fix(tui): align active voice status with capture key

fix(tui): clarify voice capture controls
fix(tui): keep voice mode from swallowing spaces
2026-11-08 09:49:34 -10:00 · 2026-08-26 16:25:15 +05:30 · 2026-08-26 15:38:35 +05:30 · 2026-08-26 14:54:23 +05:30 · 2026-08-26 13:22:43 +08:00 · 2026-08-26 13:22:05 +08:00
239 changed files with 16193 additions and 4021 deletions
@@ -1 +1 @@
-{".":"0.7.0"}
+{".":"0.8.0"}
@@ -111,3 +111,42 @@ These classes drive multi-round reviews. Fix them before requesting review:
  shipped. Wire advertised entry points or shrink the claim. Do not bundle
  unrelated fixes. Do not widen security allowlists by name alone; check
  classification and side effects too.
+- **Host tool version floors:** Zero shells out to `git` and other host tools,
+  and the project does not declare a minimum version for any of them. A flag,
+  subcommand, or config key that is not long-established therefore raises that
+  floor silently, and the failure on an older host is an unhelpful usage error
+  rather than a clear message. Before adding one, check when it landed and say
+  so where a caller would look. Record the floor for the exact subcommand you
+  call, not for the flag in general: `--end-of-options` reached Git's shared
+  parser in 2.24, but `git rev-parse` only accepted it from 2.30, and
+  `git checkout` and `git reset` later still. Likewise `--show-current` is
+  `git branch` 2.22, and `branch.autoSetupMerge=inherit` is 2.35. Then either
+  keep a fallback for older versions or gate the call. A test that depends on a
+  newer feature must skip below its floor instead of failing, and say which
+  version it needs.
+- **Prove the test fails without the change:** A regression test earns its
+  place only if it fails on the unfixed code, for the reason it claims. Run it
+  both ways and quote the failure in the PR. The recurring miss is not a
+  missing test but a test that never reaches the behavior it names, because an
+  earlier guard rejects the input first, so it passes with and without the fix.
+  When a test targets a specific layer, call that layer directly rather than
+  relying on a public entry point that may refuse earlier.
+- **Hermetic tests:** Tests must not read or write the developer's real config,
+  cache, or state directories. Redirect every root the code under test
+  resolves, not just config. `os.UserConfigDir` and `os.UserCacheDir` read
+  `XDG_CONFIG_HOME` and `XDG_CACHE_HOME` only on Linux and the BSDs. On macOS
+  they derive from `HOME`, and on Windows from `%AppData%` and `%LocalAppData%`.
+  Setting the XDG variables alone still leaves a macOS run writing to the real
+  home, so set `HOME` as well, or take the directory as a parameter. Apply it to
+  every test that reaches the same storage, not only the one where it was first
+  needed; a test that passes on a clean machine and pollutes a real one is a
+  blocker.
+- **Error codes vary by platform and by flag combination:** A check written
+  against the code one target returns can be silently inert on another while
+  still looking correct. `openat(O_DIRECTORY|O_NOFOLLOW)` on a symlink may
+  report `ENOTDIR` or `ELOOP` depending on the platform, because the kernel can
+  reject the directory mismatch before it ever resolves the link; accept both
+  rather than assuming the one POSIX names. On Windows, `\\?\` and `\\.\`
+  prefixes are not UNC paths, and an `NtCreateFile` information class must match
+  the struct actually passed. Confirm the code each supported target returns
+  instead of reasoning from the man page.
@@ -6,6 +6,27 @@ 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`.

+## [0.8.0](https://github.com/Gitlawb/zero/compare/v0.7.0...v0.8.0) (2026-08-21)
+
+
+### Features
+
+* **security:** path-jail primitive, credential-store locking, worktree git hardening ([#891](https://github.com/Gitlawb/zero/issues/891)) ([060d38c](https://github.com/Gitlawb/zero/commit/060d38ce716feb7c5b6657b082cd35cb8dda3d75))
+* **update:** recognise Homebrew installs and add mise, go install docs ([#910](https://github.com/Gitlawb/zero/issues/910)) ([01c3498](https://github.com/Gitlawb/zero/commit/01c3498205e69d26e5f929225f9455b276444f39))
+* use Exa as default search provider ([#926](https://github.com/Gitlawb/zero/issues/926)) ([1ec7219](https://github.com/Gitlawb/zero/commit/1ec7219aee7b2840481ab0905f131644e27d2a4e))
+* **zerogit:** auto-create a conventional branch before push/pr on default branch ([#671](https://github.com/Gitlawb/zero/issues/671)) ([d065467](https://github.com/Gitlawb/zero/commit/d065467cd3ec3ed91c5dc60554c36fc4b4d6de4c))
+
+
+### Bug Fixes
+
+* **acp:** three defects a desktop ACP client hits ([#915](https://github.com/Gitlawb/zero/issues/915)) ([a78c6c3](https://github.com/Gitlawb/zero/commit/a78c6c357e1d21146d7cd2e8030a754e06f7f1f5))
+* bump Go to 1.26.6 for stdlib vulnerability fixes ([#903](https://github.com/Gitlawb/zero/issues/903)) ([dc15e82](https://github.com/Gitlawb/zero/commit/dc15e822987d8d7de467c62c375518f435b74d8c))
+* **daemon:** clean up child after startup timeout ([#774](https://github.com/Gitlawb/zero/issues/774)) ([9c29209](https://github.com/Gitlawb/zero/commit/9c292092a26c9092fd873d072b0af1b0d9d39ef0))
+* **dictation:** redact API keys from streaming transcriber errors ([#852](https://github.com/Gitlawb/zero/issues/852)) ([64a783b](https://github.com/Gitlawb/zero/commit/64a783b08caa2c7b21f188033b9ed84a14e00e84))
+* **modelregistry:** expose reasoning effort for DeepSeek V4 models ([#931](https://github.com/Gitlawb/zero/issues/931)) ([90dcfd1](https://github.com/Gitlawb/zero/commit/90dcfd127e8a6d9902ec9f4e72f6d03fef1a0fc6))
+* **providers:** discover ChatGPT capabilities ([#890](https://github.com/Gitlawb/zero/issues/890)) ([2d2450e](https://github.com/Gitlawb/zero/commit/2d2450e9a744349f0d01b1d4e9ba29c24ba5650d))
+* **sandbox:** normalize launcher names before the command-prefix denylist ([#934](https://github.com/Gitlawb/zero/issues/934)) ([6edf9a8](https://github.com/Gitlawb/zero/commit/6edf9a8b78dc030dc44598919db1c7fa9d4f809a))
+
 ## [0.7.0](https://github.com/Gitlawb/zero/compare/v0.6.0...v0.7.0) (2026-08-10)


@@ -371,9 +371,13 @@ go run ./cmd/zero-perf-bench

 Experimental: `ZERO_OPENAI_TURN_SESSION=1` enables the optimized OpenAI turn
 session (background connection prewarm + request-prefix telemetry) for headless
-`zero exec` runs against official OpenAI profiles. Off by default; `0`/`false`
-disable. A/B-benchmark it by running the same `zero-perf-bench` suite with the
-variable unset and set.
+`zero exec` runs against official OpenAI profiles. Off by default; `0`, `false`,
+or `off` disable it. A/B-benchmark it by running the same `zero-perf-bench` suite
+with the variable unset and set.
+
+Native ChatGPT Responses sessions are enabled by default. Set
+`ZERO_CHATGPT_TURN_SESSION=0`, `false`, or `off` to restore stateless HTTP/SSE
+transport.

 ### Code Quality and Security Checks

@@ -33,4 +33,4 @@ Please include, where possible:
  depend on a user explicitly disabling the sandbox (`--skip-permissions-unsafe`), are generally
  out of scope — but please report anything you are unsure about.
 - Zero sends no telemetry. Network calls go to the model/tool providers you configure (and, for
-  keyless web search, to the documented Firecrawl endpoint — see the README).
+  keyless web search, to Exa's hosted MCP endpoint at `https://mcp.exa.ai/mcp`).
@@ -4,7 +4,7 @@ go 1.26.6

 require (
 	charm.land/bubbles/v2 v2.1.1
-	charm.land/bubbletea/v2 v2.0.8
+	charm.land/bubbletea/v2 v2.0.9
 	charm.land/lipgloss/v2 v2.0.5
 	github.com/Microsoft/go-winio v0.6.2
 	github.com/alecthomas/chroma/v2 v2.27.0
@@ -1,7 +1,7 @@
 charm.land/bubbles/v2 v2.1.1 h1:7r55WzBxpo/R3z98hGmY7KKPd3ET6vsf0Fb9sDHOV60=
 charm.land/bubbles/v2 v2.1.1/go.mod h1:GE6M31gaWZVXzGw73OeuTTgy4lX+OtkH0E5ymnNsHxo=
-charm.land/bubbletea/v2 v2.0.8 h1:SxTJMhCAI3lbPmy4SgX5LWZ24AdINr4I6UEqzZvYJuY=
-charm.land/bubbletea/v2 v2.0.8/go.mod h1:2SkdgoTXluXJHOUwAoRlRXF/28vklb1rFl6GcgV1/ss=
+charm.land/bubbletea/v2 v2.0.9 h1:DpJCMWKgzQK8SJv4zbKKFHAI10ymWy/evClPFk0k0f8=
+charm.land/bubbletea/v2 v2.0.9/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=
@@ -64,8 +64,6 @@ 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=
@@ -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) {
@@ -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)
+	}
+}
@@ -15,14 +15,7 @@ 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, req.PrefixApprovalEscalates)
@@ -38,6 +31,32 @@ 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).
@@ -49,8 +68,16 @@ func buildPermissionOptions(req agent.PermissionRequest) []PermissionOption {
 // 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:
@@ -70,19 +97,31 @@ func optionKindFor(action agent.PermissionDecisionAction, escalates bool) (kind,

 // 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:
@@ -90,9 +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
 		}
 	}
@@ -56,10 +56,11 @@ func TestACPPrefixOptionsStaySilentWithoutEscalation(t *testing.T) {
 // what was offered, so decorating it would fail every prefix approval closed.
 func TestACPDisclosureDoesNotDisturbTheOptionIDRoundTrip(t *testing.T) {
 	request := escalationRequest(true)
-	for _, option := range buildPermissionOptions(request) {
+	options := buildPermissionOptions(request)
+	for _, option := range options {
 		decision := decisionFromOutcome(
 			RequestPermissionOutcome{Outcome: OutcomeSelected, OptionID: option.OptionID},
-			request.AvailableDecisions,
+			options,
 		)
 		if string(decision.Action) != option.OptionID {
 			t.Errorf("option id %q round-tripped to %q (%s)", option.OptionID, decision.Action, decision.Reason)
@@ -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)
 	}
@@ -99,6 +99,43 @@ func TestProposedCommandPrefixRejectsUnsafeRequestedPrefix(t *testing.T) {
 	}
 }

+// The launcher denylist is only worth anything if it holds on the path a user
+// actually sees. A model naming its own prefix_rule is that path: before
+// launcher names were normalized, "python3.11" was offered as a one-token
+// grant, and hasStringPrefix then matched every later python3.11 invocation.
+func TestProposedCommandPrefixRejectsLauncherSpellingsInRequestedPrefix(t *testing.T) {
+	for _, testCase := range []struct {
+		command string
+		rule    []any
+	}{
+		{"python3.11 script.py", []any{"python3.11"}},
+		{"python.exe script.py", []any{"python.exe"}},
+		{"node.exe app.js", []any{"node.exe"}},
+		{"cmd /c whoami", []any{"cmd"}},
+		{"busybox sh -c id", []any{"busybox"}},
+		{"uv run main.py", []any{"uv", "run"}},
+		{"python3.11 -c import_os", []any{"python3.11", "-c"}},
+	} {
+		got := proposedCommandPrefix("bash", map[string]any{
+			"command":     testCase.command,
+			"prefix_rule": testCase.rule,
+		})
+		if got != nil {
+			t.Errorf("prefix_rule %v for %q was offered as %#v, want rejected", testCase.rule, testCase.command, got)
+		}
+	}
+}
+
+func TestProposedCommandPrefixStillOffersOrdinaryCommands(t *testing.T) {
+	got := proposedCommandPrefix("bash", map[string]any{
+		"command":     "cargo build --release",
+		"prefix_rule": []any{"cargo", "build"},
+	})
+	if len(got) != 2 || got[0] != "cargo" || got[1] != "build" {
+		t.Fatalf("ordinary prefix rule = %#v, want [cargo build]", got)
+	}
+}
+
 func TestProposedCommandPrefixRejectsUnsafeShellForms(t *testing.T) {
 	cases := []string{
 		"cat < in > out",
@@ -4,7 +4,9 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
+	"strconv"
 	"strings"
+	"unicode/utf8"

 	"github.com/Gitlawb/zero/internal/trace"
 	"github.com/Gitlawb/zero/internal/zeroruntime"
@@ -144,11 +146,17 @@ func estimateToolDefTokens(tools []zeroruntime.ToolDefinition) int {
 	for _, tool := range tools {
 		total += ApproxTextTokens(tool.Name)
 		total += ApproxTextTokens(tool.Description)
+		total += ApproxTextTokens(string(tool.Type))
 		if len(tool.Parameters) > 0 {
 			if encoded, err := json.Marshal(tool.Parameters); err == nil {
 				total += ApproxTextTokens(string(encoded))
 			}
 		}
+		if tool.Format != nil {
+			total += ApproxTextTokens(tool.Format.Type)
+			total += ApproxTextTokens(tool.Format.Syntax)
+			total += ApproxTextTokens(tool.Format.Definition)
+		}
 		total += 4 // per-tool overhead
 	}
 	return total
@@ -390,6 +398,27 @@ type compactionState struct {
 	// starts at 1.0 and converges via an EMA as each turn reports actual usage, so
 	// later turns compact nearer to real capacity. Zero is treated as 1.0.
 	calibrationRatio float64
+
+	// summarizerFactory lazily builds the dedicated (cheap) summarizer provider
+	// (Options.Summarizer) for the current main model. summarizerProvider
+	// memoizes the built provider and summarizerResolved records that the
+	// factory ran (it may legitimately return no provider: the main model is
+	// already the cheap one). summarizerBroken is the sticky fallback: once a
+	// build or call fails, the run stays on the main provider until the next
+	// model switch — a misconfigured cheap model must never break (or
+	// repeatedly delay) compaction.
+	summarizerFactory  func(ctx context.Context, mainModelID string) (Provider, error)
+	summarizerProvider Provider
+	summarizerResolved bool
+	summarizerBroken   bool
+	// window is the context window the threshold was derived from. The
+	// reactive free-prune stage compares against it (the limit the provider
+	// enforces), not against the 70% proactive threshold — a pruned history
+	// between the two would still succeed on retry.
+	window int
+	// mainModel is the model the run currently streams on; the summarizer
+	// choice is made against it and remade after a mid-run switch.
+	mainModel string
 }

 // calibrate folds one turn's (rawEstimate, actualPromptTokens) sample into the
@@ -424,17 +453,88 @@ func (state *compactionState) calibratedTokens(raw int) int {

 func newCompactionState(options Options, task *taskState) *compactionState {
 	state := &compactionState{
-		enabled:      options.ContextWindow > 0,
-		threshold:    compactionThreshold(options.ContextWindow),
-		preserveLast: options.CompactionPreserveLast,
-		onUsage:      options.OnUsage,
-		task:         task,
-		planner:      newContextPlanner(contextPlannerConfig{contextWindow: options.ContextWindow, serviceTier: options.ServiceTier}),
-		trace:        options.Trace,
+		enabled:           options.ContextWindow > 0,
+		threshold:         compactionThreshold(options.ContextWindow),
+		window:            options.ContextWindow,
+		mainModel:         options.Model,
+		preserveLast:      options.CompactionPreserveLast,
+		onUsage:           options.OnUsage,
+		task:              task,
+		planner:           newContextPlanner(contextPlannerConfig{contextWindow: options.ContextWindow, serviceTier: options.ServiceTier}),
+		trace:             options.Trace,
+		summarizerFactory: options.Summarizer,
 	}
 	return state
 }

+// updateWindow re-derives the compaction threshold after a mid-run model
+// switch. The low-water mark is reset: it was measured against the old
+// threshold, and keeping it could suppress a compaction the smaller window
+// now requires. <= 0 (unknown model) leaves everything unchanged.
+func (state *compactionState) updateWindow(window int) {
+	if window <= 0 {
+		return
+	}
+	state.enabled = true
+	state.window = window
+	state.threshold = compactionThreshold(window)
+	state.lowWaterMark = 0
+	if state.planner != nil {
+		state.planner.config.contextWindow = window
+	}
+}
+
+// switchModel records a mid-run model switch: the window is re-derived
+// (window <= 0 keeps the old one) and the summarizer choice is forgotten so
+// the next compaction re-resolves it against the new main model. A run that
+// started on the cheap model (no dedicated summarizer) and escalated to an
+// expensive one therefore regains cheap summaries — the exact workflow a
+// dedicated summarizer exists for.
+func (state *compactionState) switchModel(modelID string, window int) {
+	state.mainModel = modelID
+	state.updateWindow(window)
+	state.summarizerProvider = nil
+	state.summarizerResolved = false
+	state.summarizerBroken = false
+}
+
+// summarizeProvider returns the provider summarization calls should use and
+// whether it is the dedicated summarizer: that one when it applies to the
+// current main model and is healthy, else the main provider. The factory runs
+// at most once per main model; a build error marks the summarizer broken for
+// that model. Callers branch on the boolean rather than comparing Provider
+// values — interface comparison panics on a non-comparable dynamic type.
+func (state *compactionState) summarizeProvider(ctx context.Context, main Provider) (Provider, bool) {
+	if state.summarizerFactory == nil || state.summarizerBroken {
+		return main, false
+	}
+	if !state.summarizerResolved {
+		state.summarizerResolved = true
+		built, err := state.summarizerFactory(ctx, state.mainModel)
+		if err != nil {
+			state.summarizerBroken = true
+			return main, false
+		}
+		state.summarizerProvider = built
+	}
+	if state.summarizerProvider == nil {
+		return main, false
+	}
+	return state.summarizerProvider, true
+}
+
+// fitsWindow reports whether a calibrated size is safely under the limit the
+// provider enforces. The proactive threshold (70% of the window) is a trigger
+// for the paid summarizer, not the hard limit; the reactive path compares
+// against the window itself, with a small margin for estimate error, so a
+// history pruned to, say, 85% of the window takes the free retry.
+func (state *compactionState) fitsWindow(size int) bool {
+	if state.window <= 0 {
+		return size <= state.threshold
+	}
+	return size <= state.window-state.window/20
+}
+
 // maybeCompact runs proactive compaction at the top of a turn. It returns the
 // (possibly compacted) message slice. It is a no-op when compaction is disabled,
 // when the history is under threshold, or when the history has not grown past
@@ -528,10 +628,34 @@ func (state *compactionState) recover(
 		// context-limit error never triggers an unexpected summarization call.
 		return messages, false, nil
 	}
-	if state.reactiveAttempted {
+	if !isContextLimitError(errorMessage) {
 		return messages, false, nil
 	}
-	if !isContextLimitError(errorMessage) {
+
+	// CHEAP FIRST STAGE (mirrors maybeCompact): a context-limit failure can
+	// often be fixed for free by dropping superseded reads and pruning old
+	// tool-result bodies. It runs regardless of the one-shot reactive budget
+	// (it costs nothing and cannot loop: a second pass finds nothing left to
+	// prune). The free retry is taken only when the pruned history fits the
+	// window the provider enforces — otherwise a retry would fail the same
+	// way, so fall through to the paid summarizer in this same call.
+	toolTokens := estimateToolDefTokens(tools)
+	prunedAny := false
+	if pruned, reclaimed := pruneSupersededReadResults(messages); reclaimed > 0 {
+		messages, prunedAny = pruned, true
+	}
+	if pruned, reclaimed := pruneStaleToolOutput(messages, state.preserveLast); reclaimed > 0 {
+		messages, prunedAny = pruned, true
+	}
+	if prunedAny {
+		size := state.calibratedTokens(estimateTokens(messages) + toolTokens)
+		if state.fitsWindow(size) {
+			state.lowWaterMark = size
+			return messages, true, nil
+		}
+	}
+
+	if state.reactiveAttempted {
 		return messages, false, nil
 	}

@@ -571,11 +695,21 @@ 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.
+// The call goes to the dedicated (cheap) summarizer when one applies; if that
+// call fails the summarizer is marked broken for the current model and the
+// same slice is retried once on the main provider, so the caller sees at most
+// one (main-provider-quality) 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) {
+		chosen, dedicated := state.summarizeProvider(ctx, provider)
+		summary, err := summarizeWithPlanner(ctx, chosen, toSummarize, state.onUsage, state.planner, state.trace)
+		if err == nil || !dedicated {
+			return summary, err
+		}
+		state.summarizerBroken = true
 		return summarizeWithPlanner(ctx, provider, toSummarize, state.onUsage, state.planner, state.trace)
 	}
 }
@@ -659,8 +793,41 @@ func summarizeMessagesOnce(ctx context.Context, provider Provider, messages []ze
 	return summary, nil
 }

