
+
+// TestTerminateProcessTreeStopsRunningGroup is the positive control: a group with
+// a live member must still be seen as running and then actually stopped, so the
+// zombie tolerance above cannot degrade into ignoring real processes.
+func TestTerminateProcessTreeStopsRunningGroup(t *testing.T) {
+	cmd := exec.Command("sh", "-c", "sleep 30")
+	ConfigureProcessGroup(cmd)
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("start: %v", err)
+	}
+	pid := cmd.Process.Pid
+	defer func() { _ = cmd.Wait() }()
+
+	if !signalTargetRunning(-pid) {
+		t.Fatal("a group with a live member must count as running")
+	}
+	if err := TerminateProcessTree(pid, time.Second, 10*time.Millisecond); err != nil {
+		t.Fatalf("TerminateProcessTree: %v", err)
+	}
+	if running, ok := processGroupHasRunningMember(pid); ok && running {
+		t.Fatal("the group still has a running member after termination")
+	}
+}
+
+// TestSignalTargetRunningTreatsZombieIndividualPIDAsExited is the regression
+// test for jatmn's second #774 finding: signalTargetRunning's zombie check
+// matched the individual-PID fallback target (a process that is NOT its own
+// group leader — processSignalTarget's positive-PID case) against process-table
+// rows by PGID. That target's actual PGID differs from its own PID by
+// definition (that's exactly why processSignalTarget fell back to the
+// individual PID instead of a negative group target), so no row ever matched,
+// "unknown" resulted every time, and signalTargetRunning conservatively (and
+// incorrectly) treated a zombie individual-PID target as still running.
+func TestSignalTargetRunningTreatsZombieIndividualPIDAsExited(t *testing.T) {
+	cmd := exec.Command("sh", "-c", "exit 0")
+	// Deliberately do NOT call ConfigureProcessGroup: the child inherits this
+	// test process's group, so it is not its own leader and processSignalTarget
+	// falls back to the individual (positive) PID.
+	if err := cmd.Start(); err != nil {
+		t.Fatalf("start: %v", err)
+	}
+	pid := cmd.Process.Pid
+	t.Cleanup(func() { _ = cmd.Wait() })
+
+	deadline := time.Now().Add(5 * time.Second)
+	for {
+		if zombie, ok := processIsZombie(pid); ok && zombie {
+			break
+		}
+		if time.Now().After(deadline) {
+			t.Skip("child did not reach the zombie state; ps output is unavailable in this environment")
+		}
+		time.Sleep(10 * time.Millisecond)
+	}
+
+	target, err := processSignalTarget(pid)
+	if err != nil {
+		t.Fatalf("processSignalTarget: %v", err)
+	}
+	if target != pid {
+		t.Skip("child unexpectedly became its own group leader; cannot exercise the individual-PID fallback")
+	}
+	if signalTargetRunning(target) {
+		t.Fatal("a zombie individual-PID target must not count as running")
+	}
+}
+
+// processIsZombie reports a process's zombie state via ps. ok is false when the
+// state could not be read.
+func processIsZombie(pid int) (zombie bool, ok bool) {
+	output, err := exec.Command("ps", "-o", "stat=", "-p", strconv.Itoa(pid)).Output()
+	if err != nil {
+		return false, false
+	}
+	state := string(output)
+	for len(state) > 0 && (state[0] == ' ' || state[0] == '\n' || state[0] == '\t') {
+		state = state[1:]
+	}
+	if state == "" {
+		return false, false
+	}
+	return state[0] == 'Z', true
+}

internal/execution/process_windows.go

@@ -3,6 +3,8 @@
 package execution
 
 import (
+	"errors"
+	"fmt"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -12,10 +14,34 @@ import (
 
 func ConfigureProcessGroup(cmd *exec.Cmd) {}
 
+// KillProcessTree asks taskkill /T to kill pid and descendants it can still
+// discover from that live root. If taskkill fails, it falls back to killing pid
+// alone but still returns the tree error because descendants may have survived.
+// Neither path can recover descendants after the root has exited.
 func KillProcessTree(pid int) error {
-	if err := exec.Command(taskkillPath(), "/T", "/F", "/PID", strconv.Itoa(pid)).Run(); err == nil {
+	return killProcessTree(pid, runTaskkill, killRootProcess)
+}
+
+func killProcessTree(pid int, killTree, killRoot func(int) error) error {
+	treeErr := killTree(pid)
+	if treeErr == nil {
 		return nil
 	}
+	rootErr := killRoot(pid)
+	if rootErr != nil {
+		return errors.Join(
+			fmt.Errorf("kill process tree rooted at %d: %w", pid, treeErr),
+			fmt.Errorf("kill root process %d: %w", pid, rootErr),
+		)
+	}
+	return fmt.Errorf("kill process tree rooted at %d (root process killed directly): %w", pid, treeErr)
+}
+
+func runTaskkill(pid int) error {
+	return exec.Command(taskkillPath(), "/T", "/F", "/PID", strconv.Itoa(pid)).Run()
+}
+
+func killRootProcess(pid int) error {
 	process, err := os.FindProcess(pid)
 	if err != nil {
 		return err

internal/execution/process_windows_test.go

@@ -0,0 +1,29 @@
+//go:build windows
+
+package execution
+
+import (
+	"errors"
+	"strings"
+	"testing"
+)
+
+func TestKillProcessTreeRetainsTreeErrorWhenRootFallbackSucceeds(t *testing.T) {
+	treeErr := errors.New("taskkill failed")
+	err := killProcessTree(42, func(int) error { return treeErr }, func(int) error { return nil })
+	if !errors.Is(err, treeErr) {
+		t.Fatalf("killProcessTree error = %v, want tree error", err)
+	}
+	if !strings.Contains(err.Error(), "root process killed directly") {
+		t.Fatalf("killProcessTree error = %q, want fallback context", err)
+	}
+}
+
+func TestKillProcessTreeJoinsTreeAndRootErrors(t *testing.T) {
+	treeErr := errors.New("taskkill failed")
+	rootErr := errors.New("root kill failed")
+	err := killProcessTree(42, func(int) error { return treeErr }, func(int) error { return rootErr })
+	if !errors.Is(err, treeErr) || !errors.Is(err, rootErr) {
+		t.Fatalf("killProcessTree error = %v, want both failures", err)
+	}
+}

internal/fsutil/rename.go

@@ -3,12 +3,47 @@ package fsutil
 
 import (
 	"errors"
+	"fmt"
 	"os"
 	"runtime"
 	"syscall"
 	"time"
 )
 
+// CommittedReplacementCleanupError reports that a replacement was committed,
+// but the old destination retained at BackupPath could not be removed. Callers
+// must treat the replacement itself as successful and surface the cleanup
+// problem separately.
+type CommittedReplacementCleanupError struct {
+	BackupPath string
+	Cause      error
+}
+
+func (err *CommittedReplacementCleanupError) Error() string {
+	return fmt.Sprintf("replacement committed, but backup %s could not be removed: %v", err.BackupPath, err.Cause)
+}
+
+func (err *CommittedReplacementCleanupError) Unwrap() error {
+	return err.Cause
+}
+
+// ReplaceWithRetry publishes src over dst using the platform's replacement
+// primitive, retrying on the same transient Windows lock errors RenameWithRetry
+// handles. On Windows it uses ReplaceFileW so an existing destination keeps its
+// DACL and selected metadata instead of receiving the temporary file's inherited
+// DACL. ReplaceFileW is not observer-atomic and may briefly leave dst absent;
+// callers that cannot tolerate that must synchronize their own readers. On Unix
+// replacement uses os.Rename.
+//
+// replace overrides the platform primitive so tests can exercise the retry path;
+// pass nil for the default.
+func ReplaceWithRetry(src, dst string, replace func(src, dst string) error) error {
+	if replace == nil {
+		replace = replaceExisting
+	}
+	return RenameWithRetry(src, dst, replace)
+}
+
 // RenameWithRetry renames src to dst, retrying briefly on Windows when the
 // destination is transiently locked (antivirus scanners, search indexers, or
 // a concurrent reader holding the file open). rename overrides os.Rename so
@@ -23,6 +58,12 @@ func RenameWithRetry(src, dst string, rename func(src, dst string) error) error
 		if err == nil {
 			return nil
 		}
+		var committed *CommittedReplacementCleanupError
+		if errors.As(err, &committed) {
+			// The source has already been consumed. In particular, never retry if
+			// the cleanup cause itself is a transient Windows sharing violation.
+			break
+		}
 		if runtime.GOOS == "windows" {
 			if os.IsPermission(err) || isWindowsSharingOrLockViolation(err) {
 				time.Sleep(10 * time.Millisecond)

internal/fsutil/replace_other.go

@@ -0,0 +1,12 @@
+//go:build !windows
+
+package fsutil
+
+import "os"
+
+// replaceExisting publishes src over dst. rename(2) already replaces the
+// destination atomically within one filesystem on Unix, and it neither creates
+// nor consults an ACL, so there is nothing extra to preserve here.
+func replaceExisting(src, dst string) error {
+	return os.Rename(src, dst)
+}

internal/fsutil/replace_other_test.go

@@ -0,0 +1,50 @@
+//go:build !windows
+
+package fsutil
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// On Unix the replacement primitive is rename(2), which already publishes
+// atomically within one filesystem and neither creates nor consults an ACL. These
+// cover both shapes so the shared helper is exercised on every platform.
+func TestReplaceWithRetryPublishesOverExistingAndMissingDestinations(t *testing.T) {
+	for _, tc := range []struct {
+		name     string
+		existing bool
+	}{
+		{name: "existing destination", existing: true},
+		{name: "missing destination"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			dir := t.TempDir()
+			src := filepath.Join(dir, ".manifest.tmp")
+			dst := filepath.Join(dir, "manifest.md")
+			if err := os.WriteFile(src, []byte("new"), 0o600); err != nil {
+				t.Fatalf("WriteFile src: %v", err)
+			}
+			if tc.existing {
+				if err := os.WriteFile(dst, []byte("old"), 0o600); err != nil {
+					t.Fatalf("WriteFile dst: %v", err)
+				}
+			}
+
+			if err := ReplaceWithRetry(src, dst, nil); err != nil {
+				t.Fatalf("ReplaceWithRetry: %v", err)
+			}
+			data, err := os.ReadFile(dst)
+			if err != nil {
+				t.Fatalf("ReadFile dst: %v", err)
+			}
+			if string(data) != "new" {
+				t.Fatalf("destination content = %q, want the replacement bytes", data)
+			}
+			if _, err := os.Lstat(src); !os.IsNotExist(err) {
+				t.Fatalf("the replacement file should be consumed by the replace: %v", err)
+			}
+		})
+	}
+}

internal/fsutil/replace_windows.go

@@ -0,0 +1,237 @@
+//go:build windows
+
+package fsutil
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"syscall"
+	"time"
+	"unsafe"
+)
+
+// replaceFileFlags is deliberately ZERO. Every REPLACEFILE_* flag ReplaceFileW
+// accepts either defeats the reason this function exists or does nothing:
+//
+//   - REPLACEFILE_IGNORE_MERGE_ERRORS (0x2) and REPLACEFILE_IGNORE_ACL_ERRORS
+//     (0x4). Microsoft documents BOTH with the same consequence: "if you specify
+//     this flag and do not have WRITE_DAC access, the function succeeds but the
+//     ACLs are not preserved." A silent success that publishes the temporary
+//     file's inherited directory DACL over an explicitly restricted specialist —
+//     exposing its system prompt — is precisely the failure this function exists
+//     to prevent, so a merge failure MUST surface as an error and leave the
+//     destination untouched. Passing 0x2 while omitting only 0x4 buys nothing:
+//     ACL merging is part of the metadata merge 0x2 covers.
+//   - REPLACEFILE_WRITE_THROUGH (0x1) is documented as "This value is not
+//     supported", so it cannot be relied on to flush anything.
+const replaceFileFlags = 0
+
+const replaceBackupPattern = ".zero-replace-*.backup"
+
+const (
+	// Returned when the volume or redirector cannot provide ReplaceFileW's
+	// DACL-preserving semantics. Existing destinations must fail closed.
+	errorInvalidFunction = syscall.Errno(1)
+	errorNotSupported    = syscall.Errno(50)
+
+	// Partial-failure codes: ReplaceFileW got far enough to move or delete
+	// something, so the on-disk state needs repair rather than a bare error. See
+	// recoverPartialReplace.
+	errorUnableToRemoveReplaced   = syscall.Errno(1175)
+	errorUnableToMoveReplacement  = syscall.Errno(1176)
+	errorUnableToMoveReplacement2 = syscall.Errno(1177)
+)
+
+var (
+	replaceKernel32       = syscall.NewLazyDLL("kernel32.dll")
+	replaceProcReplaceFil = replaceKernel32.NewProc("ReplaceFileW")
+)
+
+// replaceExisting publishes src over dst with ReplaceFileW rather than
+// MoveFileEx (what os.Rename uses) to preserve destination metadata. The
+// replacement is a freshly created temporary file, so it carries the directory's
+// inherited DACL. Renaming it over the destination would therefore replace the
+// destination's ACL - silently widening access to a file that had been restricted
+// explicitly (os.File.Chmod cannot express that on Windows; Go only maps the
+// owner-write bit). ReplaceFileW carries the replaced file's DACL and selected
+// metadata over to the replacement instead.
+//
+// ReplaceFileW combines multiple filesystem steps and is not observer-atomic: an
+// external reader can briefly see dst absent even when replacement succeeds.
+// Callers that cannot tolerate that window must synchronize their own readers.
+//
+// No REPLACEFILE_* flag is passed at all — see replaceFileFlags for why each one
+// would either silently lose the descriptor this function exists to preserve or
+// do nothing. A merge failure therefore surfaces as an error, leaving the
+// destination untouched and the caller free to clean up its temporary file,
+// except in the partial-failure states recoverPartialReplace repairs.
+func replaceExisting(src, dst string) error {
+	return replaceExistingWith(src, dst, callReplaceFile, nil)
+}
+
+func replaceExistingWith(src, dst string, replace func(string, string, string) error, restore func(string, string) error) error {
+	return replaceExistingWithCleanup(src, dst, replace, restore, removeReplaceBackup)
+}
+
+func replaceExistingWithCleanup(src, dst string, replace func(string, string, string) error, restore func(string, string) error, removeBackup func(string) error) error {
+	info, err := os.Lstat(dst)
+	if err != nil {
+		if os.IsNotExist(err) {
+			// Nothing to replace and no descriptor to preserve.
+			return os.Rename(src, dst)
+		}
+		return err
+	}
+	if info.Mode()&os.ModeSymlink != 0 {
+		return fmt.Errorf("refusing to replace symlink destination: %s", dst)
+	}
+
+	backup, err := prepareReplaceBackup(dst)
+	if err != nil {
+		return fmt.Errorf("prepare replacement backup: %w", err)
+	}
+	callErr := replace(dst, src, backup)
+	if callErr == nil {
+		if err := removeBackup(backup); err != nil {
+			return &CommittedReplacementCleanupError{BackupPath: backup, Cause: err}
+		}
+		return nil
+	}
+	if errors.Is(callErr, errorInvalidFunction) || errors.Is(callErr, errorNotSupported) {
+		callErr = fmt.Errorf("DACL-preserving replacement is not supported for %s: %w", dst, callErr)
+	}
+	return recoverPartialReplace(callErr, dst, backup, restore)
+}
+
+func callReplaceFile(replacedPath, replacementPath, backupPath string) error {
+	replaced, err := syscall.UTF16PtrFromString(replacedPath)
+	if err != nil {
+		return err
+	}
+	replacement, err := syscall.UTF16PtrFromString(replacementPath)
+	if err != nil {
+		return err
+	}
+	backup, err := syscall.UTF16PtrFromString(backupPath)
+	if err != nil {
+		return err
+	}
+	result, _, callErr := replaceProcReplaceFil.Call(
+		uintptr(unsafe.Pointer(replaced)),
+		uintptr(unsafe.Pointer(replacement)),
+		uintptr(unsafe.Pointer(backup)),
+		uintptr(replaceFileFlags),
+		0,
+		0,
+	)
+	if result != 0 {
+		return nil
+	}
+	if callErr == nil || errors.Is(callErr, syscall.Errno(0)) {
+		return fmt.Errorf("replace %s: ReplaceFileW failed", replacedPath)
+	}
+	return callErr
+}
+
+func prepareReplaceBackup(dst string) (string, error) {
+	file, err := os.CreateTemp(filepath.Dir(dst), replaceBackupPattern)
+	if err != nil {
+		return "", err
+	}
+	path := file.Name()
+	if err := file.Close(); err != nil {
+		cleanupErr := removeReplaceBackup(path)
+		return "", fmt.Errorf("close backup placeholder %s: %w (cleanup error: %v)", path, err, cleanupErr)
+	}
+	if err := removeReplaceBackup(path); err != nil {
+		return "", fmt.Errorf("release backup path %s: %w", path, err)
+	}
+	return path, nil
+}
+
+func removeReplaceBackup(path string) error {
+	var err error
+	for i := 0; i < 10; i++ {
+		err = os.Remove(path)
+		if err == nil || os.IsNotExist(err) {
+			return nil
+		}
+		if os.IsPermission(err) {
+			// ReplaceFileW can leave the original's read-only attribute on the
+			// backup. Chmod clears that bit on Windows without changing its DACL.
+			_ = os.Chmod(path, 0o600)
+		}
+		if os.IsPermission(err) || isWindowsSharingOrLockViolation(err) {
+			time.Sleep(10 * time.Millisecond)
+			continue
+		}
+		break
+	}
+	return err
+}
+
+func cleanupReplaceBackup(callErr error, backup string) error {
+	if err := removeReplaceBackup(backup); err != nil {
+		return fmt.Errorf("%w (backup %s could not be removed: %v)", callErr, backup, err)
+	}
+	return callErr
+}
+
+// recoverPartialReplace restores the original after ReplaceFileW reports a
+// partial failure, then returns the original error. Supplying a managed backup
+// changes the dangerous failure states documented by Microsoft:
+//
+//   - ERROR_UNABLE_TO_MOVE_REPLACEMENT (1176) leaves both files under their
+//     original names, so the failed write can discard src normally.
+//   - ERROR_UNABLE_TO_MOVE_REPLACEMENT_2 (1177) leaves src in place and moves the
+//     original destination to backup. Moving backup back to dst rolls the failed
+//     overwrite back without losing the original content or its DACL.
+//
+// The replacement is left alone either way — nothing here deletes what it was
+// handed — but the errors below deliberately say nothing about where it ended up,
+// which is also why its path is not a parameter. Whether it still exists when the
+// error surfaces is the caller's business: the specialist writer, the only caller
+// today, removes its temporary file in a deferred cleanup, so an error promising
+// a replacement "remains at" that path would send an operator looking for a file
+// that was already gone. What these errors do describe is what this function
+// itself left on disk — the state of dst, and of the managed backup holding the
+// original.
+func recoverPartialReplace(callErr error, dst, backup string, restore func(string, string) error) error {
+	if !errors.Is(callErr, errorUnableToMoveReplacement2) {
+		// For 1175, 1176, unsupported volumes, and ordinary failures, Windows
+		// documents that dst remains at its original name. Remove any redundant
+		// backup only after confirming that the destination still exists.
+		if _, err := os.Lstat(dst); err == nil {
+			return cleanupReplaceBackup(callErr, backup)
+		} else if !os.IsNotExist(err) {
+			return fmt.Errorf("replace %s: %w (inspect destination during recovery: %v)", dst, callErr, err)
+		}
+	}
+
+	if _, err := os.Lstat(backup); err != nil {
+		return fmt.Errorf("replace %s: %w (original backup expected at %s is unavailable: %v)", dst, callErr, backup, err)
+	}
+	if _, err := os.Lstat(dst); err == nil {
+		return fmt.Errorf("replace %s: %w (destination unexpectedly exists; the original also remains at backup %s)", dst, callErr, backup)
+	} else if !os.IsNotExist(err) {
+		return fmt.Errorf("replace %s: %w (inspect destination before restoring backup %s: %v)", dst, callErr, backup, err)
+	}
+	if err := RenameWithRetry(backup, dst, restore); err != nil {
+		// Only callErr is wrapped. Exposing a sharing violation from the exhausted
+		// rollback would make the outer ReplaceWithRetry call retry after the
+		// filesystem was already mutated.
+		//
+		// This is the one terminal state that needs a human: nothing is at dst, and
+		// the original's only copy is under a name no tool looks for (the specialist
+		// loader reads *.md and skips everything else), so it is invisible until
+		// somebody moves it back. Say that outright rather than leaving an operator
+		// to infer it from a bare error code.
+		return fmt.Errorf(
+			"replace %s: %w (rolling the original back failed: %v; %s no longer exists and the original survives only as %s, which must be moved back by hand to restore it)",
+			dst, callErr, err, dst, backup,
+		)
+	}
+	return fmt.Errorf("replace %s: %w (the original was restored)", dst, callErr)
+}