+// summaryToolResultClamp bounds each tool-result body in the summarizer input.
+// Tool outputs dominate the elided middle's bulk (build logs, file reads,
+// search results), yet the summary instructions only need their gist — the
+// model that ACTED on the full output already turned it into decisions the
+// surrounding messages record. 2,000 chars (~500 tokens) keeps the useful
+// head+tail of a result while cutting the summarizer input by 5-10x on
+// tool-heavy sessions; the summarizer's own cost is the price being cut.
+const summaryToolResultClamp = 2000
+
+// summaryToolArgsClamp bounds each tool-call argument blob in the transcript:
+// a write_file call carries the whole file body in its arguments.
+const summaryToolArgsClamp = 500
+
+// clampForSummary head+tail-truncates text for the summarizer transcript,
+// snapping to rune boundaries so the clamp never splits a UTF-8 sequence.
+func clampForSummary(text string, max int) string {
+	if max <= 0 || len(text) <= max {
+		return text
+	}
+	head := max * 3 / 4
+	tail := max - head
+	for head > 0 && !utf8.RuneStart(text[head]) {
+		head--
+	}
+	start := len(text) - tail
+	for start < len(text) && !utf8.RuneStart(text[start]) {
+		start++
+	}
+	return text[:head] + "\n…[" + strconv.Itoa(len(text)-head-(len(text)-start)) + " chars omitted for summarization]…\n" + text[start:]
+}
+
 // renderTranscript flattens messages into a plain-text transcript for the
 // summarizer. Secret scrubbing already happened upstream at the tool boundary.
+// Tool-result bodies and tool-call arguments are clamped (see the constants
+// above): the summary needs what was done and decided, not the raw payloads.
 func renderTranscript(messages []zeroruntime.Message) string {
 	lines := make([]string, 0, len(messages))
 	for _, message := range messages {
@@ -670,13 +837,13 @@ func renderTranscript(messages []zeroruntime.Message) string {
 			if len(message.ToolCalls) > 0 {
 				calls := make([]string, 0, len(message.ToolCalls))
 				for _, call := range message.ToolCalls {
-					calls = append(calls, call.Name+"("+call.Arguments+")")
+					calls = append(calls, call.Name+"("+clampForSummary(call.Arguments, summaryToolArgsClamp)+")")
 				}
 				line += "\n[tool calls: " + strings.Join(calls, "; ") + "]"
 			}
 			lines = append(lines, line)
 		case zeroruntime.MessageRoleTool:
-			lines = append(lines, "tool result: "+message.Content)
+			lines = append(lines, "tool result: "+clampForSummary(message.Content, summaryToolResultClamp))
 		default:
 			lines = append(lines, string(message.Role)+": "+message.Content)
 		}
@@ -0,0 +1,469 @@
+package agent
+
+import (
+	"context"
+	"errors"
+	"strings"
+	"testing"
+
+	"github.com/Gitlawb/zero/internal/tools"
+	"github.com/Gitlawb/zero/internal/zeroruntime"
+)
+
+// compactableHistory returns a history whose middle is large enough to trip
+// the proactive threshold for a 1000-token window.
+func compactableHistory() []zeroruntime.Message {
+	return []zeroruntime.Message{
+		{Role: zeroruntime.MessageRoleSystem, Content: "sys"},
+		{Role: zeroruntime.MessageRoleUser, Content: strings.Repeat("u", 4000)},
+		{Role: zeroruntime.MessageRoleAssistant, Content: strings.Repeat("a", 4000)},
+		{Role: zeroruntime.MessageRoleUser, Content: "u2"},
+		{Role: zeroruntime.MessageRoleAssistant, Content: "a2"},
+		{Role: zeroruntime.MessageRoleUser, Content: "u3"},
+	}
+}
+
+// Summarization must run on the dedicated (cheap) summarizer when one is
+// configured — the main provider sees no summarize traffic at all.
+func TestMaybeCompactUsesDedicatedSummarizer(t *testing.T) {
+	cheap := &mockProvider{turns: [][]zeroruntime.StreamEvent{{
+		{Type: zeroruntime.StreamEventText, Content: "CHEAP SUMMARY"},
+		{Type: zeroruntime.StreamEventDone},
+	}}}
+	main := &mockProvider{}
+	factoryCalls := 0
+	state := newCompactionState(Options{
+		ContextWindow:          1000,
+		CompactionPreserveLast: 2,
+		Summarizer: func(context.Context, string) (Provider, error) {
+			factoryCalls++
+			return cheap, nil
+		},
+	}, nil)
+
+	compacted := state.maybeCompact(context.Background(), main, compactableHistory(), nil)
+
+	if len(cheap.requests) == 0 {
+		t.Fatal("dedicated summarizer never received the summarize call")
+	}
+	if len(main.requests) != 0 {
+		t.Fatalf("main provider must see no summarize traffic, got %d requests", len(main.requests))
+	}
+	if factoryCalls != 1 {
+		t.Fatalf("summarizer factory calls = %d, want 1 (lazy, memoized)", factoryCalls)
+	}
+	if estimateTokens(compacted) >= estimateTokens(compactableHistory()) {
+		t.Fatal("compaction did not shrink the history")
+	}
+	found := false
+	for _, message := range compacted {
+		if strings.Contains(message.Content, "CHEAP SUMMARY") {
+			found = true
+		}
+	}
+	if !found {
+		t.Fatal("cheap summarizer's summary missing from the compacted history")
+	}
+}
+
+// A failing summarizer falls back to the main provider for the SAME slice and
+// stays broken for the rest of the run — no repeated failed cheap calls.
+func TestSummarizerFailureFallsBackToMainAndSticks(t *testing.T) {
+	broken := &mockProvider{turns: [][]zeroruntime.StreamEvent{{
+		{Type: zeroruntime.StreamEventError, Error: "boom: model not found"},
+	}}}
+	main := &mockProvider{turns: [][]zeroruntime.StreamEvent{
+		{{Type: zeroruntime.StreamEventText, Content: "MAIN SUMMARY"}, {Type: zeroruntime.StreamEventDone}},
+		{{Type: zeroruntime.StreamEventText, Content: "MAIN SUMMARY 2"}, {Type: zeroruntime.StreamEventDone}},
+	}}
+	state := newCompactionState(Options{
+		ContextWindow:          1000,
+		CompactionPreserveLast: 2,
+		Summarizer:             func(context.Context, string) (Provider, error) { return broken, nil },
+	}, nil)
+	summarize := state.summarizeClosure(context.Background(), main)
+	input := []zeroruntime.Message{{Role: zeroruntime.MessageRoleUser, Content: "history"}}
+
+	summary, err := summarize(input)
+	if err != nil {
+		t.Fatalf("fallback must succeed via the main provider: %v", err)
+	}
+	if summary != "MAIN SUMMARY" {
+		t.Fatalf("summary = %q, want the main provider's", summary)
+	}
+	if len(broken.requests) != 1 {
+		t.Fatalf("broken summarizer requests = %d, want exactly 1", len(broken.requests))
+	}
+	if !state.summarizerBroken {
+		t.Fatal("a failed summarizer must be marked broken for the run")
+	}
+
+	// Second summarization: straight to main, no cheap retry.
+	if _, err := summarize(input); err != nil {
+		t.Fatal(err)
+	}
+	if len(broken.requests) != 1 {
+		t.Fatalf("broken summarizer was retried (%d requests)", len(broken.requests))
+	}
+	if len(main.requests) != 2 {
+		t.Fatalf("main provider requests = %d, want 2", len(main.requests))
+	}
+}
+
+// A factory that errors (misconfigured model) is equivalent to no summarizer:
+// main provider used, factory not retried.
+func TestSummarizerFactoryErrorFallsBack(t *testing.T) {
+	main := &mockProvider{turns: [][]zeroruntime.StreamEvent{{
+		{Type: zeroruntime.StreamEventText, Content: "MAIN SUMMARY"},
+		{Type: zeroruntime.StreamEventDone},
+	}}}
+	factoryCalls := 0
+	state := newCompactionState(Options{
+		ContextWindow:          1000,
+		CompactionPreserveLast: 2,
+		Summarizer: func(context.Context, string) (Provider, error) {
+			factoryCalls++
+			return nil, errors.New("unknown model")
+		},
+	}, nil)
+	summarize := state.summarizeClosure(context.Background(), main)
+
+	summary, err := summarize([]zeroruntime.Message{{Role: zeroruntime.MessageRoleUser, Content: "history"}})
+	if err != nil || summary != "MAIN SUMMARY" {
+		t.Fatalf("summary = %q, err = %v; want main provider fallback", summary, err)
+	}
+	if factoryCalls != 1 {
+		t.Fatalf("factory calls = %d, want 1 (sticky failure)", factoryCalls)
+	}
+	if _, dedicated := state.summarizeProvider(context.Background(), main); dedicated {
+		t.Fatal("after a factory failure the run must stay on the main provider")
+	}
+	if factoryCalls != 1 {
+		t.Fatalf("factory retried after failure (%d calls)", factoryCalls)
+	}
+}
+
+// Tool payloads are clamped in the summarizer transcript: results to
+// summaryToolResultClamp, call arguments to summaryToolArgsClamp.
+func TestRenderTranscriptClampsToolPayloads(t *testing.T) {
+	bigResult := strings.Repeat("r", 50_000)
+	bigArgs := strings.Repeat("w", 20_000)
+	transcript := renderTranscript([]zeroruntime.Message{
+		{Role: zeroruntime.MessageRoleAssistant, Content: "editing", ToolCalls: []zeroruntime.ToolCall{
+			{ID: "c1", Name: "write_file", Arguments: bigArgs},
+		}},
+		{Role: zeroruntime.MessageRoleTool, ToolCallID: "c1", Content: bigResult},
+		{Role: zeroruntime.MessageRoleUser, Content: "keep going"},
+	})
+
+	if len(transcript) > summaryToolResultClamp+summaryToolArgsClamp+1024 {
+		t.Fatalf("transcript is %d bytes; clamps did not apply", len(transcript))
+	}
+	if !strings.Contains(transcript, "chars omitted for summarization") {
+		t.Fatal("clamped transcript must carry the omission marker")
+	}
+	if !strings.Contains(transcript, "keep going") {
+		t.Fatal("non-tool content must survive unclamped")
+	}
+	// Head AND tail of the clamped payloads survive.
+	if !strings.HasPrefix(transcript[strings.Index(transcript, "tool result: ")+len("tool result: "):], "r") ||
+		!strings.Contains(transcript, "rrr\n\nuser: keep going") {
+		t.Fatalf("head/tail of the tool result lost:\n%s", transcript[:200])
+	}
+}
+
+// bigToolHistory returns a history with n large tool results (~40k estimated
+// tokens each): the trailing protection window keeps the newest verbatim,
+// the older ones are prunable.
+func bigToolHistory(n int) []zeroruntime.Message {
+	bigBody := strings.Repeat("x", 160_000)
+	messages := []zeroruntime.Message{{Role: zeroruntime.MessageRoleSystem, Content: "sys"}}
+	for i := 0; i < n; i++ {
+		id := string(rune('a' + i))
+		messages = append(messages,
+			zeroruntime.Message{Role: zeroruntime.MessageRoleAssistant, ToolCalls: []zeroruntime.ToolCall{{ID: id, Name: "read_file", Arguments: "{\"path\":\"" + id + "\"}"}}},
+			zeroruntime.Message{Role: zeroruntime.MessageRoleTool, ToolCallID: id, Content: bigBody},
+		)
+	}
+	return append(messages, zeroruntime.Message{Role: zeroruntime.MessageRoleUser, Content: "go"})
+}
+
+func summaryProvider(text string) *mockProvider {
+	return &mockProvider{turns: [][]zeroruntime.StreamEvent{
+		{{Type: zeroruntime.StreamEventText, Content: text}, {Type: zeroruntime.StreamEventDone}},
+		{{Type: zeroruntime.StreamEventText, Content: text}, {Type: zeroruntime.StreamEventDone}},
+	}}
+}
+
+// A context-limit error is first answered with the free prune stage; when the
+// pruned history fits the window the retry is free (no summarizer call) and
+// the one-shot reactive budget is untouched. The paid summarizer only runs
+// when a later error finds nothing left to prune.
+func TestRecoverPrunesBeforeSummarizing(t *testing.T) {
+	provider := summaryProvider("SUMMARY")
+	// The protected trailing tool output (~40k tokens) must fit the window.
+	state := newCompactionState(Options{ContextWindow: 200_000, CompactionPreserveLast: 2}, nil)
+	messages := bigToolHistory(5)
+
+	pruned, retried, err := state.recover(context.Background(), provider, messages, nil, "maximum context length exceeded")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !retried {
+		t.Fatal("prunable history that fits must produce a free retry")
+	}
+	if len(provider.requests) != 0 {
+		t.Fatalf("free prune stage must not call the summarizer (%d requests)", len(provider.requests))
+	}
+	if state.reactiveAttempted {
+		t.Fatal("a free prune retry must not consume the reactive budget")
+	}
+	if estimateTokens(pruned) >= estimateTokens(messages) {
+		t.Fatal("prune did not shrink the history")
+	}
+
+	// Second context-limit error on the pruned history: nothing meaningfully
+	// prunable remains, so the paid summarizer fires and consumes the budget.
+	_, retried, err = state.recover(context.Background(), provider, pruned, nil, "maximum context length exceeded")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !retried {
+		t.Fatal("second recover must compact and retry")
+	}
+	if len(provider.requests) == 0 {
+		t.Fatal("second recover must reach the summarizer")
+	}
+	if !state.reactiveAttempted {
+		t.Fatal("a paid recover must consume the reactive budget")
+	}
+}
+
+// When pruning reclaims something but the pruned history still exceeds the
+// window, recover falls through to the paid summarizer in the SAME call
+// instead of spending a retry that would fail the same way.
+func TestRecoverFallsThroughToSummarizerWhenPruneIsInsufficient(t *testing.T) {
+	provider := summaryProvider("SUMMARY")
+	// A 1,000-token window: even the protected trailing output overflows it.
+	state := newCompactionState(Options{ContextWindow: 1000, CompactionPreserveLast: 2}, nil)
+	messages := bigToolHistory(5)
+
+	compacted, retried, err := state.recover(context.Background(), provider, messages, nil, "maximum context length exceeded")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !retried {
+		t.Fatal("insufficient prune must still end in a retry via summarization")
+	}
+	if len(provider.requests) == 0 {
+		t.Fatal("insufficient prune must reach the summarizer in the same recover call")
+	}
+	if !state.reactiveAttempted {
+		t.Fatal("the paid summarizer consumes the reactive budget")
+	}
+	if estimateTokens(compacted) >= estimateTokens(messages) {
+		t.Fatal("recover did not shrink the history")
+	}
+}
+
+// The free prune stage is not gated behind the one-shot budget: after a paid
+// reactive compaction, a later context-limit error still gets a free retry
+// when pruning makes the history fit.
+func TestRecoverFreePruneRunsAfterBudgetIsSpent(t *testing.T) {
+	provider := summaryProvider("SUMMARY")
+	state := newCompactionState(Options{ContextWindow: 200_000, CompactionPreserveLast: 2}, nil)
+	state.reactiveAttempted = true
+	messages := bigToolHistory(5)
+
+	pruned, retried, err := state.recover(context.Background(), provider, messages, nil, "maximum context length exceeded")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !retried || len(provider.requests) != 0 {
+		t.Fatalf("free prune must retry without the summarizer even when the budget is spent (retried=%v, requests=%d)", retried, len(provider.requests))
+	}
+	if estimateTokens(pruned) >= estimateTokens(messages) {
+		t.Fatal("prune did not shrink the history")
+	}
+	// With nothing left to prune and the budget spent, the caller keeps its
+	// original error — recover neither loops nor summarizes.
+	_, retried, err = state.recover(context.Background(), provider, pruned, nil, "maximum context length exceeded")
+	if err != nil || retried || len(provider.requests) != 0 {
+		t.Fatalf("spent budget must not summarize again (retried=%v, requests=%d, err=%v)", retried, len(provider.requests), err)
+	}
+}
+
+// The free-retry gate compares against the window the provider enforces, not
+// the 70% proactive threshold: a history pruned to ~80% of the window still
+// takes the free retry.
+func TestRecoverFreeRetryGateUsesWindowNotThreshold(t *testing.T) {
+	provider := summaryProvider("SUMMARY")
+	messages := bigToolHistory(5)
+	pruned, _ := pruneStaleToolOutput(messages, 2)
+	prunedTokens := estimateTokens(pruned)
+	// Choose a window so the pruned size sits between 70% and 95% of it.
+	window := prunedTokens * 100 / 80
+	state := newCompactionState(Options{ContextWindow: window, CompactionPreserveLast: 2}, nil)
+	if prunedTokens <= state.threshold {
+		t.Fatalf("test setup: pruned size %d must exceed the proactive threshold %d", prunedTokens, state.threshold)
+	}
+
+	_, retried, err := state.recover(context.Background(), provider, messages, nil, "maximum context length exceeded")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !retried || len(provider.requests) != 0 {
+		t.Fatalf("a history that fits the window must take the free retry (retried=%v, requests=%d)", retried, len(provider.requests))
+	}
+}
+
+// After a mid-run model switch the summarizer is re-resolved against the new
+// main model: a run that started on the cheap model (no dedicated summarizer)
+// and escalated gets a cheap summarizer, and a previously broken one is
+// retried for the new model.
+func TestSwitchModelReresolvesSummarizer(t *testing.T) {
+	cheap := summaryProvider("CHEAP SUMMARY")
+	main := summaryProvider("MAIN SUMMARY")
+	var factoryModels []string
+	state := newCompactionState(Options{
+		ContextWindow:          1000,
+		CompactionPreserveLast: 2,
+		Model:                  "cheap-model",
+		Summarizer: func(_ context.Context, mainModelID string) (Provider, error) {
+			factoryModels = append(factoryModels, mainModelID)
+			if mainModelID == "cheap-model" {
+				return nil, nil // main already is the cheap model
+			}
+			return cheap, nil
+		},
+	}, nil)
+
+	if _, dedicated := state.summarizeProvider(context.Background(), main); dedicated {
+		t.Fatal("on the cheap model the main provider must summarize")
+	}
+	if _, dedicated := state.summarizeProvider(context.Background(), main); dedicated || len(factoryModels) != 1 {
+		t.Fatalf("factory must run once per main model, calls=%v", factoryModels)
+	}
+
+	state.switchModel("big-model", 400_000)
+	if state.threshold != compactionThreshold(400_000) || state.window != 400_000 {
+		t.Fatalf("switchModel must re-derive the window, got threshold=%d window=%d", state.threshold, state.window)
+	}
+	if got, dedicated := state.summarizeProvider(context.Background(), main); !dedicated || got != Provider(cheap) {
+		t.Fatal("after escalating to an expensive model the dedicated cheap summarizer must be used")
+	}
+	if len(factoryModels) != 2 || factoryModels[1] != "big-model" {
+		t.Fatalf("factory must be re-invoked with the new main model, calls=%v", factoryModels)
+	}
+
+	// A broken summarizer is retried after the next switch.
+	state.summarizerBroken = true
+	if _, dedicated := state.summarizeProvider(context.Background(), main); dedicated {
+		t.Fatal("a broken summarizer must fall back to main")
+	}
+	state.switchModel("other-model", 0)
+	if got, dedicated := state.summarizeProvider(context.Background(), main); !dedicated || got != Provider(cheap) {
+		t.Fatal("a model switch must clear the broken flag and rebuild the summarizer")
+	}
+}
+
+func TestCompactionUpdateWindow(t *testing.T) {
+	state := newCompactionState(Options{ContextWindow: 100_000, CompactionPreserveLast: 2}, nil)
+	state.lowWaterMark = 50_000
+	before := state.threshold
+
+	state.updateWindow(0) // unknown model: unchanged
+	if state.threshold != before || state.lowWaterMark != 50_000 {
+		t.Fatal("updateWindow(0) must be a no-op")
+	}
+
+	state.updateWindow(10_000)
+	if state.threshold >= before {
+		t.Fatalf("threshold = %d, want re-derived below %d", state.threshold, before)
+	}
+	if state.lowWaterMark != 0 {
+		t.Fatal("low-water mark must reset on a window change")
+	}
+	if !state.enabled {
+		t.Fatal("a positive window must keep compaction enabled")
+	}
+}
+
+// End-to-end: after escalate_model switches providers, the loop re-derives the
+// context window via ContextWindowFor, visible in the OnContext report.
+func TestRunEscalationRederivesContextWindow(t *testing.T) {
+	registry := tools.NewRegistry()
+	registry.Register(escalatingTool{target: "big-model"})
+	switched := &mockProvider{turns: [][]zeroruntime.StreamEvent{{
+		{Type: zeroruntime.StreamEventText, Content: "done"},
+		{Type: zeroruntime.StreamEventDone},
+	}}}
+	provider := &mockProvider{turns: [][]zeroruntime.StreamEvent{{
+		{Type: zeroruntime.StreamEventToolCallStart, ToolCallID: "call-1", ToolName: "escalate"},
+		{Type: zeroruntime.StreamEventToolCallDelta, ToolCallID: "call-1", ArgumentsFragment: `{}`},
+		{Type: zeroruntime.StreamEventToolCallEnd, ToolCallID: "call-1"},
+		{Type: zeroruntime.StreamEventDone},
+	}}}
+
+	var windows []int
+	result, err := Run(context.Background(), "go", provider, Options{
+		Registry:      registry,
+		ContextWindow: 100_000,
+		Model:         "small-model",
+		ModelSwitcher: func(context.Context, string) (Provider, error) { return switched, nil },
+		ContextWindowFor: func(modelID string) int {
+			if modelID == "big-model" {
+				return 400_000
+			}
+			return 0
+		},
+		OnContext: func(breakdown ContextBreakdown) { windows = append(windows, breakdown.ContextWindow) },
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if result.FinalAnswer != "done" {
+		t.Fatalf("final answer = %q", result.FinalAnswer)
+	}
+	if len(windows) < 2 {
+		t.Fatalf("expected at least 2 OnContext reports, got %d", len(windows))
+	}
+	if windows[0] != 100_000 {
+		t.Fatalf("turn 1 window = %d, want the original 100000", windows[0])
+	}
+	if windows[len(windows)-1] != 400_000 {
+		t.Fatalf("post-escalation window = %d, want 400000", windows[len(windows)-1])
+	}
+}
+
+// nonComparableProvider has a slice field, so comparing two Provider interface
+// values holding it would panic; the summarizer path must never compare them.
+type nonComparableProvider struct {
+	inner *mockProvider
+	tags  []string
+}
+
+func (p nonComparableProvider) StreamCompletion(ctx context.Context, request zeroruntime.CompletionRequest) (<-chan zeroruntime.StreamEvent, error) {
+	return p.inner.StreamCompletion(ctx, request)
+}
+
+func TestSummarizeClosureNeverComparesProviderValues(t *testing.T) {
+	broken := &mockProvider{turns: [][]zeroruntime.StreamEvent{{
+		{Type: zeroruntime.StreamEventError, Error: "boom: model not found"},
+	}}}
+	main := nonComparableProvider{inner: summaryProvider("MAIN SUMMARY"), tags: []string{"x"}}
+	state := newCompactionState(Options{
+		ContextWindow:          1000,
+		CompactionPreserveLast: 2,
+		Summarizer:             func(context.Context, string) (Provider, error) { return nonComparableProvider{inner: broken}, nil },
+	}, nil)
+	summary, err := state.summarizeClosure(context.Background(), main)([]zeroruntime.Message{{Role: zeroruntime.MessageRoleUser, Content: "history"}})
+	if err != nil || summary != "MAIN SUMMARY" {
+		t.Fatalf("fallback with non-comparable providers must not panic and must use main, got %q err=%v", summary, err)
+	}
+	// And with no dedicated summarizer at all the closure still works.
+	state = newCompactionState(Options{ContextWindow: 1000, CompactionPreserveLast: 2}, nil)
+	if _, err := state.summarizeClosure(context.Background(), main)([]zeroruntime.Message{{Role: zeroruntime.MessageRoleUser, Content: "history"}}); err != nil {
+		t.Fatal(err)
+	}
+}
@@ -126,8 +126,11 @@ func capCompactionBrief(brief string) (string, bool) {

 func compactionToolCallLine(call zeroruntime.ToolCall) string {
 	detail := ""
+	if call.Freeform && call.Name == "apply_patch" {
+		detail = strings.Join(patchPaths(call.Arguments), ", ")
+	}
 	var arguments map[string]any
-	if json.Unmarshal([]byte(strings.TrimSpace(call.Arguments)), &arguments) == nil {
+	if detail == "" && 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
@@ -73,6 +73,7 @@ func TestProjectCompactionInputRetainsAskUserExchangeAndSemanticArguments(t *tes
 		{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: "raw-patch", Name: "apply_patch", Freeform: true, Arguments: "*** Begin Patch\n*** Update File: internal/api.go\n*** Add File: internal/config.go\n*** End Patch\n"},
 			{ID: "fetch", Name: "web_fetch", Arguments: `{"url":"https://example.com/spec"}`},
 			{ID: "task", Name: "task", Arguments: `{"prompt":"Inspect the Windows implementation"}`},
 		}},
@@ -80,7 +81,7 @@ func TestProjectCompactionInputRetainsAskUserExchangeAndSemanticArguments(t *tes
 	}

 	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"} {
+	for _, want := range []string{"Which database should remain?", "Postgres only; do not touch MySQL", "internal/db.go", "internal/api.go", "internal/config.go", "https://example.com/spec", "Inspect the Windows implementation"} {
 		if !strings.Contains(content, want) {
 			t.Fatalf("projection missing %q: %q", want, content)
 		}
@@ -275,6 +275,27 @@ func TestEstimateToolDefTokensCountsDefinitions(t *testing.T) {
 	if estimateToolDefTokens(one) <= 0 {
 		t.Fatal("a tool definition (name + description + schema) should estimate > 0 tokens")
 	}
+	typed := append([]zeroruntime.ToolDefinition(nil), one...)
+	typed[0].Type = zeroruntime.ToolDefinitionFreeform
+	if estimateToolDefTokens(typed) <= estimateToolDefTokens(one) {
+		t.Fatal("a non-empty tool type must increase the estimated request cost")
+	}
+	for _, test := range []struct {
+		name   string
+		format zeroruntime.ToolDefinitionFormat
+	}{
+		{name: "type", format: zeroruntime.ToolDefinitionFormat{Type: "grammar"}},
+		{name: "syntax", format: zeroruntime.ToolDefinitionFormat{Syntax: "lark"}},
+		{name: "definition", format: zeroruntime.ToolDefinitionFormat{Definition: "start: WORD"}},
+	} {
+		t.Run("format "+test.name, func(t *testing.T) {
+			formatted := append([]zeroruntime.ToolDefinition(nil), one...)
+			formatted[0].Format = &test.format
+			if estimateToolDefTokens(formatted) <= estimateToolDefTokens(one) {
+				t.Fatalf("a non-empty format %s must increase the estimated request cost", test.name)
+			}
+		})
+	}
 	two := append(append([]zeroruntime.ToolDefinition{}, one...), zeroruntime.ToolDefinition{
 		Name:        "write_file",
 		Description: "Write contents to a file in the workspace.",
@@ -102,6 +102,10 @@ func copyToolDefinitions(toolDefs []zeroruntime.ToolDefinition) []zeroruntime.To
 	for index, definition := range toolDefs {
 		copied[index] = definition
 		copied[index].Parameters = copySchemaMap(definition.Parameters)
+		if definition.Format != nil {
+			format := *definition.Format
+			copied[index].Format = &format
+		}
 	}
 	return copied
 }
@@ -15,6 +15,7 @@ func TestContextPlannerPreservesProviderRequest(t *testing.T) {
 	}
 	toolDefs := []zeroruntime.ToolDefinition{{
 		Name: "read_file", Description: "Read a file",
+		Format: &zeroruntime.ToolDefinitionFormat{Type: "grammar", Syntax: "lark", Definition: "start: PATH"},
 		Parameters: map[string]any{
 			"type":       "object",
 			"required":   []string{"path"},
@@ -53,10 +54,12 @@ func TestContextPlannerPreservesProviderRequest(t *testing.T) {
 	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"
+	toolDefs[0].Format.Definition = "changed"
 	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].Format == nil || plan.Request.Tools[0].Format.Definition != "start: PATH" ||
 		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" {
@@ -0,0 +1,378 @@
+package agent
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+
+	"github.com/Gitlawb/zero/internal/sandbox"
+	"github.com/Gitlawb/zero/internal/tools"
+	"github.com/Gitlawb/zero/internal/zeroruntime"
+)
+
+type customApplyPatchTool struct {
+	calls int
+}
+
+type fixedPathScope struct {
+	roots []string
+}
+
+func (scope fixedPathScope) Roots() []string {
+	return append([]string(nil), scope.roots...)
+}
+
+func newFixedPathScope(t *testing.T, roots ...string) fixedPathScope {
+	t.Helper()
+	resolved := make([]string, 0, len(roots))
+	for _, root := range roots {
+		absolute, err := filepath.Abs(root)
+		if err != nil {
+			t.Fatalf("Abs(%q): %v", root, err)
+		}
+		if physical, err := filepath.EvalSymlinks(absolute); err == nil {
+			absolute = physical
+		}
+		resolved = append(resolved, absolute)
+	}
+	return fixedPathScope{roots: resolved}
+}
+
+func (*customApplyPatchTool) Name() string        { return "apply_patch" }
+func (*customApplyPatchTool) Description() string { return "custom JSON tool" }
+func (*customApplyPatchTool) Parameters() tools.Schema {
+	return tools.Schema{Type: "object", Properties: map[string]tools.PropertySchema{"value": {Type: "string"}}}
+}
+func (*customApplyPatchTool) Safety() tools.Safety {
+	return tools.Safety{Permission: tools.PermissionAllow, SideEffect: tools.SideEffectRead}
+}
+func (tool *customApplyPatchTool) Run(context.Context, map[string]any) tools.Result {
+	tool.calls++
+	return tools.Result{Status: tools.StatusOK}
+}
+
+func TestFreeformApplyPatchUsesExistingToolExecutionPath(t *testing.T) {
+	root := t.TempDir()
+	registry := tools.NewRegistry()
+	registry.Register(tools.NewScopedApplyPatchTool(root, nil))
+	patch := "*** Begin Patch\n*** Add File: hello.txt\n+hello\n*** End Patch\n"
+
+	result, err := executeToolCall(context.Background(), registry, zeroruntime.ToolCall{
+		ID:        "call-1",
+		Name:      "apply_patch",
+		Arguments: patch,
+		Freeform:  true,
+	}, PermissionModeUnsafe, Options{Cwd: root, FileTracker: tools.NewFileTracker()})
+	if err != nil {
+		t.Fatalf("executeToolCall: %v", err)
+	}
+	if result.Status != tools.StatusOK {
+		t.Fatalf("freeform apply_patch status = %s: %s", result.Status, result.Output)
+	}
+	content, err := os.ReadFile(filepath.Join(root, "hello.txt"))
+	if err != nil {
+		t.Fatalf("read patched file: %v", err)
+	}
+	if string(content) != "hello\n" {
+		t.Fatalf("patched content = %q, want hello newline", content)
+	}
+}
+
+func TestFreeformApplyPatchSupportsGrantedExtraRoot(t *testing.T) {
+	root := t.TempDir()
+	extra := t.TempDir()
+	scope, err := sandbox.NewScope(root, []string{extra})
+	if err != nil {
+		t.Fatalf("NewScope: %v", err)
+	}
+	registry := tools.NewRegistry()
+	registry.Register(tools.NewScopedApplyPatchTool(root, scope))
+	target := filepath.Join(extra, "hello.txt")
+	patch := "*** Begin Patch\n*** Add File: " + target + "\n+hello\n*** End Patch\n"
+
+	result, err := executeToolCall(context.Background(), registry, zeroruntime.ToolCall{
+		ID: "call-1", Name: "apply_patch", Arguments: patch, Freeform: true,
+	}, PermissionModeUnsafe, Options{Cwd: root, FileTracker: tools.NewFileTracker()})
+	if err != nil {
+		t.Fatalf("executeToolCall: %v", err)
+	}
+	if result.Status != tools.StatusOK {
+		t.Fatalf("freeform extra-root apply_patch status = %s: %s", result.Status, result.Output)
+	}
+	content, err := os.ReadFile(target)
+	if err != nil {
+		t.Fatalf("read extra-root patched file: %v", err)
+	}
+	if string(content) != "hello\n" {
+		t.Fatalf("patched content = %q, want hello newline", content)
+	}
+}
+
+func TestFreeformApplyPatchRejectsMixedWorkspaceAndExtraRoots(t *testing.T) {
+	for _, extraHasMatchingPath := range []bool{false, true} {
+		name := "extra target missing"
+		if extraHasMatchingPath {
+			name = "extra target exists"
+		}
+		t.Run(name, func(t *testing.T) {
+			workspace := t.TempDir()
+			extra := t.TempDir()
+			if err := os.MkdirAll(filepath.Join(workspace, "src"), 0o755); err != nil {
+				t.Fatal(err)
+			}
+			workspaceTarget := filepath.Join(workspace, "src", "a.go")
+			if err := os.WriteFile(workspaceTarget, []byte("old\n"), 0o644); err != nil {
+				t.Fatal(err)
+			}
+			extraTarget := filepath.Join(extra, "src", "a.go")
+			if extraHasMatchingPath {
+				if err := os.MkdirAll(filepath.Dir(extraTarget), 0o755); err != nil {
+					t.Fatal(err)
+				}
+				if err := os.WriteFile(extraTarget, []byte("old\n"), 0o644); err != nil {
+					t.Fatal(err)
+				}
+			}
+			scope, err := sandbox.NewScope(workspace, []string{extra})
+			if err != nil {
+				t.Fatal(err)
+			}
+			registry := tools.NewRegistry()
+			registry.Register(tools.NewScopedApplyPatchTool(workspace, scope))
+			extraCreated := filepath.Join(extra, "b.go")
+			patch := strings.Join([]string{
+				"*** Begin Patch",
+				"*** Update File: src/a.go",
+				"@@",
+				"-old",
+				"+new",
+				"*** Add File: " + extraCreated,
+				"+extra",
+				"*** End Patch",
+			}, "\n")
+
+			result, err := executeToolCall(context.Background(), registry, zeroruntime.ToolCall{
+				ID: "call-1", Name: "apply_patch", Arguments: patch, Freeform: true,
+			}, PermissionModeUnsafe, Options{Cwd: workspace, FileTracker: tools.NewFileTracker()})
+			if err != nil {
+				t.Fatalf("executeToolCall: %v", err)
+			}
+			if result.Status != tools.StatusError || !strings.Contains(result.Output, "mixes workspace-relative paths with an extra write root") {
+				t.Fatalf("mixed-root patch result = %s: %s", result.Status, result.Output)
+			}
+			if content, err := os.ReadFile(workspaceTarget); err != nil || string(content) != "old\n" {
+				t.Fatalf("workspace target changed: content=%q err=%v", content, err)
+			}
+			if extraHasMatchingPath {
+				if content, err := os.ReadFile(extraTarget); err != nil || string(content) != "old\n" {
+					t.Fatalf("extra-root target changed: content=%q err=%v", content, err)
+				}
+			}
+			if _, err := os.Stat(extraCreated); !os.IsNotExist(err) {
+				t.Fatalf("mixed-root patch created extra file: %v", err)
+			}
+		})
+	}
+}
+
+func TestFreeformApplyPatchAcceptsOneSemanticRoot(t *testing.T) {
+	for _, test := range []struct {
+		name         string
+		useExtraRoot bool
+	}{
+		{name: "workspace"},
+		{name: "extra root", useExtraRoot: true},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			workspace := t.TempDir()
+			extra := t.TempDir()
+			scope, err := sandbox.NewScope(workspace, []string{extra})
+			if err != nil {
+				t.Fatal(err)
+			}
+			root := workspace
+			if test.useExtraRoot {
+				root = extra
+			}
+			if err := os.MkdirAll(filepath.Join(root, "src"), 0o755); err != nil {
+				t.Fatal(err)
+			}
+			target := filepath.Join(root, "src", "a.go")
+			if err := os.WriteFile(target, []byte("old\n"), 0o644); err != nil {
+				t.Fatal(err)
+			}
+			updatePath := target
+			if !test.useExtraRoot {
+				updatePath = filepath.Join("src", "a.go")
+			}
+			created := filepath.Join(root, "b.go")
+			patch := strings.Join([]string{
+				"*** Begin Patch",
+				"*** Update File: " + updatePath,
+				"@@",
+				"-old",
+				"+new",
+				"*** Add File: " + created,
+				"+created",
+				"*** End Patch",
+			}, "\n")
+			registry := tools.NewRegistry()
+			registry.Register(tools.NewScopedApplyPatchTool(workspace, scope))
+			result, err := executeToolCall(context.Background(), registry, zeroruntime.ToolCall{
+				ID: "call-1", Name: "apply_patch", Arguments: patch, Freeform: true,
+			}, PermissionModeUnsafe, Options{Cwd: workspace, FileTracker: tools.NewFileTracker()})
+			if err != nil {
+				t.Fatalf("executeToolCall: %v", err)
+			}
+			if result.Status != tools.StatusOK {
+				t.Fatalf("single-root patch status = %s: %s", result.Status, result.Output)
+			}
+			if content, err := os.ReadFile(target); err != nil || string(content) != "new\n" {
+				t.Fatalf("updated content=%q err=%v", content, err)
+			}
+			if content, err := os.ReadFile(created); err != nil || string(content) != "created\n" {
+				t.Fatalf("created content=%q err=%v", content, err)
+			}
+		})
+	}
+}
+
+func TestFreeformApplyPatchRejectsAbsolutePathOutsideGrantedRoots(t *testing.T) {
+	root := t.TempDir()
+	granted := t.TempDir()
+	outside := t.TempDir()
+	scope := newFixedPathScope(t, root, granted)
+	registry := tools.NewRegistry()
+	registry.Register(tools.NewScopedApplyPatchTool(root, scope))
+	target := filepath.Join(outside, "blocked.txt")
+	patch := "*** Begin Patch\n*** Add File: " + target + "\n+blocked\n*** End Patch\n"
+
+	result, err := executeToolCall(context.Background(), registry, zeroruntime.ToolCall{
+		ID: "call-1", Name: "apply_patch", Arguments: patch, Freeform: true,
+	}, PermissionModeUnsafe, Options{Cwd: root})
+	if err != nil {
+		t.Fatalf("executeToolCall: %v", err)
+	}
+	if result.Status != tools.StatusError {
+		t.Fatalf("ungranted absolute patch status = %s, want error: %s", result.Status, result.Output)
+	}
+	if _, err := os.Stat(target); !os.IsNotExist(err) {
+		t.Fatalf("ungranted absolute patch created target: %v", err)
+	}
+}
+
+func TestPreparedFreeformPatchRejectsIntermediateSymlinkSwap(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("creating directory symlinks requires privileges on Windows")
+	}
+	root := t.TempDir()
+	extra := t.TempDir()
+	outside := t.TempDir()
+	intermediate := filepath.Join(extra, "nested")
+	if err := os.Mkdir(intermediate, 0o755); err != nil {
+		t.Fatalf("Mkdir: %v", err)
+	}
+	scope := newFixedPathScope(t, root, extra)
+	tool := tools.NewScopedApplyPatchTool(root, scope)
+	target := filepath.Join(intermediate, "blocked.txt")
+	patch := "*** Begin Patch\n*** Add File: " + target + "\n+blocked\n*** End Patch\n"
+	args, err := tools.PrepareFreeformApplyPatchArguments(tool, patch)
+	if err != nil {
+		t.Fatalf("PrepareFreeformApplyPatchArguments: %v", err)
+	}
+
+	if err := os.Remove(intermediate); err != nil {
+		t.Fatalf("Remove intermediate: %v", err)
+	}
+	if err := os.Symlink(outside, intermediate); err != nil {
+		t.Fatalf("Symlink: %v", err)
+	}
+	result := tool.Run(context.Background(), args)
+	if result.Status != tools.StatusError {
+		t.Fatalf("symlink-swapped patch status = %s, want error: %s", result.Status, result.Output)
+	}
+	if _, err := os.Stat(filepath.Join(outside, "blocked.txt")); !os.IsNotExist(err) {
+		t.Fatalf("symlink-swapped patch wrote outside root: %v", err)
+	}
+}
+
+func TestUnknownFreeformToolFailsClosed(t *testing.T) {
+	result, err := executeToolCall(context.Background(), tools.NewRegistry(), zeroruntime.ToolCall{
+		ID: "call-1", Name: "unknown", Arguments: "raw", Freeform: true,
+	}, PermissionModeUnsafe, Options{})
+	if err != nil {
+		t.Fatalf("executeToolCall: %v", err)
+	}
+	if result.Status != tools.StatusError {
+		t.Fatalf("unknown freeform status = %s, want error", result.Status)
+	}
+}
+
+func TestCustomApplyPatchCannotUseFreeformContract(t *testing.T) {
+	custom := &customApplyPatchTool{}
+	registry := tools.NewRegistry()
+	registry.Register(custom)
+
+	result, err := executeToolCall(context.Background(), registry, zeroruntime.ToolCall{
+		ID: "call-1", Name: "apply_patch", Arguments: "raw patch", Freeform: true,
+	}, PermissionModeUnsafe, Options{})
+	if err != nil {
+		t.Fatalf("executeToolCall: %v", err)
+	}
+	if result.Status != tools.StatusError || !strings.Contains(result.Output, "Unsupported freeform tool call") {
+		t.Fatalf("custom freeform apply_patch result = %#v, want unsupported error", result)
+	}
+	if custom.calls != 0 {
+		t.Fatalf("custom apply_patch executed %d times", custom.calls)
+	}
+}
+
+func TestDeniedFreeformApplyPatchDoesNotWrite(t *testing.T) {
+	root := t.TempDir()
+	registry := tools.NewRegistry()
+	registry.Register(tools.NewScopedApplyPatchTool(root, nil))
+	patch := "*** Begin Patch\n*** Add File: denied.txt\n+must not exist\n*** End Patch\n"
+
+	result, err := executeToolCall(context.Background(), registry, zeroruntime.ToolCall{
+		ID:        "call-1",
+		Name:      "apply_patch",
+		Arguments: patch,
+		Freeform:  true,
+	}, PermissionModeAsk, Options{
+		Cwd: root,
+		OnPermissionRequest: func(context.Context, PermissionRequest) (PermissionDecision, error) {
+			return PermissionDecision{Action: PermissionDecisionDeny, Reason: "test denial"}, nil
+		},
+	})
+	if err != nil {
+		t.Fatalf("executeToolCall: %v", err)
+	}
+	if result.Status != tools.StatusError {
+		t.Fatalf("denied freeform status = %s, want error", result.Status)
+	}
+	if _, err := os.Stat(filepath.Join(root, "denied.txt")); !os.IsNotExist(err) {
+		t.Fatalf("denied freeform patch changed the workspace: %v", err)
+	}
+}
+
+func TestHistorySafeToolCallsPreservesRawFreeformArguments(t *testing.T) {
+	raw := "*** Begin Patch\n*** Update File: internal/main.go\n@@\n-old\n+new\n*** End Patch\n"
+	safe := historySafeToolCalls([]ToolCall{{
+		ID: "call-1", ProviderCallID: "provider-1", Name: "apply_patch", Arguments: raw, Freeform: true,
+	}})
+	if len(safe) != 1 || safe[0].Arguments != raw || safe[0].ProviderCallID != "provider-1" || !safe[0].Freeform {
+		t.Fatalf("freeform history changed raw call: %#v", safe)
+	}
+}
+
+func TestAbortedToolResultPreservesProviderCallID(t *testing.T) {
+	messages := appendAbortedToolResults(nil, []ToolCall{{
+		ID: "call-1", ProviderCallID: "provider-1", Name: "read_file",
+	}})
+	if len(messages) != 1 || messages[0].ToolCallID != "call-1" || messages[0].ToolCallProviderID != "provider-1" || !messages[0].IsError {
+		t.Fatalf("aborted tool result lost provider identity: %#v", messages)
+	}
+}
@@ -33,11 +33,11 @@ const (
 	// knows before spending more tool turns.
 	toolOnlyProgressReminderAt = 6