internal/fsutil/replace_windows_test.go

@@ -0,0 +1,559 @@
+//go:build windows
+
+package fsutil
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+	"strings"
+	"syscall"
+	"testing"
+
+	"golang.org/x/sys/windows"
+)
+
+// TestReplaceWithRetryPreservesDestinationCreationTime proves the publish goes
+// through ReplaceFileW and not os.Rename: ReplaceFileW carries selected metadata,
+// including creation time, from the destination to the replacement. A rename
+// would carry the temporary file's creation time over instead.
+func TestReplaceWithRetryPreservesDestinationCreationTime(t *testing.T) {
+	dir := t.TempDir()
+	dst := filepath.Join(dir, "manifest.md")
+	if err := os.WriteFile(dst, []byte("old"), 0o600); err != nil {
+		t.Fatalf("WriteFile dst: %v", err)
+	}
+	created := creationTime(t, dst)
+
+	src := filepath.Join(dir, ".manifest.tmp")
+	if err := os.WriteFile(src, []byte("new"), 0o600); err != nil {
+		t.Fatalf("WriteFile src: %v", err)
+	}
+	// Push the replacement's own creation time clearly past the destination's so a
+	// rename would be visible in the comparison below.
+	future := windows.NsecToFiletime(created.Nanoseconds() + int64(10*1e9))
+	setCreationTime(t, src, future)
+
+	if err := ReplaceWithRetry(src, dst, nil); err != nil {
+		t.Fatalf("ReplaceWithRetry: %v", err)
+	}
+	data, err := os.ReadFile(dst)
+	if err != nil {
+		t.Fatalf("ReadFile dst: %v", err)
+	}
+	if string(data) != "new" {
+		t.Fatalf("destination content = %q, want the replacement bytes", data)
+	}
+	if _, err := os.Lstat(src); !os.IsNotExist(err) {
+		t.Fatalf("the replacement file should be consumed by the replace: %v", err)
+	}
+	assertNoReplaceBackups(t, dir)
+	if got := creationTime(t, dst); got != created {
+		t.Fatalf("creation time = %v, want the replaced file's %v (a rename would not preserve it)", got, created)
+	}
+}
+
+// TestReplaceWithRetryPreservesDestinationDACL is the regression test for the
+// second half of the finding: the replacement is a freshly created temporary file
+// carrying the directory's inherited DACL, so publishing it with a rename would
+// REPLACE the restrictive descriptor an explicitly locked-down file had.
+func TestReplaceWithRetryPreservesDestinationDACL(t *testing.T) {
+	dir := t.TempDir()
+	dst := filepath.Join(dir, "manifest.md")
+	if err := os.WriteFile(dst, []byte("old"), 0o600); err != nil {
+		t.Fatalf("WriteFile dst: %v", err)
+	}
+	// A protected DACL granting only the owner: distinct from whatever the temp
+	// file inherits from the directory.
+	restricted, err := windows.SecurityDescriptorFromString("D:P(A;;FA;;;OW)")
+	if err != nil {
+		t.Skipf("cannot build a test security descriptor: %v", err)
+	}
+	dacl, _, err := restricted.DACL()
+	if err != nil {
+		t.Skipf("cannot read the test DACL: %v", err)
+	}
+	if err := windows.SetNamedSecurityInfo(
+		dst,
+		windows.SE_FILE_OBJECT,
+		windows.DACL_SECURITY_INFORMATION|windows.PROTECTED_DACL_SECURITY_INFORMATION,
+		nil, nil, dacl, nil,
+	); err != nil {
+		t.Skipf("cannot apply a restrictive DACL on this filesystem: %v", err)
+	}
+	want := describeDACL(t, dst)
+
+	src := filepath.Join(dir, ".manifest.tmp")
+	if err := os.WriteFile(src, []byte("new"), 0o600); err != nil {
+		t.Fatalf("WriteFile src: %v", err)
+	}
+	if inherited := describeDACL(t, src); inherited == want {
+		t.Skip("the temporary file already carries the same DACL; this filesystem cannot show the difference")
+	}
+
+	if err := ReplaceWithRetry(src, dst, nil); err != nil {
+		t.Fatalf("ReplaceWithRetry: %v", err)
+	}
+	if got := describeDACL(t, dst); got != want {
+		t.Fatalf("DACL after replace = %q, want the destination's own %q", got, want)
+	}
+	assertNoReplaceBackups(t, dir)
+}
+
+// TestReplaceWithRetryPublishesWhenDestinationIsMissing covers the no-destination
+// case: ReplaceFileW requires an existing file to replace, so there is a rename
+// fallback (and nothing to preserve).
+func TestReplaceWithRetryPublishesWhenDestinationIsMissing(t *testing.T) {
+	dir := t.TempDir()
+	src := filepath.Join(dir, ".manifest.tmp")
+	dst := filepath.Join(dir, "manifest.md")
+	if err := os.WriteFile(src, []byte("new"), 0o600); err != nil {
+		t.Fatalf("WriteFile src: %v", err)
+	}
+	if err := ReplaceWithRetry(src, dst, nil); err != nil {
+		t.Fatalf("ReplaceWithRetry: %v", err)
+	}
+	if data, err := os.ReadFile(dst); err != nil || string(data) != "new" {
+		t.Fatalf("destination = %q err=%v, want the replacement bytes", data, err)
+	}
+	assertNoReplaceBackups(t, dir)
+}
+
+// TestReplaceWithRetryRetriesTransientLockViolation keeps the retry behavior that
+// RenameWithRetry provides for antivirus/indexer holds.
+func TestReplaceWithRetryRetriesTransientLockViolation(t *testing.T) {
+	attempts := 0
+	err := ReplaceWithRetry("src", "dst", func(src, dst string) error {
+		attempts++
+		if attempts < 3 {
+			return &os.PathError{Op: "replace", Path: dst, Err: syscall.Errno(32)} // ERROR_SHARING_VIOLATION
+		}
+		return nil
+	})
+	if err != nil {
+		t.Fatalf("ReplaceWithRetry: %v", err)
+	}
+	if attempts != 3 {
+		t.Fatalf("attempts = %d, want the transient violations retried", attempts)
+	}
+}
+
+// TestReplaceFileFlagsDoNotIgnoreMergeErrors is the regression test for jatmn's
+// #757 P1 finding on flags: the call used to pass REPLACEFILE_IGNORE_MERGE_ERRORS
+// (0x2) while the comment claimed ACL failures were fail-closed. Microsoft
+// documents 0x2 and REPLACEFILE_IGNORE_ACL_ERRORS (0x4) identically — with either
+// one set, a call lacking WRITE_DAC "succeeds but the ACLs are not preserved" —
+// so passing 0x2 let a --force overwrite silently publish the temporary file's
+// inherited directory DACL over a restricted specialist and expose its system
+// prompt.
+//
+// This asserts the flag word directly rather than a live denied merge because a
+// denied merge is not constructible for a file this process owns: Windows grants
+// an object's owner READ_CONTROL and WRITE_DAC implicitly, so no DACL a test can
+// apply to its own temp file can withhold WRITE_DAC from it. Pinning the flags is
+// what actually prevents the regression — re-adding either bit fails here.
+func TestReplaceFileFlagsDoNotIgnoreMergeErrors(t *testing.T) {
+	const (
+		ignoreMergeErrors = 0x00000002
+		ignoreACLErrors   = 0x00000004
+	)
+	if replaceFileFlags&ignoreMergeErrors != 0 {
+		t.Error("REPLACEFILE_IGNORE_MERGE_ERRORS must not be set: it makes ReplaceFileW succeed WITHOUT preserving ACLs when it cannot obtain WRITE_DAC")
+	}
+	if replaceFileFlags&ignoreACLErrors != 0 {
+		t.Error("REPLACEFILE_IGNORE_ACL_ERRORS must not be set: it makes ReplaceFileW succeed WITHOUT preserving ACLs when it cannot obtain WRITE_DAC")
+	}
+}
+
+func TestReplaceExistingRejectsUnsupportedDACLReplacement(t *testing.T) {
+	for _, tc := range []struct {
+		name string
+		code syscall.Errno
+	}{
+		{name: "ERROR_INVALID_FUNCTION", code: errorInvalidFunction},
+		{name: "ERROR_NOT_SUPPORTED", code: errorNotSupported},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			dir := t.TempDir()
+			src := filepath.Join(dir, ".manifest.tmp")
+			dst := filepath.Join(dir, "manifest.md")
+			if err := os.WriteFile(src, []byte("new"), 0o600); err != nil {
+				t.Fatalf("WriteFile src: %v", err)
+			}
+			if err := os.WriteFile(dst, []byte("old"), 0o600); err != nil {
+				t.Fatalf("WriteFile dst: %v", err)
+			}
+
+			err := replaceExistingWith(src, dst, func(replaced, replacement, backup string) error {
+				if replaced != dst || replacement != src {
+					t.Fatalf("ReplaceFileW paths = (%q, %q), want (%q, %q)", replaced, replacement, dst, src)
+				}
+				if filepath.Dir(backup) != dir {
+					t.Fatalf("backup directory = %q, want sibling directory %q", filepath.Dir(backup), dir)
+				}
+				return tc.code
+			}, nil)
+			if !errors.Is(err, tc.code) {
+				t.Fatalf("error = %v, want unsupported error %v", err, tc.code)
+			}
+			if !strings.Contains(err.Error(), "DACL-preserving replacement is not supported") {
+				t.Fatalf("error = %v, want a DACL-preserving-replacement explanation", err)
+			}
+			assertFileContent(t, dst, "old")
+			assertFileContent(t, src, "new")
+			assertNoReplaceBackups(t, dir)
+		})
+	}
+}
+
+func TestReplaceExistingCleansManagedBackup(t *testing.T) {
+	dir := t.TempDir()
+	src := filepath.Join(dir, ".manifest.tmp")
+	dst := filepath.Join(dir, "manifest.md")
+	if err := os.WriteFile(src, []byte("new"), 0o600); err != nil {
+		t.Fatalf("WriteFile src: %v", err)
+	}
+	if err := os.WriteFile(dst, []byte("old"), 0o600); err != nil {
+		t.Fatalf("WriteFile dst: %v", err)
+	}
+
+	var backupPath string
+	err := replaceExistingWith(src, dst, func(replaced, replacement, backup string) error {
+		backupPath = backup
+		if matched, matchErr := filepath.Match(replaceBackupPattern, filepath.Base(backup)); matchErr != nil || !matched {
+			t.Fatalf("backup path = %q, want pattern %q (match error: %v)", backup, replaceBackupPattern, matchErr)
+		}
+		if _, statErr := os.Lstat(backup); !os.IsNotExist(statErr) {
+			t.Fatalf("backup path must be vacant before ReplaceFileW: %v", statErr)
+		}
+		if renameErr := os.Rename(replaced, backup); renameErr != nil {
+			t.Fatalf("stage backup: %v", renameErr)
+		}
+		// Windows refuses to remove a read-only file. The cleanup path must clear
+		// that attribute without changing the backup's DACL, then remove it.
+		if chmodErr := os.Chmod(backup, 0o400); chmodErr != nil {
+			t.Fatalf("make backup read-only: %v", chmodErr)
+		}
+		return os.Rename(replacement, replaced)
+	}, nil)
+	if err != nil {
+		t.Fatalf("replaceExistingWith: %v", err)
+	}
+	assertFileContent(t, dst, "new")
+	if _, err := os.Lstat(src); !os.IsNotExist(err) {
+		t.Fatalf("replacement source should be consumed: %v", err)
+	}
+	if _, err := os.Lstat(backupPath); !os.IsNotExist(err) {
+		t.Fatalf("managed backup should be removed: %v", err)
+	}
+	assertNoReplaceBackups(t, dir)
+}
+
+func TestReplaceWithRetryDoesNotRetryCommittedReplacementWhenBackupCleanupFails(t *testing.T) {
+	dir := t.TempDir()
+	src := filepath.Join(dir, ".manifest.tmp")
+	dst := filepath.Join(dir, "manifest.md")
+	if err := os.WriteFile(src, []byte("new"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(dst, []byte("old"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	attempts := 0
+	cleanupErr := &os.PathError{Op: "remove", Path: "managed backup", Err: syscall.Errno(32)}
+	var backupPath string
+	err := ReplaceWithRetry(src, dst, func(src, dst string) error {
+		attempts++
+		return replaceExistingWithCleanup(src, dst, func(replaced, replacement, backup string) error {
+			backupPath = backup
+			if err := os.Rename(replaced, backup); err != nil {
+				return err
+			}
+			return os.Rename(replacement, replaced)
+		}, nil, func(got string) error {
+			if got != backupPath {
+				t.Fatalf("cleanup backup path = %q, want %q", got, backupPath)
+			}
+			return cleanupErr
+		})
+	})
+	var outcome *CommittedReplacementCleanupError
+	if !errors.As(err, &outcome) {
+		t.Fatalf("error = %v, want committed cleanup outcome", err)
+	}
+	if outcome.BackupPath != backupPath || !errors.Is(outcome, syscall.Errno(32)) {
+		t.Fatalf("outcome = %#v, want backup %q and sharing violation", outcome, backupPath)
+	}
+	if attempts != 1 {
+		t.Fatalf("replacement attempts = %d, want 1", attempts)
+	}
+	assertFileContent(t, dst, "new")
+	assertFileContent(t, backupPath, "old")
+}
+
+func TestReplaceExistingKeeps1176FilesAtOriginalNames(t *testing.T) {
+	dir := t.TempDir()
+	src := filepath.Join(dir, ".manifest.tmp")
+	dst := filepath.Join(dir, "manifest.md")
+	if err := os.WriteFile(src, []byte("new"), 0o600); err != nil {
+		t.Fatalf("WriteFile src: %v", err)
+	}
+	if err := os.WriteFile(dst, []byte("old"), 0o600); err != nil {
+		t.Fatalf("WriteFile dst: %v", err)
+	}
+
+	err := replaceExistingWith(src, dst, func(_, _, _ string) error {
+		// With a backup name, Microsoft documents that 1176 leaves the replaced
+		// and replacement files under their original names.
+		return errorUnableToMoveReplacement
+	}, nil)
+	if !errors.Is(err, errorUnableToMoveReplacement) {
+		t.Fatalf("error = %v, want %v", err, errorUnableToMoveReplacement)
+	}
+	assertFileContent(t, dst, "old")
+	assertFileContent(t, src, "new")
+	assertNoReplaceBackups(t, dir)
+}
+
+func TestReplaceExistingRollsBack1177AndRetriesTransientRestore(t *testing.T) {
+	dir := t.TempDir()
+	src := filepath.Join(dir, ".manifest.tmp")
+	dst := filepath.Join(dir, "manifest.md")
+	if err := os.WriteFile(src, []byte("new"), 0o600); err != nil {
+		t.Fatalf("WriteFile src: %v", err)
+	}
+	if err := os.WriteFile(dst, []byte("old"), 0o600); err != nil {
+		t.Fatalf("WriteFile dst: %v", err)
+	}
+
+	var backupPath string
+	restoreAttempts := 0
+	err := replaceExistingWith(src, dst, func(replaced, _, backup string) error {
+		backupPath = backup
+		if renameErr := os.Rename(replaced, backup); renameErr != nil {
+			t.Fatalf("stage documented 1177 backup: %v", renameErr)
+		}
+		return errorUnableToMoveReplacement2
+	}, func(backup, destination string) error {
+		restoreAttempts++
+		if restoreAttempts < 3 {
+			return &os.PathError{Op: "rename", Path: backup, Err: syscall.Errno(32)}
+		}
+		return os.Rename(backup, destination)
+	})
+	if !errors.Is(err, errorUnableToMoveReplacement2) {
+		t.Fatalf("error = %v, want %v", err, errorUnableToMoveReplacement2)
+	}
+	if restoreAttempts != 3 {
+		t.Fatalf("restore attempts = %d, want transient lock failures retried", restoreAttempts)
+	}
+	assertErrorDoesNotAdvertiseReplacement(t, err, src)
+	assertFileContent(t, dst, "old")
+	assertFileContent(t, src, "new")
+	if _, err := os.Lstat(backupPath); !os.IsNotExist(err) {
+		t.Fatalf("backup should be consumed by rollback: %v", err)
+	}
+	assertNoReplaceBackups(t, dir)
+}
+
+func TestReplaceExistingPreserves1177BackupWhenRollbackFails(t *testing.T) {
+	dir := t.TempDir()
+	src := filepath.Join(dir, ".manifest.tmp")
+	dst := filepath.Join(dir, "manifest.md")
+	if err := os.WriteFile(src, []byte("new"), 0o600); err != nil {
+		t.Fatalf("WriteFile src: %v", err)
+	}
+	if err := os.WriteFile(dst, []byte("old"), 0o600); err != nil {
+		t.Fatalf("WriteFile dst: %v", err)
+	}
+
+	var backupPath string
+	replaceAttempts := 0
+	err := ReplaceWithRetry(src, dst, func(src, dst string) error {
+		replaceAttempts++
+		return replaceExistingWith(src, dst, func(replaced, _, backup string) error {
+			backupPath = backup
+			if renameErr := os.Rename(replaced, backup); renameErr != nil {
+				t.Fatalf("stage documented 1177 backup: %v", renameErr)
+			}
+			return errorUnableToMoveReplacement2
+		}, func(_, _ string) error {
+			return &os.PathError{Op: "rename", Path: backupPath, Err: syscall.Errno(32)}
+		})
+	})
+	if !errors.Is(err, errorUnableToMoveReplacement2) {
+		t.Fatalf("error = %v, want %v", err, errorUnableToMoveReplacement2)
+	}
+	if replaceAttempts != 1 {
+		t.Fatalf("replace attempts = %d, want no retry after a partial failure", replaceAttempts)
+	}
+	if os.IsPermission(err) || isWindowsSharingOrLockViolation(err) {
+		t.Fatalf("partial-failure error exposes the rollback lock error to the outer retry loop: %v", err)
+	}
+	if !strings.Contains(err.Error(), backupPath) {
+		t.Fatalf("error = %v, want retained backup path %q", err, backupPath)
+	}
+	// The terminal state an operator has to fix by hand: the original exists only
+	// under the backup name and nothing is at dst, so the error has to name both
+	// and say what to do, not just report the Windows code.
+	if !strings.Contains(err.Error(), dst) {
+		t.Fatalf("error = %v, want the destination %q an operator must restore to", err, dst)
+	}
+	if !strings.Contains(err.Error(), "moved back by hand") {
+		t.Fatalf("error = %v, want an explicit instruction to move the backup back", err)
+	}
+	assertErrorDoesNotAdvertiseReplacement(t, err, src)
+	if _, err := os.Lstat(dst); !os.IsNotExist(err) {
+		t.Fatalf("destination should remain absent after failed rollback: %v", err)
+	}
+	assertFileContent(t, backupPath, "old")
+	assertFileContent(t, src, "new")
+}
+
+func TestReplaceExistingRejectsSymlinkDestination(t *testing.T) {
+	dir := t.TempDir()
+	target := filepath.Join(dir, "target.md")
+	dst := filepath.Join(dir, "manifest.md")
+	src := filepath.Join(dir, ".manifest.tmp")
+	if err := os.WriteFile(target, []byte("old"), 0o600); err != nil {
+		t.Fatalf("WriteFile target: %v", err)
+	}
+	if err := os.WriteFile(src, []byte("new"), 0o600); err != nil {
+		t.Fatalf("WriteFile src: %v", err)
+	}
+	if err := os.Symlink(target, dst); err != nil {
+		t.Skipf("symlink unavailable: %v", err)
+	}
+
+	called := false
+	err := replaceExistingWith(src, dst, func(_, _, _ string) error {
+		called = true
+		return nil
+	}, nil)
+	if err == nil || !strings.Contains(err.Error(), "refusing to replace symlink") {
+		t.Fatalf("symlink replacement error = %v", err)
+	}
+	if called {
+		t.Fatal("ReplaceFileW callback was called for a symlink destination")
+	}
+	assertFileContent(t, target, "old")
+	assertFileContent(t, src, "new")
+	if info, err := os.Lstat(dst); err != nil || info.Mode()&os.ModeSymlink == 0 {
+		t.Fatalf("destination symlink was changed: info=%v err=%v", info, err)
+	}
+	assertNoReplaceBackups(t, dir)
+}
+
+func TestRecoverPartialReplaceLeavesIntactStatesAlone(t *testing.T) {
+	for _, tc := range []struct {
+		name string
+		code syscall.Errno
+	}{
+		{name: "ERROR_UNABLE_TO_REMOVE_REPLACED", code: errorUnableToRemoveReplaced},
+		{name: "ERROR_ACCESS_DENIED", code: syscall.Errno(5)},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			dir := t.TempDir()
+			src := filepath.Join(dir, ".manifest.tmp")
+			dst := filepath.Join(dir, "manifest.md")
+			backup := filepath.Join(dir, ".zero-replace-test.backup")
+			if err := os.WriteFile(src, []byte("new"), 0o600); err != nil {
+				t.Fatalf("WriteFile src: %v", err)
+			}
+			if err := os.WriteFile(dst, []byte("old"), 0o600); err != nil {
+				t.Fatalf("WriteFile dst: %v", err)
+			}
+
+			if err := recoverPartialReplace(tc.code, dst, backup, nil); !errors.Is(err, tc.code) {
+				t.Fatalf("error = %v, want the original %v unchanged", err, tc.code)
+			}
+			assertFileContent(t, dst, "old")
+			assertFileContent(t, src, "new")
+			if _, err := os.Lstat(backup); !os.IsNotExist(err) {
+				t.Fatalf("unexpected backup residue: %v", err)
+			}
+		})
+	}
+}
+
+// assertErrorDoesNotAdvertiseReplacement guards the messaging fixed for jatmn's
+// #757 P3 finding: recovery errors used to say the replacement "remains at" the
+// caller's temporary path, but the only caller removes that file in a deferred
+// cleanup before the error ever surfaces. Recovery is always about the original,
+// so an operator must never be sent looking for the replacement.
+func assertErrorDoesNotAdvertiseReplacement(t *testing.T, err error, replacement string) {
+	t.Helper()
+	if err == nil {
+		t.Fatal("expected a partial-replacement error")
+	}
+	if strings.Contains(err.Error(), replacement) {
+		t.Fatalf("error = %v, must not point an operator at the replacement %q, which its caller deletes", err, replacement)
+	}
+}
+
+func assertFileContent(t *testing.T, path, want string) {
+	t.Helper()
+	data, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("ReadFile %s: %v", path, err)
+	}
+	if string(data) != want {
+		t.Fatalf("content of %s = %q, want %q", path, data, want)
+	}
+}
+
+func assertNoReplaceBackups(t *testing.T, dir string) {
+	t.Helper()
+	matches, err := filepath.Glob(filepath.Join(dir, replaceBackupPattern))
+	if err != nil {
+		t.Fatalf("Glob replacement backups: %v", err)
+	}
+	if len(matches) != 0 {
+		t.Fatalf("replacement backups remain: %v", matches)
+	}
+}
+
+func creationTime(t *testing.T, path string) syscall.Filetime {
+	t.Helper()
+	info, err := os.Stat(path)
+	if err != nil {
+		t.Fatalf("Stat %s: %v", path, err)
+	}
+	data, ok := info.Sys().(*syscall.Win32FileAttributeData)
+	if !ok {
+		t.Skipf("no Windows file attributes for %s", path)
+	}
+	return data.CreationTime
+}
+
+func setCreationTime(t *testing.T, path string, created windows.Filetime) {
+	t.Helper()
+	pathPtr, err := windows.UTF16PtrFromString(path)
+	if err != nil {
+		t.Fatalf("UTF16PtrFromString: %v", err)
+	}
+	handle, err := windows.CreateFile(pathPtr, windows.FILE_WRITE_ATTRIBUTES, 0, nil, windows.OPEN_EXISTING, windows.FILE_ATTRIBUTE_NORMAL, 0)
+	if err != nil {
+		t.Fatalf("CreateFile %s: %v", path, err)
+	}
+	defer func() {
+		_ = windows.CloseHandle(handle)
+	}()
+	if err := windows.SetFileTime(handle, &created, nil, nil); err != nil {
+		t.Fatalf("SetFileTime %s: %v", path, err)
+	}
+}
+
+func describeDACL(t *testing.T, path string) string {
+	t.Helper()
+	sd, err := windows.GetNamedSecurityInfo(path, windows.SE_FILE_OBJECT, windows.DACL_SECURITY_INFORMATION)
+	if err != nil {
+		t.Skipf("cannot read the security descriptor of %s: %v", path, err)
+	}
+	text := sd.String()
+	if index := strings.Index(text, "D:"); index >= 0 {
+		return text[index:]
+	}
+	return text
+}

internal/lsp/client.go

@@ -13,8 +13,14 @@ import (
 )
 