-	// planReminderTurn is the turn (1-based) by the end of which a multi-step
-	// task should have called update_plan; if it hasn't, a one-time reminder is
-	// injected. Set to 3 (not 2) so short, legitimate two-step tasks finish
-	// without a spurious planning nag.
-	planReminderTurn = 3
+	// planReminderTurn and planReminderToolThreshold keep bounded implementation
+	// work plan-free while still nudging a genuinely sustained run that has not
+	// established any structured progress. Both thresholds must be met.
+	planReminderTurn          = 7
+	planReminderToolThreshold = 7

 	// planToolName is the planning tool the loop watches for by name.
 	planToolName = "update_plan"
@@ -591,13 +591,12 @@ func (state *guardState) planReminder(turn int) string {
 		return planStaleReminder(state.toolCallsSincePlanUpdate)
 	}

-	// NOT-CALLED reminder: by the end of planReminderTurn the model should have
-	// called update_plan if it's doing a multi-step task (>=1 other tool call).
-	// One-shot for the whole run.
+	// NOT-CALLED reminder: once both the turn and tool-call thresholds are met,
+	// sustained work should have called update_plan. One-shot for the whole run.
 	if !state.notCalledReminderSent &&
 		!state.planEverCalled &&
 		turn >= planReminderTurn &&
-		state.totalToolCalls >= 1 {
+		state.totalToolCalls >= planReminderToolThreshold {
 		state.notCalledReminderSent = true
 		return planNotCalledReminder()
 	}
@@ -257,19 +257,16 @@ func TestRunDoesNotCountDroppedToolCallTurnsAsEmpty(t *testing.T) {
 }

 func TestRunInjectsPlanNotCalledReminderForMultiStepTask(t *testing.T) {
+	const expectedThreshold = 7
+	if planReminderToolThreshold != expectedThreshold {
+		t.Fatalf("plan reminder tool threshold = %d, want %d", planReminderToolThreshold, expectedThreshold)
+	}
 	root := t.TempDir()
 	writeAgentTestFile(t, root+"/notes.txt", "alpha")
 	registry := tools.NewRegistry()
 	registry.Register(tools.NewScopedReadFileTool(root, nil))

-	provider := &mockProvider{
-		turns: [][]zeroruntime.StreamEvent{
-			toolTurn("call-1", "read_file", `{"path":"notes.txt"}`), // turn 1: other tool call
-			toolTurn("call-2", "read_file", `{"path":"notes.txt"}`), // turn 2: still no update_plan
-			toolTurn("call-3", "read_file", `{"path":"notes.txt"}`), // turn 3: reminder fires here
-			textTurn("done"),
-		},
-	}
+	provider := &mockProvider{turns: append(repeatedReadTurns(expectedThreshold), textTurn("done"))}

 	result, err := Run(context.Background(), "go", provider, Options{
 		Registry: registry,
@@ -287,6 +284,44 @@ func TestRunInjectsPlanNotCalledReminderForMultiStepTask(t *testing.T) {
 	}
 }

+func TestRunDoesNotInjectPlanReminderForBoundedToolSequence(t *testing.T) {
+	const expectedThreshold = 7
+	root := t.TempDir()
+	writeAgentTestFile(t, root+"/notes.txt", "alpha")
+	registry := tools.NewRegistry()
+	registry.Register(tools.NewScopedReadFileTool(root, nil))
+
+	provider := &mockProvider{turns: append(repeatedReadTurns(expectedThreshold-1), textTurn("done"))}
+	result, err := Run(context.Background(), "go", provider, Options{Registry: registry, MaxTurns: 12})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if result.FinalAnswer != "done" {
+		t.Fatalf("expected final answer, got %q", result.FinalAnswer)
+	}
+	if count := countUserMessagesContaining(result.Messages, planNotCalledReminderMarker); count != 0 {
+		t.Fatalf("bounded tool sequence must not draw a plan reminder, got %d", count)
+	}
+}
+
+func TestPlanReminderWaitsForTurnThresholdAfterEnoughToolCalls(t *testing.T) {
+	state := guardState{totalToolCalls: 7}
+	if got := state.planReminder(6); got != "" {
+		t.Fatalf("planReminder(6) = %q, want no reminder before turn threshold", got)
+	}
+	if state.notCalledReminderSent {
+		t.Fatal("early turn marked the not-called reminder as sent")
+	}
+}
+
+func repeatedReadTurns(count int) [][]zeroruntime.StreamEvent {
+	turns := make([][]zeroruntime.StreamEvent, 0, count)
+	for range count {
+		turns = append(turns, toolTurn("call", "read_file", `{"path":"notes.txt"}`))
+	}
+	return turns
+}
+
 func TestRunDoesNotInjectPlanReminderForTrivialTask(t *testing.T) {
 	root := t.TempDir()
 	writeAgentTestFile(t, root+"/notes.txt", "alpha")
@@ -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
@@ -133,6 +141,7 @@ func Run(ctx context.Context, prompt string, provider Provider, options Options)
 			}
 			options.Trace.Counter(trace.CounterInputTokens, int64(usage.InputTokens))
 			options.Trace.Counter(trace.CounterCachedInputTokens, int64(usage.CachedInputTokens))
+			options.Trace.Counter(trace.CounterCacheWriteTokens, int64(usage.CacheWriteTokens))
 			options.Trace.Counter(trace.CounterOutputTokens, int64(usage.OutputTokens))
 		}
 	}
@@ -689,11 +698,12 @@ func Run(ctx context.Context, prompt string, provider Provider, options Options)
 				turnRequestedModel = toolResult.RequestedModel
 			}
 			messages = append(messages, zeroruntime.Message{
-				Role:         zeroruntime.MessageRoleTool,
-				Content:      toolResult.ModelOutput(),
-				ToolCallID:   toolResult.ToolCallID,
-				IsError:      toolResult.Status == tools.StatusError,
-				ChangedFiles: append([]string(nil), toolResult.ChangedFiles...),
+				Role:               zeroruntime.MessageRoleTool,
+				Content:            toolResult.ModelOutput(),
+				ToolCallID:         toolResult.ToolCallID,
+				ToolCallProviderID: call.ProviderCallID,
+				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 —
@@ -836,11 +846,21 @@ func Run(ctx context.Context, prompt string, provider Provider, options Options)
 					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
-					// here, so a switch to a model with a different window keeps compacting
-					// against the original budget. Fixing it needs the switcher to also
-					// report the new window — out of scope for this change.
+					// Re-derive the context window for the new model so compaction and
+					// the OnContext budget report track the model actually in force —
+					// without this a switch to a smaller-window model can overflow the
+					// target, and a switch to a larger one over-compacts. An unknown
+					// model (<= 0) keeps the original window. The compactor also
+					// re-resolves its dedicated summarizer against the new model.
+					window := 0
+					if options.ContextWindowFor != nil {
+						window = options.ContextWindowFor(turnRequestedModel)
+					}
+					if window > 0 {
+						options.ContextWindow = window
+						planner.config.contextWindow = window
+					}
+					compactor.switchModel(turnRequestedModel, window)
 				}
 			}
 		}
@@ -1027,6 +1047,9 @@ func historySafeToolCalls(calls []ToolCall) []ToolCall {
 	safe := make([]ToolCall, len(calls))
 	for i, call := range calls {
 		safe[i] = call
+		if call.Freeform {
+			continue
+		}
 		args := strings.TrimSpace(call.Arguments)
 		switch {
 		case args == "":
@@ -1110,8 +1133,28 @@ func decodeToolArguments(arguments string, v any) error {
 }

 func executeToolCall(ctx context.Context, registry *tools.Registry, call ToolCall, permissionMode PermissionMode, options Options) (ToolResult, error) {
+	tool, toolFound := registry.Get(call.Name)
 	args := map[string]any{}
-	if call.Arguments != "" {
+	if call.Freeform {
+		if !toolFound || !tools.IsBuiltInApplyPatch(tool) {
+			return ToolResult{
+				ToolCallID: call.ID,
+				Name:       call.Name,
+				Status:     tools.StatusError,
+				Output:     "Error: Unsupported freeform tool call for " + call.Name + ".",
+			}, nil
+		}
+		prepared, err := tools.PrepareFreeformApplyPatchArguments(tool, call.Arguments)
+		if err != nil {
+			return ToolResult{
+				ToolCallID: call.ID,
+				Name:       call.Name,
+				Status:     tools.StatusError,
+				Output:     "Error: Invalid freeform apply_patch input: " + err.Error(),
+			}, nil
+		}
+		args = prepared
+	} else if call.Arguments != "" {
 		if err := decodeToolArguments(call.Arguments, &args); err != nil {
 			return ToolResult{
 				ToolCallID: call.ID,
@@ -1139,7 +1182,6 @@ func executeToolCall(ctx context.Context, registry *tools.Registry, call ToolCal
 			DenialReason: DenialFiltered,
 		}, nil
 	}
-	tool, toolFound := registry.Get(call.Name)
 	if (permissionMode == PermissionModeSpecDraft || permissionMode == PermissionModePlan) && toolFound && !ToolAdvertised(tool, permissionMode) {
 		modeName := string(permissionMode)
 		return ToolResult{
@@ -1364,7 +1406,7 @@ 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
@@ -1548,7 +1590,7 @@ 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)
@@ -1596,7 +1638,7 @@ 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)
@@ -3087,13 +3129,15 @@ func partitionToolsCached(registry *tools.Registry, permissionMode PermissionMod
 	// Deferral may activate only when tool_search is actually runnable; otherwise
 	// the loop would hide deferred tools behind a loader the dispatch gate rejects
 	// — an inescapable dead-end. "Runnable" mirrors executeToolCall's gate:
-	// registered, not in DisabledTools, and advertised in the current permission
-	// mode (e.g. not spec-draft, where tool_search is not advertised). The
+	// registered, model-visible, not in DisabledTools, and advertised in the
+	// current permission mode (e.g. not spec-draft, where tool_search is not
+	// advertised). The
 	// EnabledTools allowlist is intentionally NOT checked here — tool_search is
 	// exempt from the allowlist at dispatch, so an allowlist that omits it must
 	// not disable deferral.
 	loader, loaderFound := registry.Get(tools.ToolSearchToolName)
 	loaderUsable := loaderFound &&
+		tools.ModelVisible(loader) &&
 		!containsToolName(options.DisabledTools, tools.ToolSearchToolName) &&
 		ToolAdvertised(loader, permissionMode)

@@ -3200,15 +3244,21 @@ func cachedRuntimeToolDefinition(defCache map[string]zeroruntime.ToolDefinition,
 // runtimeToolDefinition renders a tool's advertised definition (name, description,
 // JSON-schema parameters) as sent to the provider.
 func runtimeToolDefinition(tool tools.Tool) zeroruntime.ToolDefinition {
-	return zeroruntime.ToolDefinition{
+	definition := zeroruntime.ToolDefinition{
 		Name:        tool.Name(),
 		Description: tool.Description(),
 		Parameters:  schemaToRuntimeMap(tool.Parameters()),
 	}
+	if tools.IsBuiltInApplyPatch(tool) {
+		definition.Type = zeroruntime.ToolDefinitionFreeform
+	}
+	return definition
 }

 func ToolVisible(tool tools.Tool, permissionMode PermissionMode, enabledTools []string, disabledTools []string) bool {
-	return ToolAllowedByFilters(tool.Name(), enabledTools, disabledTools) && ToolAdvertised(tool, permissionMode)
+	return tools.ModelVisible(tool) &&
+		ToolAllowedByFilters(tool.Name(), enabledTools, disabledTools) &&
+		ToolAdvertised(tool, permissionMode)
 }

 func ToolAllowedByFilters(name string, enabledTools []string, disabledTools []string) bool {
@@ -3357,10 +3407,11 @@ func loadedToolsFromResult(meta map[string]string) []string {
 func appendAbortedToolResults(messages []Message, remaining []ToolCall) []Message {
 	for _, call := range remaining {
 		messages = append(messages, zeroruntime.Message{
-			Role:       zeroruntime.MessageRoleTool,
-			Content:    abortedToolResultNotice,
-			ToolCallID: call.ID,
-			IsError:    true,
+			Role:               zeroruntime.MessageRoleTool,
+			Content:            abortedToolResultNotice,
+			ToolCallID:         call.ID,
+			ToolCallProviderID: call.ProviderCallID,
+			IsError:            true,
 		})
 	}
 	return messages
@@ -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 != "" {
@@ -4096,7 +4096,7 @@ func TestRunDoesNotFlagCleanToolOutput(t *testing.T) {
 // caller's callback AND stamps token counters, and the run completes.
 func TestRunTracingWrapperStampsUsage(t *testing.T) {
 	provider := &mockProvider{turns: [][]zeroruntime.StreamEvent{{
-		{Type: zeroruntime.StreamEventUsage, Usage: zeroruntime.Usage{InputTokens: 100, CachedInputTokens: 20, OutputTokens: 40}},
+		{Type: zeroruntime.StreamEventUsage, Usage: zeroruntime.Usage{PromptTokens: 100, CachedInputTokens: 20, CacheWriteTokens: 10, CompletionTokens: 40}},
 		{Type: zeroruntime.StreamEventText, Content: "done"},
 		{Type: zeroruntime.StreamEventDone},
 	}}}
@@ -4135,6 +4135,9 @@ func TestRunTracingWrapperStampsUsage(t *testing.T) {
 	if got := tr.Counter(trace.CounterCachedInputTokens); got != 20 {
 		t.Fatalf("cached input token counter = %d, want 20", got)
 	}
+	if got := tr.Counter(trace.CounterCacheWriteTokens); got != 10 {
+		t.Fatalf("cache-write token counter = %d, want 10", got)
+	}
 	if got := tr.Counter(trace.CounterOutputTokens); got != 40 {
 		t.Fatalf("output token counter = %d, want 40", got)
 	}
@@ -4340,3 +4343,95 @@ func TestPlanModeHonorsBeforeToolVeto(t *testing.T) {
 		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)
+			}
+		})
+	}
+}
@@ -31,6 +31,19 @@ func (t countingSchemaTool) Run(_ context.Context, _ map[string]any) tools.Resul
 	return tools.Result{Status: tools.StatusOK}
 }

+func TestRuntimeToolDefinitionMarksOnlyBuiltInApplyPatchFreeform(t *testing.T) {
+	builtIn := runtimeToolDefinition(tools.NewScopedApplyPatchTool(t.TempDir(), nil))
+	if builtIn.Type != zeroruntime.ToolDefinitionFreeform {
+		t.Fatalf("built-in apply_patch type = %q, want freeform", builtIn.Type)
+	}
+
+	calls := 0
+	custom := runtimeToolDefinition(countingSchemaTool{name: "apply_patch", calls: &calls})
+	if custom.Type != "" {
+		t.Fatalf("custom apply_patch type = %q, want legacy function shape", custom.Type)
+	}
+}
+
 // The cache renders a tool's schema once and reuses it across calls, and its
 // output is identical to the uncached path.
 func TestPartitionToolsCacheRendersOnceAndMatchesUncached(t *testing.T) {
@@ -67,3 +67,21 @@ func TestEagerToolSchemaTokenBudget(t *testing.T) {
 		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)
 	}
 }
+
+func TestAgentAdvertisesBothEditTools(t *testing.T) {
+	registry := tools.NewRegistry()
+	for _, tool := range tools.CoreToolsScoped(t.TempDir(), nil) {
+		registry.Register(tool)
+	}
+	exposed, _ := partitionTools(registry, PermissionModeAsk, Options{}, map[string]bool{})
+	names := make(map[string]bool, len(exposed))
+	for _, definition := range exposed {
+		names[definition.Name] = true
+	}
+	if !names["apply_patch"] {
+		t.Fatal("agent must retain apply_patch for multi-hunk changes")
+	}
+	if !names["edit_file"] {
+		t.Fatal("agent must receive edit_file for targeted exact replacements")
+	}
+}
@@ -58,12 +58,18 @@ func toolSubstrings(exposed []zeroruntime.ToolDefinition) (toolsSubstr, schemaSu
 	for _, def := range exposed {
 		writeLengthPrefixed(&toolsSB, def.Name)
 		writeLengthPrefixed(&toolsSB, def.Description)
+		writeLengthPrefixed(&toolsSB, string(def.Type))
 		// Parameters is rendered to a canonical JSON string per tool. The
 		// schema-render cache in internal/agent (used by partitionToolsCached)
 		// guarantees the same render is byte-identical across turns for the
 		// same tool, so this substring is a stable hash input.
 		writeLengthPrefixed(&schemaSB, def.Name)
 		writeLengthPrefixed(&schemaSB, canonicalSchemaString(def.Parameters))
+		if def.Format != nil {
+			writeLengthPrefixed(&schemaSB, def.Format.Type)
+			writeLengthPrefixed(&schemaSB, def.Format.Syntax)
+			writeLengthPrefixed(&schemaSB, def.Format.Definition)
+		}
 	}
 	return toolsSB.String(), schemaSB.String()
 }
@@ -73,6 +73,38 @@ func TestComputePrefixFingerprintSchemaChangeChangesSchemaHash(t *testing.T) {
 	}
 }

+func TestComputePrefixFingerprintIncludesToolTypeAndFormat(t *testing.T) {
+	opts := Options{Cwd: t.TempDir(), SystemPrompt: "core"}
+	base := zeroruntime.ToolDefinition{Name: "apply_patch", Description: "Patch files"}
+	baseFingerprint := ComputePrefixFingerprint(opts, []zeroruntime.ToolDefinition{base})
+
+	typed := base
+	typed.Type = zeroruntime.ToolDefinitionFreeform
+	if got := ComputePrefixFingerprint(opts, []zeroruntime.ToolDefinition{typed}); got.ToolsHash == baseFingerprint.ToolsHash {
+		t.Fatal("ToolsHash must change when tool Type changes")
+	}
+
+	formatCases := []struct {
+		name   string
+		format zeroruntime.ToolDefinitionFormat
+	}{
+		{name: "type", format: zeroruntime.ToolDefinitionFormat{Type: "grammar"}},
+		{name: "syntax", format: zeroruntime.ToolDefinitionFormat{Syntax: "lark"}},
+		{name: "definition", format: zeroruntime.ToolDefinitionFormat{Definition: "start: PATCH"}},
+		{name: "empty", format: zeroruntime.ToolDefinitionFormat{}},
+	}
+	for _, test := range formatCases {
+		t.Run(test.name, func(t *testing.T) {
+			withFormat := base
+			withFormat.Format = &test.format
+			got := ComputePrefixFingerprint(opts, []zeroruntime.ToolDefinition{withFormat})
+			if got.SchemaHash == baseFingerprint.SchemaHash {
+				t.Fatalf("SchemaHash must change for %s format input", test.name)
+			}
+		})
+	}
+}
+
 // TestComputePrefixFingerprintSystemPromptChangeChangesBaseHash asserts the
 // most common drift path: a system-prompt edit (e.g. an agent.md update, a
 // model addendum change) must move the base-instructions hash, which moves
@@ -30,13 +30,10 @@ work.
   read-before-edit discipline: inspect the target file and nearby callers,
   tests, or config before you modify behavior. Never edit a file you have not
   read.
-2. **Plan.** Use update_plan for implementation or investigation that has at
-   least three meaningful dependent steps, then keep it current at milestones.
-   Mark completed work and the next in-progress step together when practical;
-   do not spend separate turns updating it after every file or command. Keep at
-   most one item in_progress. Skip plans for simple lookups, explanations, code
-   navigation, and other short tasks. Never create a plan after the work is
-   already complete merely to describe what you did.
+2. **Plan.** Use update_plan for multi-component, sequencing-uncertain, or long
+   work. Skip it for bounded changes in one component. Update only when the
+   overall phase changes, keep at most one item in_progress, and never create a
+   plan after the work is complete.
 3. **Implement.** Make focused changes that match the surrounding code's style,
   naming, and conventions. Prefer the smallest change that fully solves the
   problem. Avoid broad refactors, unrelated rewrites, dependency churn, and
@@ -52,37 +49,48 @@ work.

 - Choose the narrowest tool that safely accomplishes the step. Prefer native
  file tools - read_file, read_minified_file, list_directory, glob, grep,
-  write_file, edit_file, apply_patch - over shelling out to
+  edit_file, apply_patch, write_file - over shelling out to
  cat/sed/awk/python for file operations.
  They are safer, reviewable, and produce clean diffs.
- Prefer read_minified_file when initially exploring source code; it preserves
-  code while removing comments and redundant whitespace. Use read_file when
-  exact text, comments, or line numbers are needed.
+- Use read_minified_file only to explore large or unfamiliar source. Use
+  read_file for small or likely edit targets and exact text, comments, or line
+  numbers. Do not read both unless a new need for exact content appears.
 - Keep edits focused and reviewable. A single patch may update several related
  files when they form one coherent change; do not hide unrelated edits in a
  bulk shell or script rewrite.
- For edits to existing files, prefer edit_file or apply_patch with minimal,
-  targeted diffs. Match the existing indentation, imports, and idioms. Match the
-  file's comment density: do not add explanatory comments unless the user asks or
-  the code is already comment-dense.
+- For edits to existing files, use edit_file for a targeted change (old_string
+  must match the file exactly and be unique, so include a few surrounding
+  lines) and apply_patch when one coherent change spans several hunks or
+  files. Use write_file only to create a file or when most of it changes; do
+  not rewrite a whole file to change a few lines. Match the existing
+  indentation, imports, and idioms. Match the file's comment density: do not
+  add explanatory comments unless the user asks or the code is already
+  comment-dense.
+- A successful edit result already confirms the change; do not re-read a file
+  just to verify an edit that succeeded. If an edit fails, read the error, fix
+  the old_string or hunk, and retry the same tool rather than switching to a
+  full rewrite.
 - Solve the problem as posed, not a more general version of it. Add no
  speculative abstraction, configurability, or handling for cases that cannot
  occur, and nothing the user did not ask for. A small diff can still be
-  over-built; if a 200-line solution could be 50, rewrite it.
+  over-built; if a 200-line solution could be 50, rewrite it. Once the required
+  behavior passes validation, stop instead of adding optional cleanup.
 - Preserve behavior you were not asked to change. Do not delete or rewrite code
  you did not author unless the task requires it; if you must, say so.

 ## Testing gate (mandatory)

- After any change to code, verify after edits by running the project's
-  validators before you summarize or commit: tests, type-checks, linters, and/or
-  the build, as appropriate. Scope them to the change while iterating; reserve
-  full-suite runs for milestones.
- If you are unsure which validators apply, search the repo (Makefile, package
-  manifests, CI config) to find them.
+- After code changes, run the project's documented appropriate validators.
+  Scope iteration checks, combine compatible commands when diagnostics stay
+  useful, and run the final set once after the last edit. Rerun only after a
+  change or failure.
+- If unsure which entry points apply, inspect the Makefile, manifests, or CI;
+  do not invent a parallel flow.
 - Never claim a task is done, and never commit, while validators are failing. If
  they fail, fix the cause and rerun; do not paper over it. If you could not run
  a validator, say so explicitly rather than implying success.
+- A successful native patch confirms the edit. Reread only when the next change
+  needs exact content or the result was ambiguous.