 // NotificationHandler receives server->client notifications (e.g.
-// textDocument/publishDiagnostics). params is the raw JSON payload.
-type NotificationHandler func(method string, params json.RawMessage)
+// textDocument/publishDiagnostics). params is the raw JSON payload. seq is the
+// notification's receipt sequence (see Client.ReceiptSeq): the position of the
+// frame it arrived in, stamped the moment that frame came off the wire — NOT
+// when this handler happens to run, which can lag receipt when the queue is
+// backed up. A caller that needs to know whether something newer than a given
+// point has arrived must compare against seq, not against when its own handling
+// code runs.
+type NotificationHandler func(method string, params json.RawMessage, seq int64)
 
 // Client speaks JSON-RPC 2.0 with LSP framing (Content-Length headers) over a
 // reader/writer pair. It is transport-agnostic: server.go wires it to a process's
@@ -32,8 +38,60 @@ type Client struct {
 	closeOnce sync.Once
 	closed    chan struct{}
 	readErr   error
+
+	notifyMu     sync.Mutex
+	notifyQueue  []notification
+	notifyBytes  int
+	notifyReady  chan struct{}
+	notifyClosed bool
+	// notificationDrained is closed by notificationLoop, and only after
+	// closeNotifications has stopped admission and every accepted notification
+	// (including an in-flight handler) has finished.
+	notificationDrained chan struct{}
+	receiptSeq          int64 // frames read off the wire so far (see ReceiptSeq)
+	// acceptedSeq is the receipt seq of the last notification queued for the
+	// worker, handledSeq the seq of the last one whose handler has returned, and
+	// handledWait a channel closed (and replaced) each time handledSeq advances.
+	// Together they let a waiter tell whether the worker has caught up with what
+	// the reader accepted. Both track notifications only; receiptSeq counts every
+	// frame, so the two are compared against each other, never against it.
+	acceptedSeq int64
+	handledSeq  int64
+	handledWait chan struct{}
 }
 
+type notification struct {
+	method string
+	params json.RawMessage
+	seq    int64
+}
+
+// The notification backlog is bounded by both message count and retained
+// payload bytes. A well-behaved handler drains far faster than any single burst
+// fills either limit; sustained overload — a language server emitting faster
+// than the single handler can consume, or a handler stuck waiting on a
+// re-entrant Call — is a fatal condition for this client, not something to
+// paper over by growing the queue without bound. Hitting either limit fails the
+// client (see enqueueNotification): IsClosed becomes true, and the manager
+// evicts and restarts the session on next use, exactly as it does for any other
+// dead client.
+const (
+	notifyQueueLimit     = 4096
+	notifyQueueByteLimit = 16 << 20 // 16 MiB
+)
+
+// maxFrameBytes is the largest single frame this transport will read. Without
+// it the byte budget above would not be authoritative: readMessage allocates the
+// whole body before anything can classify it, so one notification with a huge
+// Content-Length would be materialized in full and only then rejected by
+// enqueueNotification. Capping at the same value keeps that impossible — a
+// notification can never allocate past the budget it is measured against — and
+// bounds what a malformed or hostile header can make this client allocate. A
+// legitimate LSP frame is orders of magnitude smaller; one that is not is a
+// protocol error, and failing the read closes the client so the manager restarts
+// the session.
+const maxFrameBytes = notifyQueueByteLimit
+
 type rpcError struct {
 	Code    int             `json:"code"`
 	Message string          `json:"message"`
@@ -81,10 +139,14 @@ type incomingMessage struct {
 // server process exits); call Close to stop using the client.
 func NewClient(r io.Reader, w io.Writer) *Client {
 	client := &Client{
-		writer:  w,
-		pending: make(map[int64]chan rpcResponse),
-		closed:  make(chan struct{}),
+		writer:              w,
+		pending:             make(map[int64]chan rpcResponse),
+		closed:              make(chan struct{}),
+		notifyReady:         make(chan struct{}, 1),
+		notificationDrained: make(chan struct{}),
+		handledWait:         make(chan struct{}),
 	}
+	go client.notificationLoop()
 	go client.readLoop(bufio.NewReader(r))
 	return client
 }
@@ -155,6 +217,15 @@ func (c *Client) readLoop(reader *bufio.Reader) {
 			c.failPending(err)
 			return
 		}
+		// Stamp the receipt boundary here — while the frame is nothing but bytes
+		// that have left the wire — rather than at enqueue. Everything below
+		// (json.Unmarshal of a peer-sized payload, then enqueue) runs on this
+		// goroutine while another can be capturing a baseline from ReceiptSeq, so
+		// stamping later would let a publish that was already read be numbered
+		// above a baseline taken after it arrived, and a superseded publish would
+		// then look fresh. Frames that turn out not to be notifications consume a
+		// number too: the sequence is a receipt clock, and gaps in it are fine.
+		seq := c.stampReceipt()
 		var msg incomingMessage
 		if err := json.Unmarshal(body, &msg); err != nil {
 			continue // skip a malformed frame rather than tearing down the session
@@ -166,12 +237,7 @@ func (c *Client) readLoop(reader *bufio.Reader) {
 			// required or the server can block waiting on it (e.g. registerCapability).
 			_ = c.write(outgoingReply{JSONRPC: "2.0", ID: msg.ID, Result: nil})
 		case msg.Method != "":
-			c.mu.Lock()
-			handler := c.handler
-			c.mu.Unlock()
-			if handler != nil {
-				handler(msg.Method, msg.Params)
-			}
+			c.enqueueNotification(notification{method: msg.Method, params: msg.Params, seq: seq})
 		case hasID:
 			var id int64
 			if err := json.Unmarshal(msg.ID, &id); err == nil {
@@ -181,6 +247,171 @@ func (c *Client) readLoop(reader *bufio.Reader) {
 	}
 }
 
+func (c *Client) notificationLoop() {
+	defer close(c.notificationDrained)
+	for {
+		<-c.notifyReady
+		for {
+			notification, ok, closed := c.dequeueNotification()
+			if !ok {
+				if closed {
+					return
+				}
+				break
+			}
+			c.mu.Lock()
+			handler := c.handler
+			c.mu.Unlock()
+			if handler != nil {
+				handler(notification.method, notification.params, notification.seq)
+			}
+			c.markHandled(notification.seq)
+		}
+	}
+}
+
+// markHandled records that everything received through seq has now been handled
+// and wakes anyone waiting for the worker to catch up.
+func (c *Client) markHandled(seq int64) {
+	c.notifyMu.Lock()
+	if seq > c.handledSeq {
+		c.handledSeq = seq
+	}
+	wait := c.handledWait
+	c.handledWait = make(chan struct{})
+	c.notifyMu.Unlock()
+	if wait != nil {
+		close(wait)
+	}
+}
+
+// handledThrough returns the receipt seq the worker has finished handling, plus
+// a channel closed the next time that advances. The channel is nil for a Client
+// built without NewClient (some unit tests), which has no worker to advance it.
+func (c *Client) handledThrough() (int64, <-chan struct{}) {
+	c.notifyMu.Lock()
+	defer c.notifyMu.Unlock()
+	return c.handledSeq, c.handledWait
+}
+
+// acceptedNotificationSeq returns the receipt seq of the most recently queued
+// notification (0 if none). It is the point the worker must reach to have
+// handled everything the reader had accepted at the time of the call.
+func (c *Client) acceptedNotificationSeq() int64 {
+	c.notifyMu.Lock()
+	defer c.notifyMu.Unlock()
+	return c.acceptedSeq
+}
+
+// notificationsDone returns the worker completion signal. A nil result means
+// this Client was constructed without NewClient (as some unit-test clients are)
+// and has no notification worker to wait for.
+func (c *Client) notificationsDone() <-chan struct{} {
+	return c.notificationDrained
+}
+
+// enqueueNotification hands a server notification to the worker loop. item.seq
+// must already carry the receipt stamp from stampReceipt: the receipt boundary
+// belongs to the moment the frame left the wire, not to this call, which happens
+// a full json.Unmarshal later. It never blocks and never silently discards a
+// message the handler could still act on: the queue grows instead, up to its
+// message and byte limits.
+//
+// The alternatives to growing are worse. Blocking the read loop when a buffer
+// fills is the deadlock this dispatch exists to avoid — a handler that calls
+// Client.Call waits for a response frame the blocked reader can no longer
+// deliver. Dropping the oldest queued item instead loses protocol state
+// permanently: a textDocument/publishDiagnostics for one URI is the server's
+// only report for that URI, so discarding it makes session.waitForDiagnostics
+// time out and Manager.Check return nothing even though the server published
+// findings.
+//
+// Growth is bounded in practice by how much the server emits while a handler
+// runs, and the queue is released as soon as it drains. But "in practice" is
+// not a limit: a handler that never returns, or a server that sustains a
+// higher rate than the single handler can drain, would otherwise grow this
+// queue's full json.RawMessage payloads without bound until the heap gives
+// out. The count limit alone is insufficient because notification payloads are
+// peer-controlled and can be large; the byte limit prevents a few large
+// diagnostics publishes from exhausting the heap before the count limit is
+// reached. Either limit turns overload into an explicit, observable failure —
+// the client is failed and closed — rather than unbounded protocol retention.
+func (c *Client) enqueueNotification(item notification) {
+	c.notifyMu.Lock()
+	if c.notifyClosed {
+		// The worker loop has already stopped, so anything queued now would never
+		// be handled. Retaining it would grow the queue for as long as the
+		// transport stays readable after Close — Server.Shutdown closes the client
+		// before closing stdin, so a server emitting notifications while it handles
+		// shutdown/exit keeps the read loop feeding a queue nobody drains.
+		c.notifyMu.Unlock()
+		return
+	}
+	itemBytes := len(item.method) + len(item.params)
+	if len(c.notifyQueue) >= notifyQueueLimit || itemBytes > notifyQueueByteLimit-c.notifyBytes {
+		c.notifyMu.Unlock()
+		c.failPending(fmt.Errorf(
+			"lsp client: notification backlog exceeded %d messages or %d bytes",
+			notifyQueueLimit,
+			notifyQueueByteLimit,
+		))
+		return
+	}
+	c.notifyQueue = append(c.notifyQueue, item)
+	c.notifyBytes += itemBytes
+	c.acceptedSeq = item.seq
+	c.notifyMu.Unlock()
+
+	select {
+	case c.notifyReady <- struct{}{}:
+	default:
+		// A wake-up is already pending; the worker drains the whole queue per wake,
+		// so this item is covered by it.
+	}
+}
+
+// stampReceipt claims the next receipt number for a frame that has just been
+// read off the wire. The read loop calls it for every frame before parsing one,
+// so a notification's seq reflects when it arrived rather than when this client
+// got around to decoding and queueing it.
+func (c *Client) stampReceipt() int64 {
+	c.notifyMu.Lock()
+	defer c.notifyMu.Unlock()
+	c.receiptSeq++
+	return c.receiptSeq
+}
+
+// ReceiptSeq returns how many frames have been read off the wire so far,
+// including any notification still waiting to be dispatched to the handler. A
+// caller that wants to know whether a notification newer than "now" has arrived
+// should snapshot this before triggering whatever produces it, then require a
+// subsequently-observed seq to be strictly greater: a notification whose frame
+// had already been read at snapshot time has seq <= the snapshot, even if it is
+// still queued and its handler doesn't run until afterward.
+func (c *Client) ReceiptSeq() int64 {
+	c.notifyMu.Lock()
+	defer c.notifyMu.Unlock()
+	return c.receiptSeq
+}
+
+func (c *Client) dequeueNotification() (notification, bool, bool) {
+	c.notifyMu.Lock()
+	defer c.notifyMu.Unlock()
+	if len(c.notifyQueue) == 0 {
+		return notification{}, false, c.notifyClosed
+	}
+	item := c.notifyQueue[0]
+	c.notifyBytes -= len(item.method) + len(item.params)
+	c.notifyQueue[0] = notification{}
+	c.notifyQueue = c.notifyQueue[1:]
+	if len(c.notifyQueue) == 0 {
+		// Release the backing array once drained; re-slicing alone would keep a
+		// burst's worth of capacity (and its already-consumed items) alive.
+		c.notifyQueue = nil
+	}
+	return item, true, false
+}
+
 func (c *Client) deliver(id int64, resp rpcResponse) {
 	c.mu.Lock()
 	ch, ok := c.pending[id]
@@ -204,9 +435,27 @@ func (c *Client) failPending(err error) {
 			ch <- rpcResponse{Err: &rpcError{Code: -1, Message: err.Error()}}
 		}
 		close(c.closed)
+		c.closeNotifications()
 	})
 }
 
+// closeNotifications atomically stops accepting notifications, then wakes the
+// worker so everything accepted before that boundary is delivered in FIFO order.
+// It deliberately does not wait: a user handler may be blocked, and transport
+// failure, overload, and concurrent Close must never deadlock teardown. The
+// worker exits itself after the accepted queue (including any in-flight handler)
+// has drained. An enqueue racing with shutdown is therefore either accepted and
+// delivered before worker exit, or observes notifyClosed and is rejected.
+func (c *Client) closeNotifications() {
+	c.notifyMu.Lock()
+	c.notifyClosed = true
+	c.notifyMu.Unlock()
+	select {
+	case c.notifyReady <- struct{}{}:
+	default:
+	}
+}
+
 func (c *Client) readError() error {
 	c.mu.Lock()
 	defer c.mu.Unlock()
@@ -283,6 +532,9 @@ func readMessage(reader *bufio.Reader) ([]byte, error) {
 	if contentLength < 0 {
 		return nil, errors.New("message missing Content-Length header")
 	}
+	if contentLength > maxFrameBytes {
+		return nil, fmt.Errorf("lsp frame of %d bytes exceeds the %d byte limit", contentLength, maxFrameBytes)
+	}
 	body := make([]byte, contentLength)
 	if _, err := io.ReadFull(reader, body); err != nil {
 		return nil, err

internal/lsp/client_test.go

@@ -7,7 +7,9 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"runtime"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 )
@@ -208,7 +210,7 @@ func TestClientNotificationHandler(t *testing.T) {
 	_ = serverReader
 
 	received := make(chan string, 1)
-	client.SetNotificationHandler(func(method string, _ json.RawMessage) {
+	client.SetNotificationHandler(func(method string, _ json.RawMessage, _ int64) {
 		received <- method
 	})
 	_ = writeMessage(serverWriter, map[string]any{
@@ -227,6 +229,438 @@ func TestClientNotificationHandler(t *testing.T) {
 	}
 }
 
+func TestClientNotificationHandlerCanCallClient(t *testing.T) {
+	clientReader, serverWriter := io.Pipe()
+	serverReader, clientWriter := io.Pipe()
+	client := NewClient(clientReader, clientWriter)
+	defer client.Close()
+	defer serverWriter.Close()
+	defer clientWriter.Close()
+
+	serverDone := make(chan error, 1)
+	go func() {
+		body, err := readMessage(bufio.NewReader(serverReader))
+		if err != nil {
+			serverDone <- err
+			return
+		}
+		var request incomingMessage
+		if err := json.Unmarshal(body, &request); err != nil {
+			serverDone <- err
+			return
+		}
+		serverDone <- writeMessage(serverWriter, map[string]any{
+			"jsonrpc": "2.0",
+			"id":      request.ID,
+			"result":  map[string]bool{"applied": true},
+		})
+	}()
+
+	handlerDone := make(chan error, 1)
+	client.SetNotificationHandler(func(_ string, _ json.RawMessage, _ int64) {
+		ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+		defer cancel()
+		_, err := client.Call(ctx, "workspace/applyEdit", nil)
+		handlerDone <- err
+	})
+	if err := writeMessage(serverWriter, map[string]any{
+		"jsonrpc": "2.0",
+		"method":  "workspace/requestEdit",
+	}); err != nil {
+		t.Fatal(err)
+	}
+
+	select {
+	case err := <-handlerDone:
+		if err != nil {
+			t.Fatalf("notification handler call failed: %v", err)
+		}
+	case <-time.After(2 * time.Second):
+		t.Fatal("notification handler deadlocked waiting for its response")
+	}
+	if err := <-serverDone; err != nil {
+		t.Fatalf("server failed: %v", err)
+	}
+}
+
+func TestClientNotificationHandlersPreserveOrder(t *testing.T) {
+	clientReader, serverWriter := io.Pipe()
+	client := NewClient(clientReader, io.Discard)
+	defer client.Close()
+	defer serverWriter.Close()
+
+	received := make(chan string, 2)
+	client.SetNotificationHandler(func(method string, _ json.RawMessage, _ int64) {
+		received <- method
+	})
+	for _, method := range []string{"first", "second"} {
+		if err := writeMessage(serverWriter, map[string]any{
+			"jsonrpc": "2.0",
+			"method":  method,
+		}); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	for _, want := range []string{"first", "second"} {
+		select {
+		case got := <-received:
+			if got != want {
+				t.Fatalf("notification = %q, want %q", got, want)
+			}
+		case <-time.After(2 * time.Second):
+			t.Fatalf("timed out waiting for notification %q", want)
+		}
+	}
+}
+
+func TestClientNotificationBurstDoesNotBlockResponse(t *testing.T) {
+	clientReader, serverWriter := io.Pipe()
+	serverReader, clientWriter := io.Pipe()
+	client := NewClient(clientReader, clientWriter)
+	defer client.Close()
+	defer serverWriter.Close()
+	defer clientWriter.Close()
+
+	handlerStarted := make(chan struct{})
+	handlerDone := make(chan error, 1)
+	var mu sync.Mutex
+	var queued []string
+	allQueued := make(chan struct{})
+	client.SetNotificationHandler(func(method string, _ json.RawMessage, _ int64) {
+		if method != "blocking" {
+			mu.Lock()
+			queued = append(queued, method)
+			complete := len(queued) == notificationBurstSize
+			mu.Unlock()
+			if complete {
+				close(allQueued)
+			}
+			return
+		}
+		close(handlerStarted)
+		ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+		defer cancel()
+		_, err := client.Call(ctx, "workspace/applyEdit", nil)
+		handlerDone <- err
+	})
+
+	serverDone := make(chan error, 1)
+	go func() {
+		reader := bufio.NewReader(serverReader)
+		body, err := readMessage(reader)
+		if err != nil {
+			serverDone <- err
+			return
+		}
+		var request incomingMessage
+		if err := json.Unmarshal(body, &request); err != nil {
+			serverDone <- err
+			return
+		}
+		for i := 0; i < notificationBurstSize; i++ {
+			if err := writeMessage(serverWriter, map[string]any{
+				"jsonrpc": "2.0",
+				"method":  fmt.Sprintf("queued-%03d", i),
+			}); err != nil {
+				serverDone <- err
+				return
+			}
+		}
+		serverDone <- writeMessage(serverWriter, map[string]any{
+			"jsonrpc": "2.0",
+			"id":      request.ID,
+			"result":  nil,
+		})
+	}()
+
+	if err := writeMessage(serverWriter, map[string]any{
+		"jsonrpc": "2.0",
+		"method":  "blocking",
+	}); err != nil {
+		t.Fatal(err)
+	}
+	select {
+	case <-handlerStarted:
+	case <-time.After(time.Second):
+		t.Fatal("blocking notification handler did not start")
+	}
+	select {
+	case err := <-handlerDone:
+		if err != nil {
+			t.Fatalf("notification handler call failed under burst: %v", err)
+		}
+	case <-time.After(2 * time.Second):
+		t.Fatal("notification burst blocked the response read loop")
+	}
+	if err := <-serverDone; err != nil {
+		t.Fatalf("server failed: %v", err)
+	}
+	// Not blocking the reader is only half the requirement: every notification the
+	// server sent during the burst must still reach the handler, in order. A
+	// bounded queue that drops the oldest would silently lose the head of this
+	// sequence — and with it a publishDiagnostics the checker is waiting for.
+	select {
+	case <-allQueued:
+	case <-time.After(5 * time.Second):
+		mu.Lock()
+		received := len(queued)
+		mu.Unlock()
+		t.Fatalf("received %d of %d burst notifications; the queue lost messages", received, notificationBurstSize)
+	}
+	mu.Lock()
+	defer mu.Unlock()
+	for i, method := range queued {
+		if want := fmt.Sprintf("queued-%03d", i); method != want {
+			t.Fatalf("burst notification %d = %q, want %q (order must survive the burst)", i, method, want)
+		}
+	}
+}
+
+// notificationBurstSize is far past any buffer the dispatch used to have, so a
+// bounded queue would be visible as either a blocked read loop or a lost message.
+const notificationBurstSize = 512
+
+// TestClientNotificationQueueIsLossless is the regression test for the overflow
+// policy: a queued notification must never be discarded. A dropped
+// textDocument/publishDiagnostics is the server's only report for that URI, so
+// losing it makes session.waitForDiagnostics time out and Manager.Check return
+// nothing even though the server published findings.
+func TestClientNotificationQueueIsLossless(t *testing.T) {
+	client := &Client{notifyReady: make(chan struct{}, 1)}
+	for i := 0; i < notificationBurstSize; i++ {
+		client.enqueueNotification(notification{method: fmt.Sprintf("notification-%03d", i)})
+	}
+
+	for i := 0; i < notificationBurstSize; i++ {
+		item, ok, _ := client.dequeueNotification()
+		if !ok {
+			t.Fatalf("notification %d was discarded by the queue", i)
+		}
+		want := fmt.Sprintf("notification-%03d", i)
+		if item.method != want {
+			t.Fatalf("notification = %q, want %q (queue must stay FIFO)", item.method, want)
+		}
+	}
+	if _, ok, _ := client.dequeueNotification(); ok {
+		t.Fatal("queue returned more notifications than were enqueued")
+	}
+	if client.notifyQueue != nil {
+		t.Fatalf("drained queue retained %d slots of capacity", cap(client.notifyQueue))
+	}
+	if client.notifyBytes != 0 {
+		t.Fatalf("drained queue retained byte accounting: %d", client.notifyBytes)
+	}
+}
+
+func TestClientDrainsAcceptedNotificationsAfterTransportEOF(t *testing.T) {
+	clientReader, serverWriter := io.Pipe()
+	client := NewClient(clientReader, io.Discard)
+
+	blockStarted := make(chan struct{})
+	releaseBlock := make(chan struct{})
+	handled := make(chan string, 2)
+	client.SetNotificationHandler(func(method string, _ json.RawMessage, _ int64) {
+		if method == "block" {
+			close(blockStarted)
+			<-releaseBlock
+		}
+		handled <- method
+	})
+
+	if err := writeMessage(serverWriter, map[string]any{"jsonrpc": "2.0", "method": "block"}); err != nil {
+		t.Fatal(err)
+	}
+	<-blockStarted
+	if err := writeMessage(serverWriter, map[string]any{
+		"jsonrpc": "2.0", "method": "textDocument/publishDiagnostics",
+	}); err != nil {
+		t.Fatal(err)
+	}
+	// Wait until the reader has accepted the publish, then fail it while the
+	// sole worker is still in the preceding handler and cannot dequeue it.
+	deadline := time.Now().Add(time.Second)
+	for client.ReceiptSeq() != 2 {
+		if time.Now().After(deadline) {
+			t.Fatal("publish was not accepted by the read loop")
+		}
+		runtime.Gosched()
+	}
+	if err := serverWriter.Close(); err != nil {
+		t.Fatal(err)
+	}
+	// Fresh budget: the wait above may have consumed most of the previous one,
+	// which would make this loop fail on nothing worse than slow scheduling.
+	deadline = time.Now().Add(time.Second)
+	for !client.IsClosed() {
+		if time.Now().After(deadline) {
+			t.Fatal("transport EOF did not close client")
+		}
+		runtime.Gosched()
+	}
+	close(releaseBlock)
+
+	for _, want := range []string{"block", "textDocument/publishDiagnostics"} {
+		select {
+		case got := <-handled:
+			if got != want {
+				t.Fatalf("handled %q, want %q", got, want)
+			}
+		case <-time.After(time.Second):
+			t.Fatalf("accepted notification %q was not delivered after EOF", want)
+		}
+	}
+	select {
+	case <-client.notificationDrained:
+	case <-time.After(time.Second):
+		t.Fatal("notification worker did not report the accepted queue drained")
+	}
+}
+
+// TestReceiptStampedAtReadNotEnqueue is the regression test for the review gap
+// on #759 (pullrequestreview-4834747507): TestPublishBaselineRejectsFrameReadBeforeBaseline
+// calls stampReceipt itself and never drives readLoop, so it pins the seq
+// comparison but not WHERE the stamp is taken — a refactor that moved stamping
+// back to the enqueue call site (reverting the read-time fix) left that test
+// green.
+//
+// This test distinguishes the two call sites directly: a response frame is
+// read off the wire but never reaches enqueueNotification (see the `hasID`
+// branch in readLoop). Under read-time stamping every frame consumes a receipt
+// number — "gaps in it are fine", per stampReceipt's doc comment — so
+// ReceiptSeq must advance even though nothing was queued. Under enqueue-time
+// stamping it would not, since stampReceipt would never run for this frame.
+func TestReceiptStampedAtReadNotEnqueue(t *testing.T) {
+	clientReader, serverWriter := io.Pipe()
+	client := NewClient(clientReader, io.Discard)
+	defer serverWriter.Close()
+
+	// A plain response frame: has an id, no method, so it is delivered via
+	// c.deliver and never passed to enqueueNotification.
+	if err := writeMessage(serverWriter, map[string]any{
+		"jsonrpc": "2.0", "id": 1, "result": nil,
+	}); err != nil {
+		t.Fatal(err)
+	}
+
+	deadline := time.Now().Add(time.Second)
+	for client.ReceiptSeq() == 0 {
+		if time.Now().After(deadline) {
+			t.Fatal("ReceiptSeq did not advance for a frame that was read but never enqueued as a notification")
+		}
+		runtime.Gosched()
+	}
+}
+
+// TestReadMessageRejectsOversizedFrame covers jatmn's P3 finding on #759: the
+// notification byte budget was enforced only at enqueue, but readMessage
+// allocates the whole body before anything can tell a notification from a
+// response. A single frame declaring a huge Content-Length was therefore
+// materialized in full and only then measured against a budget it had already
+// blown past. The header is now rejected before the allocation.
+func TestReadMessageRejectsOversizedFrame(t *testing.T) {
+	header := fmt.Sprintf("Content-Length: %d\r\n\r\n", maxFrameBytes+1)
+	_, err := readMessage(bufio.NewReader(strings.NewReader(header)))
+	if err == nil {
+		t.Fatal("an oversized frame must be rejected, not allocated and read")
+	}
+	if !strings.Contains(err.Error(), "exceeds") {
+		t.Fatalf("error = %v, want the frame-size limit to reject it before reading the body", err)
+	}
+	// A frame at the limit is still legal: the cap rejects what is over it, not
+	// what merely approaches it.
+	body := strings.Repeat("x", 16)
+	atLimit := fmt.Sprintf("Content-Length: %d\r\n\r\n%s", len(body), body)
+	if _, err := readMessage(bufio.NewReader(strings.NewReader(atLimit))); err != nil {
+		t.Fatalf("readMessage of an ordinary frame: %v", err)
+	}
+}
+
+// TestClientFailsOnNotificationBacklogOverload is the regression test for
+// jatmn's #759 P2 finding: the lossless queue above had no failure policy — a
+// language server sustaining a higher notification rate than the single
+// handler can drain (no permanently-stuck handler required, just a sustained
+// producer faster than the consumer) would retain every full json.RawMessage
+// payload on Zero's heap without bound. Hitting notifyQueueLimit must fail
+// (and close) the client observably instead of continuing to grow.
+func TestClientFailsOnNotificationBacklogOverload(t *testing.T) {
+	client := &Client{
+		notifyReady: make(chan struct{}, 1),
+		pending:     make(map[int64]chan rpcResponse),
+		closed:      make(chan struct{}),
+	}
+	for i := 0; i < notifyQueueLimit; i++ {
+		client.enqueueNotification(notification{method: "spam"})
+	}
+	if client.IsClosed() {
+		t.Fatal("client closed before the backlog limit was reached")
+	}
+	client.notifyMu.Lock()
+	queued := len(client.notifyQueue)
+	client.notifyMu.Unlock()
+	if queued != notifyQueueLimit {
+		t.Fatalf("queued = %d, want %d before the limit is exceeded", queued, notifyQueueLimit)
+	}
+
+	// One push past the limit must fail the client rather than growing the
+	// queue further.
+	client.enqueueNotification(notification{method: "spam"})
+	if !client.IsClosed() {
+		t.Fatal("client must be closed once the notification backlog exceeds notifyQueueLimit")
+	}
+	client.notifyMu.Lock()
+	queuedAfter := len(client.notifyQueue)
+	bytesAfter := client.notifyBytes
+	client.notifyMu.Unlock()
+	if queuedAfter != notifyQueueLimit {
+		t.Fatalf("closed client retained %d accepted notifications, want %d pending worker drain", queuedAfter, notifyQueueLimit)
+	}
+	if bytesAfter == 0 {
+		t.Fatal("accepted notifications were discarded instead of left for worker drain")
+	}
+}
+
+func TestClientFailsOnNotificationBacklogByteOverload(t *testing.T) {
+	client := &Client{
+		notifyReady: make(chan struct{}, 1),
+		pending:     make(map[int64]chan rpcResponse),
+		closed:      make(chan struct{}),
+	}
+	const messageCount = 16
+	const method = "spam"
+	for i := 0; i < messageCount; i++ {
+		client.enqueueNotification(notification{
+			method: method,
+			params: make(json.RawMessage, notifyQueueByteLimit/messageCount-len(method)),
+		})
+	}
+	if client.IsClosed() {
+		t.Fatal("client closed before the notification byte limit was exceeded")
+	}
+	client.notifyMu.Lock()
+	queued := len(client.notifyQueue)
+	queuedBytes := client.notifyBytes
+	client.notifyMu.Unlock()
+	if queued != messageCount {
+		t.Fatalf("queued = %d, want %d at the byte limit", queued, messageCount)
+	}
+	if queuedBytes != notifyQueueByteLimit {
+		t.Fatalf("queued bytes = %d, want limit %d", queuedBytes, notifyQueueByteLimit)
+	}
+
+	client.enqueueNotification(notification{method: "x"})
+	if !client.IsClosed() {
+		t.Fatal("client must close before retaining notification bytes past the limit")
+	}
+	client.notifyMu.Lock()
+	queuedAfter := len(client.notifyQueue)
+	bytesAfter := client.notifyBytes
+	client.notifyMu.Unlock()
+	if queuedAfter != messageCount || bytesAfter != notifyQueueByteLimit {
+		t.Fatalf("accepted backlog changed during close: %d notifications and %d accounted bytes", queuedAfter, bytesAfter)
+	}
+}
+
 func TestClientRejectsCallsAfterClose(t *testing.T) {
 	clientReader, serverWriter := io.Pipe()
 	serverReader, clientWriter := io.Pipe()
@@ -243,3 +677,79 @@ func TestClientRejectsCallsAfterClose(t *testing.T) {
 		t.Fatal("Notify after Close must return an error")
 	}
 }
+
+// TestClientDropsNotificationsAfterClose covers the shutdown path: Close stops
+// the worker loop, but the read loop keeps reading until the transport ends —
+// Server.Shutdown closes the client BEFORE closing stdin, so a server emitting
+// notifications while it handles shutdown/exit would otherwise pile them into a
+// queue nobody drains. Nothing may be handled or retained after Close.
+func TestClientDropsNotificationsAfterClose(t *testing.T) {
+	clientReader, serverWriter := io.Pipe()
+	serverReader, clientWriter := io.Pipe()
+	client := NewClient(clientReader, clientWriter)
+	defer serverWriter.Close()
+	defer clientWriter.Close()
+	go func() {
+		// Drain anything the client writes so no write can block the test.
+		_, _ = io.Copy(io.Discard, serverReader)
+	}()
+
+	handled := make(chan string, 4)
+	client.SetNotificationHandler(func(method string, _ json.RawMessage, _ int64) {
+		handled <- method
+	})
+
+	// A notification before Close still reaches the handler.
+	if err := writeMessage(serverWriter, map[string]any{"jsonrpc": "2.0", "method": "before-close"}); err != nil {
+		t.Fatal(err)
+	}
+	select {
+	case method := <-handled:
+		if method != "before-close" {
+			t.Fatalf("handled %q, want before-close", method)
+		}
+	case <-time.After(2 * time.Second):
+		t.Fatal("notification before Close was not handled")
+	}
+
+	if err := client.Close(); err != nil {
+		t.Fatalf("Close: %v", err)
+	}
+	// The transport stays writable, exactly as it does between Client.Close and
+	// stdin.Close in Server.Shutdown.
+	for i := 0; i < 64; i++ {
+		if err := writeMessage(serverWriter, map[string]any{
+			"jsonrpc": "2.0",
+			"method":  fmt.Sprintf("after-close-%03d", i),
+		}); err != nil {
+			t.Fatalf("write notification after Close: %v", err)
+		}
+	}
+
+	select {
+	case method := <-handled:
+		t.Fatalf("handler ran for %q after Close", method)
+	case <-time.After(200 * time.Millisecond):
+	}
+
+	// Give the read loop time to consume every frame it was handed, then require
+	// the queue to hold nothing: dropping on enqueue is what keeps a closed client
+	// from growing for as long as its reader stays open.
+	deadline := time.Now().Add(2 * time.Second)
+	for {
+		client.notifyMu.Lock()
+		queued := len(client.notifyQueue)
+		closed := client.notifyClosed
+		client.notifyMu.Unlock()
+		if !closed {
+			t.Fatal("Close did not mark the notification queue closed")
+		}
+		if queued != 0 {
+			t.Fatalf("closed client retained %d queued notifications", queued)
+		}
+		if time.Now().After(deadline) {
+			return
+		}
+		time.Sleep(10 * time.Millisecond)
+	}
+}