 ## Tool use

@@ -104,7 +112,7 @@ work.
  you need to clean up a running foreground command yourself, use write_stdin.
 - write_stdin's session_id is only ever an id returned by a still-running
  exec_command; never guess or probe ids. If you have no such session, start one
-  with exec_command, or use write_file/edit_file/apply_patch for file changes.
+  with exec_command, or use edit_file/apply_patch/write_file for file changes.
 - write_stdin with empty input polls an existing exec_command session, and
  `\u0003` interrupts it. Sending other stdin bytes may require approval because
  it can drive the running process beyond the original command. Non-tty sessions
@@ -140,6 +148,7 @@ work.
 - Default to concise, skimmable output. Lead with the answer or the result.
 - Use GitHub-flavored Markdown: headings to structure longer replies, fenced
  code blocks for code, and `inline code` for file paths, commands, symbols, and
-  short snippets. Reference code as `file:line` so it is clickable.
+  short snippets. Reference code with file paths and include line numbers when
+  already known; do not look them up solely for the final summary.
 - Report outcomes faithfully: if tests failed, show it; if a step was skipped,
  say so; when something is done and verified, state it plainly without hedging.
@@ -60,8 +60,11 @@ const openAIPromptAddendum = `<model_guidance>
  longer answers, fenced code blocks for code, and ` + "`inline code`" + ` for paths,
  commands, and symbols.
 - Strongly prefer the native file tools (read_file, list_directory, grep, glob,
-  write_file, edit_file, apply_patch) over shelling out to cat/sed/awk/python for
-  file work. Make one tool call per file; do not batch file writes into a script.
+  edit_file, apply_patch, write_file) over shelling out to cat/sed/awk/python for
+  file work. Use them directly; never run apply_patch through exec_command.
+  read_file, edit_file and write_file take one file per call, while one coherent
+  apply_patch may span several files. Keep independent native calls in the same
+  turn, and do not batch file writes into a script.
 - Persist until the task is fully handled this turn: gather context, implement,
  run the validators, and report — do not stop at a partial result.
 </model_guidance>`
@@ -29,6 +29,9 @@ func TestBuildSystemPromptAppendsModelAddendum(t *testing.T) {
 	if got := buildSystemPrompt(Options{Model: "gpt-5"}); !strings.Contains(got, openAIPromptAddendum) {
 		t.Fatalf("expected the OpenAI addendum in the gpt-5 prompt")
 	}
+	if got := strings.Join(strings.Fields(strings.ToLower(buildSystemPrompt(Options{Model: "gpt-5"}))), " "); !strings.Contains(got, "never run apply_patch through exec_command") {
+		t.Fatalf("OpenAI prompt must route edits through the native patch tool:\n%s", got)
+	}
 	// Claude is aligned with the core prompt and gets no family addendum now that
 	// comment discipline is universal; it must not pick up another family's block.
 	claude := buildSystemPrompt(Options{Model: "claude-opus-4-6"})
@@ -29,14 +29,17 @@ func TestMain(m *testing.M) {
 }

 func TestCoreSystemPromptIncludesCodingQualityRules(t *testing.T) {
-	prompt := strings.ToLower(buildSystemPrompt(Options{}))
+	prompt := strings.Join(strings.Fields(strings.ToLower(buildSystemPrompt(Options{}))), " ")
+	if strings.Contains(prompt, "clickable file paths") {
+		t.Fatalf("system prompt must not claim inline-code file paths are clickable: %s", prompt)
+	}

 	for _, want := range []string{
 		"read-before-edit",
 		"inspect the target file",
 		"plan then act",
 		"choose the narrowest tool",
-		"prefer edit_file or apply_patch",
+		"for edits to existing files, use edit_file",
 		"verify after edits",
 		"honor the active permission mode",
 		"avoid broad refactors",
@@ -44,6 +47,13 @@ func TestCoreSystemPromptIncludesCodingQualityRules(t *testing.T) {
 		"do not recognize",
 		"scaled to the work",
 		"comment density",
+		"skip it for bounded changes in one component",
+		"do not read both unless a new need for exact content appears",
+		"combine compatible commands when diagnostics stay useful",
+		"do not invent a parallel flow",
+		"a successful native patch confirms the edit",
+		"once the required behavior passes validation, stop",
+		"do not look them up solely for the final summary",
 	} {
 		if !strings.Contains(prompt, want) {
 			t.Fatalf("expected core system prompt to include %q, got:\n%s", want, buildSystemPrompt(Options{}))
@@ -348,10 +348,26 @@ type Options struct {
 	// CompactionPreserveLast is how many trailing messages compaction keeps
 	// verbatim. <= 0 falls back to defaultCompactionPreserveLast.
 	CompactionPreserveLast int
-	Registry               *tools.Registry
-	PermissionMode         PermissionMode
-	Autonomy               string
-	Sandbox                *sandbox.Engine
+	// Summarizer, when set, lazily builds the provider used for compaction
+	// summarization calls — typically a cheap/fast model, since summaries at
+	// main-model prices are the single most expensive recurring event in a
+	// long run. It receives the main model currently in force and may return
+	// (nil, nil) when no dedicated summarizer applies to it (the main model is
+	// already the cheap one). Built on the first paid compaction and again
+	// after a mid-run model switch. Any failure (build or call) falls back to
+	// the run's main provider until the next switch, so a misconfigured
+	// summarizer can never break compaction. nil keeps today's behavior.
+	Summarizer func(ctx context.Context, mainModelID string) (Provider, error)
+	// ContextWindowFor, when set, resolves a model ID to its context window so
+	// the compactor can re-derive its threshold after a mid-run model switch
+	// (escalate_model). Without it a switch keeps compacting against the
+	// original model's window — overflowing a smaller target or over-compacting
+	// a larger one. Return <= 0 when the model is unknown (window unchanged).
+	ContextWindowFor func(modelID string) int
+	Registry         *tools.Registry
+	PermissionMode   PermissionMode
+	Autonomy         string
+	Sandbox          *sandbox.Engine
 	// FileTracker records per-session file read/write versions so the write tools
 	// can detect a file changed on disk outside Zero since it was last read. nil
 	// disables the check. Created once per session and threaded into every tool run.
@@ -453,7 +453,12 @@ func (manager *Manager) normalizeLoadedTask(fileTaskID string, task Task) (Task,
 	}
 	outputFile, err := manager.outputFile(task.ID, task.OutputFile)
 	if err != nil {
-		return Task{}, false, err
+		var migrated bool
+		outputFile, migrated = manager.migrateLegacyOutputFile(task.ID, task.OutputFile)
+		if !migrated {
+			return Task{}, false, err
+		}
+		changed = true
 	}
 	if outputFile != task.OutputFile {
 		changed = true
@@ -562,6 +567,32 @@ func (manager *Manager) outputFile(taskID string, requested string) (string, err
 	return path, nil
 }

+// migrateLegacyOutputFile recovers task metadata written under a previous home
+// or XDG data root. It accepts only the canonical per-task output
+// name in the historic zero/background layout, and only when the corresponding
+// regular file already exists inside the active manager root.
+func (manager *Manager) migrateLegacyOutputFile(taskID string, requested string) (string, bool) {
+	requested = strings.TrimSpace(requested)
+	if !filepath.IsAbs(requested) {
+		return "", false
+	}
+	requested = filepath.Clean(requested)
+	expectedName := taskID + ".ndjson"
+	if filepath.Base(requested) != expectedName {
+		return "", false
+	}
+	legacyRoot := filepath.Dir(requested)
+	if filepath.Base(legacyRoot) != "background" || filepath.Base(filepath.Dir(legacyRoot)) != "zero" {
+		return "", false
+	}
+	canonical := filepath.Join(manager.rootDir, expectedName)
+	info, err := os.Lstat(canonical)
+	if err != nil || !info.Mode().IsRegular() {
+		return "", false
+	}
+	return canonical, true
+}
+
 func validTaskID(taskID string) bool {
 	return taskIDPattern.MatchString(strings.TrimSpace(taskID))
 }
@@ -1,6 +1,7 @@
 package background

 import (
+	"encoding/json"
 	"errors"
 	"os"
 	"path/filepath"
@@ -191,6 +192,88 @@ func TestManagerSkipsInvalidPersistedMetadata(t *testing.T) {
 	}
 }

+func TestManagerMigratesLegacyOutputPathWhenCanonicalOutputExists(t *testing.T) {
+	root := t.TempDir()
+	const taskID = "legacy_task"
+	canonicalOutput := filepath.Join(root, taskID+".ndjson")
+	if err := os.WriteFile(canonicalOutput, []byte("legacy output\n"), 0o600); err != nil {
+		t.Fatalf("write canonical output: %v", err)
+	}
+	legacyOutput := filepath.Join(t.TempDir(), "zero", "background", taskID+".ndjson")
+	metadata, err := json.Marshal(Task{
+		ID:         taskID,
+		Type:       "specialist",
+		Status:     StatusCompleted,
+		OutputFile: legacyOutput,
+		StartedAt:  time.Date(2026, 8, 1, 10, 0, 0, 0, time.UTC),
+	})
+	if err != nil {
+		t.Fatalf("marshal legacy metadata: %v", err)
+	}
+	if err := os.WriteFile(filepath.Join(root, taskID+".json"), append(metadata, '\n'), 0o600); err != nil {
+		t.Fatalf("write legacy metadata: %v", err)
+	}
+
+	manager, err := NewManager(root)
+	if err != nil {
+		t.Fatalf("NewManager returned error: %v", err)
+	}
+	task, ok := manager.Get(taskID)
+	if !ok {
+		t.Fatal("manager did not load migrated task")
+	}
+	if task.OutputFile != canonicalOutput {
+		t.Fatalf("migrated output file = %q, want %q", task.OutputFile, canonicalOutput)
+	}
+	if warnings := manager.LoadWarnings(); len(warnings) != 0 {
+		t.Fatalf("migration produced load warnings: %#v", warnings)
+	}
+
+	persisted, err := os.ReadFile(filepath.Join(root, taskID+".json"))
+	if err != nil {
+		t.Fatalf("read migrated metadata: %v", err)
+	}
+	var saved Task
+	if err := json.Unmarshal(persisted, &saved); err != nil {
+		t.Fatalf("decode migrated metadata: %v", err)
+	}
+	if saved.OutputFile != canonicalOutput {
+		t.Fatalf("persisted output file = %q, want %q", saved.OutputFile, canonicalOutput)
+	}
+}
+
+func TestManagerRejectsUnrelatedAbsoluteOutputPathDuringMigration(t *testing.T) {
+	root := t.TempDir()
+	const taskID = "legacy_task"
+	if err := os.WriteFile(filepath.Join(root, taskID+".ndjson"), []byte("output\n"), 0o600); err != nil {
+		t.Fatalf("write canonical output: %v", err)
+	}
+	metadata, err := json.Marshal(Task{
+		ID:         taskID,
+		Type:       "specialist",
+		Status:     StatusCompleted,
+		OutputFile: filepath.Join(t.TempDir(), taskID+".ndjson"),
+		StartedAt:  time.Date(2026, 8, 1, 10, 0, 0, 0, time.UTC),
+	})
+	if err != nil {
+		t.Fatalf("marshal metadata: %v", err)
+	}
+	if err := os.WriteFile(filepath.Join(root, taskID+".json"), append(metadata, '\n'), 0o600); err != nil {
+		t.Fatalf("write metadata: %v", err)
+	}
+
+	manager, err := NewManager(root)
+	if err != nil {
+		t.Fatalf("NewManager returned error: %v", err)
+	}
+	if _, ok := manager.Get(taskID); ok {
+		t.Fatal("manager loaded task with an unrelated absolute output path")
+	}
+	if warnings := strings.Join(manager.LoadWarnings(), "\n"); !strings.Contains(warnings, "output file must be inside") {
+		t.Fatalf("load warnings = %q, want containment rejection", warnings)
+	}
+}
+
 func TestManagerMarksReloadedRunningTaskNonKillable(t *testing.T) {
 	root := t.TempDir()
 	manager, err := NewManager(root)
@@ -839,24 +839,26 @@ func runInteractiveTUIWithSetup(stderr io.Writer, deps appDeps, permissionMode a
 		mcpTokenStore = nil
 		err = nil
 	}
+	criticalMCPConfig, optionalMCPConfig := splitMCPStartupConfig(mcpConfig)
 	mcpRuntime := mcpToolRuntime(noopMCPRuntime{})
-	if len(mcpConfig.Servers) > 0 {
-		mcpRuntime, err = deps.registerMCPTools(context.Background(), registry, mcpConfig, mcp.RegisterOptions{
+	if len(criticalMCPConfig.Servers) > 0 {
+		runtime, registerErr := deps.registerMCPTools(context.Background(), registry, criticalMCPConfig, mcp.RegisterOptions{
 			PermissionStore: mcpPermissionStore,
 			Autonomy:        mcp.AutonomyLow,
 			Execution:       executionRunner,
 			WorkspaceRoot:   workspaceRoot,
 		})
-	}
-	if err != nil {
-		closeMCPRuntime(stderr, mcpRuntime)
-		return writeAppError(stderr, err.Error(), 1)
+		if registerErr != nil {
+			closeMCPRuntime(stderr, runtime)
+			return writeAppError(stderr, redaction.ErrorMessage(registerErr, redaction.Options{}), 1)
+		}
+		mcpRuntime = runtime
 	}
 	defer closeMCPRuntime(stderr, mcpRuntime)
 	// A server that could not be reached or validated is skipped, not fatal (one
 	// bad MCP server must not abort startup) — surface each so a missing tool set is
 	// explained rather than silently absent. A built-in default the user never
-	// configured (e.g. keyless Firecrawl with no credentials) is the exception: it
+	// configured (e.g. keyless Exa with no credentials) is the exception: it
 	// was never asked for, so its failure is not worth a startup warning — only
 	// servers the user actually configured warn on failure (issue #552).
 	for _, skipped := range mcpRuntime.Skipped() {
@@ -909,11 +911,35 @@ func runInteractiveTUIWithSetup(stderr io.Writer, deps appDeps, permissionMode a
 	}
 	// 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
-	// count is accurate; below threshold this is a no-op and the surface is
-	// unchanged. The interactive surface applies no operator tool filters, so
-	// enabled/disabled are nil — matching the AgentOptions below.
+	// This first pass covers every prompt-critical tool. Optional built-in MCP
+	// defaults re-run the same gate after publishing their atomic batch, so a
+	// later catalog generation cannot miss its loader. The interactive surface
+	// applies no operator tool filters, so enabled/disabled are nil — matching the
+	// AgentOptions below.
 	registerToolSearchIfEligible(registry, resolved.Tools.DeferThreshold, permissionMode, nil, nil)
+	var optionalMCPRuntime *optionalMCPStartup
+	var awaitToolReadiness func(context.Context)
+	if len(optionalMCPConfig.Servers) > 0 {
+		optionalMCPRuntime = startOptionalMCP(
+			context.Background(),
+			registry,
+			optionalMCPConfig,
+			mcp.RegisterOptions{
+				PermissionStore: mcpPermissionStore,
+				Autonomy:        mcp.AutonomyLow,
+				Execution:       executionRunner,
+				WorkspaceRoot:   workspaceRoot,
+			},
+			deps.registerMCPTools,
+			func() {
+				registerToolSearchIfEligible(registry, resolved.Tools.DeferThreshold, permissionMode, nil, nil)
+			},
+		)
+		defer closeMCPRuntime(stderr, optionalMCPRuntime)
+		awaitToolReadiness = func(ctx context.Context) {
+			optionalMCPRuntime.Await(ctx, optionalMCPPromptGrace)
+		}
+	}
 	lastKnownMCPConfig := mcpConfig
 	fileTracker := tools.NewFileTracker()
 	var scratchBaseline scratchFileBaseline
@@ -948,10 +974,20 @@ func runInteractiveTUIWithSetup(stderr io.Writer, deps appDeps, permissionMode a
 		FavoriteModels:       resolved.Preferences.FavoriteModels,
 		RecentModels:         resolved.Preferences.RecentModels,
 		RecapsEnabled:        resolved.Preferences.RecapsEnabled(),
+		CompactionModel:      resolved.Preferences.CompactionModel,
 		Provider:             provider,
 		NewProvider:          deps.newProvider,
-		ProbeProviderHealth:  deps.probeProviderHealth,
-		UserAgent:            userAgent(),
+		NewTurnSessionProvider: func(profile config.ProviderProfile, provider zeroruntime.Provider) zeroruntime.TurnSessionProvider {
+			if provider == nil {
+				return nil
+			}
+			if optimized, ok := providers.OptimizedTurnSessions(profile, provider, providers.Options{}); ok {
+				return optimized
+			}
+			return providers.DefaultTurnSessions(profile, provider, providers.Options{})
+		},
+		ProbeProviderHealth: deps.probeProviderHealth,
+		UserAgent:           userAgent(),
 		PrepareRunCompletionWarning: func() {
 			scratchBaseline = scratchFileSnapshot(workspaceRoot)
 		},
@@ -959,6 +995,7 @@ func runInteractiveTUIWithSetup(stderr io.Writer, deps appDeps, permissionMode a
 			return scratchFileWarning(workspaceRoot, scratchBaseline)
 		},
 		Registry:           registry,
+		AwaitToolReadiness: awaitToolReadiness,
 		SessionStore:       sessionStore,
 		PeerService:        peerService,
 		SandboxStore:       sandboxStore,
@@ -17,6 +17,7 @@ import (
 	"github.com/Gitlawb/zero/internal/agent"
 	"github.com/Gitlawb/zero/internal/config"
 	"github.com/Gitlawb/zero/internal/mcp"
+	"github.com/Gitlawb/zero/internal/redaction"
 	"github.com/Gitlawb/zero/internal/tools"
 	"github.com/Gitlawb/zero/internal/tui"
 	"github.com/Gitlawb/zero/internal/update"
@@ -211,12 +212,12 @@ func TestTUIStartupSuppressesWarningForUnconfiguredDefaultServer(t *testing.T) {
 		},
 		resolveMCPConfig: func(workspaceRoot string, excludeProject bool) (config.MCPConfig, error) {
 			return config.MCPConfig{Servers: map[string]config.MCPServerConfig{
-				"firecrawl": config.DefaultMCPServers()["firecrawl"],
+				"exa": config.DefaultMCPServers()["exa"],
 			}}, nil
 		},
 		registerMCPTools: func(context.Context, *tools.Registry, config.MCPConfig, mcp.RegisterOptions) (mcpToolRuntime, error) {
 			return fakeMCPRuntimeWithSkips{skipped: []mcp.SkippedServer{
-				{Name: "firecrawl", Err: errors.New("returned HTTP 401"), UnconfiguredDefault: true},
+				{Name: "exa", Err: errors.New("returned HTTP 401"), UnconfiguredDefault: true},
 			}}, nil
 		},
 		runTUI: func(ctx context.Context, options tui.Options) int {
@@ -227,7 +228,7 @@ func TestTUIStartupSuppressesWarningForUnconfiguredDefaultServer(t *testing.T) {
 	if exitCode != 0 {
 		t.Fatalf("exitCode = %d stderr=%s", exitCode, stderr.String())
 	}
-	if strings.Contains(stderr.String(), "firecrawl") {
+	if strings.Contains(stderr.String(), "exa") {
 		t.Fatalf("stderr = %q, want no warning for an unconfigured default server", stderr.String())
 	}
 }
@@ -486,6 +487,74 @@ func TestRunNoArgsLaunchesTUIWithMCPState(t *testing.T) {
 	}
 }

+func TestRunNoArgsPaintsBeforeOptionalDefaultMCPIsReady(t *testing.T) {
+	var stdout bytes.Buffer
+	var stderr bytes.Buffer
+	cwd := t.TempDir()
+	userConfigPath := filepath.Join(t.TempDir(), "zero", "config.json")
+	permissionStore, err := mcp.NewPermissionStore(mcp.StoreOptions{FilePath: filepath.Join(t.TempDir(), "mcp-permissions.json")})
+	if err != nil {
+		t.Fatalf("NewPermissionStore() error = %v", err)
+	}
+	tokenStore, err := mcp.NewTokenStore(mcp.TokenStoreOptions{FilePath: filepath.Join(t.TempDir(), "mcp-oauth.json")})
+	if err != nil {
+		t.Fatalf("NewTokenStore() error = %v", err)
+	}
+	started := make(chan struct{})
+	release := make(chan struct{})
+	configResult := make(chan error, 1)
+
+	exitCode := runWithDeps([]string{}, &stdout, &stderr, appDeps{
+		getwd:          func() (string, error) { return cwd, nil },
+		userConfigPath: func() (string, error) { return userConfigPath, nil },
+		resolveConfig: func(string, config.Overrides) (config.ResolvedConfig, error) {
+			return config.ResolvedConfig{MaxTurns: 8}, nil
+		},
+		resolveMCPConfig: func(string, bool) (config.MCPConfig, error) {
+			return config.MCPConfig{Servers: config.DefaultMCPServers()}, nil
+		},
+		newMCPStore:      func() (*mcp.PermissionStore, error) { return permissionStore, nil },
+		newMCPTokenStore: func() (*mcp.TokenStore, error) { return tokenStore, nil },
+		registerMCPTools: func(_ context.Context, registry *tools.Registry, cfg config.MCPConfig, _ mcp.RegisterOptions) (mcpToolRuntime, error) {
+			var configErr error
+			if _, ok := cfg.Servers["exa"]; !ok || len(cfg.Servers) != 1 {
+				configErr = fmt.Errorf("optional MCP config = %#v, want only exa", cfg.Servers)
+			}
+			configResult <- configErr
+			close(started)
+			<-release
+			registry.Register(cliFakeMCPRegistryTool{})
+			return noopMCPRuntime{}, nil
+		},
+		runTUI: func(ctx context.Context, options tui.Options) int {
+			select {
+			case <-started:
+			case <-time.After(time.Second):
+				t.Fatal("optional MCP initialization did not start")
+			}
+			if options.AwaitToolReadiness == nil {
+				t.Fatal("TUI did not receive optional tool readiness barrier")
+			}
+			if _, ok := options.Registry.Get("mcp_docs_lookup"); ok {
+				t.Fatal("optional MCP tool was published before registration completed")
+			}
+			close(release)
+			options.AwaitToolReadiness(ctx)
+			if _, ok := options.Registry.Get("mcp_docs_lookup"); !ok {
+				t.Fatal("optional MCP tool was not visible after readiness completed")
+			}
+			return 0
+		},
+	})
+
+	if exitCode != 0 {
+		t.Fatalf("exitCode = %d stderr=%s", exitCode, stderr.String())
+	}
+	if configErr := <-configResult; configErr != nil {
+		t.Fatal(configErr)
+	}
+}
+
 func TestTUIMCPCommandUsesLastGoodConfigOnRefreshError(t *testing.T) {
 	var stdout bytes.Buffer
 	var stderr bytes.Buffer
@@ -565,6 +634,7 @@ func TestRunNoArgsClosesPartialMCPRuntimeWhenRegistrationFails(t *testing.T) {
 		t.Fatalf("NewTokenStore() error = %v", err)
 	}
 	runtimeClosed := false
+	secret := "sk-proj-" + strings.Repeat("a", 23) + "0"

 	exitCode := runWithDeps([]string{}, &stdout, &stderr, appDeps{
 		getwd: func() (string, error) {
@@ -591,7 +661,7 @@ func TestRunNoArgsClosesPartialMCPRuntimeWhenRegistrationFails(t *testing.T) {
 			return closeFunc(func() error {
 				runtimeClosed = true
 				return nil
-			}), errors.New("register mcp tools failed")
+			}), fmt.Errorf("register mcp tools failed: %s", secret)
 		},
 		runTUI: func(ctx context.Context, options tui.Options) int {
 			t.Fatal("TUI should not launch after MCP registration fails")
@@ -605,6 +675,12 @@ func TestRunNoArgsClosesPartialMCPRuntimeWhenRegistrationFails(t *testing.T) {
 	if !strings.Contains(stderr.String(), "register mcp tools failed") {
 		t.Fatalf("stderr missing registration error: %s", stderr.String())
 	}
+	if strings.Contains(stderr.String(), secret) {
+		t.Fatalf("stderr leaked MCP registration secret: %s", stderr.String())
+	}
+	if !strings.Contains(stderr.String(), redaction.RedactedSecret) {
+		t.Fatalf("stderr missing redaction marker: %s", stderr.String())
+	}
 	if !runtimeClosed {
 		t.Fatal("partial MCP runtime was not closed after registration error")
 	}
@@ -682,16 +682,20 @@ func runExec(args []string, stdout io.Writer, stderr io.Writer, deps appDeps) in
 		ModelSwitcher:        modelSwitcher,
 		TurnSessionProvider:  turnSessions,
 		ModelSessionSwitcher: modelSessionSwitcher,
-		ReasoningEffort:      forwardEffort,
-		Trace:                traceRecorder,
-		Cwd:                  workspaceRoot,
-		Images:               images,
-		Registry:             registry,
-		PermissionMode:       permissionMode,
-		Autonomy:             options.autonomy,
-		SelfCorrect:          selfCorrector,
-		FileDiagnostics:      fileDiagnostics,
-		Profile:              execProfile.Policy(displacedMaxTurns, execProfileFilledEffort),
+		Summarizer:           summarizerFactory(resolved, deps.newProvider),
+		ContextWindowFor: func(modelID string) int {
+			return modelregistry.AgentContextWindow(modelContextWindow(modelRegistry, modelID))
+		},
+		ReasoningEffort: forwardEffort,
+		Trace:           traceRecorder,
+		Cwd:             workspaceRoot,
+		Images:          images,
+		Registry:        registry,
+		PermissionMode:  permissionMode,
+		Autonomy:        options.autonomy,
+		SelfCorrect:     selfCorrector,
+		FileDiagnostics: fileDiagnostics,
+		Profile:         execProfile.Policy(displacedMaxTurns, execProfileFilledEffort),
 		// Headless exec: don't accept a no-tool-call turn as "done" while work
 		// clearly remains (pending plan items / a mid-step continuation cue) —
 		// nudge to continue, and finalize as INCOMPLETE rather than false success
@@ -939,6 +943,9 @@ func registerToolSearchIfEligible(registry *tools.Registry, deferThreshold int,
 	if deferThreshold <= 0 {
 		return
 	}
+	if _, registered := registry.Get(tools.ToolSearchToolName); registered {
+		return
+	}
 	if deferredEligibleCount(registry, permissionMode, enabledTools, disabledTools) < deferThreshold {
 		return
 	}
@@ -267,23 +267,29 @@ func streamJSONPermissionEventType(event agent.PermissionEvent) streamjson.Event
 func (writer *execEventWriter) usage(usage agent.Usage) {
 	if writer.format == execOutputJSON {
 		writer.writeJSON(map[string]any{
-			"type":              "usage",
-			"prompt_tokens":     usage.PromptTokens,
-			"completion_tokens": usage.CompletionTokens,
-			"total_tokens":      usage.TotalTokens(),
+			"type":                "usage",
+			"prompt_tokens":       usage.PromptTokens,
+			"completion_tokens":   usage.CompletionTokens,
+			"cached_input_tokens": usage.CachedInputTokens,
+			"cache_write_tokens":  usage.CacheWriteTokens,
+			"total_tokens":        usage.TotalTokens(),
 		})
 		return
 	}
 	if writer.format == execOutputStreamJSON {
 		promptTokens := usage.EffectiveInputTokens()
 		completionTokens := usage.EffectiveOutputTokens()
+		cachedInputTokens := usage.CachedInputTokens
+		cacheWriteTokens := usage.CacheWriteTokens
 		totalTokens := usage.TotalTokens()
 		writer.writeStreamJSON(streamjson.Event{
-			Type:             streamjson.EventUsage,
-			RunID:            writer.runID,
-			PromptTokens:     &promptTokens,
-			CompletionTokens: &completionTokens,
-			TotalTokens:      &totalTokens,
+			Type:              streamjson.EventUsage,
+			RunID:             writer.runID,
+			PromptTokens:      &promptTokens,
+			CompletionTokens:  &completionTokens,
+			CachedInputTokens: &cachedInputTokens,
+			CacheWriteTokens:  &cacheWriteTokens,
+			TotalTokens:       &totalTokens,
 		})
 	}
 }
@@ -52,3 +52,39 @@ func TestExecWriterPropagatesToolResultTruncation(t *testing.T) {
 		})
 	}
 }
+
+func TestExecWriterPropagatesCacheUsage(t *testing.T) {
+	for _, format := range []execOutputFormat{execOutputJSON, execOutputStreamJSON} {
+		t.Run(string(format), func(t *testing.T) {
+			var stdout bytes.Buffer
+			writer := execEventWriter{
+				stdout:       &stdout,
+				format:       format,
+				runID:        "run_usage",
+				streamedText: &strings.Builder{},
+			}
+			writer.usage(agent.Usage{
+				InputTokens:       100,
+				OutputTokens:      20,
+				PromptTokens:      100,
+				CompletionTokens:  20,
+				CachedInputTokens: 60,
+				CacheWriteTokens:  10,
+			})
+			if writer.err != nil {
+				t.Fatalf("usage: %v", writer.err)
+			}
+			var payload map[string]any
+			if err := json.Unmarshal(bytes.TrimSpace(stdout.Bytes()), &payload); err != nil {
+				t.Fatalf("decode output %q: %v", stdout.String(), err)
+			}
+			cachedKey, writeKey := "cached_input_tokens", "cache_write_tokens"
+			if format == execOutputStreamJSON {
+				cachedKey, writeKey = "cachedInputTokens", "cacheWriteTokens"
+			}
+			if payload[cachedKey] != float64(60) || payload[writeKey] != float64(10) {
+				t.Fatalf("cache usage missing from payload: %#v", payload)
+			}
+		})
+	}
+}
@@ -9,15 +9,15 @@ import (
 	"github.com/Gitlawb/zero/internal/config"
 )

-// `zero mcp disable firecrawl` must work even though firecrawl is a built-in
+// `zero mcp disable exa` must work even though exa is a built-in
 // default that is not written to the user's config file until overridden.
-func TestRunMCPDisableSeededFirecrawlDefault(t *testing.T) {
+func TestRunMCPDisableSeededExaDefault(t *testing.T) {
 	configPath := filepath.Join(t.TempDir(), "zero", "config.json")
-	// A config with no firecrawl entry — the default lives in code, not the file.
+	// A config with no Exa entry — the default lives in code, not the file.
 	writeMCPCommandRawConfig(t, configPath, `{"activeProvider":"fast"}`)

 	var out, errBuf bytes.Buffer
-	code := runWithDeps([]string{"mcp", "disable", "firecrawl", "--json"}, &out, &errBuf, appDeps{
+	code := runWithDeps([]string{"mcp", "disable", "exa", "--json"}, &out, &errBuf, appDeps{
 		userConfigPath: func() (string, error) { return configPath, nil },
 	})
 	if code != exitSuccess {
@@ -31,8 +31,8 @@ func TestRunMCPDisableSeededFirecrawlDefault(t *testing.T) {
 	if err := json.Unmarshal(out.Bytes(), &payload); err != nil {
 		t.Fatalf("decode disable JSON: %v\n%s", err, out.String())
 	}
-	if payload.ServerName != "firecrawl" || !payload.Disabled || !payload.Changed {
-		t.Fatalf("disable payload = %#v, want firecrawl disabled+changed", payload)
+	if payload.ServerName != "exa" || !payload.Disabled || !payload.Changed {
+		t.Fatalf("disable payload = %#v, want exa disabled+changed", payload)
 	}

 	// End-to-end: resolving that config now turns the default off.
@@ -40,7 +40,7 @@ func TestRunMCPDisableSeededFirecrawlDefault(t *testing.T) {
 	if err != nil {
 		t.Fatalf("ResolveMCP: %v", err)
 	}
-	if !cfg.Servers["firecrawl"].Disabled {
-		t.Fatal("expected `mcp disable firecrawl` to turn the seeded default off in the resolved config")
+	if !cfg.Servers["exa"].Disabled {
+		t.Fatal("expected `mcp disable exa` to turn the seeded default off in the resolved config")
 	}
 }
@@ -0,0 +1,147 @@
+package cli
+
+import (
+	"context"
+	"sync"
+	"time"
+
+	"github.com/Gitlawb/zero/internal/config"
+	"github.com/Gitlawb/zero/internal/mcp"
+	"github.com/Gitlawb/zero/internal/tools"
+)
+
+const (
+	optionalMCPPromptGrace = time.Second
+	optionalMCPCloseGrace  = 250 * time.Millisecond
+)
+
+// splitMCPStartupConfig keeps explicitly configured servers on the
+// prompt-critical path. Only unchanged built-in defaults may initialize after
+// first paint; their failure was already intentionally silent.
+func splitMCPStartupConfig(cfg config.MCPConfig) (critical config.MCPConfig, optional config.MCPConfig) {
+	critical.Servers = map[string]config.MCPServerConfig{}
+	optional.Servers = map[string]config.MCPServerConfig{}
+	for name, server := range cfg.Servers {
+		if server.Disabled {
+			continue
+		}
+		if config.IsUnconfiguredDefault(name, server) {
+			optional.Servers[name] = server
+			continue
+		}
+		critical.Servers[name] = server
+	}
+	return critical, optional
+}
+
+type optionalMCPStartup struct {
+	cancel context.CancelFunc
+	done   chan struct{}
+
+	mu      sync.Mutex
+	runtime mcpToolRuntime
+
+	closeOnce        sync.Once
+	runtimeCloseOnce sync.Once
+	closeErr         error
+}
+
+func startOptionalMCP(
+	parent context.Context,
+	registry *tools.Registry,
+	cfg config.MCPConfig,
+	options mcp.RegisterOptions,
+	register func(context.Context, *tools.Registry, config.MCPConfig, mcp.RegisterOptions) (mcpToolRuntime, error),
+	onReady func(),
+) *optionalMCPStartup {
+	ctx, cancel := context.WithCancel(parent)
+	startup := &optionalMCPStartup{cancel: cancel, done: make(chan struct{})}
+	go func() {
+		runtime, err := register(ctx, registry, cfg, options)
+		if err == nil && onReady != nil {
+			onReady()
+		}
+		startup.mu.Lock()
+		startup.runtime = runtime
+		startup.mu.Unlock()
+		close(startup.done)
+	}()
+	return startup
+}
+
+// Await gives optional tools one bounded opportunity to join the next turn's
+// immutable registry snapshot. A timeout leaves this turn on the existing core
+// tool set; a later turn observes the completed generation.
+func (startup *optionalMCPStartup) Await(ctx context.Context, timeout time.Duration) bool {
+	if startup == nil {
+		return true
+	}
+	select {
+	case <-startup.done:
+		return true
+	default:
+	}
+	if timeout <= 0 {
+		select {
+		case <-startup.done:
+			return true
+		case <-ctx.Done():
+			return false
+		}
+	}
+	timer := time.NewTimer(timeout)
+	defer timer.Stop()
+	select {
+	case <-startup.done:
+		return true
+	case <-timer.C:
+		return false
+	case <-ctx.Done():
+		return false
+	}
+}
+
+func (startup *optionalMCPStartup) Close() error {
+	if startup == nil {
+		return nil
+	}
+	startup.closeOnce.Do(func() {
+		startup.cancel()
+		reaped := make(chan struct{})
+		go func() {
+			defer close(reaped)
+			<-startup.done
+			startup.closeRuntime()
+		}()
+		timer := time.NewTimer(optionalMCPCloseGrace)
+		defer timer.Stop()
+		select {
+		case <-reaped:
+		case <-timer.C:
+		}
+	})
+	startup.mu.Lock()
+	defer startup.mu.Unlock()
+	return startup.closeErr
+}
+
+func (startup *optionalMCPStartup) closeRuntime() {
+	startup.runtimeCloseOnce.Do(func() {
+		startup.mu.Lock()
+		runtime := startup.runtime
+		startup.mu.Unlock()
+		if runtime == nil {
+			return
+		}
+		err := runtime.Close()
+		startup.mu.Lock()
+		if err != nil && startup.closeErr == nil {
+			startup.closeErr = err
+		}
+		startup.mu.Unlock()
+	})
+}
+
+func (startup *optionalMCPStartup) Skipped() []mcp.SkippedServer {
+	return nil
+}
@@ -0,0 +1,187 @@
+package cli
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+
+	"github.com/Gitlawb/zero/internal/config"
+	"github.com/Gitlawb/zero/internal/mcp"
+	"github.com/Gitlawb/zero/internal/tools"
+)
+
+type closeTrackingMCPRuntime struct {
+	closed chan struct{}
+	err    error
+}
+
+func (runtime *closeTrackingMCPRuntime) Close() error {
+	close(runtime.closed)
+	return runtime.err
+}
+
+func (*closeTrackingMCPRuntime) Skipped() []mcp.SkippedServer { return nil }
+
+func TestSplitMCPStartupConfigDefersOnlyUnconfiguredDefaults(t *testing.T) {
+	defaults := config.DefaultMCPServers()
+	cfg := config.MCPConfig{Servers: map[string]config.MCPServerConfig{
+		"exa":      defaults["exa"],
+		"docs":     {Type: "http", URL: "https://docs.example.test/mcp"},
+		"disabled": {Type: "http", URL: "https://disabled.example.test/mcp", Disabled: true},
+	}}
+
+	critical, optional := splitMCPStartupConfig(cfg)
+	if _, ok := critical.Servers["docs"]; !ok || len(critical.Servers) != 1 {
+		t.Fatalf("critical servers = %#v, want only docs", critical.Servers)
+	}
+	if _, ok := optional.Servers["exa"]; !ok || len(optional.Servers) != 1 {
+		t.Fatalf("optional servers = %#v, want only exa", optional.Servers)
+	}
+}
+
+func TestOptionalMCPAwaitTimesOutThenObservesPublishedTools(t *testing.T) {
+	registry := tools.NewRegistry()
+	release := make(chan struct{})
+	started := make(chan struct{})
+	startup := startOptionalMCP(
+		context.Background(),
+		registry,
+		config.MCPConfig{Servers: config.DefaultMCPServers()},
+		mcp.RegisterOptions{},
+		func(ctx context.Context, registry *tools.Registry, _ config.MCPConfig, _ mcp.RegisterOptions) (mcpToolRuntime, error) {
+			close(started)
+			select {
+			case <-release:
+				registry.RegisterBatch([]tools.Tool{tools.NewScopedReadFileTool(t.TempDir(), nil)})
+				return noopMCPRuntime{}, nil
+			case <-ctx.Done():
+				return noopMCPRuntime{}, ctx.Err()
+			}
+		},
+		nil,
+	)
+	defer func() { _ = startup.Close() }()
+	<-started
+
+	if startup.Await(t.Context(), time.Millisecond) {
+		t.Fatal("optional startup unexpectedly completed before release")
+	}
+	if got := len(registry.All()); got != 0 {
+		t.Fatalf("registry published tools before readiness: %d", got)
+	}
+	close(release)
+	if !startup.Await(t.Context(), time.Second) {
+		t.Fatal("optional startup did not complete after release")
+	}
+	if _, ok := registry.Get("read_file"); !ok {
+		t.Fatal("completed optional startup did not publish its tool batch")
+	}
+}
+
+func TestOptionalMCPFailedRegistrationSkipsReadinessCallback(t *testing.T) {
+	readyCalls := 0
+	startup := startOptionalMCP(
+		context.Background(),
+		tools.NewRegistry(),
+		config.MCPConfig{Servers: config.DefaultMCPServers()},
+		mcp.RegisterOptions{},
+		func(context.Context, *tools.Registry, config.MCPConfig, mcp.RegisterOptions) (mcpToolRuntime, error) {
+			return noopMCPRuntime{}, errors.New("connect failed")
+		},
+		func() { readyCalls++ },
+	)
+	defer func() { _ = startup.Close() }()
+
+	if !startup.Await(t.Context(), time.Second) {
+		t.Fatal("failed optional startup did not settle")
+	}
+	if readyCalls != 0 {
+		t.Fatalf("readiness callback ran after failed registration: %d", readyCalls)
+	}
+}
+
+func TestOptionalMCPCloseCancelsBlockedStartup(t *testing.T) {
+	started := make(chan struct{})
+	startup := startOptionalMCP(
+		context.Background(),
+		tools.NewRegistry(),
+		config.MCPConfig{Servers: config.DefaultMCPServers()},
+		mcp.RegisterOptions{},
+		func(ctx context.Context, _ *tools.Registry, _ config.MCPConfig, _ mcp.RegisterOptions) (mcpToolRuntime, error) {
+			close(started)
+			<-ctx.Done()
+			return noopMCPRuntime{}, nil
+		},
+		nil,
+	)
+	<-started
+	if err := startup.Close(); err != nil {
+		t.Fatalf("Close() error = %v", err)
+	}
+}
+
+func TestOptionalMCPCloseReturnsRuntimeErrorWithinGrace(t *testing.T) {
+	closeErr := errors.New("close failed")
+	runtime := &closeTrackingMCPRuntime{closed: make(chan struct{}), err: closeErr}
+	startup := startOptionalMCP(
+		context.Background(),
+		tools.NewRegistry(),
+		config.MCPConfig{Servers: config.DefaultMCPServers()},
+		mcp.RegisterOptions{},
+		func(context.Context, *tools.Registry, config.MCPConfig, mcp.RegisterOptions) (mcpToolRuntime, error) {
+			return runtime, nil
+		},
+		nil,
+	)
+	if !startup.Await(t.Context(), time.Second) {
+		t.Fatal("optional startup did not settle")
+	}
+	if err := startup.Close(); !errors.Is(err, closeErr) {
+		t.Fatalf("Close() error = %v, want %v", err, closeErr)
+	}
+}
+
+func TestOptionalMCPCloseBoundsRegistrationThatIgnoresCancellation(t *testing.T) {
+	started := make(chan struct{})
+	release := make(chan struct{})
+	released := false
+	defer func() {
+		if !released {
+			close(release)
+		}
+	}()
+	runtime := &closeTrackingMCPRuntime{closed: make(chan struct{})}
+	startup := startOptionalMCP(
+		context.Background(),
+		tools.NewRegistry(),
+		config.MCPConfig{Servers: config.DefaultMCPServers()},
+		mcp.RegisterOptions{},
+		func(context.Context, *tools.Registry, config.MCPConfig, mcp.RegisterOptions) (mcpToolRuntime, error) {
+			close(started)
+			<-release
+			return runtime, nil
+		},
+		nil,
+	)
+	<-started
+
+	closeResult := make(chan error, 1)
+	go func() { closeResult <- startup.Close() }()
+	select {
+	case err := <-closeResult:
+		if err != nil {
+			t.Fatalf("Close() error = %v", err)
+		}
+	case <-time.After(time.Second):
+		t.Fatal("Close blocked on registration after cancellation")
+	}
+
+	close(release)
+	released = true
+	select {
+	case <-runtime.closed:
+	case <-time.After(time.Second):
+		t.Fatal("late optional MCP runtime was not closed")
+	}
+}
@@ -0,0 +1,17 @@
+package cli
+
+import (
+	"context"
+
+	"github.com/Gitlawb/zero/internal/agent"
+	"github.com/Gitlawb/zero/internal/config"
+	"github.com/Gitlawb/zero/internal/providers"
+	"github.com/Gitlawb/zero/internal/zeroruntime"
+)
+
+// summarizerFactory adapts the resolved profile and the authenticated provider
+// builder into agent.Options.Summarizer; the selection rules live in
+// providers.CompactionSummarizerFactory, shared with the TUI.
+func summarizerFactory(resolved config.ResolvedConfig, newProvider func(config.ProviderProfile) (zeroruntime.Provider, error)) func(context.Context, string) (agent.Provider, error) {
+	return providers.CompactionSummarizerFactory(resolved.Provider, resolved.Preferences.CompactionModel, newProvider)
+}
@@ -105,7 +105,17 @@ func TestLoadProviderCommandTimeout(t *testing.T) {
 //
 // This is a hang-breaker, not a tuned margin. Nothing in a healthy run waits on
 // it, since both tests return about one WaitDelay after the fixture exits.
-const providerCommandTestBudget = 60 * time.Second
+const (
+	providerCommandTestBudget        = 90 * time.Second
+	providerCommandReadyWaitAttempts = 45
+)
+
+func TestProviderCommandBudgetLeavesCleanupMargin(t *testing.T) {
+	readyWaitCeiling := time.Duration(providerCommandReadyWaitAttempts) * time.Second
+	if providerCommandTestBudget < 2*readyWaitCeiling {
+		t.Fatalf("provider command test budget %s leaves less than one readiness window for cleanup after %s", providerCommandTestBudget, readyWaitCeiling)
+	}
+}

 // backgroundChildLifetime must exceed providerCommandTestBudget so that a child
 // dying of old age is unobservable: any run where runProviderCommand has not
@@ -341,15 +351,15 @@ func writeCommand(t *testing.T, script commandScript) string {
 			// assertion fail is far more diagnosable than blocking until the
 			// timeout fires and reporting an unrelated error. Each iteration is
 			// about a second, since `ping -n 2` sleeps between its two echoes,
-			// so the ceiling is roughly 15s: far longer than any cold PowerShell
-			// start seen on a runner, and far shorter than
-			// providerCommandTestBudget, so giving up surfaces a legible
+			// so the ceiling is roughly 45s: enough for a heavily loaded Windows
+			// runner while leaving the other half of providerCommandTestBudget for
+			// process exit, PID-file verification, and cleanup. Giving up surfaces a legible
 			// PID-file failure rather than a timeout that hides the real cause.
 			lines = append(lines,
 				":zeroWaitReady",
 				"if exist \""+readyFile+"\" goto zeroReady",
 				"set /a ZERO_READY_TRIES+=1",
-				"if %ZERO_READY_TRIES% GEQ 15 goto zeroReady",
+				"if %ZERO_READY_TRIES% GEQ "+itoa(providerCommandReadyWaitAttempts)+" goto zeroReady",
 				"ping -n 2 127.0.0.1 >nul",
 				"goto zeroWaitReady",
 				":zeroReady",
@@ -5,22 +5,20 @@ import (
 	"strings"
 )

-// DefaultMCPServers returns the MCP servers Zero ships ENABLED by default so web
-// search and scraping work out of the box with no setup and no API key. They are
-// seeded before user/project config is merged (see ResolveMCP), so a user can
-// override any field — for example point firecrawl at a self-hosted instance, or
-// add an API-key header to lift the free-tier limit — or disable it entirely with
+// DefaultMCPServers returns the MCP servers Zero ships ENABLED by default so
+// web search and page fetching work out of the box with no setup and no API
+// key. They are seeded before user/project config is merged (see ResolveMCP),
+// so a user can override any field — for example add an API-key header to lift
+// Exa's anonymous rate limit — or disable it entirely with
 // `zero mcp disable <name>` (which writes `"disabled": true`).
 //
-// Keyless Firecrawl routes requests through firecrawl.dev (1,000 free credits per
-// month, no account). Self-host Firecrawl (AGPL-3.0) for unlimited and private
-// use. Zero only calls it over the network, so Firecrawl's license never reaches
-// into Zero's own code.
+// Exa's hosted MCP server works anonymously with rate limits. Users can add an
+// Exa API key for higher limits.
 func DefaultMCPServers() map[string]MCPServerConfig {
 	return map[string]MCPServerConfig{
-		"firecrawl": {
+		"exa": {
 			Type: "http",
-			URL:  "https://mcp.firecrawl.dev/v2/mcp",
+			URL:  "https://mcp.exa.ai/mcp",
 		},
 	}
 }
@@ -35,13 +33,13 @@ func IsDefaultMCPServer(name string) bool {

 // IsUnconfiguredDefault reports whether server is one of Zero's built-in
 // defaults that the user never wrote an entry for in their config — i.e. it is
-// running with whatever Zero ships (e.g. keyless Firecrawl, no credentials).
+// running with whatever Zero ships (e.g. keyless Exa, no credentials).
 //
 // Both conditions below must hold:
 //   - !server.configured: the user's JSON never declared an object for this
 //     server key at all (set by MCPServerConfig.UnmarshalJSON only when it
 //     actually ran for this key). Any explicit action — including a
-//     disable/enable toggle like `zero mcp enable firecrawl` that leaves the
+//     disable/enable toggle like `zero mcp enable exa` that leaves the
 //     resolved value unchanged — sets configured, so it always counts as
 //     user-configured, even though the value comparison below could not tell
 //     the difference on its own.
@@ -58,3 +56,90 @@ func IsUnconfiguredDefault(name string, server MCPServerConfig) bool {
 	def, ok := DefaultMCPServers()[strings.TrimSpace(name)]
 	return ok && !server.configured && reflect.DeepEqual(def, server)
 }
+
+// retiredDefaultMCPServer describes a built-in default Zero no longer ships.
+type retiredDefaultMCPServer struct {
+	// successor is the default that replaced it.
+	successor string
+	// shipped is the value Zero used to seed for this name. A user entry
+	// written while the default was still shipped may name only an override
+	// (a header, say) and rely on these fields for the rest, so they have to
+	// outlive the default itself.
+	shipped MCPServerConfig
+}
+
+// retiredDefaultMCPServers maps a retired built-in default to what replaced it
+// and to the value Zero used to ship for it.
+var retiredDefaultMCPServers = map[string]retiredDefaultMCPServer{
+	"firecrawl": {
+		successor: "exa",
+		shipped: MCPServerConfig{
+			Type: "http",
+			URL:  "https://mcp.firecrawl.dev/v2/mcp",
+		},
+	},
+}
+
+// migrateRetiredDefaultMCPServers keeps an upgrade across a default-provider
+// swap from changing what the user's config means. It handles the two ways a
+// rename can break a config written against the old default:
+//
+//   - A user who ran `zero mcp disable <old default>` made an explicit choice
+//     not to open that outbound connection. Without carrying that decision to
+//     the successor, the upgrade re-opens it under the new name — and because
+//     the replacement looks like an untouched default, even the startup
+//     warning stays quiet (see IsUnconfiguredDefault and issue #552).
+//   - A user who customized the old default could name only the field they
+//     were changing, because the seeded default supplied the transport. Once
+//     the default stops being seeded that entry resolves to a server with no
+//     type, url, or command, which fails NormalizeConfig and takes the whole
+//     startup down rather than just that one server.
+//
+// It runs immediately after the user layer merges (see ResolveMCP), which
+// scopes it to user-level decisions — the only scope whose disable is sticky.
+// The carried-over disable applies only when the user never declared the
+// successor themselves: an explicit `exa` entry wins whether it enables or
+// disables. Because the disable is recorded as a user-level decision, the
+// lower-trust project layer cannot lift it, while `zero mcp enable exa` still
+// can (the CLI override scope merges with canReenable=true).
+func migrateRetiredDefaultMCPServers(cfg *MCPConfig) {
+	for name, retired := range retiredDefaultMCPServers {
+		entry, ok := cfg.Servers[name]
+		if !ok {
+			continue
+		}
+		if inheritsRetiredTransport(entry) {
+			// Re-seed what Zero used to ship underneath the user's fields, so a
+			// partial entry still resolves to the complete server it named when
+			// it was written. Their own values still win — this only fills the
+			// gap the retired default used to cover.
+			entry = mergeMCPServer(retired.shipped, entry, true)
+			cfg.Servers[name] = entry
+		}
+		if !entry.disabledSet || !entry.Disabled {
+			continue
+		}
+		replacement, ok := cfg.Servers[retired.successor]
+		if !ok || replacement.configured {
+			continue
+		}
+		replacement.Disabled = true
+		replacement.disabledSet = true
+		cfg.Servers[retired.successor] = replacement
+	}
+}
+
+// inheritsRetiredTransport reports whether entry named no transport of its own
+// — no type, url, command, or args — and so relied entirely on the retired
+// default to supply one.
+//
+// Anything else is a complete definition the user owns (a self-hosted url, a
+// stdio command) and must be left alone: grafting the retired default's http
+// type onto an entry that names a command produces a server that is rejected
+// outright, turning a working config into a startup failure.
+func inheritsRetiredTransport(entry MCPServerConfig) bool {
+	return strings.TrimSpace(entry.Type) == "" &&
+		strings.TrimSpace(entry.URL) == "" &&
+		strings.TrimSpace(entry.Command) == "" &&
+		len(entry.Args) == 0
+}
@@ -7,10 +7,10 @@ import (
 )

 func TestIsDefaultMCPServer(t *testing.T) {
-	if !IsDefaultMCPServer("firecrawl") {
-		t.Fatal("firecrawl should be a built-in default")
+	if !IsDefaultMCPServer("exa") {
+		t.Fatal("exa should be a built-in default")
 	}
-	if IsDefaultMCPServer("  firecrawl  ") == false {
+	if IsDefaultMCPServer("  exa  ") == false {
 		t.Fatal("IsDefaultMCPServer should trim whitespace")
 	}
 	if IsDefaultMCPServer("not-a-default") {
@@ -18,45 +18,45 @@ func TestIsDefaultMCPServer(t *testing.T) {
 	}
 }

-func TestResolveMCPSeedsEnabledFirecrawlDefault(t *testing.T) {
+func TestResolveMCPSeedsEnabledExaDefault(t *testing.T) {
 	cfg, err := ResolveMCP(ResolveOptions{})
 	if err != nil {
 		t.Fatalf("ResolveMCP: %v", err)
 	}
-	firecrawl, ok := cfg.Servers["firecrawl"]
+	exa, ok := cfg.Servers["exa"]
 	if !ok {
-		t.Fatal("expected the firecrawl default to be seeded with no user config")
+		t.Fatal("expected the exa default to be seeded with no user config")
 	}
-	if firecrawl.Type != "http" || firecrawl.URL != "https://mcp.firecrawl.dev/v2/mcp" {
-		t.Fatalf("unexpected firecrawl default: %#v", firecrawl)
+	if exa.Type != "http" || exa.URL != "https://mcp.exa.ai/mcp" {
+		t.Fatalf("unexpected exa default: %#v", exa)
 	}
-	if firecrawl.Disabled {
-		t.Fatal("the firecrawl default must be enabled out of the box")
+	if exa.Disabled {
+		t.Fatal("the exa default must be enabled out of the box")
 	}
 }

 func TestResolveMCPUserCanDisableDefault(t *testing.T) {
 	path := filepath.Join(t.TempDir(), "config.json")
-	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"firecrawl":{"disabled":true}}}}`), 0o600); err != nil {
+	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"exa":{"disabled":true}}}}`), 0o600); err != nil {
 		t.Fatal(err)
 	}
 	cfg, err := ResolveMCP(ResolveOptions{UserConfigPath: path})
 	if err != nil {
 		t.Fatalf("ResolveMCP: %v", err)
 	}
-	if !cfg.Servers["firecrawl"].Disabled {
+	if !cfg.Servers["exa"].Disabled {
 		t.Fatal("a user must be able to disable the default by writing over it")
 	}
 }

 func TestIsUnconfiguredDefault(t *testing.T) {
-	if !IsUnconfiguredDefault("firecrawl", DefaultMCPServers()["firecrawl"]) {
-		t.Fatal("an untouched firecrawl default should be reported as unconfigured")
+	if !IsUnconfiguredDefault("exa", DefaultMCPServers()["exa"]) {
+		t.Fatal("an untouched exa default should be reported as unconfigured")
 	}
-	if IsUnconfiguredDefault("firecrawl", MCPServerConfig{Type: "http", URL: "http://localhost:3002/mcp"}) {
+	if IsUnconfiguredDefault("exa", MCPServerConfig{Type: "http", URL: "https://example.com/mcp"}) {
 		t.Fatal("a server overriding the default URL is no longer unconfigured")
 	}
-	if IsUnconfiguredDefault("firecrawl", MCPServerConfig{Type: "http", URL: "https://mcp.firecrawl.dev/v2/mcp", Auth: "bearer"}) {
+	if IsUnconfiguredDefault("exa", MCPServerConfig{Type: "http", URL: "https://mcp.exa.ai/mcp", Auth: "bearer"}) {
 		t.Fatal("a server with credentials added is no longer unconfigured")
 	}
 	if IsUnconfiguredDefault("not-a-default", MCPServerConfig{}) {
@@ -65,57 +65,173 @@ func TestIsUnconfiguredDefault(t *testing.T) {
 }

 func TestResolveMCPExplicitReenableIsNotUnconfiguredDefault(t *testing.T) {
-	// `zero mcp enable firecrawl` after a prior disable writes {"disabled":false}
+	// `zero mcp enable exa` after a prior disable writes {"disabled":false}
 	// explicitly. The resolved value is identical to the untouched default (both
 	// enabled, no credentials), but the user DID take an explicit action here, so
 	// IsUnconfiguredDefault must not treat it as untouched (issue #563 review).
 	path := filepath.Join(t.TempDir(), "config.json")
-	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"firecrawl":{"disabled":false}}}}`), 0o600); err != nil {
+	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"exa":{"disabled":false}}}}`), 0o600); err != nil {
 		t.Fatal(err)
 	}
 	cfg, err := ResolveMCP(ResolveOptions{UserConfigPath: path})
 	if err != nil {
 		t.Fatalf("ResolveMCP: %v", err)
 	}
-	firecrawl := cfg.Servers["firecrawl"]
-	if firecrawl.Disabled {
-		t.Fatalf("explicit re-enable should leave the server enabled: %#v", firecrawl)
+	exa := cfg.Servers["exa"]
+	if exa.Disabled {
+		t.Fatalf("explicit re-enable should leave the server enabled: %#v", exa)
 	}
-	if IsUnconfiguredDefault("firecrawl", firecrawl) {
+	if IsUnconfiguredDefault("exa", exa) {
 		t.Fatal("an explicit enable/disable toggle must count as user-configured, even though the resolved value matches the default")
 	}
 }

 func TestResolveMCPExplicitRedeclareOfDefaultValuesIsNotUnconfiguredDefault(t *testing.T) {
-	// A user who copies firecrawl's exact default type/url into their config
+	// A user who copies Exa's exact default type/url into their config
 	// (e.g. from an example file, planning to add credentials later) produces a
-	// resolved value byte-identical to DefaultMCPServers()["firecrawl"] — the
+	// resolved value byte-identical to DefaultMCPServers()["exa"] — the
 	// same trap TestResolveMCPExplicitReenableIsNotUnconfiguredDefault covers for
 	// the disabled toggle. IsUnconfiguredDefault must still treat this as
 	// user-configured because the user's JSON declared an entry for it, even
 	// though a plain resolved-value comparison could not tell the difference.
 	path := filepath.Join(t.TempDir(), "config.json")
-	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"firecrawl":{"type":"http","url":"https://mcp.firecrawl.dev/v2/mcp"}}}}`), 0o600); err != nil {
+	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"exa":{"type":"http","url":"https://mcp.exa.ai/mcp"}}}}`), 0o600); err != nil {
 		t.Fatal(err)
 	}
 	cfg, err := ResolveMCP(ResolveOptions{UserConfigPath: path})
 	if err != nil {
 		t.Fatalf("ResolveMCP: %v", err)
 	}
-	firecrawl := cfg.Servers["firecrawl"]
-	want := DefaultMCPServers()["firecrawl"]
-	if firecrawl.Type != want.Type || firecrawl.URL != want.URL || firecrawl.Disabled != want.Disabled {
-		t.Fatalf("expected the resolved value to match the default's fields exactly: %#v", firecrawl)
+	exa := cfg.Servers["exa"]
+	want := DefaultMCPServers()["exa"]
+	if exa.Type != want.Type || exa.URL != want.URL || exa.Disabled != want.Disabled {
+		t.Fatalf("expected the resolved value to match the default's fields exactly: %#v", exa)
 	}
-	if IsUnconfiguredDefault("firecrawl", firecrawl) {
+	if IsUnconfiguredDefault("exa", exa) {
 		t.Fatal("redeclaring the default's exact values is still an explicit user configuration, not an untouched default")
 	}
 }