internal/lsp/documents.go

@@ -20,34 +20,39 @@ type lspServer interface {
 type session struct {
 	server lspServer
 	client *Client
+	// catchUpGrace bounds catchUpNotifications on a live client. Zero means "do
+	// not wait", which is what the hand-built sessions in tests get by default.
+	catchUpGrace time.Duration
 
-	mu           sync.Mutex
-	open         map[string]bool            // uri -> didOpen sent
-	versions     map[string]int             // uri -> current (committed) version
-	diagnostics  map[string][]Diagnostic    // uri -> latest published diagnostics
-	lastPublish  map[string]time.Time       // uri -> time of last publish
-	publishCount map[string]int             // uri -> monotonic publish count
-	waiters      map[string][]chan struct{} // uri -> goroutines awaiting the next publish
-	fileLocks    map[string]*sync.Mutex     // uri -> per-document sync serializer
+	mu          sync.Mutex
+	open        map[string]bool            // uri -> didOpen sent
+	versions    map[string]int             // uri -> current (committed) version
+	diagnostics map[string][]Diagnostic    // uri -> latest published diagnostics
+	lastPublish map[string]time.Time       // uri -> time of last publish
+	publishSeq  map[string]int64           // uri -> receipt seq of latest publish (see Client.ReceiptSeq)
+	waiters     map[string][]chan struct{} // uri -> goroutines awaiting the next publish
+	fileLocks   map[string]*sync.Mutex     // uri -> per-document sync serializer
 }
 
 func newSession(server lspServer) *session {
 	s := &session{
 		server:       server,
 		client:       server.Client(),
-		open:         map[string]bool{},
-		versions:     map[string]int{},
-		diagnostics:  map[string][]Diagnostic{},
-		lastPublish:  map[string]time.Time{},
-		publishCount: map[string]int{},
-		waiters:      map[string][]chan struct{}{},
-		fileLocks:    map[string]*sync.Mutex{},
+		catchUpGrace: notificationCatchUpGrace,
+
+		open:        map[string]bool{},
+		versions:    map[string]int{},
+		diagnostics: map[string][]Diagnostic{},
+		lastPublish: map[string]time.Time{},
+		publishSeq:  map[string]int64{},
+		waiters:     map[string][]chan struct{}{},
+		fileLocks:   map[string]*sync.Mutex{},
 	}
 	s.client.SetNotificationHandler(s.handleNotification)
 	return s
 }
 
-func (s *session) handleNotification(method string, params json.RawMessage) {
+func (s *session) handleNotification(method string, params json.RawMessage, seq int64) {
 	if method != "textDocument/publishDiagnostics" {
 		return
 	}
@@ -66,7 +71,7 @@ func (s *session) handleNotification(method string, params json.RawMessage) {
 	}
 	s.diagnostics[payload.URI] = payload.Diagnostics
 	s.lastPublish[payload.URI] = time.Now()
-	s.publishCount[payload.URI]++
+	s.publishSeq[payload.URI] = seq
 	waiters := s.waiters[payload.URI]
 	delete(s.waiters, payload.URI)
 	s.mu.Unlock()
@@ -133,36 +138,65 @@ func (s *session) diagnosticsFor(uri string) []Diagnostic {
 	return append([]Diagnostic(nil), s.diagnostics[uri]...)
 }
 
-// publishBaseline snapshots the current publish count for a URI, captured before
-// a sync so waitForDiagnostics can wait specifically for the publish that sync
-// triggers (not be satisfied by a stale earlier publish).
-func (s *session) publishBaseline(uri string) int {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	return s.publishCount[uri]
+// publishBaseline snapshots the client's current notification receipt
+// sequence, captured before a sync so waitForDiagnostics can require a publish
+// that was RECEIVED after this point. This must baseline against receipt, not
+// against session.publishSeq (which only advances once handleNotification
+// actually runs): dispatch happens off a queue, so a publish for a since-
+// superseded version can already be sitting in that queue, still unprocessed,
+// at the moment a later Check captures its baseline. If baseline were instead
+// "how many publishes has this session recorded so far", that stale publish
+// would land afterward, still satisfy "more than baseline", and hand the new
+// check diagnostics for the wrong text — silently, since many servers omit the
+// version field the staleness check in handleNotification relies on.
+// Baselining against receipt sequence closes that: a notification whose frame
+// had already come off the wire before this call has seq <= baseline no matter
+// when it is decoded, queued, or handled.
+func (s *session) publishBaseline() int64 {
+	return s.client.ReceiptSeq()
 }
 
+// notificationCatchUpGrace is the live-client catch-up budget a real session
+// runs with. It exists for the case where the caller's own deadline has already
+// passed: dropping a publish that is sitting accepted-but-unhandled in the queue
+// would report "no diagnostics" for text the server had in fact already answered
+// for, so a brief overrun is preferable to discarding it. It stays short because
+// the caller is by then out of budget, and it costs nothing in the ordinary case
+// — the session's own handler only parses and records, so the worker is
+// virtually always caught up already and no wait happens at all. A closed client
+// is deliberately not bounded by this; see catchUpNotifications.
+const notificationCatchUpGrace = 50 * time.Millisecond
+
 // waitForDiagnostics blocks until a publish newer than baseline arrives for the
 // URI and the server then goes quiet for the debounce window, or until ctx is
-// done. It returns true when a fresh publish was observed and false when ctx
-// expired before any did — so a caller can avoid returning a stale prior result
-// for newer text. Servers don't signal "analysis complete", so the debounce
-// approximates it: once a fresh publish lands, wait debounce for a follow-up,
-// resetting on each new publish.
-func (s *session) waitForDiagnostics(ctx context.Context, uri string, debounce time.Duration, baseline int) bool {
+// done or the client closes. It returns true when a fresh publish was observed
+// and false when the wait ended before any did — so a caller can avoid returning
+// a stale prior result for newer text. Servers don't signal "analysis complete",
+// so the debounce approximates it: once a fresh publish lands, wait debounce for
+// a follow-up, resetting on each new publish.
+func (s *session) waitForDiagnostics(ctx context.Context, uri string, debounce time.Duration, baseline int64) bool {
 	for {
 		s.mu.Lock()
 		ch := make(chan struct{})
 		s.waiters[uri] = append(s.waiters[uri], ch)
-		count := s.publishCount[uri]
+		seq := s.publishSeq[uri]
 		last := s.lastPublish[uri]
 		s.mu.Unlock()
 
-		if count <= baseline {
+		if seq <= baseline {
 			select {
 			case <-ctx.Done():
 				s.cancelWaiter(uri, ch)
-				return false // no fresh publish for this sync arrived in time
+				// Cancellation, like closure below, ends the wait on a signal that
+				// says nothing about what the server sent, and either can win a race
+				// against a publish this session has already received. Deciding
+				// "nothing arrived" straight out of the select would discard it, so
+				// both settle identically: let the worker finish what it accepted,
+				// then re-read what got recorded.
+				return s.freshAfterCatchUp(uri, baseline)
+			case <-s.client.closed:
+				s.cancelWaiter(uri, ch)
+				return s.freshAfterCatchUp(uri, baseline)
 			case <-ch:
 				continue // a fresh publish arrived; loop into the debounce check
 			}
@@ -171,6 +205,7 @@ func (s *session) waitForDiagnostics(ctx context.Context, uri string, debounce t
 		remaining := debounce - time.Since(last)
 		if remaining <= 0 {
 			s.cancelWaiter(uri, ch)
+			s.catchUpNotifications()
 			return true
 		}
 		timer := time.NewTimer(remaining)
@@ -178,17 +213,83 @@ func (s *session) waitForDiagnostics(ctx context.Context, uri string, debounce t
 		case <-ctx.Done():
 			timer.Stop()
 			s.cancelWaiter(uri, ch)
-			return true // a fresh publish did arrive; ctx merely cut the debounce short
+			// A fresh publish did arrive; ctx merely cut the debounce short. Catch
+			// the worker up regardless: the caller reads diagnosticsFor the moment
+			// this returns, and a newer publish for this URI may be sitting accepted
+			// but unhandled — it should get the newest received, not the older one
+			// that happened to wake this wait.
+			s.catchUpNotifications()
+			return true
+		case <-s.client.closed:
+			timer.Stop()
+			s.cancelWaiter(uri, ch)
+			// Same, for whatever the server managed to publish before it died.
+			s.catchUpNotifications()
+			return true // preserve the fresh publish already received before failure
 		case <-ch:
 			timer.Stop()
 			continue // a newer publish arrived; re-arm the debounce
 		case <-timer.C:
 			s.cancelWaiter(uri, ch)
+			s.catchUpNotifications()
 			return true // quiet for the full window
 		}
 	}
 }
 
+// freshAfterCatchUp reports whether a publish received after baseline has been
+// recorded for the URI, having first let the notification worker finish frames
+// it already accepted. Receipt is what the answer turns on: a publish that was
+// read off the wire but is still queued would otherwise read as "never arrived".
+func (s *session) freshAfterCatchUp(uri string, baseline int64) bool {
+	s.catchUpNotifications()
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	return s.publishSeq[uri] > baseline
+}
+
+// catchUpNotifications waits for the client's notification worker to handle
+// every notification it had already accepted, so a decision made right after
+// cannot miss a publish that was on the wire before it. It returns immediately
+// in the ordinary case, where the worker is already caught up.
+func (s *session) catchUpNotifications() {
+	drained := s.client.notificationsDone()
+	if drained == nil {
+		return // hand-built client (some unit tests): no worker to catch up on
+	}
+	if s.client.IsClosed() {
+		// Wait the worker out instead of time-boxing it. Admission is already
+		// closed so the backlog cannot grow, and a handler's re-entrant Call now
+		// fails immediately rather than blocking on a response that will never
+		// come — the drain is bounded, and it is the last chance these frames get.
+		<-drained
+		return
+	}
+	timer := time.NewTimer(s.catchUpGrace)
+	defer timer.Stop()
+	for {
+		// Re-read the target every pass rather than snapshotting it once. The
+		// reader keeps running while this waits, so a snapshot goes stale: the
+		// worker finishing the item that was last when we started satisfies
+		// `handled >= target` while a newer publish for the same URI sits queued,
+		// and the caller then answers from diagnosticsFor with the older one —
+		// the exact failure the closed-client drain exists to prevent, on the
+		// live path. Growth is not unbounded: the grace below caps the wait no
+		// matter how fast the server publishes.
+		handled, advanced := s.client.handledThrough()
+		if handled >= s.client.acceptedNotificationSeq() {
+			return
+		}
+		select {
+		case <-advanced:
+		case <-drained:
+			return
+		case <-timer.C:
+			return
+		}
+	}
+}
+
 // cancelWaiter removes a still-open waiter (one a publish has not already closed
 // and cleared) so it can't leak or be closed twice.
 func (s *session) cancelWaiter(uri string, target chan struct{}) {

internal/lsp/manager.go

@@ -73,7 +73,7 @@ func (m *Manager) Check(ctx context.Context, path, text string) ([]Diagnostic, e
 		}
 		return nil, err
 	}
-	baseline := sess.publishBaseline(uri)
+	baseline := sess.publishBaseline()
 	if err := sess.sync(ctx, abs, languageID, text); err != nil {
 		return nil, err
 	}

internal/lsp/manager_test.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"io"
 	"os/exec"
+	"runtime"
 	"strings"
 	"sync"
 	"testing"
@@ -228,18 +229,748 @@ func TestSessionDropsStaleVersionPublish(t *testing.T) {
 	sess.mu.Unlock()
 
 	stale, _ := json.Marshal(PublishDiagnosticsParams{URI: uri, Version: 2, Diagnostics: []Diagnostic{{Message: "stale"}}})
-	sess.handleNotification("textDocument/publishDiagnostics", stale)
+	sess.handleNotification("textDocument/publishDiagnostics", stale, 1)
 	if len(sess.diagnosticsFor(uri)) != 0 {
 		t.Fatal("a publish for an older version must be ignored")
 	}
 
 	fresh, _ := json.Marshal(PublishDiagnosticsParams{URI: uri, Version: 3, Diagnostics: []Diagnostic{{Message: "fresh"}}})
-	sess.handleNotification("textDocument/publishDiagnostics", fresh)
+	sess.handleNotification("textDocument/publishDiagnostics", fresh, 2)
 	if d := sess.diagnosticsFor(uri); len(d) != 1 || d[0].Message != "fresh" {
 		t.Fatalf("a current-version publish must apply, got %#v", d)
 	}
 }
 
+// TestPublishBaselineRejectsAlreadyQueuedPublish is the regression test for
+// jatmn's #759 P1 finding: publishBaseline used to snapshot how many publishes
+// session.handleNotification had already RUN for a URI. Dispatch happens off a
+// queue, though, so a publish for a version Check is about to supersede can
+// already be sitting RECEIVED but undispatched at the moment a later Check
+// captures its baseline — then run only afterward, incrementing the old
+// count-based baseline and wrongly looking "new". Since many servers omit the
+// version field, handleNotification's own staleness check (which only fires
+// for a positive version) can't catch this either, so the stale result would
+// reach the caller for the new text, and the debounce could finish before the
+// real response even arrives.
+//
+// This drives the exact interleaving through the real production path: the
+// stale publish is enqueued first (fixing its receipt seq), THEN a baseline is
+// captured, THEN the stale item is dispatched — reproducing "received before
+// baseline, handled after" without depending on goroutine scheduling luck. A
+// bare Client (no background loops, like TestClientNotificationQueueIsLossless
+// uses) makes the enqueue/dequeue ordering fully explicit.
+func TestPublishBaselineRejectsAlreadyQueuedPublish(t *testing.T) {
+	client := &Client{notifyReady: make(chan struct{}, 1)}
+	sess := &session{
+		client:      client,
+		versions:    map[string]int{},
+		diagnostics: map[string][]Diagnostic{},
+		lastPublish: map[string]time.Time{},
+		publishSeq:  map[string]int64{},
+		waiters:     map[string][]chan struct{}{},
+	}
+	uri := PathToURI("/repo/main.go")
+
+	// The stale (version-less — the common case) publish is RECEIVED first: the
+	// read loop stamps a frame's receipt before it decodes or queues it, so the
+	// stamp here comes first too.
+	stale, _ := json.Marshal(PublishDiagnosticsParams{URI: uri, Diagnostics: []Diagnostic{{Message: "stale"}}})
+	client.enqueueNotification(notification{
+		method: "textDocument/publishDiagnostics", params: stale, seq: client.stampReceipt(),
+	})
+
+	// A later Check captures its baseline only now — after the stale publish's
+	// receipt, exactly as publishBaseline does between two Checks whose
+	// notification queue has backed up.
+	baseline := sess.publishBaseline()
+
+	// Dispatch the stale item exactly as notificationLoop would: dequeue and
+	// call the handler with the receipt seq it was actually stamped with.
+	item, ok, _ := client.dequeueNotification()
+	if !ok {
+		t.Fatal("stale notification was not queued")
+	}
+	sess.handleNotification(item.method, item.params, item.seq)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
+	defer cancel()
+	if sess.waitForDiagnostics(ctx, uri, 10*time.Millisecond, baseline) {
+		t.Fatal("a publish received before baseline must not satisfy waitForDiagnostics merely because it was handled afterward")
+	}
+
+	// The real response — received (and handled) after baseline — must satisfy it.
+	fresh, _ := json.Marshal(PublishDiagnosticsParams{URI: uri, Diagnostics: []Diagnostic{{Message: "fresh"}}})
+	client.enqueueNotification(notification{
+		method: "textDocument/publishDiagnostics", params: fresh, seq: client.stampReceipt(),
+	})
+	item2, ok, _ := client.dequeueNotification()
+	if !ok {
+		t.Fatal("fresh notification was not queued")
+	}
+	sess.handleNotification(item2.method, item2.params, item2.seq)
+
+	ctx2, cancel2 := context.WithTimeout(context.Background(), time.Second)
+	defer cancel2()
+	if !sess.waitForDiagnostics(ctx2, uri, 10*time.Millisecond, baseline) {
+		t.Fatal("a publish received after baseline must satisfy waitForDiagnostics")
+	}
+	if d := sess.diagnosticsFor(uri); len(d) != 1 || d[0].Message != "fresh" {
+		t.Fatalf("diagnostics = %#v, want the fresh publish", d)
+	}
+}
+
+// TestPublishBaselineRejectsFrameReadBeforeBaseline is the regression test for
+// jatmn's follow-up P1 finding on #759: stamping receipt at ENQUEUE left a
+// window async dispatch had opened. The read loop consumes a frame, then decodes
+// it (a full json.Unmarshal of a peer-sized payload) and only then enqueues it,
+// all while another goroutine can capture a baseline. A publishDiagnostics for
+// text the new Check is about to supersede could therefore be numbered above a
+// baseline taken after it had already come off the wire, and — since most
+// servers omit the version field that handleNotification's staleness check needs
+// — reach the caller as if it answered the new text.
+//
+// The interleaving is driven at the seam itself: stamp (the frame leaves the
+// wire), baseline (a concurrent Check), then enqueue and dispatch (the read loop
+// finishes decoding). Stamping at enqueue put this publish above the baseline;
+// stamping at read puts it at or below.
+func TestPublishBaselineRejectsFrameReadBeforeBaseline(t *testing.T) {
+	client := &Client{notifyReady: make(chan struct{}, 1)}
+	sess := &session{
+		client:      client,
+		versions:    map[string]int{},
+		diagnostics: map[string][]Diagnostic{},
+		lastPublish: map[string]time.Time{},
+		publishSeq:  map[string]int64{},
+		waiters:     map[string][]chan struct{}{},
+	}
+	uri := PathToURI("/repo/main.go")
+
+	// The read loop pulls the stale frame off the wire and stamps it...
+	seq := client.stampReceipt()
+
+	// ...a concurrent Check baselines while that frame is still being decoded...
+	baseline := sess.publishBaseline()
+
+	// ...and only now does the frame reach the queue and the handler.
+	stale, _ := json.Marshal(PublishDiagnosticsParams{URI: uri, Diagnostics: []Diagnostic{{Message: "stale"}}})
+	client.enqueueNotification(notification{
+		method: "textDocument/publishDiagnostics", params: stale, seq: seq,
+	})
+	item, ok, _ := client.dequeueNotification()
+	if !ok {
+		t.Fatal("stale notification was not queued")
+	}
+	sess.handleNotification(item.method, item.params, item.seq)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
+	defer cancel()
+	if sess.waitForDiagnostics(ctx, uri, 10*time.Millisecond, baseline) {
+		t.Fatal("a publish whose frame was read before baseline must not satisfy waitForDiagnostics merely because it was decoded and queued afterward")
+	}
+	if d := sess.diagnosticsFor(uri); len(d) != 1 || d[0].Message != "stale" {
+		t.Fatalf("diagnostics = %#v, want the stale publish still recorded (rejected as an answer, not dropped)", d)
+	}
+}
+
+func TestWaitForDiagnosticsReturnsWhenClientCloses(t *testing.T) {
+	client := &Client{
+		pending: make(map[int64]chan rpcResponse),
+		closed:  make(chan struct{}),
+	}
+	uri := PathToURI("/repo/main.go")
+	sess := &session{
+		client:      client,
+		diagnostics: map[string][]Diagnostic{},
+		lastPublish: map[string]time.Time{},
+		publishSeq:  map[string]int64{},
+		waiters:     map[string][]chan struct{}{},
+	}
+	waitDone := make(chan bool, 1)
+	go func() {
+		waitDone <- sess.waitForDiagnostics(context.Background(), uri, time.Second, 0)
+	}()
+
+	deadline := time.Now().Add(time.Second)
+	for {
+		sess.mu.Lock()
+		waiting := len(sess.waiters[uri]) == 1
+		sess.mu.Unlock()
+		if waiting {
+			break
+		}
+		if time.Now().After(deadline) {
+			t.Fatal("diagnostic wait was not registered")
+		}
+		time.Sleep(time.Millisecond)
+	}
+
+	client.failPending(errors.New("notification backlog exceeded"))
+	select {
+	case fresh := <-waitDone:
+		if fresh {
+			t.Fatal("client failure without a fresh publish must not report fresh diagnostics")
+		}
+	case <-time.After(time.Second):
+		t.Fatal("diagnostic wait did not wake when the client failed")
+	}
+	sess.mu.Lock()
+	waiters := len(sess.waiters[uri])
+	sess.mu.Unlock()
+	if waiters != 0 {
+		t.Fatalf("client failure left %d diagnostic waiters registered", waiters)
+	}
+}
+
+func TestWaitForDiagnosticsPreservesPublishHandledBeforeClientCloses(t *testing.T) {
+	// Keep the test goroutine running while it closes both signals so the waiter
+	// observes the publish and client closure as simultaneously ready. Without
+	// re-checking publishSeq, select could randomly choose closure and discard the
+	// fresh diagnostics that handleNotification had already recorded.
+	previousProcs := runtime.GOMAXPROCS(1)
+	defer runtime.GOMAXPROCS(previousProcs)
+
+	params, err := json.Marshal(PublishDiagnosticsParams{
+		URI:         PathToURI("/repo/main.go"),
+		Diagnostics: []Diagnostic{{Message: "fresh"}},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	for i := 0; i < 100; i++ {
+		client := &Client{
+			pending: make(map[int64]chan rpcResponse),
+			closed:  make(chan struct{}),
+		}
+		uri := PathToURI("/repo/main.go")
+		sess := &session{
+			client:      client,
+			diagnostics: map[string][]Diagnostic{},
+			lastPublish: map[string]time.Time{},
+			publishSeq:  map[string]int64{},
+			waiters:     map[string][]chan struct{}{},
+		}
+		waitDone := make(chan bool, 1)
+		go func() {
+			waitDone <- sess.waitForDiagnostics(context.Background(), uri, time.Second, 0)
+		}()
+
+		deadline := time.Now().Add(time.Second)
+		for {
+			sess.mu.Lock()
+			waiting := len(sess.waiters[uri]) == 1
+			sess.mu.Unlock()
+			if waiting {
+				break
+			}
+			if time.Now().After(deadline) {
+				t.Fatal("diagnostic wait was not registered")
+			}
+			time.Sleep(time.Millisecond)
+		}
+
+		sess.handleNotification("textDocument/publishDiagnostics", params, 1)
+		client.failPending(errors.New("server exited after publishing"))
+		select {
+		case fresh := <-waitDone:
+			if !fresh {
+				t.Fatalf("iteration %d discarded diagnostics handled before client closure", i)
+			}
+		case <-time.After(time.Second):
+			t.Fatal("diagnostic wait did not wake when the client failed")
+		}
+	}
+}
+
+func TestWaitForDiagnosticsDrainsAcceptedPublishAfterTransportEOF(t *testing.T) {
+	clientReader, serverWriter := io.Pipe()
+	client := NewClient(clientReader, io.Discard)
+	uri := PathToURI("/repo/main.go")
+	sess := &session{
+		client:      client,
+		diagnostics: map[string][]Diagnostic{},
+		lastPublish: map[string]time.Time{},
+		publishSeq:  map[string]int64{},
+		waiters:     map[string][]chan struct{}{},
+	}
+	blocked := make(chan struct{})
+	release := make(chan struct{})
+	client.SetNotificationHandler(func(method string, params json.RawMessage, seq int64) {
+		if method == "test/block" {
+			close(blocked)
+			<-release
+			return
+		}
+		sess.handleNotification(method, params, seq)
+	})
+
+	if err := writeMessage(serverWriter, map[string]any{"jsonrpc": "2.0", "method": "test/block"}); err != nil {
+		t.Fatal(err)
+	}
+	<-blocked
+	params := PublishDiagnosticsParams{URI: uri, Diagnostics: []Diagnostic{{Message: "fresh"}}}
+	if err := writeMessage(serverWriter, map[string]any{
+		"jsonrpc": "2.0", "method": "textDocument/publishDiagnostics", "params": params,
+	}); err != nil {
+		t.Fatal(err)
+	}
+	deadline := time.Now().Add(time.Second)
+	for client.ReceiptSeq() != 2 {
+		if time.Now().After(deadline) {
+			t.Fatal("publish was not accepted before EOF")
+		}
+		runtime.Gosched()
+	}
+
+	waitDone := make(chan bool, 1)
+	go func() { waitDone <- sess.waitForDiagnostics(context.Background(), uri, 0, 0) }()
+	if err := serverWriter.Close(); err != nil {
+		t.Fatal(err)
+	}
+	// Fresh budget: the wait above may have consumed most of the previous one,
+	// which would make this loop fail on nothing worse than slow scheduling.
+	deadline = time.Now().Add(time.Second)
+	for !client.IsClosed() {
+		if time.Now().After(deadline) {
+			t.Fatal("transport EOF did not close client")
+		}
+		runtime.Gosched()
+	}
+	select {
+	case fresh := <-waitDone:
+		t.Fatalf("wait returned %v before accepted notifications drained", fresh)
+	case <-time.After(25 * time.Millisecond):
+	}
+	close(release)
+	select {
+	case fresh := <-waitDone:
+		if !fresh {
+			t.Fatal("wait missed publish accepted before transport EOF")
+		}
+	case <-time.After(time.Second):
+		t.Fatal("wait did not finish after notification drain")
+	}
+	if got := sess.diagnosticsFor(uri); len(got) != 1 || got[0].Message != "fresh" {
+		t.Fatalf("diagnostics = %#v, want fresh publish", got)
+	}
+}
+
+// TestWaitForDiagnosticsCatchesUpOnContextCancellation covers jatmn's P2 finding
+// (1): the cancellation arm used to re-check only what the handler had already
+// RUN. A publishDiagnostics accepted off the wire but still queued behind a busy
+// worker therefore read as "never arrived", and Manager.Check returned (nil,
+// nil) for text the server had in fact answered. Cancellation now settles like
+// closure does — let the worker finish what it accepted, then re-read.
+// TestCatchUpNotificationsFollowsPublishesAcceptedWhileWaiting covers jatmn's
+// #759 finding: catch-up snapshotted the accepted sequence once, so a publish
+// the reader accepted DURING the wait was not waited for. The worker finishing
+// the stale target satisfied the check, and the caller then read diagnosticsFor
+// while a newer publish for the same URI was still queued — the same
+// "newest received, not the one that woke the wait" failure the closed-client
+// drain regression was written for, on the live path.
+func TestCatchUpNotificationsFollowsPublishesAcceptedWhileWaiting(t *testing.T) {
+	clientReader, serverWriter := io.Pipe()
+	defer serverWriter.Close()
+	client := NewClient(clientReader, io.Discard)
+	uri := PathToURI("/repo/main.go")