 func TestResolveMCPUserCanOverrideDefaultURLKeepingOtherFields(t *testing.T) {
 	path := filepath.Join(t.TempDir(), "config.json")
-	// Point firecrawl at a self-hosted instance; the default's Type must survive.
-	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"firecrawl":{"url":"http://localhost:3002/mcp"}}}}`), 0o600); err != nil {
+	// Point Exa at a proxy; the default's Type must survive.
+	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"exa":{"url":"https://example.com/mcp"}}}}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	cfg, err := ResolveMCP(ResolveOptions{UserConfigPath: path})
+	if err != nil {
+		t.Fatalf("ResolveMCP: %v", err)
+	}
+	exa := cfg.Servers["exa"]
+	if exa.URL != "https://example.com/mcp" {
+		t.Fatalf("user override of the default URL did not apply: %#v", exa)
+	}
+	if exa.Type != "http" {
+		t.Fatalf("override should keep the default's other fields (type), got %#v", exa)
+	}
+}
+
+func TestResolveMCPCarriesLegacyDefaultDisableToSuccessor(t *testing.T) {
+	// Upgrade path: the user disabled the firecrawl default Zero used to ship.
+	// Swapping the default to exa must not re-open an outbound connection they
+	// explicitly switched off.
+	path := filepath.Join(t.TempDir(), "config.json")
+	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"firecrawl":{"disabled":true}}}}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	cfg, err := ResolveMCP(ResolveOptions{UserConfigPath: path})
+	if err != nil {
+		t.Fatalf("ResolveMCP: %v", err)
+	}
+	if !cfg.Servers["exa"].Disabled {
+		t.Fatalf("a prior disable of the retired default must carry to its replacement: %#v", cfg.Servers["exa"])
+	}
+}
+
+func TestResolveMCPExplicitSuccessorBeatsLegacyDefaultDisable(t *testing.T) {
+	// The user disabled the old default but has since explicitly configured exa.
+	// Their newer, explicit choice wins — the migration must not override it.
+	path := filepath.Join(t.TempDir(), "config.json")
+	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"firecrawl":{"disabled":true},"exa":{"disabled":false}}}}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	cfg, err := ResolveMCP(ResolveOptions{UserConfigPath: path})
+	if err != nil {
+		t.Fatalf("ResolveMCP: %v", err)
+	}
+	exa := cfg.Servers["exa"]
+	if exa.Disabled {
+		t.Fatalf("an explicit exa entry must survive the legacy-disable migration: %#v", exa)
+	}
+	if IsUnconfiguredDefault("exa", exa) {
+		t.Fatal("an explicitly configured exa is not an untouched default")
+	}
+}
+
+func TestResolveMCPLegacyDefaultLeftEnabledDoesNotDisableSuccessor(t *testing.T) {
+	// A user who configured firecrawl without disabling it (e.g. added a header)
+	// never opted out of the default search server, so exa stays enabled.
+	path := filepath.Join(t.TempDir(), "config.json")
+	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"firecrawl":{"headers":{"Authorization":"Bearer k"}}}}}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	cfg, err := ResolveMCP(ResolveOptions{UserConfigPath: path})
+	if err != nil {
+		t.Fatalf("ResolveMCP: %v", err)
+	}
+	if cfg.Servers["exa"].Disabled {
+		t.Fatal("only an explicit disable of the retired default should carry over")
+	}
+}
+
+func TestResolveMCPLegacyDefaultDisableIsLiftableByOverride(t *testing.T) {
+	// The carried-over disable is a user-level decision, not a permanent one:
+	// `zero mcp enable exa` merges through the CLI override scope, which is the
+	// one layer allowed to re-enable.
+	path := filepath.Join(t.TempDir(), "config.json")
+	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"firecrawl":{"disabled":true}}}}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	enabled := MCPServerConfig{Disabled: false, disabledSet: true}
+	cfg, err := ResolveMCP(ResolveOptions{
+		UserConfigPath: path,
+		Overrides:      Overrides{MCP: MCPConfig{Servers: map[string]MCPServerConfig{"exa": enabled}}},
+	})
+	if err != nil {
+		t.Fatalf("ResolveMCP: %v", err)
+	}
+	if cfg.Servers["exa"].Disabled {
+		t.Fatalf("an explicit enable must lift the carried-over disable: %#v", cfg.Servers["exa"])
+	}
+}
+
+func TestResolveMCPLegacyDisableSurvivesProjectReenable(t *testing.T) {
+	// The project layer is lower-trust and must not lift the carried-over
+	// user-level disable — the same guard a direct `zero mcp disable exa` gets.
+	dir := t.TempDir()
+	userPath := filepath.Join(dir, "config.json")
+	if err := os.WriteFile(userPath, []byte(`{"mcp":{"servers":{"firecrawl":{"disabled":true}}}}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	projectPath := filepath.Join(dir, "project.json")
+	if err := os.WriteFile(projectPath, []byte(`{"mcp":{"servers":{"exa":{"disabled":false}}}}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	cfg, err := ResolveMCP(ResolveOptions{UserConfigPath: userPath, ProjectConfigPath: projectPath})
+	if err != nil {
+		t.Fatalf("ResolveMCP: %v", err)
+	}
+	if !cfg.Servers["exa"].Disabled {
+		t.Fatal("project config must not re-enable a server the user disabled")
+	}
+}
+
+func TestResolveMCPKeepsRetiredDefaultTransportForPartialEntry(t *testing.T) {
+	// A user who added an API key to the firecrawl default wrote only the header
+	// — the seeded default supplied the http type and URL. Retiring the default
+	// must not strip those out from under them and leave an unusable server.
+	path := filepath.Join(t.TempDir(), "config.json")
+	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"firecrawl":{"headers":{"Authorization":"Bearer k"}}}}}`), 0o600); err != nil {
 		t.Fatal(err)
 	}
 	cfg, err := ResolveMCP(ResolveOptions{UserConfigPath: path})
@@ -123,10 +239,55 @@ func TestResolveMCPUserCanOverrideDefaultURLKeepingOtherFields(t *testing.T) {
 		t.Fatalf("ResolveMCP: %v", err)
 	}
 	firecrawl := cfg.Servers["firecrawl"]
-	if firecrawl.URL != "http://localhost:3002/mcp" {
-		t.Fatalf("user override of the default URL did not apply: %#v", firecrawl)
+	if firecrawl.Type != "http" || firecrawl.URL != "https://mcp.firecrawl.dev/v2/mcp" {
+		t.Fatalf("a partial entry must keep the retired default's transport: %#v", firecrawl)
 	}
-	if firecrawl.Type != "http" {
-		t.Fatalf("override should keep the default's other fields (type), got %#v", firecrawl)
+	if firecrawl.Headers["Authorization"] != "Bearer k" {
+		t.Fatalf("the user's own field must still win: %#v", firecrawl)
+	}
+}
+
+func TestResolveMCPDoesNotGraftRetiredDefaultOntoOwnTransport(t *testing.T) {
+	// A self-hosted firecrawl over stdio is a complete definition the user owns.
+	// Re-seeding the retired http default under it would produce an http server
+	// carrying a command, which NormalizeConfig rejects outright.
+	path := filepath.Join(t.TempDir(), "config.json")
+	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"firecrawl":{"command":"firecrawl-mcp"}}}}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	cfg, err := ResolveMCP(ResolveOptions{UserConfigPath: path})
+	if err != nil {
+		t.Fatalf("ResolveMCP: %v", err)
+	}
+	firecrawl := cfg.Servers["firecrawl"]
+	if firecrawl.Type != "" || firecrawl.URL != "" {
+		t.Fatalf("an entry naming its own transport must be left alone: %#v", firecrawl)
+	}
+	if firecrawl.Command != "firecrawl-mcp" {
+		t.Fatalf("the user's command must survive: %#v", firecrawl)
+	}
+}
+
+func TestResolveMCPDisabledRetiredEntryStaysReEnableable(t *testing.T) {
+	// The disable carries to exa, and the retired entry itself keeps a usable
+	// transport so a later `zero mcp enable firecrawl` does not resolve to a
+	// server with no type, url, or command.
+	path := filepath.Join(t.TempDir(), "config.json")
+	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"firecrawl":{"disabled":true}}}}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	cfg, err := ResolveMCP(ResolveOptions{UserConfigPath: path})
+	if err != nil {
+		t.Fatalf("ResolveMCP: %v", err)
+	}
+	firecrawl := cfg.Servers["firecrawl"]
+	if !firecrawl.Disabled {
+		t.Fatalf("the retired entry must stay disabled: %#v", firecrawl)
+	}
+	if firecrawl.Type != "http" || firecrawl.URL != "https://mcp.firecrawl.dev/v2/mcp" {
+		t.Fatalf("a disabled retired entry should still carry a usable transport: %#v", firecrawl)
+	}
+	if !cfg.Servers["exa"].Disabled {
+		t.Fatal("the disable must still carry to the successor")
 	}
 }
@@ -34,7 +34,7 @@ func TestResolveMCPExcludeProjectDropsProjectServers(t *testing.T) {
 		if _, ok := cfg.Servers["user-srv"]; !ok {
 			t.Fatal("the user server must always be present")
 		}
-		if _, ok := cfg.Servers["firecrawl"]; !ok {
+		if _, ok := cfg.Servers["exa"]; !ok {
 			t.Fatal("the built-in default must always be present")
 		}
 	})
@@ -54,7 +54,7 @@ func TestResolveMCPExcludeProjectDropsProjectServers(t *testing.T) {
 		if _, ok := cfg.Servers["user-srv"]; !ok {
 			t.Fatal("the user server must survive when the project layer is dropped")
 		}
-		if _, ok := cfg.Servers["firecrawl"]; !ok {
+		if _, ok := cfg.Servers["exa"]; !ok {
 			t.Fatal("the built-in default must survive when the project layer is dropped")
 		}
 	})
@@ -180,7 +180,7 @@ func Resolve(options ResolveOptions) (ResolvedConfig, error) {
 }

 func ResolveMCP(options ResolveOptions) (MCPConfig, error) {
-	// Seed Zero's built-in default MCP servers (e.g. keyless Firecrawl for free,
+	// Seed Zero's built-in default MCP servers (e.g. keyless Exa for free,
 	// no-setup web search/scrape) BEFORE merging user/project config, so the user
 	// can override any field or disable a default by writing over it.
 	cfg := FileConfig{MCP: MCPConfig{Servers: DefaultMCPServers()}}
@@ -194,6 +194,10 @@ func ResolveMCP(options ResolveOptions) (MCPConfig, error) {
 		// server the user disabled (a user-level disable is sticky, but the user
 		// scope itself may lift it).
 		mergeMCPConfig(&cfg.MCP, fileConfig.MCP, true)
+		// Reconcile config written against a default Zero has since retired,
+		// here while the user layer is the only one merged — so a carried-over
+		// disable counts as a user-level decision the project layer cannot lift.
+		migrateRetiredDefaultMCPServers(&cfg.MCP)
 	}
 	// Drop the project layer when the workspace is untrusted, so a cloned repo's
 	// ./.zero/config.json cannot register (and spawn) MCP servers. Fail-closed:
@@ -119,6 +119,12 @@ type PreferencesConfig struct {
 	// the user turned idle recaps off. A *bool is its own tri-state, so no
 	// custom unmarshal is needed (unlike ToolsConfig.DeferThreshold's int).
 	Recaps *bool `json:"recaps,omitempty"`
+	// CompactionModel routes compaction summarization calls to this model
+	// instead of the session's main model (summaries at main-model prices are
+	// the most expensive recurring event in long runs). Empty = automatic: a
+	// curated cheap model on official endpoints, the main model elsewhere.
+	// "main" forces the main model. ZERO_COMPACTION_MODEL overrides.
+	CompactionModel string `json:"compactionModel,omitempty"`
 }

 // RecentModelEntry is one provider-qualified model selection recorded in
@@ -151,7 +157,8 @@ type KeyBindingsConfig struct {
 	ToggleMouse KeyBindingDef `json:"toggleMouse,omitempty"`
 	// CycleReasoning cycles through reasoning effort levels (default: ctrl+t).
 	CycleReasoning KeyBindingDef `json:"cycleReasoning,omitempty"`
-	// TogglePlan toggles the plan panel expansion (default: ctrl+p).
+	// TogglePlan is retained for configuration compatibility. Plan updates render
+	// in the transcript and no longer have a persistent panel to toggle.
 	TogglePlan KeyBindingDef `json:"togglePlan,omitempty"`
 	// ToggleSidebar toggles the right context sidebar (default: ctrl+b).
 	ToggleSidebar KeyBindingDef `json:"toggleSidebar,omitempty"`
@@ -464,7 +471,7 @@ type MCPServerConfig struct {
 	// fields it set or what values they hold. A built-in default seeded by
 	// DefaultMCPServers() is never unmarshaled from JSON, so it starts false;
 	// any explicit entry in the user/project file — even one that happens to
-	// repeat a default's exact field values (e.g. re-declaring firecrawl's
+	// repeat a default's exact field values (e.g. re-declaring Exa's
 	// default URL) — sets it true. IsUnconfiguredDefault checks this alongside
 	// a resolved-value comparison, so redeclaring default values verbatim still
 	// counts as user-configured.
@@ -5,31 +5,23 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
-	"sync/atomic"
 	"time"

 	"github.com/Gitlawb/zero/internal/lockutil"
 )

 // Cross-process lock tuning. The lock is held only for a single metadata
-// read-modify-write (milliseconds), never across a job's exec, so the timeout is
-// generous and the stale threshold sits far above any real hold.
+// read-modify-write (milliseconds), never across a job's exec, so the timeout
+// is generous relative to any real hold.
 const (
 	cronLockTimeout    = 10 * time.Second
-	cronLockStaleAfter = 60 * time.Second
 	cronLockRetryDelay = 20 * time.Millisecond
 )

-var cronLockSeq atomic.Uint64
-
-// lockJob takes a cross-process exclusive lock for one job by O_EXCL-creating a
-// sibling "<id>.lock" file next to the job directory (so Remove's RemoveAll of
-// the job dir never deletes a live lock). It serializes the read-modify-write of
-// a job's metadata across concurrent schedulers and commands. The lock file is
-// removed on release; a stale lock from a crashed holder (older than
-// cronLockStaleAfter) is reclaimed. Wall-clock time.Now is used deliberately
-// (not the injectable Store.now) so lock timing never depends on a frozen test
-// clock and the stale check compares against real file mtimes.
+// lockJob takes a cross-process advisory lock for one job on a stable sibling
+// "<id>.lock" file next to the job directory. It serializes the read-modify-write
+// of a job's metadata across concurrent schedulers and commands. The kernel
+// releases the lock when a holder exits; the file is never renamed or removed.
 func (s *Store) lockJob(id string) (func(), error) {
 	if !validID(id) {
 		return nil, fmt.Errorf("invalid cron job id %q", id)
@@ -38,64 +30,15 @@ func (s *Store) lockJob(id string) (func(), error) {
 	if err := os.MkdirAll(filepath.Dir(lockPath), 0o700); err != nil {
 		return nil, err
 	}
-	token := fmt.Sprintf("%d-%d-%d", os.Getpid(), time.Now().UnixNano(), cronLockSeq.Add(1))
 	deadline := time.Now().Add(cronLockTimeout)
 	for {
-		f, err := os.OpenFile(lockPath, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o600)
+		lock, err := lockutil.TryAcquireFileLock(lockPath)
 		if err == nil {
-			// A partial write would leave a lock file without our token, so the
-			// releaser could never delete it — stranding the lock. Fail closed.
-			if _, werr := f.WriteString(token); werr != nil {
-				_ = f.Close()
-				_ = lockutil.RemoveLockFile(lockPath)
-				return nil, fmt.Errorf("cron: write job lock: %w", werr)
-			}
-			if cerr := f.Close(); cerr != nil {
-				_ = lockutil.RemoveLockFile(lockPath)
-				return nil, fmt.Errorf("cron: close job lock: %w", cerr)
-			}
-			var released bool
-			return func() {
-				if released {
-					return
-				}
-				released = true
-				if data, rerr := os.ReadFile(lockPath); rerr == nil && string(data) == token {
-					_ = lockutil.RemoveLockFile(lockPath)
-				}
-			}, nil
+			return func() { _ = lock.Release() }, nil
 		}
-		// On Windows a concurrent holder's os.Remove leaves the lock file in a
-		// "delete pending" state, so an O_EXCL create races it with
-		// ERROR_ACCESS_DENIED (os.ErrPermission) rather than ErrExist. Treat that
-		// as contention and retry, exactly like ErrExist — otherwise the lock
-		// spuriously fails under concurrency on Windows.
-		if !errors.Is(err, os.ErrExist) && !errors.Is(err, os.ErrPermission) {
+		if !errors.Is(err, lockutil.ErrLockHeld) {
 			return nil, fmt.Errorf("cron: acquire job lock: %w", err)
 		}
-		// Reclaim a stale lock left by a crashed holder — atomically (H3). A blind
-		// Remove lets two racers both "reclaim" and recreate, so both hold the lock;
-		// reclaimStaleLock renames the file aside (only one rename of a given file
-		// wins) and restores it if it turns out fresh, so a live lock is never deleted
-		// out from under its holder.
-		if info, statErr := os.Stat(lockPath); statErr == nil && time.Since(info.ModTime()) > cronLockStaleAfter {
-			cleared, rerr := lockutil.ReclaimStaleLock(lockPath, token, func(reclaimedPath string) bool {
-				info, err := os.Stat(reclaimedPath)
-				return err == nil && time.Since(info.ModTime()) <= cronLockStaleAfter
-			})
-			if rerr != nil {
-				// Reclaim hit a hard failure: the rename aside failed outright, or a
-				// live holder's lock could not be put back (the lock path may be
-				// missing, so re-acquiring would break mutual exclusion). Fail closed
-				// instead of spinning to the deadline.
-				return nil, fmt.Errorf("cron: reclaim stale job lock: %w", rerr)
-			}
-			if cleared {
-				continue // cleared a genuinely stale lock; retry the O_EXCL create now
-			}
-			// Lost the reclaim race (or it was actually fresh) — fall through to the
-			// bounded wait instead of hot-spinning on a reclaim that never wins (L13).
-		}
 		if !time.Now().Before(deadline) {
 			return nil, fmt.Errorf("cron: timed out acquiring job lock for %q", id)
 		}
@@ -64,7 +64,7 @@ func TestMutateRemovedJobReturnsNotFound(t *testing.T) {
 	if !errors.Is(err, ErrJobNotFound) {
 		t.Fatalf("Mutate on removed job = %v, want ErrJobNotFound", err)
 	}
-	// And the lock file left no litter / did not resurrect the job dir.
+	// The stable advisory-lock file does not resurrect the removed job dir.
 	if _, gerr := store.Get(job.ID); !errors.Is(gerr, ErrJobNotFound) {
 		t.Fatalf("job should remain removed, Get = %v", gerr)
 	}
@@ -3,107 +3,60 @@ package daemon
 import (
 	"errors"
 	"fmt"
-	"io/fs"
 	"os"
 	"strconv"
 	"strings"
-	"sync/atomic"

 	"github.com/Gitlawb/zero/internal/lockutil"
 )

-// Single-instance lock. Mirrors reference-daemon-code-agent-js/supervisor.js's
-// lock file: a PID file created with O_EXCL. A second start fails; a STALE lock
-// left by a dead daemon (the recorded PID is no longer alive) is reclaimed so the
-// daemon recovers from an unclean shutdown without manual cleanup.
+// Single-instance lock. The stable PID file carries a kernel advisory lock for
+// the daemon's full lifetime. Process exit releases the lock automatically, so
+// stale metadata needs no rename/remove recovery protocol.

 // ErrAlreadyRunning is returned when a live daemon already holds the lock.
 var ErrAlreadyRunning = errors.New("daemon: another instance is already running")

 // fileLock is an acquired single-instance lock.
 type fileLock struct {
-	path string
+	lock *lockutil.FileLock
 }

 // processAlive reports whether pid is a live process. Implemented per-platform
 // (lock_posix.go / lock_windows.go). It is a package var so tests can stub it.
 var processAlive = osProcessAlive

-// acquireLock takes the single-instance lock at path, reclaiming a stale lock
-// whose recorded PID is dead. isAlive overrides the liveness check (tests pass a
-// stub); nil uses the real processAlive.
+// acquireLock takes the single-instance advisory lock at path. isAlive is used
+// only to enrich a contention error with the current holder's PID; the kernel
+// lock, not PID metadata, is authoritative.
 func acquireLock(path string, isAlive func(pid int) bool) (*fileLock, error) {
 	if isAlive == nil {
 		isAlive = processAlive
 	}
-	// At most two passes: create, or detect-stale-then-retry once.
-	for attempt := 0; attempt < 2; attempt++ {
-		f, err := os.OpenFile(path, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o600)
-		if err == nil {
-			// A failed PID write would leave a malformed lock file that another
-			// process reads as stale (unparsable PID) and wrongly reclaims, breaking
-			// the single-instance guarantee — so on write failure, remove it and fail.
-			if _, werr := fmt.Fprintf(f, "%d\n", os.Getpid()); werr != nil {
-				_ = f.Close()
-				_ = lockutil.RemoveLockFile(path)
-				return nil, werr
-			}
-			if cerr := f.Close(); cerr != nil {
-				_ = lockutil.RemoveLockFile(path)
-				return nil, cerr
-			}
-			return &fileLock{path: path}, nil
-		}
-		if !errors.Is(err, fs.ErrExist) && !errors.Is(err, os.ErrPermission) {
+	lock, err := lockutil.TryAcquireFileLock(path)
+	if err != nil {
+		if !errors.Is(err, lockutil.ErrLockHeld) {
 			return nil, err
 		}
 		pid, perr := readPidFile(path)
 		if perr == nil && pid > 0 && isAlive(pid) {
 			return nil, fmt.Errorf("%w (pid %d)", ErrAlreadyRunning, pid)
 		}
-		// Stale lock (dead PID or unreadable) — reclaim it atomically, then retry the
-		// O_EXCL create. A blind Remove here races: two daemons starting at once could
-		// both read the stale PID, both Remove, and then one Removes the OTHER's
-		// freshly-created lock — leaving both "holding" the single-instance lock.
-		// reclaimStaleLock renames the file aside so only one racer wins the rename,
-		// and restores it if a live holder reacquired in the gap (D6).
-		if _, rerr := reclaimStaleLock(path, isAlive); rerr != nil {
-			// Reclaim hit a hard failure: the rename aside failed outright, or a
-			// live holder's lock could not be put back (the lock path may be
-			// missing, so re-acquiring would break the single-instance guarantee).
-			// Fail closed instead of spinning to the deadline.
-			return nil, fmt.Errorf("daemon: reclaim stale lock: %w", rerr)
-		}
+		return nil, ErrAlreadyRunning
 	}
-	return nil, ErrAlreadyRunning
+	if err := lock.WriteMetadata([]byte(fmt.Sprintf("%d\n", os.Getpid()))); err != nil {
+		return nil, errors.Join(err, lock.Release())
+	}
+	return &fileLock{lock: lock}, nil
 }

-// daemonLockSeq makes each reclaim attempt's sidelined filename unique per process.
-var daemonLockSeq atomic.Uint64
-
-// reclaimStaleLock atomically reclaims a single-instance lock whose recorded
-// PID is dead, via lockutil.ReclaimStaleLock: the lock file is renamed aside
-// (only one racer can win the rename) and stolen only if the moved file's PID
-// is still dead; a holder that reacquired the lock in the gap between the
-// stale check and the rename carries a LIVE pid and is restored rather than
-// stolen. Returns true only when a genuinely stale lock was removed. A
-// non-nil error means the caller must fail closed instead of re-acquiring
-// (see lockutil.ReclaimStaleLock).
-func reclaimStaleLock(path string, isAlive func(pid int) bool) (bool, error) {
-	suffix := fmt.Sprintf("%d-%d", os.Getpid(), daemonLockSeq.Add(1))
-	return lockutil.ReclaimStaleLock(path, suffix, func(reclaimedPath string) bool {
-		pid, err := readPidFile(reclaimedPath)
-		return err == nil && pid > 0 && isAlive(pid)
-	})
-}
-
-// release removes the lock file. Safe to call once. An already-missing lock
-// file is not an error (lockutil.RemoveLockFile swallows it on every platform).
+// release drops the kernel lock and closes its handle. The stable PID file is
+// deliberately retained so contenders always address the same inode.
 func (l *fileLock) release() error {
-	if l == nil || l.path == "" {
+	if l == nil || l.lock == nil {
 		return nil
 	}
-	return lockutil.RemoveLockFile(l.path)
+	return l.lock.Release()
 }

 // readPidFile reads and parses the PID recorded in a lock file.
@@ -112,5 +65,20 @@ func readPidFile(path string) (int, error) {
 	if err != nil {
 		return 0, err
 	}
-	return strconv.Atoi(strings.TrimSpace(string(data)))
+	metadata := strings.TrimSpace(string(data))
+	if pid, err := strconv.Atoi(metadata); err == nil {
+		return pid, nil
+	}
+	pidText, sequenceText, ok := strings.Cut(metadata, "-")
+	if !ok || pidText == "" || sequenceText == "" || strings.Contains(sequenceText, "-") {
+		return 0, fmt.Errorf("daemon: parse lock PID metadata %q", metadata)
+	}
+	if _, err := strconv.ParseUint(sequenceText, 10, 64); err != nil {
+		return 0, fmt.Errorf("daemon: parse lock holder sequence: %w", err)
+	}
+	pid, err := strconv.Atoi(pidText)
+	if err != nil {
+		return 0, fmt.Errorf("daemon: parse lock PID: %w", err)
+	}
+	return pid, nil
 }
@@ -32,27 +32,48 @@ func TestLockSingleInstance(t *testing.T) {
 	_ = l2.release()
 }

-func TestLockStaleRecovery(t *testing.T) {
+// A PID liveness probe is diagnostic only. Even if it reports the recorded PID
+// dead, a contended kernel lock proves that the holder is active and must win.
+// The old rename-aside protocol trusted this stale observation and admitted a
+// second daemon while the first one was still inside its critical section.
+func TestLockDoesNotOverrideKernelHolderWithStalePIDProbe(t *testing.T) {
 	path := filepath.Join(t.TempDir(), "daemon.lock")
-	// Simulate a stale lock from a crashed daemon: a PID file whose process is
-	// dead.
+	first, err := acquireLock(path, func(int) bool { return true })
+	if err != nil {
+		t.Fatalf("first acquireLock: %v", err)
+	}
+	defer first.release()
+
+	second, err := acquireLock(path, func(int) bool { return false })
+	if second != nil {
+		_ = second.release()
+	}
+	if !errors.Is(err, ErrAlreadyRunning) {
+		t.Fatalf("contended acquire with stale PID probe = %v, want ErrAlreadyRunning", err)
+	}
+}
+
+func TestLockIgnoresStaleMetadataWhenKernelLockIsFree(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "daemon.lock")
+	// A crashed daemon may leave PID metadata behind, but its kernel lock is
+	// released automatically, so the next daemon can acquire without moving it.
 	if err := os.WriteFile(path, []byte("4242\n"), 0o600); err != nil {
 		t.Fatalf("write stale lock: %v", err)
 	}
 	dead := func(int) bool { return false }
 	l, err := acquireLock(path, dead)
 	if err != nil {
-		t.Fatalf("stale-lock recovery failed: %v", err)
+		t.Fatalf("acquire over stale metadata: %v", err)
 	}
 	// The lock now records OUR pid, not the stale one.
 	data, _ := os.ReadFile(path)
 	if strings.TrimSpace(string(data)) != strconv.Itoa(os.Getpid()) {
-		t.Fatalf("reclaimed lock pid = %q, want %d", strings.TrimSpace(string(data)), os.Getpid())
+		t.Fatalf("lock pid = %q, want %d", strings.TrimSpace(string(data)), os.Getpid())
 	}
 	_ = l.release()
 }

-func TestLockReleaseRemovesFile(t *testing.T) {
+func TestLockReleaseKeepsStableFile(t *testing.T) {
 	path := filepath.Join(t.TempDir(), "daemon.lock")
 	l, err := acquireLock(path, func(int) bool { return true })
 	if err != nil {
@@ -61,46 +82,37 @@ func TestLockReleaseRemovesFile(t *testing.T) {
 	if err := l.release(); err != nil {
 		t.Fatalf("release: %v", err)
 	}
-	if _, err := os.Stat(path); !errors.Is(err, os.ErrNotExist) {
-		t.Fatalf("lock file still present after release: %v", err)
+	if _, err := os.Stat(path); err != nil {
+		t.Fatalf("release removed stable lock file: %v", err)
 	}
 }

-func TestReclaimStaleLockRemovesDeadHolder(t *testing.T) {
+func TestReadPidFileMetadataFormats(t *testing.T) {
 	path := filepath.Join(t.TempDir(), "daemon.lock")
-	if err := os.WriteFile(path, []byte("4242\n"), 0o600); err != nil {
-		t.Fatalf("write stale lock: %v", err)
-	}
-	if ok, err := reclaimStaleLock(path, func(int) bool { return false }); err != nil || !ok {
-		t.Fatalf("reclaimStaleLock must report a genuinely stale (dead-PID) lock reclaimed (ok=%v err=%v)", ok, err)
-	}
-	if _, err := os.Stat(path); !errors.Is(err, os.ErrNotExist) {
-		t.Fatalf("a reclaimed stale lock must be removed, stat = %v", err)
-	}
-}
-
-func TestReclaimStaleLockRestoresLiveHolder(t *testing.T) {
-	// If a holder reacquires the lock in the gap between the stale check and the
-	// rename, the moved file carries a LIVE pid; reclaim must restore it untouched
-	// rather than steal it — otherwise two daemons both "hold" the lock (D6).
-	path := filepath.Join(t.TempDir(), "daemon.lock")
-	if err := os.WriteFile(path, []byte("4242\n"), 0o600); err != nil {
-		t.Fatalf("write lock: %v", err)
-	}
-	if ok, err := reclaimStaleLock(path, func(int) bool { return true }); err != nil || ok {
-		t.Fatalf("reclaimStaleLock must NOT report a live-PID lock reclaimed (ok=%v err=%v)", ok, err)
-	}
-	data, err := os.ReadFile(path)
-	if err != nil {
-		t.Fatalf("live lock must be restored in place, read = %v", err)
-	}
-	if strings.TrimSpace(string(data)) != "4242" {
-		t.Fatalf("restored lock content = %q, want %q (unchanged)", strings.TrimSpace(string(data)), "4242")
-	}
-	// No sidelined ".stale" leftovers.
-	matches, _ := filepath.Glob(path + ".stale.*")
-	if len(matches) != 0 {
-		t.Fatalf("reclaim left sidelined files: %v", matches)
+	for _, test := range []struct {
+		name     string
+		metadata string
+		wantPID  int
+		wantErr  bool
+	}{
+		{name: "legacy PID", metadata: "4242\n", wantPID: 4242},
+		{name: "PID and holder sequence", metadata: "4242-7\n", wantPID: 4242},
+		{name: "missing sequence", metadata: "4242-", wantErr: true},
+		{name: "non-numeric sequence", metadata: "4242-next", wantErr: true},
+		{name: "extra component", metadata: "4242-7-8", wantErr: true},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			if err := os.WriteFile(path, []byte(test.metadata), 0o600); err != nil {
+				t.Fatal(err)
+			}
+			got, err := readPidFile(path)
+			if (err != nil) != test.wantErr {
+				t.Fatalf("readPidFile() error = %v, wantErr %v", err, test.wantErr)
+			}
+			if !test.wantErr && got != test.wantPID {
+				t.Fatalf("readPidFile() = %d, want %d", got, test.wantPID)
+			}
+		})
 	}
 }

@@ -124,12 +124,16 @@ func TestServerEndToEnd(t *testing.T) {
 	case <-time.After(3 * time.Second):
 		t.Fatal("Serve did not return after shutdown")
 	}
-	// Socket, status, and lock files are removed on exit.
-	for _, p := range []string{paths.Socket, paths.Status, paths.Lock} {
+	// Runtime endpoints are removed on exit. The advisory lock file remains as
+	// a stable inode, but the kernel lock on it has been released.
+	for _, p := range []string{paths.Socket, paths.Status} {
 		if _, err := os.Stat(p); !errors.Is(err, os.ErrNotExist) {
 			t.Fatalf("file %s not cleaned up after shutdown: %v", p, err)
 		}
 	}
+	if _, err := os.Stat(paths.Lock); err != nil {
+		t.Fatalf("stable lock file missing after shutdown: %v", err)
+	}
 }

 func TestServerSecondInstanceFails(t *testing.T) {
@@ -9,7 +9,16 @@ import (
 	"strings"
 )

-const PolicyVersion = 1
+// PolicyVersion is the version of the approval policy that recorded grants were
+// evaluated under. Bump it whenever a change narrows what may be approved: the
+// grant store then backs the file up, keeps deny grants, invalidates prior
+// approvals, and tells the user once, instead of silently honoring approvals
+// that the current rules would have refused.
+//
+// v2 tightened command-prefix validation so a launcher spelled with a version
+// or an executable extension ("python3.11", "python.exe") can no longer be
+// approved as an ordinary command.
+const PolicyVersion = 2

 type Origin string

@@ -3,13 +3,93 @@
 package execution

 import (
+	"errors"
+	"os"
 	"os/exec"
 	"strconv"
+	"strings"
 	"syscall"
 	"testing"
 	"time"
 )

+// requireProcessState refuses to let a broken ps pipeline masquerade as passing
+// coverage. Every test in this file proves something about zombie detection,
+// and every one of those proofs is read out of ps — so if ps cannot report
+// state, the tests verify nothing whatever they do next.
+//
+// The old code answered that with t.Skip, which is indistinguishable from
+// success in CI output. This probes BOTH ps pipelines against this test
+// process, which is by definition alive and not a zombie, so a working ps must
+// report a live state for it. Failing that:
+//
+//   - In CI (or with ZERO_REQUIRE_PS=1) it is a hard failure. ps is present on
+//     every image used today, so its absence means the pipeline regressed and
+//     that has to surface immediately rather than as skipped-green.
+//   - Elsewhere it stays a skip, so a contributor on an exotic box is not
+//     blocked by an environment the project does not claim to support.
+//
+// This only covers "ps cannot report state at all". Once it passes, a later
+// failure to observe an EXPECTED state is a real defect, and the tests below
+// treat it as one.
+func requireProcessState(t *testing.T) {
+	t.Helper()
+	self := os.Getpid()
+	var reasons []string
+	// The production path: ps -A -o pid=,pgid=,stat=, parsed by
+	// processTableStateMatches. This is what signalTargetRunning consults.
+	if running, ok := processIsRunning(self); !ok || !running {
+		reasons = append(reasons, "the process table read used by signalTargetRunning reported no live state for this test process")
+	}
+	// This file's independent oracle: ps -o stat= -p <pid>. It is deliberately
+	// NOT the production parser, so a regression in that parser cannot hide by
+	// breaking the test's own precondition check in the same way.
+	if zombie, ok := processIsZombie(self); !ok || zombie {
+		reasons = append(reasons, "the per-PID state read used by this test file reported no live state for this test process")
+	}
+	if len(reasons) == 0 {
+		return
+	}
+	reason := "cannot read process state, so ps-based zombie detection is unverifiable here: " + strings.Join(reasons, "; ")
+	if requireWorkingPS() {
+		t.Fatal(reason + " — failing rather than skipping because CI (or ZERO_REQUIRE_PS) is set, where ps is expected to work")
+	}
+	t.Skip(reason)
+}
+
+// requireWorkingPS reports whether an unusable ps must fail the run instead of
+// skipping it. ZERO_REQUIRE_PS lets a developer opt into the strict behavior
+// locally to reproduce what CI does.
+func requireWorkingPS() bool {
+	if strings.TrimSpace(os.Getenv("ZERO_REQUIRE_PS")) != "" {
+		return true
+	}
+	return strings.TrimSpace(os.Getenv("CI")) != ""
+}
+
+// awaitZombie blocks until pid is an unreaped zombie. The caller must not have
+// waited on the child, so the zombie is a stable state rather than a race: it
+// persists until something reaps it. Failing to reach it therefore means the
+// child never exited or ps stopped reporting its state, and both are defects
+// rather than reasons to skip.
+func awaitZombie(t *testing.T, pid int) {
+	t.Helper()
+	deadline := time.Now().Add(5 * time.Second)
+	for {
+		zombie, ok := processIsZombie(pid)
+		if ok && zombie {
+			return
+		}
+		if time.Now().After(deadline) {
+			if !ok {
+				t.Fatalf("pid %d left the process table without being reaped; this test never waited on it, so its zombie row must persist", pid)
+			}
+			t.Fatalf("pid %d did not reach the zombie state within 5s", pid)
+		}
+		time.Sleep(10 * time.Millisecond)
+	}
+}
+
 // 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
@@ -17,6 +97,8 @@ import (
 // as "did not exit after SIGKILL" — a spurious cleanup failure whose timing
 // depended on when the reaper ran.
 func TestTerminateProcessTreeTreatsZombieGroupAsExited(t *testing.T) {
+	requireProcessState(t)
+
 	cmd := exec.Command("sh", "-c", "exit 0")
 	ConfigureProcessGroup(cmd)
 	if err := cmd.Start(); err != nil {
@@ -27,23 +109,59 @@ func TestTerminateProcessTreeTreatsZombieGroupAsExited(t *testing.T) {
 	// 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
+	awaitZombie(t, pid)
+
+	// Whether a zombie-only group can be signalled is a KERNEL difference, not a
+	// ps one. On Linux the zombie still occupies the process table and
+	// kill(-pid, 0) succeeds, so signalTargetRunning goes on to consult ps —
+	// which is the branch this test was written for. Darwin returns EPERM for
+	// the same call, so signalTargetRunning short-circuits on the kill and never
+	// reaches the ps check.
+	//
+	// The OUTCOME is identical and is asserted on every platform below. Only the
+	// branch that produces it differs, so record that instead of skipping the
+	// whole test (which would drop Darwin's coverage of the outcome) or failing
+	// it (which would report a supported platform as broken). Any errno other
+	// than EPERM means the group is not in the state this test needs.
+	psPathReachable := true
+	if err := syscall.Kill(-pid, syscall.Signal(0)); err != nil {
+		if !errors.Is(err, syscall.EPERM) {
+			t.Fatalf("zombie group %d is unsignalable with an unexpected error (%v); the zombie case is not present, so nothing below would be meaningful", pid, err)
 		}
-		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")
+		psPathReachable = false
+		t.Logf("kernel refuses to signal zombie-only group %d (EPERM); signalTargetRunning answers from kill(2) rather than ps here, so the ps-based zombie check is asserted directly on platforms that allow the signal", pid)
 	}

+	// Where the signal IS permitted, pin the ps-based check itself. This is the
+	// regression #774 was about, and asserting only signalTargetRunning would
+	// let a ps-side regression hide behind the kill result.
+	if psPathReachable {
+		running, ok := processGroupHasRunningMember(pid)
+		if !ok {
+			t.Fatalf("process group %d has no rows while its zombie is unreaped; ps stopped reporting the group rather than the group being gone", pid)
+		}
+		if running {
+			t.Fatal("the ps-based group check must not report a zombie-only group as running")
+		}
+	}
+
+	// Valid on every platform: whichever branch answers, a zombie-only group is
+	// not running. On a kernel that refuses the signal this is the whole of the
+	// coverage, and it is more than the previous skip provided.
 	if signalTargetRunning(-pid) {
 		t.Fatal("a group holding only a zombie must not count as running")
 	}
+
+	if !psPathReachable {
+		// terminateTarget's own kill(2) would hit the same EPERM and be returned
+		// as a cleanup error, so this assertion cannot be made where the kernel
+		// refuses the signal. That may be a real gap in TerminateProcessTree on
+		// such a platform rather than a test limitation — a zombie-only tree is
+		// already exited and should terminate cleanly — but confirming and
+		// changing that is a production fix, not this test's business.
+		t.Log("skipping the TerminateProcessTree assertion: its kill(2) would hit the same EPERM as the probe above")
+		return
+	}
 	if err := TerminateProcessTree(pid, 50*time.Millisecond, 10*time.Millisecond); err != nil {
 		t.Fatalf("TerminateProcessTree on an already-exited tree: %v", err)
 	}
@@ -53,6 +171,8 @@ func TestTerminateProcessTreeTreatsZombieGroupAsExited(t *testing.T) {
 // 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) {
+	requireProcessState(t)
+
 	cmd := exec.Command("sh", "-c", "sleep 30")
 	ConfigureProcessGroup(cmd)
 	if err := cmd.Start(); err != nil {
@@ -67,7 +187,15 @@ func TestTerminateProcessTreeStopsRunningGroup(t *testing.T) {
 	if err := TerminateProcessTree(pid, time.Second, 10*time.Millisecond); err != nil {
 		t.Fatalf("TerminateProcessTree: %v", err)
 	}
-	if running, ok := processGroupHasRunningMember(pid); ok && running {
+	// ok reports whether ANY row for this group was found. This test never waits
+	// on the child, so its zombie row must still be there — an unknown state
+	// means ps stopped answering, not that the group is gone. Treating that as a
+	// pass is what let this assertion succeed without checking anything.
+	running, ok := processGroupHasRunningMember(pid)
+	if !ok {
+		t.Fatalf("process group %d has no rows after termination; the unreaped child's zombie row must persist, so the group's state is undeterminable rather than clean", pid)
+	}
+	if running {
 		t.Fatal("the group still has a running member after termination")
 	}
 }
@@ -82,6 +210,8 @@ func TestTerminateProcessTreeStopsRunningGroup(t *testing.T) {
 // "unknown" resulted every time, and signalTargetRunning conservatively (and
 // incorrectly) treated a zombie individual-PID target as still running.
 func TestSignalTargetRunningTreatsZombieIndividualPIDAsExited(t *testing.T) {
+	requireProcessState(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
@@ -92,40 +222,38 @@ func TestSignalTargetRunningTreatsZombieIndividualPIDAsExited(t *testing.T) {
 	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)
-	}
+	awaitZombie(t, pid)

 	target, err := processSignalTarget(pid)
 	if err != nil {
 		t.Fatalf("processSignalTarget: %v", err)
 	}
+	// The child inherited this process's group, so its PGID is this process's
+	// PID and can never equal its own PID. A negative target here would mean
+	// processSignalTarget misread the group, which is the very thing the
+	// individual-PID fallback exists to handle.
 	if target != pid {
-		t.Skip("child unexpectedly became its own group leader; cannot exercise the individual-PID fallback")
+		t.Fatalf("processSignalTarget(%d) = %d, want the individual PID: the child inherited this process's group, so it is not its own leader", pid, target)
 	}
 	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.
+// processIsZombie reports a process's zombie state via ps. It is deliberately a
+// separate, per-PID ps invocation rather than a reuse of the production
+// process-table parser: these tests assert what that parser concludes, so
+// borrowing it to establish their own preconditions would let one regression
+// silence both sides at once.
+//
+// ok is false when no state could be read, which after requireProcessState has
+// passed means the process left the table rather than that ps is broken.
 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:]
-	}
+	state := strings.TrimLeft(string(output), " \n\t")
 	if state == "" {
 		return false, false
 	}
@@ -5,93 +5,39 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
-	"sync/atomic"
 	"time"

 	"github.com/Gitlawb/zero/internal/lockutil"
 )

 // Cross-process lock tuning for the audit log. The lock is held only across a
-// single read-then-append (milliseconds), so the timeout is generous and the
-// stale threshold sits far above any real hold.
+// single read-then-append (milliseconds), so the timeout is generous relative
+// to any real hold.
 const (
 	auditLockTimeout    = 10 * time.Second
-	auditLockStaleAfter = 60 * time.Second
 	auditLockRetryDelay = 20 * time.Millisecond
 )

-var auditLockSeq atomic.Uint64
-
-// lockAudit takes a cross-process exclusive lock on the audit log by
-// O_EXCL-creating a sibling "<auditPath>.lock" file (removed on release). It makes
+// lockAudit takes a cross-process advisory lock on the audit log through a
+// stable sibling "<auditPath>.lock" file. It makes
 // the lastSequence()+append in append() atomic across processes; the audit log is
 // a shared global file, so without it two processes can read the same last
-// sequence and write duplicate numbers. A stale lock from a crashed holder (older
-// than auditLockStaleAfter) is reclaimed. Wall-clock time is used deliberately so
-// lock timing never depends on the store's injectable clock and the stale check
-// compares against real file mtimes. This mirrors internal/cron/lock.go and
-// internal/oauth/lock.go. Uses internal/lockutil for lock restore and reclaim.
+// sequence and write duplicate numbers. Kernel lock lifetime provides crash
+// recovery without moving or deleting the lock path.
 func (store *AuditStore) lockAudit() (func(), error) {
 	lockPath := store.auditPath + ".lock"
 	if err := os.MkdirAll(filepath.Dir(lockPath), 0o700); err != nil {
 		return nil, err
 	}
-	token := fmt.Sprintf("%d-%d-%d", os.Getpid(), time.Now().UnixNano(), auditLockSeq.Add(1))
 	deadline := time.Now().Add(auditLockTimeout)
 	for {
-		f, err := os.OpenFile(lockPath, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o600)
+		lock, err := lockutil.TryAcquireFileLock(lockPath)
 		if err == nil {
-			// A partial write would leave a lock file without our token, so the
-			// releaser could never delete it — stranding the lock. Fail closed.
-			if _, werr := f.WriteString(token); werr != nil {
-				_ = f.Close()
-				_ = lockutil.RemoveLockFile(lockPath)
-				return nil, fmt.Errorf("hooks: write audit lock: %w", werr)
-			}
-			if cerr := f.Close(); cerr != nil {
-				_ = lockutil.RemoveLockFile(lockPath)
-				return nil, fmt.Errorf("hooks: close audit lock: %w", cerr)
-			}
-			var released bool
-			return func() {
-				if released {
-					return
-				}
-				released = true
-				if data, rerr := os.ReadFile(lockPath); rerr == nil && string(data) == token {
-					_ = lockutil.RemoveLockFile(lockPath)
-				}
-			}, nil
+			return func() { _ = lock.Release() }, nil
 		}
-		// On Windows a concurrent holder's os.Remove leaves the lock file in a
-		// "delete pending" state, so an O_EXCL create races it with
-		// ERROR_ACCESS_DENIED (os.ErrPermission) rather than ErrExist. Treat both
-		// as contention and retry.
-		if !errors.Is(err, os.ErrExist) && !errors.Is(err, os.ErrPermission) {
+		if !errors.Is(err, lockutil.ErrLockHeld) {
 			return nil, fmt.Errorf("hooks: acquire audit lock: %w", err)
 		}
-		// Reclaim a stale lock left by a crashed holder — atomically (H3). A blind
-		// Remove lets two racers both reclaim + recreate and so both hold the lock;
-		// reclaimStaleLock renames the file aside (only one rename wins) and restores
-		// it if it turns out fresh, so a live lock is never deleted out from under it.
-		if info, statErr := os.Stat(lockPath); statErr == nil && time.Since(info.ModTime()) > auditLockStaleAfter {
-			cleared, rerr := lockutil.ReclaimStaleLock(lockPath, token, func(reclaimedPath string) bool {
-				info, err := os.Stat(reclaimedPath)
-				return err == nil && time.Since(info.ModTime()) <= auditLockStaleAfter
-			})
-			if rerr != nil {
-				// Reclaim hit a hard failure: the rename aside failed outright, or a
-				// live holder's lock could not be put back (the lock path may be
-				// missing, so re-acquiring would break mutual exclusion). Fail closed
-				// instead of spinning to the deadline.
-				return nil, fmt.Errorf("hooks: reclaim stale audit lock: %w", rerr)
-			}
-			if cleared {
-				continue
-			}
-			// Lost the reclaim race (or it was actually fresh) — fall through to the
-			// bounded wait rather than hot-spinning on a reclaim that never wins.
-		}
 		if !time.Now().Before(deadline) {
 			return nil, fmt.Errorf("hooks: timed out acquiring audit lock")
 		}
@@ -1,64 +1,127 @@
-// Package lockutil provides the platform-specific file primitives behind the
-// O_EXCL lock files in cron, daemon, hooks, oauth, and swarm: a no-overwrite
-// restore for locks that were sidelined during a stale-reclaim attempt, and a
-// lock file remover with one cross-platform contract (missing files are a
-// no-op; Windows retries transient sharing violations).
+// Package lockutil provides cross-process advisory file locks used by cron,
+// daemon, hooks, oauth, and swarm. Locks are held by the kernel for the lifetime
+// of an open file handle, so process exit releases them without a stale-file
+// reclaim protocol. The lock file itself is stable: holders never rename or
+// remove it while another process may still have its inode locked.
 package lockutil

 import (
-	"io"
+	"errors"
+	"fmt"
 	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+	"sync/atomic"
 )

-// restoreByCopy restores reclaimed to path without overwriting an existing
-// path, as a fallback for when the platform's primary no-replace primitive
-// (hard link on POSIX, MoveFileEx on Windows) fails for a reason other than
-// the destination existing. It stages a full copy under a private name next
-// to reclaimed and publishes it to path with publish (the same no-replace
-// primitive the caller's platform uses for the primary restore), so path
-// never appears in a partially-copied state: a crash between staging and
-// publish leaves path exactly as it was (missing or, if a competing holder
-// created it, untouched), never a truncated file that a PID/content-based
-// liveness check could mistake for dead. Leaving path missing here would let
-// the next O_EXCL create succeed while the sidelined holder is still live,
-// breaking mutual exclusion. publish keeps the no-overwrite guarantee: a new
-// holder that appeared in the meantime wins and this returns os.ErrExist. The
-// copy resets the lock's mtime to now, which only makes the restored lock
-// look fresher; that is safe, since it is being handed back to a live holder.
-func restoreByCopy(reclaimed, path string, publish func(from, to string) error) error {
-	staged := reclaimed + ".copy"
-	src, err := os.Open(reclaimed)
+var (
+	// ErrLockHeld reports that another process or goroutine currently holds the
+	// advisory lock. Callers may wait and retry until their own deadline.
+	ErrLockHeld = errors.New("lockutil: lock is held")
+	// ErrLockReleased reports an attempt to update metadata after Release.
+	ErrLockReleased = errors.New("lockutil: lock is released")
+)
+
+var holderSequence atomic.Uint64
+
+// FileLock is an exclusive advisory lock held through an open file handle.
+// Release is idempotent. The lock path remains on disk after release; deleting
+// or replacing it would let different processes lock different inodes.
+type FileLock struct {
+	mu         sync.Mutex
+	file       *os.File
+	state      platformLockState
+	released   bool
+	releaseErr error
+}
+
+// TryAcquireFileLock attempts to take an exclusive advisory lock without
+// waiting. A contended lock returns ErrLockHeld. The kernel releases a lock if
+// its process exits, so an old unlocked file never needs stale reclamation.
+func TryAcquireFileLock(path string) (*FileLock, error) {
+	return TryAcquireFileLockAt(filepath.Dir(path), path)
+}
+
+// TryAcquireFileLockAt attempts to lock path while confining every component
+// below root to a handle-relative traversal. root is the caller's trusted
+// boundary and may itself be reached through a legitimate link; links and
+// reparse points below it are rejected before metadata can be written.
+func TryAcquireFileLockAt(root, path string) (*FileLock, error) {
+	if root == "" {
+		return nil, errors.New("lockutil: lock root is empty")
+	}
+	relative, err := filepath.Rel(root, path)
 	if err != nil {
-		return err
+		return nil, fmt.Errorf("lockutil: resolve lock path relative to root: %w", err)
 	}
-	dst, err := os.OpenFile(staged, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o600)
+	relative = filepath.Clean(relative)
+	if relative == "." || relative == ".." || filepath.IsAbs(relative) || strings.HasPrefix(relative, ".."+string(filepath.Separator)) {
+		return nil, fmt.Errorf("lockutil: lock path %q escapes root %q", path, root)
+	}
+
+	file, err := openLockFileAt(root, relative, path)
 	if err != nil {
-		_ = src.Close()
-		return err
+		return nil, fmt.Errorf("lockutil: open lock file: %w", err)
 	}
-	_, err = io.Copy(dst, src)
-	// Close the source before removing anything below: Go opens files without
-	// FILE_SHARE_DELETE on Windows, so deleting reclaimed or staged while src
-	// is open would fail with a sharing violation.
-	_ = src.Close()
+	state, contended, err := tryLockFile(file)
 	if err != nil {
-		_ = dst.Close()
-		_ = os.Remove(staged)
-		return err
+		_ = file.Close()
+		return nil, fmt.Errorf("lockutil: acquire advisory lock: %w", err)
 	}
-	if err := dst.Close(); err != nil {
-		_ = os.Remove(staged)
-		return err
+	if contended {
+		_ = file.Close()
+		return nil, ErrLockHeld
 	}
-	if err := publish(staged, path); err != nil {
-		_ = os.Remove(staged)
-		return err
+
+	lock := &FileLock{file: file, state: state}
+	metadata := []byte(fmt.Sprintf("%d-%d\n", os.Getpid(), holderSequence.Add(1)))
+	if err := lock.WriteMetadata(metadata); err != nil {
+		return nil, errors.Join(err, lock.Release())
+	}
+	return lock, nil
+}
+
+// WriteMetadata replaces the diagnostic contents of the lock file while the
+// caller holds it. Metadata does not establish ownership; the kernel lock does.
+func (lock *FileLock) WriteMetadata(data []byte) error {
+	if lock == nil {
+		return ErrLockReleased
+	}
+	lock.mu.Lock()
+	defer lock.mu.Unlock()
+	if lock.released || lock.file == nil {
+		return ErrLockReleased
+	}
+	if err := lock.file.Truncate(0); err != nil {
+		return fmt.Errorf("lockutil: truncate lock metadata: %w", err)
+	}
+	if _, err := lock.file.Seek(0, 0); err != nil {
+		return fmt.Errorf("lockutil: seek lock metadata: %w", err)
+	}
+	if _, err := lock.file.Write(data); err != nil {
+		return fmt.Errorf("lockutil: write lock metadata: %w", err)
 	}
-	// publish may leave staged behind (a hard-link publish keeps both names),
-	// so remove it explicitly; a move-based publish already made this a no-op.
-	_ = os.Remove(staged)
-	// The lock is back at path, so the restore has succeeded; failing to clean
-	// up the sidelined name must not be reported as a failed restore.
-	_ = RemoveLockFile(reclaimed)
 	return nil
 }
+
+// Release unlocks and closes the held file handle. It deliberately leaves the
+// stable lock file in place. Repeated calls return the first release result.
+func (lock *FileLock) Release() error {
+	if lock == nil {
+		return nil
+	}
+	lock.mu.Lock()
+	defer lock.mu.Unlock()
+	if lock.released {
+		return lock.releaseErr
+	}
+	lock.released = true
+	unlockErr := unlockFile(lock.file, &lock.state)
+	closeErr := lock.file.Close()
+	lock.file = nil
+	if err := errors.Join(unlockErr, closeErr); err != nil {
+		lock.releaseErr = fmt.Errorf("lockutil: release advisory lock: %w", err)
+	}
+	return lock.releaseErr
+}
@@ -4,43 +4,92 @@ package lockutil

 import (
 	"errors"
-	"io/fs"
+	"fmt"
 	"os"
+	"path/filepath"
+	"strings"
+
+	"golang.org/x/sys/unix"
 )

-// RestoreLockFile restores a sidelined lock file on non-Windows platforms. It
-// uses os.Link so a competing lock created at path in the meantime wins: the
-// link fails with os.ErrExist instead of overwriting it. If the link fails for
-// any other reason (hardlink-incapable filesystems such as FAT or some
-// FUSE/network mounts, ENOSPC, EPERM), it falls back to an O_EXCL copy rather
-// than leaving path missing and the live holder's lock stranded in reclaimed.
-// Once the lock is back at path the restore has succeeded, so a failed cleanup
-// of the sidelined name is not reported as an error; the leftover file is
-// invisible to the lock protocol.
-func RestoreLockFile(reclaimed, path string) error {
-	err := os.Link(reclaimed, path)
+type platformLockState struct{}
+
+func openLockFileAt(root, relative, displayPath string) (_ *os.File, resultErr error) {
+	parentFD, err := unix.Open(root, unix.O_RDONLY|unix.O_DIRECTORY|unix.O_CLOEXEC, 0)
+	if err != nil {
+		return nil, fmt.Errorf("open lock root: %w", err)
+	}
+	defer func() {
+		if parentFD >= 0 {
+			resultErr = errors.Join(resultErr, unix.Close(parentFD))
+		}
+	}()
+
+	components := strings.Split(filepath.Clean(relative), string(filepath.Separator))
+	for _, component := range components[:len(components)-1] {
+		nextFD, openErr := unix.Openat(parentFD, component, unix.O_RDONLY|unix.O_DIRECTORY|unix.O_CLOEXEC|unix.O_NOFOLLOW, 0)
+		if openErr != nil {
+			return nil, fmt.Errorf("open lock path component %q: %w", component, openErr)
+		}
+		if closeErr := unix.Close(parentFD); closeErr != nil {
+			_ = unix.Close(nextFD)
+			parentFD = -1
+			return nil, fmt.Errorf("close lock path component: %w", closeErr)
+		}
+		parentFD = nextFD
+	}
+
+	name := components[len(components)-1]
+	fd := -1
+	// Darwin can transiently return ENOENT when many callers race to create the
+	// same O_NOFOLLOW entry. The bound parent handle cannot be redirected, so a
+	// bounded retry preserves first-use contention without weakening no-follow.
+	for attempt := 0; attempt < 10; attempt++ {
+		fd, err = unix.Openat(parentFD, name, unix.O_CREAT|unix.O_RDWR|unix.O_CLOEXEC|unix.O_NOFOLLOW, 0o600)
+		if !errors.Is(err, unix.ENOENT) {
+			break
+		}
+	}
+	if err != nil {
+		return nil, err
+	}
+	file := os.NewFile(uintptr(fd), displayPath)
+	if file == nil {
+		_ = unix.Close(fd)
+		return nil, errors.New("convert lock handle to file")
+	}
+	var stat unix.Stat_t
+	if err := unix.Fstat(fd, &stat); err != nil {
+		return nil, errors.Join(fmt.Errorf("inspect lock file: %w", err), file.Close())
+	}
+	if stat.Mode&unix.S_IFMT != unix.S_IFREG {
+		return nil, errors.Join(errors.New("refusing non-regular lock file"), file.Close())
+	}
+	if stat.Nlink != 1 {
+		return nil, errors.Join(errors.New("refusing multiply-linked lock file"), file.Close())
+	}
+	if err := unix.Close(parentFD); err != nil {
+		parentFD = -1
+		return nil, errors.Join(fmt.Errorf("close lock parent: %w", err), file.Close())
+	}
+	parentFD = -1
+	return file, nil
+}
+
+func tryLockFile(file *os.File) (platformLockState, bool, error) {
+	err := unix.Flock(int(file.Fd()), unix.LOCK_EX|unix.LOCK_NB)
 	if err == nil {
-		_ = RemoveLockFile(reclaimed)
+		return platformLockState{}, false, nil
+	}
+	if errors.Is(err, unix.EWOULDBLOCK) || errors.Is(err, unix.EAGAIN) {
+		return platformLockState{}, true, nil
+	}
+	return platformLockState{}, false, err
+}
+
+func unlockFile(file *os.File, _ *platformLockState) error {
+	if file == nil {
 		return nil
 	}
-	if errors.Is(err, os.ErrExist) {
-		return err
-	}
-	return restoreByCopy(reclaimed, path, os.Link)
-}
-
-// isReclaimContended reports whether a failed rename-aside of a suspected
-// stale lock means it was lost to a racer rather than a hard failure. POSIX
-// rename has no contention errno (a lost race surfaces only as ENOENT, which
-// ReclaimStaleLock already treats as benign), so nothing extra is benign here.
-func isReclaimContended(error) bool { return false }
-
-// RemoveLockFile removes a lock file on non-Windows platforms. Removing an
-// already-missing file reports nil, matching the Windows implementation, so
-// callers see one cross-platform contract.
-func RemoveLockFile(path string) error {
-	if err := os.Remove(path); err != nil && !errors.Is(err, fs.ErrNotExist) {
-		return err
-	}
-	return nil
+	return unix.Flock(int(file.Fd()), unix.LOCK_UN)
 }
@@ -1,116 +1,220 @@
 package lockutil

 import (
+	"bufio"
 	"errors"
+	"fmt"
+	"io"
 	"os"
+	"os/exec"
 	"path/filepath"
+	"runtime"
+	"strings"
+	"sync"
 	"testing"
 )