+	sess := &session{
+		client:       client,
+		catchUpGrace: 5 * time.Second,
+		diagnostics:  map[string][]Diagnostic{},
+		lastPublish:  map[string]time.Time{},
+		publishSeq:   map[string]int64{},
+		waiters:      map[string][]chan struct{}{},
+	}
+
+	publish := func(message string) {
+		t.Helper()
+		params := PublishDiagnosticsParams{URI: uri, Diagnostics: []Diagnostic{{Message: message}}}
+		if err := writeMessage(serverWriter, map[string]any{
+			"jsonrpc": "2.0", "method": "textDocument/publishDiagnostics", "params": params,
+		}); err != nil {
+			t.Error(err)
+		}
+	}
+
+	blocked := make(chan struct{})
+	release := make(chan struct{})
+	secondEntered := make(chan struct{})
+	releaseSecond := make(chan struct{})
+	client.SetNotificationHandler(func(method string, params json.RawMessage, seq int64) {
+		switch {
+		case method == "test/block":
+			close(blocked)
+			<-release
+			return
+		case strings.Contains(string(params), `"first"`):
+			// Handling "first" is what makes "second" arrive mid-catch-up: it goes
+			// on the wire and is confirmed accepted before this handler returns, so
+			// the worker's handled count only reaches "first" once a newer item is
+			// already queued behind it.
+			publish("second")
+			deadline := time.Now().Add(time.Second)
+			for client.acceptedNotificationSeq() < 3 {
+				if time.Now().After(deadline) {
+					t.Error("follow-up publish was not accepted while the worker was busy")
+					break
+				}
+				runtime.Gosched()
+			}
+		case strings.Contains(string(params), `"second"`):
+			// Hold the worker inside this handler so the assertion below observes
+			// the state the bug produced: caught up by the stale target, with the
+			// newer publish still unrecorded.
+			close(secondEntered)
+			<-releaseSecond
+		}
+		sess.handleNotification(method, params, seq)
+	})
+
+	if err := writeMessage(serverWriter, map[string]any{"jsonrpc": "2.0", "method": "test/block"}); err != nil {
+		t.Fatal(err)
+	}
+	<-blocked
+	publish("first")
+	deadline := time.Now().Add(time.Second)
+	for client.ReceiptSeq() != 2 {
+		if time.Now().After(deadline) {
+			t.Fatal("first publish was not accepted")
+		}
+		runtime.Gosched()
+	}
+
+	done := make(chan struct{})
+	go func() {
+		sess.catchUpNotifications()
+		close(done)
+	}()
+	// Catch-up must be parked in its wait before the worker is released, so the
+	// sequence it started from is the one that goes stale.
+	select {
+	case <-done:
+		t.Fatal("catch-up returned while the worker was still behind")
+	case <-time.After(25 * time.Millisecond):
+	}
+	close(release)
+
+	// The worker is now inside the handler for "second", which means "first" is
+	// recorded and its sequence — the one catch-up started from — is satisfied.
+	// A snapshot-based catch-up returns here, with the newer publish unrecorded.
+	select {
+	case <-secondEntered:
+	case <-time.After(3 * time.Second):
+		t.Fatal("worker never reached the follow-up publish")
+	}
+	select {
+	case <-done:
+		t.Fatalf("catch-up returned on a stale target; diagnostics = %#v", sess.diagnosticsFor(uri))
+	case <-time.After(25 * time.Millisecond):
+	}
+
+	close(releaseSecond)
+	select {
+	case <-done:
+	case <-time.After(5 * time.Second):
+		t.Fatal("catch-up did not finish")
+	}
+	if got := sess.diagnosticsFor(uri); len(got) != 1 || got[0].Message != "second" {
+		t.Fatalf("diagnostics = %#v, want the publish accepted during catch-up", got)
+	}
+}
+
+// TestCatchUpNotificationsGivesUpAfterTheLiveGrace spells out the tradeoff the
+// live-client timeout represents: an unbounded wait would hang Check past a
+// deadline the caller has already blown, so a worker that never catches up
+// costs the grace and no more. Production sessions use a 50ms grace; this uses
+// the same order of magnitude rather than the generous one the other tests pin.
+func TestCatchUpNotificationsGivesUpAfterTheLiveGrace(t *testing.T) {
+	clientReader, serverWriter := io.Pipe()
+	defer serverWriter.Close()
+	client := NewClient(clientReader, io.Discard)
+	sess := &session{
+		client:       client,
+		catchUpGrace: 25 * time.Millisecond,
+		diagnostics:  map[string][]Diagnostic{},
+		lastPublish:  map[string]time.Time{},
+		publishSeq:   map[string]int64{},
+		waiters:      map[string][]chan struct{}{},
+	}
+	blocked := make(chan struct{})
+	release := make(chan struct{})
+	defer close(release)
+	client.SetNotificationHandler(func(method string, _ json.RawMessage, _ int64) {
+		if method == "test/block" {
+			close(blocked)
+			<-release
+		}
+	})
+	if err := writeMessage(serverWriter, map[string]any{"jsonrpc": "2.0", "method": "test/block"}); err != nil {
+		t.Fatal(err)
+	}
+	<-blocked
+
+	done := make(chan struct{})
+	start := time.Now()
+	go func() {
+		sess.catchUpNotifications()
+		close(done)
+	}()
+	select {
+	case <-done:
+		if elapsed := time.Since(start); elapsed < sess.catchUpGrace {
+			t.Fatalf("catch-up returned after %v, before its %v grace", elapsed, sess.catchUpGrace)
+		}
+	case <-time.After(3 * time.Second):
+		t.Fatal("catch-up on a permanently-behind worker must give up after the grace, not hang")
+	}
+}
+
+func TestWaitForDiagnosticsCatchesUpOnContextCancellation(t *testing.T) {
+	clientReader, serverWriter := io.Pipe()
+	defer serverWriter.Close()
+	client := NewClient(clientReader, io.Discard)
+	uri := PathToURI("/repo/main.go")
+	sess := &session{
+		client: client,
+		// Generous, so the catch-up is decided by the worker rather than by how
+		// fast this test's goroutines happen to be scheduled.
+		catchUpGrace: 5 * time.Second,
+		diagnostics:  map[string][]Diagnostic{},
+		lastPublish:  map[string]time.Time{},
+		publishSeq:   map[string]int64{},
+		waiters:      map[string][]chan struct{}{},
+	}
+	blocked := make(chan struct{})
+	release := make(chan struct{})
+	client.SetNotificationHandler(func(method string, params json.RawMessage, seq int64) {
+		if method == "test/block" {
+			close(blocked)
+			<-release
+			return
+		}
+		sess.handleNotification(method, params, seq)
+	})
+
+	// Occupy the sole worker, then let a publish queue up behind it.
+	if err := writeMessage(serverWriter, map[string]any{"jsonrpc": "2.0", "method": "test/block"}); err != nil {
+		t.Fatal(err)
+	}
+	<-blocked
+	params := PublishDiagnosticsParams{URI: uri, Diagnostics: []Diagnostic{{Message: "fresh"}}}
+	if err := writeMessage(serverWriter, map[string]any{
+		"jsonrpc": "2.0", "method": "textDocument/publishDiagnostics", "params": params,
+	}); err != nil {
+		t.Fatal(err)
+	}
+	deadline := time.Now().Add(time.Second)
+	for client.ReceiptSeq() != 2 {
+		if time.Now().After(deadline) {
+			t.Fatal("publish was not accepted before cancellation")
+		}
+		runtime.Gosched()
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	waitDone := make(chan bool, 1)
+	go func() { waitDone <- sess.waitForDiagnostics(ctx, uri, 0, 0) }()
+	deadline = time.Now().Add(time.Second)
+	for {
+		sess.mu.Lock()
+		waiting := len(sess.waiters[uri]) == 1
+		sess.mu.Unlock()
+		if waiting {
+			break
+		}
+		if time.Now().After(deadline) {
+			t.Fatal("diagnostic wait was not registered")
+		}
+		runtime.Gosched()
+	}
+
+	cancel()
+	select {
+	case fresh := <-waitDone:
+		t.Fatalf("wait returned %v while an accepted publish was still queued", fresh)
+	case <-time.After(25 * time.Millisecond):
+	}
+	close(release)
+	select {
+	case fresh := <-waitDone:
+		if !fresh {
+			t.Fatal("cancellation discarded a publish that was already off the wire")
+		}
+	case <-time.After(5 * time.Second):
+		t.Fatal("wait did not finish after the worker caught up")
+	}
+	if got := sess.diagnosticsFor(uri); len(got) != 1 || got[0].Message != "fresh" {
+		t.Fatalf("diagnostics = %#v, want the publish accepted before cancellation", got)
+	}
+}
+
+// TestWaitForDiagnosticsDrainsFollowUpPublishOnCloseDuringDebounce covers
+// jatmn's P2 finding (2): the debounce-phase closure arm returned true without
+// draining, so Manager.Check read diagnosticsFor while a NEWER publish was still
+// queued and handed back the older one. It also pins the drain as
+// ctx-independent — cancelling mid-drain (finding (1)'s second clause) must not
+// cut it short, since after closure the backlog can no longer grow.
+func TestWaitForDiagnosticsDrainsFollowUpPublishOnCloseDuringDebounce(t *testing.T) {
+	clientReader, serverWriter := io.Pipe()
+	client := NewClient(clientReader, io.Discard)
+	uri := PathToURI("/repo/main.go")
+	sess := &session{
+		client: client,
+		// Zero on purpose: the post-closure drain must not be bounded by the
+		// live-client grace.
+		catchUpGrace: 0,
+		diagnostics:  map[string][]Diagnostic{},
+		lastPublish:  map[string]time.Time{},
+		publishSeq:   map[string]int64{},
+		waiters:      map[string][]chan struct{}{},
+	}
+	blocked := make(chan struct{})
+	release := make(chan struct{})
+	client.SetNotificationHandler(func(method string, params json.RawMessage, seq int64) {
+		if method == "test/block" {
+			close(blocked)
+			<-release
+			return
+		}
+		sess.handleNotification(method, params, seq)
+	})
+
+	publish := func(message string) {
+		t.Helper()
+		params := PublishDiagnosticsParams{URI: uri, Diagnostics: []Diagnostic{{Message: message}}}
+		if err := writeMessage(serverWriter, map[string]any{
+			"jsonrpc": "2.0", "method": "textDocument/publishDiagnostics", "params": params,
+		}); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	// A first publish lands and is handled, so the wait below starts out in its
+	// debounce phase rather than waiting for a first result.
+	publish("first")
+	deadline := time.Now().Add(time.Second)
+	for {
+		if got := sess.diagnosticsFor(uri); len(got) == 1 && got[0].Message == "first" {
+			break
+		}
+		if time.Now().After(deadline) {
+			t.Fatal("first publish was never handled")
+		}
+		runtime.Gosched()
+	}
+	// Now occupy the worker and queue a newer publish behind it.
+	if err := writeMessage(serverWriter, map[string]any{"jsonrpc": "2.0", "method": "test/block"}); err != nil {
+		t.Fatal(err)
+	}
+	<-blocked
+	publish("second")
+	deadline = time.Now().Add(time.Second)
+	for client.ReceiptSeq() != 3 {
+		if time.Now().After(deadline) {
+			t.Fatal("follow-up publish was not accepted before closure")
+		}
+		runtime.Gosched()
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	waitDone := make(chan bool, 1)
+	go func() { waitDone <- sess.waitForDiagnostics(ctx, uri, 5*time.Second, 0) }()
+	select {
+	case fresh := <-waitDone:
+		t.Fatalf("wait returned %v instead of debouncing", fresh)
+	case <-time.After(25 * time.Millisecond):
+	}
+
+	if err := serverWriter.Close(); err != nil {
+		t.Fatal(err)
+	}
+	deadline = time.Now().Add(time.Second)
+	for !client.IsClosed() {
+		if time.Now().After(deadline) {
+			t.Fatal("transport EOF did not close client")
+		}
+		runtime.Gosched()
+	}
+	// Cancelling now must not cut the drain short.
+	cancel()
+	select {
+	case fresh := <-waitDone:
+		t.Fatalf("wait returned %v before the accepted follow-up publish drained", fresh)
+	case <-time.After(25 * time.Millisecond):
+	}
+
+	close(release)
+	select {
+	case fresh := <-waitDone:
+		if !fresh {
+			t.Fatal("wait dropped the publish it had already observed")
+		}
+	case <-time.After(time.Second):
+		t.Fatal("wait did not finish after the notification drain")
+	}
+	if got := sess.diagnosticsFor(uri); len(got) != 1 || got[0].Message != "second" {
+		t.Fatalf("diagnostics = %#v, want the follow-up publish accepted before closure", got)
+	}
+}
+
+func TestWaitForDiagnosticsPreservesPublishHandledAtDeadline(t *testing.T) {
+	previousProcs := runtime.GOMAXPROCS(1)
+	defer runtime.GOMAXPROCS(previousProcs)
+	params, err := json.Marshal(PublishDiagnosticsParams{
+		URI: PathToURI("/repo/main.go"), Diagnostics: []Diagnostic{{Message: "fresh"}},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	for i := 0; i < 100; i++ {
+		client := &Client{closed: make(chan struct{})}
+		uri := PathToURI("/repo/main.go")
+		sess := &session{
+			client:      client,
+			diagnostics: map[string][]Diagnostic{},
+			lastPublish: map[string]time.Time{},
+			publishSeq:  map[string]int64{},
+			waiters:     map[string][]chan struct{}{},
+		}
+		ctx, cancel := context.WithCancel(context.Background())
+		waitDone := make(chan bool, 1)
+		go func() {
+			waitDone <- sess.waitForDiagnostics(ctx, uri, time.Second, 0)
+		}()
+
+		deadline := time.Now().Add(time.Second)
+		for {
+			sess.mu.Lock()
+			waiting := len(sess.waiters[uri]) == 1
+			sess.mu.Unlock()
+			if waiting {
+				break
+			}
+			if time.Now().After(deadline) {
+				t.Fatal("diagnostic wait was not registered")
+			}
+			runtime.Gosched()
+		}
+
+		// handleNotification records the publish and closes the waiter. Cancel
+		// before yielding under GOMAXPROCS(1), making both cases ready together.
+		sess.handleNotification("textDocument/publishDiagnostics", params, 1)
+		cancel()
+
+		select {
+		case fresh := <-waitDone:
+			if !fresh {
+				t.Fatalf("iteration %d: deadline discarded a publish handled before cancellation", i)
+			}
+		case <-time.After(time.Second):
+			t.Fatalf("iteration %d: wait did not return", i)
+		}
+	}
+}
+
 func TestManagerCheckDegradesWhenServerBinaryMissing(t *testing.T) {
 	// A configured extension whose binary isn't on PATH (exec.ErrNotFound) must
 	// degrade to no diagnostics, exactly like an unsupported extension.