-func TestRestoreLockFile(t *testing.T) {
-	tempDir := t.TempDir()
-	path := filepath.Join(tempDir, "lock")
-	reclaimed := filepath.Join(tempDir, "lock.stale.token")
-
-	// 1. Successful restore when target does not exist
-	if err := os.WriteFile(reclaimed, []byte("token"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	if err := RestoreLockFile(reclaimed, path); err != nil {
-		t.Fatalf("RestoreLockFile failed: %v", err)
-	}
-	if data, err := os.ReadFile(path); err != nil || string(data) != "token" {
-		t.Fatalf("restored lock content = %q, err %v; want %q intact", data, err, "token")
-	}
-	if _, err := os.Stat(reclaimed); !os.IsNotExist(err) {
-		t.Fatalf("expected sidelined lock to be cleaned up/removed: %v", err)
-	}
-
-	// 2. Fail when target already exists (prevent overwrite)
-	if err := os.WriteFile(reclaimed, []byte("token"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	if err := os.WriteFile(path, []byte("competing"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-
-	err := RestoreLockFile(reclaimed, path)
-	if err == nil {
-		t.Fatal("expected RestoreLockFile to fail when target exists")
-	}
-	if !errors.Is(err, os.ErrExist) {
-		t.Fatalf("expected os.ErrExist, got: %v", err)
-	}
-
-	// The sidelined lock must still exist on failure, and the competing lock
-	// must be untouched.
-	if _, err := os.Stat(reclaimed); err != nil {
-		t.Fatalf("expected sidelined lock to still exist: %v", err)
-	}
-	if data, _ := os.ReadFile(path); string(data) != "competing" {
-		t.Fatalf("competing lock was clobbered: %q", data)
-	}
-}
-
-func TestRestoreByCopy(t *testing.T) {
-	tempDir := t.TempDir()
-	path := filepath.Join(tempDir, "lock")
-	reclaimed := filepath.Join(tempDir, "lock.stale.token")
-
-	// 1. Restores content and cleans up the sidelined file when the target is
-	// free (the fallback taken when the platform's no-replace primitive fails
-	// for a reason other than the destination existing).
-	if err := os.WriteFile(reclaimed, []byte("token"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	if err := restoreByCopy(reclaimed, path, os.Link); err != nil {
-		t.Fatalf("restoreByCopy failed: %v", err)
-	}
-	if data, err := os.ReadFile(path); err != nil || string(data) != "token" {
-		t.Fatalf("restored lock content = %q, err %v; want %q intact", data, err, "token")
-	}
-	if _, err := os.Stat(reclaimed); !errors.Is(err, os.ErrNotExist) {
-		t.Fatalf("expected sidelined lock to be cleaned up after copy: %v", err)
-	}
-	if _, err := os.Stat(reclaimed + ".copy"); !errors.Is(err, os.ErrNotExist) {
-		t.Fatalf("expected staged copy to be cleaned up: %v", err)
-	}
-
-	// 2. Keeps the no-overwrite guarantee: a competing lock at the target wins
-	// and the sidelined lock survives for the caller's ErrExist cleanup.
-	if err := os.WriteFile(reclaimed, []byte("token"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	if err := os.WriteFile(path, []byte("competing"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	if err := restoreByCopy(reclaimed, path, os.Link); !errors.Is(err, os.ErrExist) {
-		t.Fatalf("expected os.ErrExist when target exists, got: %v", err)
-	}
-	if data, _ := os.ReadFile(path); string(data) != "competing" {
-		t.Fatalf("competing lock was clobbered: %q", data)
-	}
-	if _, err := os.Stat(reclaimed); err != nil {
-		t.Fatalf("expected sidelined lock to still exist: %v", err)
-	}
-	if _, err := os.Stat(reclaimed + ".copy"); !errors.Is(err, os.ErrNotExist) {
-		t.Fatalf("expected staged copy to be cleaned up after a failed publish: %v", err)
-	}
-}
-
-func TestRemoveLockFile(t *testing.T) {
+func TestFileLockSerializesAndKeepsStablePath(t *testing.T) {
 	path := filepath.Join(t.TempDir(), "lock")
-	if err := os.WriteFile(path, []byte("token"), 0o600); err != nil {
-		t.Fatal(err)
+	first, err := TryAcquireFileLock(path)
+	if err != nil {
+		t.Fatalf("first acquire: %v", err)
 	}
-	if err := RemoveLockFile(path); err != nil {
-		t.Fatalf("RemoveLockFile failed: %v", err)
+	firstInfo, err := os.Stat(path)
+	if err != nil {
+		t.Fatalf("stat first lock path: %v", err)
 	}
-	if _, err := os.Stat(path); !errors.Is(err, os.ErrNotExist) {
-		t.Fatalf("expected lock file to be removed: %v", err)
+	if _, err := TryAcquireFileLock(path); !errors.Is(err, ErrLockHeld) {
+		t.Fatalf("contended acquire = %v, want ErrLockHeld", err)
 	}
-	// Removing an already-missing lock file is a no-op on every platform.
-	if err := RemoveLockFile(path); err != nil {
-		t.Fatalf("RemoveLockFile on a missing file = %v, want nil", err)
+	if err := first.Release(); err != nil {
+		t.Fatalf("release first: %v", err)
+	}
+	releasedInfo, err := os.Stat(path)
+	if err != nil {
+		t.Fatalf("release removed stable lock path: %v", err)
+	}
+	if !os.SameFile(firstInfo, releasedInfo) {
+		t.Fatal("release replaced the stable lock file")
+	}
+
+	second, err := TryAcquireFileLock(path)
+	if err != nil {
+		t.Fatalf("acquire after release: %v", err)
+	}
+	secondInfo, err := os.Stat(path)
+	if err != nil {
+		t.Fatalf("stat second lock path: %v", err)
+	}
+	if !os.SameFile(firstInfo, secondInfo) {
+		t.Fatal("reacquire used a different lock file")
+	}
+	if err := second.Release(); err != nil {
+		t.Fatalf("release second: %v", err)
+	}
+	if err := second.Release(); err != nil {
+		t.Fatalf("idempotent release: %v", err)
 	}
 }
+
+func TestFileLockMetadata(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "lock")
+	lock, err := TryAcquireFileLock(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := lock.WriteMetadata([]byte("holder\n")); err != nil {
+		t.Fatalf("write metadata: %v", err)
+	}
+	data, err := os.ReadFile(path)
+	if err != nil || string(data) != "holder\n" {
+		t.Fatalf("metadata = %q, err %v", data, err)
+	}
+	if err := lock.Release(); err != nil {
+		t.Fatal(err)
+	}
+	if err := lock.WriteMetadata(nil); !errors.Is(err, ErrLockReleased) {
+		t.Fatalf("write after release = %v, want ErrLockReleased", err)
+	}
+}
+
+func TestFileLockConcurrentFirstAcquisition(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "lock")
+	const contenders = 200
+	start := make(chan struct{})
+	results := make(chan error, contenders)
+	locks := make(chan *FileLock, contenders)
+	var ready sync.WaitGroup
+	ready.Add(contenders)
+	for range contenders {
+		go func() {
+			ready.Done()
+			<-start
+			lock, err := TryAcquireFileLock(path)
+			if lock != nil {
+				locks <- lock
+			}
+			results <- err
+		}()
+	}
+	ready.Wait()
+	close(start)
+	acquired := 0
+	for range contenders {
+		err := <-results
+		switch {
+		case err == nil:
+			acquired++
+		case !errors.Is(err, ErrLockHeld):
+			t.Errorf("concurrent first acquire: %v", err)
+		}
+	}
+	close(locks)
+	for lock := range locks {
+		if err := lock.Release(); err != nil {
+			t.Error(err)
+		}
+	}
+	if acquired != 1 {
+		t.Fatalf("concurrent first acquire: got %d holders, want 1", acquired)
+	}
+}
+
+func TestFileLockRefusesMultiplyLinkedEntry(t *testing.T) {
+	dir := t.TempDir()
+	target := filepath.Join(dir, "target")
+	lockPath := filepath.Join(dir, "lock")
+	const sentinel = "do not overwrite"
+	if err := os.WriteFile(target, []byte(sentinel), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Link(target, lockPath); err != nil {
+		t.Fatalf("create redirected hard link: %v", err)
+	}
+	if lock, err := TryAcquireFileLock(lockPath); err == nil {
+		_ = lock.Release()
+		t.Fatal("TryAcquireFileLock accepted a multiply-linked entry")
+	}
+	data, err := os.ReadFile(target)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(data) != sentinel {
+		t.Fatalf("redirected target was modified: %q", data)
+	}
+}
+
+func TestFileLockAtRejectsEscapingPath(t *testing.T) {
+	base := t.TempDir()
+	outside := filepath.Join(filepath.Dir(base), "outside.lock")
+	if lock, err := TryAcquireFileLockAt(base, outside); err == nil {
+		_ = lock.Release()
+		t.Fatal("TryAcquireFileLockAt accepted a path outside its root")
+	}
+	if _, err := os.Stat(outside); !errors.Is(err, os.ErrNotExist) {
+		t.Fatalf("escaping path was created: %v", err)
+	}
+}
+
+// TestFileLockReleasedByProcessExit proves crash recovery is provided by the
+// kernel lock lifetime. The child exits without calling Release; the next
+// process can then lock the same persistent file without moving or deleting it.
+func TestFileLockReleasedByProcessExit(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "lock")
+	cmd := exec.Command(os.Args[0], "-test.run=^TestFileLockHelperProcess$")
+	cmd.Env = append(os.Environ(), "ZERO_LOCKUTIL_HELPER=1", "ZERO_LOCKUTIL_PATH="+path)
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	stdin, err := cmd.StdinPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	cmd.Stderr = os.Stderr
+	if err := cmd.Start(); err != nil {
+		t.Fatal(err)
+	}
+
+	ready, err := bufio.NewReader(stdout).ReadString('\n')
+	if err != nil || strings.TrimSpace(ready) != "ready" {
+		_ = cmd.Process.Kill()
+		_ = cmd.Wait()
+		t.Fatalf("helper readiness = %q, err %v", ready, err)
+	}
+	if _, err := TryAcquireFileLock(path); !errors.Is(err, ErrLockHeld) {
+		_ = cmd.Process.Kill()
+		_ = cmd.Wait()
+		t.Fatalf("acquire while helper holds lock = %v, want ErrLockHeld", err)
+	}
+	if err := stdin.Close(); err != nil {
+		t.Fatal(err)
+	}
+	if err := cmd.Wait(); err != nil {
+		t.Fatalf("helper exit: %v", err)
+	}
+
+	lock, err := TryAcquireFileLock(path)
+	if err != nil {
+		t.Fatalf("acquire after helper exit: %v", err)
+	}
+	if err := lock.Release(); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestFileLockHelperProcess(t *testing.T) {
+	if os.Getenv("ZERO_LOCKUTIL_HELPER") != "1" {
+		return
+	}
+	lock, err := TryAcquireFileLock(os.Getenv("ZERO_LOCKUTIL_PATH"))
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(2)
+	}
+	if _, err := fmt.Fprintln(os.Stdout, "ready"); err != nil {
+		os.Exit(3)
+	}
+	_, _ = io.Copy(io.Discard, os.Stdin)
+	runtime.KeepAlive(lock) // deliberately exit without Release
+}
@@ -4,77 +4,202 @@ package lockutil

 import (
 	"errors"
+	"fmt"
 	"os"
-	"syscall"
-	"time"
+	"path/filepath"
+	"strings"
+	"unsafe"

 	"golang.org/x/sys/windows"
 )

-// RestoreLockFile restores a sidelined lock file on Windows. It moves the file
-// with a no-replace MoveFileEx so a competing lock created at path in the
-// meantime wins: the move fails with os.ErrExist instead of overwriting it. If
-// the move fails for any other reason (ERROR_SHARING_VIOLATION or
-// ERROR_ACCESS_DENIED under concurrent access to the file), it falls back to
-// an O_EXCL copy rather than leaving path missing and the live holder's lock
-// stranded in reclaimed.
-func RestoreLockFile(reclaimed, path string) error {
-	err := moveFileNoReplace(reclaimed, path)
-	if err == nil || errors.Is(err, os.ErrExist) {
-		return err
-	}
-	return restoreByCopy(reclaimed, path, moveFileNoReplace)
+type platformLockState struct {
+	overlapped windows.Overlapped
 }

-// moveFileNoReplace renames from to to, failing if to already exists. It calls
-// MoveFileExW directly via golang.org/x/sys/windows (the standard library's
-// syscall package does not export MoveFileEx on this platform) with no flags,
-// so an existing destination fails with ERROR_ALREADY_EXISTS, which satisfies
-// errors.Is(err, os.ErrExist) (pinned by
-// TestMoveFileNoReplaceMapsAlreadyExistsToErrExist), instead of overwriting it
-// the way os.Rename does on Windows (it passes MOVEFILE_REPLACE_EXISTING to
-// match POSIX rename semantics cross-platform).
-func moveFileNoReplace(from, to string) error {
-	fromPtr, err := windows.UTF16PtrFromString(from)
+const lockByteOffsetHigh = 1
+
+func openLockFileAt(root, relative, displayPath string) (_ *os.File, resultErr error) {
+	rootPtr, err := windows.UTF16PtrFromString(root)
 	if err != nil {
-		return err
+		return nil, err
 	}
-	toPtr, err := windows.UTF16PtrFromString(to)
+	parent, err := windows.CreateFile(
+		rootPtr,
+		windows.FILE_READ_ATTRIBUTES|windows.FILE_TRAVERSE|windows.SYNCHRONIZE,
+		windows.FILE_SHARE_READ|windows.FILE_SHARE_WRITE|windows.FILE_SHARE_DELETE,
+		nil,
+		windows.OPEN_EXISTING,
+		windows.FILE_FLAG_BACKUP_SEMANTICS,
+		0,
+	)
 	if err != nil {
-		return err
+		return nil, fmt.Errorf("open lock root: %w", err)
 	}
-	return windows.MoveFileEx(fromPtr, toPtr, 0)
-}
-
-// isReclaimContended reports whether a failed rename-aside of a suspected
-// stale lock means the file was concurrently open or pending deletion (which
-// surfaces as ERROR_SHARING_VIOLATION or ERROR_ACCESS_DENIED on Windows)
-// rather than a hard failure, so ReclaimStaleLock reports a lost race instead
-// of an error. Neither errno satisfies errors.Is(err, os.ErrExist), and
-// ERROR_SHARING_VIOLATION does not satisfy errors.Is(err, os.ErrPermission)
-// either, so the classification compares raw errnos like RemoveLockFile below.
-func isReclaimContended(err error) bool {
-	var errno syscall.Errno
-	return errors.As(err, &errno) && (errno == windows.ERROR_SHARING_VIOLATION || errno == windows.ERROR_ACCESS_DENIED)
-}
-
-// RemoveLockFile removes a lock file on Windows, retrying on the sharing
-// violation or access denied errors that are common under heavy concurrent
-// contention. Removing an already-missing file reports nil, matching the
-// non-Windows implementation, so callers see one cross-platform contract.
-func RemoveLockFile(path string) error {
-	var err error
-	for i := 0; i < 15; i++ {
-		err = os.Remove(path)
-		if err == nil || os.IsNotExist(err) {
-			return nil
+	defer func() {
+		if parent != 0 {
+			resultErr = errors.Join(resultErr, windows.CloseHandle(parent))
 		}
-		var errno syscall.Errno
-		if errors.As(err, &errno) && (errno == windows.ERROR_SHARING_VIOLATION || errno == windows.ERROR_ACCESS_DENIED) {
-			time.Sleep(5 * time.Millisecond)
+	}()
+
+	components := strings.Split(filepath.Clean(relative), string(filepath.Separator))
+	for _, component := range components[:len(components)-1] {
+		next, openErr := openLockDirectoryAt(parent, component)
+		if openErr != nil {
+			return nil, fmt.Errorf("open lock path component %q: %w", component, openErr)
+		}
+		if closeErr := windows.CloseHandle(parent); closeErr != nil {
+			_ = windows.CloseHandle(next)
+			parent = 0
+			return nil, fmt.Errorf("close lock path component: %w", closeErr)
+		}
+		parent = next
+	}
+
+	handle, err := openLockFileHandleAt(parent, components[len(components)-1])
+	if err != nil {
+		return nil, err
+	}
+	file := os.NewFile(uintptr(handle), displayPath)
+	if file == nil {
+		_ = windows.CloseHandle(handle)
+		return nil, errors.New("convert lock handle to file")
+	}
+	if err := windows.CloseHandle(parent); err != nil {
+		parent = 0
+		return nil, errors.Join(fmt.Errorf("close lock parent: %w", err), file.Close())
+	}
+	parent = 0
+	return file, nil
+}
+
+func openLockDirectoryAt(parent windows.Handle, name string) (windows.Handle, error) {
+	handle, err := openLockPathAt(
+		parent,
+		name,
+		windows.FILE_READ_ATTRIBUTES|windows.FILE_TRAVERSE|windows.SYNCHRONIZE,
+		windows.FILE_OPEN,
+		windows.FILE_ATTRIBUTE_DIRECTORY,
+		windows.FILE_DIRECTORY_FILE|windows.FILE_SYNCHRONOUS_IO_NONALERT|windows.FILE_OPEN_REPARSE_POINT,
+	)
+	if err != nil {
+		return 0, err
+	}
+	if err := validateWindowsLockHandle(handle, true); err != nil {
+		return 0, errors.Join(err, windows.CloseHandle(handle))
+	}
+	return handle, nil
+}
+
+func openLockFileHandleAt(parent windows.Handle, name string) (windows.Handle, error) {
+	for attempt := 0; attempt < 10; attempt++ {
+		handle, err := openLockPathAt(
+			parent,
+			name,
+			windows.GENERIC_READ|windows.GENERIC_WRITE|windows.SYNCHRONIZE,
+			windows.FILE_OPEN,
+			windows.FILE_ATTRIBUTE_NORMAL,
+			windows.FILE_NON_DIRECTORY_FILE|windows.FILE_SYNCHRONOUS_IO_NONALERT|windows.FILE_OPEN_REPARSE_POINT,
+		)
+		if err == nil {
+			if err := validateWindowsLockHandle(handle, false); err != nil {
+				return 0, errors.Join(err, windows.CloseHandle(handle))
+			}
+			return handle, nil
+		}
+		if !windowsLockPathMissing(err) {
+			return 0, err
+		}
+
+		handle, err = openLockPathAt(
+			parent,
+			name,
+			windows.GENERIC_READ|windows.GENERIC_WRITE|windows.SYNCHRONIZE,
+			windows.FILE_CREATE,
+			windows.FILE_ATTRIBUTE_NORMAL,
+			windows.FILE_NON_DIRECTORY_FILE|windows.FILE_SYNCHRONOUS_IO_NONALERT|windows.FILE_OPEN_REPARSE_POINT,
+		)
+		if err == windows.STATUS_OBJECT_NAME_COLLISION || errors.Is(err, windows.ERROR_ALREADY_EXISTS) {
 			continue
 		}
-		return err
+		if err != nil {
+			return 0, err
+		}
+		if err := validateWindowsLockHandle(handle, false); err != nil {
+			return 0, errors.Join(err, windows.CloseHandle(handle))
+		}
+		return handle, nil
 	}
-	return err
+	return 0, errors.New("lock file creation did not stabilize")
+}
+
+func windowsLockPathMissing(err error) bool {
+	return err == windows.STATUS_NO_SUCH_FILE ||
+		err == windows.STATUS_OBJECT_NAME_NOT_FOUND ||
+		err == windows.STATUS_OBJECT_PATH_NOT_FOUND ||
+		errors.Is(err, windows.ERROR_FILE_NOT_FOUND) ||
+		errors.Is(err, windows.ERROR_PATH_NOT_FOUND)
+}
+
+func openLockPathAt(parent windows.Handle, name string, access, disposition, attributes, options uint32) (windows.Handle, error) {
+	objectName, err := windows.NewNTUnicodeString(name)
+	if err != nil {
+		return 0, err
+	}
+	objectAttributes := &windows.OBJECT_ATTRIBUTES{
+		Length:        uint32(unsafe.Sizeof(windows.OBJECT_ATTRIBUTES{})),
+		RootDirectory: parent,
+		ObjectName:    objectName,
+		Attributes:    windows.OBJ_CASE_INSENSITIVE | windows.OBJ_DONT_REPARSE,
+	}
+	var handle windows.Handle
+	err = windows.NtCreateFile(
+		&handle,
+		access,
+		objectAttributes,
+		&windows.IO_STATUS_BLOCK{},
+		nil,
+		attributes,
+		windows.FILE_SHARE_READ|windows.FILE_SHARE_WRITE|windows.FILE_SHARE_DELETE,
+		disposition,
+		options,
+		0,
+		0,
+	)
+	return handle, err
+}
+
+func validateWindowsLockHandle(handle windows.Handle, wantDirectory bool) error {
+	var info windows.ByHandleFileInformation
+	if err := windows.GetFileInformationByHandle(handle, &info); err != nil {
+		return fmt.Errorf("inspect lock path handle: %w", err)
+	}
+	isDirectory := info.FileAttributes&windows.FILE_ATTRIBUTE_DIRECTORY != 0
+	if info.FileAttributes&windows.FILE_ATTRIBUTE_REPARSE_POINT != 0 || isDirectory != wantDirectory {
+		return errors.New("refusing non-file or reparse-point lock path")
+	}
+	if !wantDirectory && info.NumberOfLinks != 1 {
+		return errors.New("refusing multiply-linked lock file")
+	}
+	return nil
+}
+
+func tryLockFile(file *os.File) (platformLockState, bool, error) {
+	state := platformLockState{overlapped: windows.Overlapped{OffsetHigh: lockByteOffsetHigh}}
+	flags := uint32(windows.LOCKFILE_EXCLUSIVE_LOCK | windows.LOCKFILE_FAIL_IMMEDIATELY)
+	err := windows.LockFileEx(windows.Handle(file.Fd()), flags, 0, 1, 0, &state.overlapped)
+	if err == nil {
+		return state, false, nil
+	}
+	if errors.Is(err, windows.ERROR_LOCK_VIOLATION) || errors.Is(err, windows.ERROR_SHARING_VIOLATION) {
+		return platformLockState{}, true, nil
+	}
+	return platformLockState{}, false, err
+}
+
+func unlockFile(file *os.File, state *platformLockState) error {
+	if file == nil {
+		return nil
+	}
+	return windows.UnlockFileEx(windows.Handle(file.Fd()), 0, 1, 0, &state.overlapped)
 }
@@ -1,83 +0,0 @@
-//go:build windows
-
-package lockutil
-
-import (
-	"errors"
-	"os"
-	"path/filepath"
-	"testing"
-	"time"
-
-	"golang.org/x/sys/windows"
-)
-
-// TestMoveFileNoReplaceMapsAlreadyExistsToErrExist pins the errno coupling
-// every caller keys its cleanup on: with no flags, MoveFileEx fails with
-// ERROR_ALREADY_EXISTS when the destination exists, and that errno must
-// satisfy errors.Is(err, os.ErrExist).
-func TestMoveFileNoReplaceMapsAlreadyExistsToErrExist(t *testing.T) {
-	dir := t.TempDir()
-	from := filepath.Join(dir, "from")
-	to := filepath.Join(dir, "to")
-	if err := os.WriteFile(from, []byte("sidelined"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	if err := os.WriteFile(to, []byte("competing"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	err := moveFileNoReplace(from, to)
-	if !errors.Is(err, windows.ERROR_ALREADY_EXISTS) {
-		t.Fatalf("MoveFileEx with an existing destination = %v, want ERROR_ALREADY_EXISTS", err)
-	}
-	if !errors.Is(err, os.ErrExist) {
-		t.Fatalf("ERROR_ALREADY_EXISTS must satisfy errors.Is(err, os.ErrExist), got: %v", err)
-	}
-	if data, _ := os.ReadFile(to); string(data) != "competing" {
-		t.Fatalf("destination was overwritten: %q", data)
-	}
-}
-
-// TestRemoveLockFileRetriesSharingViolation holds the file open briefly (Go
-// opens files without FILE_SHARE_DELETE on Windows, so a concurrent DeleteFile
-// fails with ERROR_SHARING_VIOLATION while the handle is open); RemoveLockFile
-// must ride its retry loop (15 x 5ms) past the window and succeed once the
-// handle closes.
-func TestRemoveLockFileRetriesSharingViolation(t *testing.T) {
-	path := filepath.Join(t.TempDir(), "lock")
-	if err := os.WriteFile(path, []byte("token"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	f, err := os.Open(path)
-	if err != nil {
-		t.Fatal(err)
-	}
-	go func() {
-		time.Sleep(10 * time.Millisecond)
-		_ = f.Close()
-	}()
-	if err := RemoveLockFile(path); err != nil {
-		t.Fatalf("RemoveLockFile should succeed once the contending handle closes: %v", err)
-	}
-	if _, err := os.Stat(path); !errors.Is(err, os.ErrNotExist) {
-		t.Fatalf("expected lock file to be removed: %v", err)
-	}
-}
-
-// TestRemoveLockFileSharingViolationExhausts verifies the retry loop is
-// bounded: with the contending handle held for the whole call, RemoveLockFile
-// surfaces the sharing violation instead of retrying forever.
-func TestRemoveLockFileSharingViolationExhausts(t *testing.T) {
-	path := filepath.Join(t.TempDir(), "lock")
-	if err := os.WriteFile(path, []byte("token"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	f, err := os.Open(path)
-	if err != nil {
-		t.Fatal(err)
-	}
-	defer f.Close()
-	if err := RemoveLockFile(path); !errors.Is(err, windows.ERROR_SHARING_VIOLATION) {
-		t.Fatalf("RemoveLockFile with a held handle = %v, want ERROR_SHARING_VIOLATION", err)
-	}
-}
@@ -1,82 +0,0 @@
-package lockutil
-
-import (
-	"errors"
-	"os"
-)
-
-// restoreLockFile is swappable so tests can force the fail-closed path of
-// ReclaimStaleLock, which requires both the fast restore and its no-replace
-// fallback (with its own copy fallback) to fail; that cannot be provoked
-// portably on a healthy filesystem.
-var restoreLockFile = restoreLiveLock
-
-// restoreLiveLock puts a lock that turned out to be live back at path after
-// ReclaimStaleLock moved it aside to inspect it. It first tries a fast,
-// replacing rename straight from reclaimed to path: a single syscall, which
-// keeps the window during which path does not exist (and so is open to a
-// fourth process's unrelated O_EXCL create landing on it) as short as
-// possible. RestoreLockFile's no-replace restore (with its slower copy
-// fallback on some failures) is a correctness-preserving fallback for when
-// the fast path itself fails (e.g. a cross-device sidelined name): it is a
-// much longer version of the identical race, but still detects rather than
-// silently clobbers a competing lock, which the fast path's replacing rename
-// cannot do. Neither path makes the race impossible, only unlikely; see
-// ReclaimStaleLock's doc comment.
-func restoreLiveLock(reclaimed, path string) error {
-	if err := os.Rename(reclaimed, path); err == nil {
-		return nil
-	}
-	return RestoreLockFile(reclaimed, path)
-}
-
-// ReclaimStaleLock atomically reclaims a suspected-stale lock file. It renames
-// lockPath aside to "<lockPath>.stale.<suffix>" (only one racer can win the
-// rename of a given file, so two racers can never both reclaim the same lock),
-// then consults isLive on the moved file; if the lock turns out to be live (a
-// holder reacquired it in the gap between the caller's stale check and the
-// rename) it is restored rather than stolen. The suffix must be unique per
-// acquirer attempt. Returns true only when a genuinely stale lock was removed,
-// so the caller knows it is safe to retry its exclusive create immediately; on
-// a lost race it returns false. A non-nil error means either the rename aside
-// failed for a reason that is not contention (so retrying cannot help and the
-// caller should fail fast instead of spinning to its deadline), or a live
-// holder's lock could not be restored (both restoreLiveLock's fast path and
-// its no-replace fallback failed), so lockPath may be missing; callers must
-// fail closed instead of re-acquiring. The sidelined file is removed on every
-// restore failure: once the restore has failed it has no protocol function
-// (release only consults the lock path), so keeping it would only leak files.
-//
-// The live-restore path has an inherent, unclosed race: between the rename
-// aside above and restoreLiveLock putting the lock back, lockPath does not
-// exist, so an unrelated caller's O_EXCL create can legitimately succeed
-// there. restoreLiveLock's fast path then silently overwrites that new
-// claimant's lock file, which does not corrupt release (it is
-// ownership-aware, so the new claimant's later release safely no-ops against
-// content it no longer owns) but does mean the new claimant can still run
-// its critical section concurrently with the original live holder. Making
-// this race actually impossible would need an OS-level advisory lock (flock
-// / LockFileEx) held for a holder's whole critical section, checked
-// non-destructively instead of by moving the file; restoreLiveLock only
-// shrinks the window to roughly one syscall, it does not close it.
-func ReclaimStaleLock(lockPath, suffix string, isLive func(reclaimedPath string) bool) (bool, error) {
-	reclaimed := lockPath + ".stale." + suffix
-	if err := os.Rename(lockPath, reclaimed); err != nil {
-		if errors.Is(err, os.ErrNotExist) || isReclaimContended(err) {
-			return false, nil // another racer already moved/removed it, or it vanished
-		}
-		return false, err
-	}
-	if isLive(reclaimed) {
-		// Put the live lock back instead of stealing it, and let the caller wait.
-		if rerr := restoreLockFile(reclaimed, lockPath); rerr != nil {
-			_ = RemoveLockFile(reclaimed)
-			if !errors.Is(rerr, os.ErrExist) {
-				return false, rerr
-			}
-		}
-		return false, nil
-	}
-	_ = RemoveLockFile(reclaimed)
-	return true, nil
-}
@@ -1,31 +0,0 @@
-//go:build !windows
-
-package lockutil
-
-import (
-	"os"
-	"path/filepath"
-	"testing"
-)
-
-// TestReclaimStaleLockPropagatesRenameFailure pins the fail-fast contract of
-// the rename aside: a failure that is not a lost race must reach the caller.
-// Mapping it to the benign lost-race result would leave acquirers spinning
-// until their deadline and reporting a timeout instead of the real cause. A
-// directory squatting on the sidelined name makes os.Rename fail with EISDIR,
-// which matches neither os.ErrNotExist nor a contention errno.
-func TestReclaimStaleLockPropagatesRenameFailure(t *testing.T) {
-	lockPath := filepath.Join(t.TempDir(), "lock")
-	if err := os.WriteFile(lockPath, []byte("stale-holder"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	if err := os.Mkdir(lockPath+".stale.tok", 0o755); err != nil {
-		t.Fatal(err)
-	}
-	if ok, err := ReclaimStaleLock(lockPath, "tok", func(string) bool { return false }); err == nil || ok {
-		t.Fatalf("a hard rename failure must surface an error (ok=%v err=%v)", ok, err)
-	}
-	if _, err := os.Stat(lockPath); err != nil {
-		t.Fatalf("the lock file must be left in place on a failed rename: %v", err)
-	}
-}
@@ -1,112 +0,0 @@
-package lockutil
-
-import (
-	"errors"
-	"os"
-	"path/filepath"
-	"testing"
-)
-
-func TestReclaimStaleLock(t *testing.T) {
-	lockPath := filepath.Join(t.TempDir(), "lock")
-	dead := func(string) bool { return false }
-	live := func(string) bool { return true }
-
-	// A lock the predicate reports dead is reclaimed and removed.
-	if err := os.WriteFile(lockPath, []byte("crashed-holder"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	if ok, err := ReclaimStaleLock(lockPath, "tok-a", dead); err != nil || !ok {
-		t.Fatalf("a dead lock should be reclaimed (ok=%v err=%v)", ok, err)
-	}
-	if _, err := os.Stat(lockPath); !errors.Is(err, os.ErrNotExist) {
-		t.Fatalf("reclaimed dead lock should be gone, stat err=%v", err)
-	}
-
-	// A LIVE lock (a holder reacquired in the gap) must be RESTORED intact.
-	if err := os.WriteFile(lockPath, []byte("live-holder"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	if ok, err := ReclaimStaleLock(lockPath, "tok-b", live); err != nil || ok {
-		t.Fatalf("a live lock must not be reclaimed (ok=%v err=%v)", ok, err)
-	}
-	if data, err := os.ReadFile(lockPath); err != nil || string(data) != "live-holder" {
-		t.Fatalf("live lock must be left intact, got %q err %v", data, err)
-	}
-
-	// A missing lock reports no reclaim (nothing to steal).
-	_ = os.Remove(lockPath)
-	if ok, err := ReclaimStaleLock(lockPath, "tok-c", live); err != nil || ok {
-		t.Fatalf("a missing lock should not report a reclaim (ok=%v err=%v)", ok, err)
-	}
-}
-
-// restoreLiveLock's fast path is a single replacing rename, chosen to
-// minimize (not eliminate) the window during which lockPath is absent and
-// open to an unrelated O_EXCL create; see ReclaimStaleLock's doc comment for
-// why that residual race exists. This test pins the resulting behavior: the
-// fast path overwrites a competing file at path rather than detecting it,
-// unlike RestoreLockFile's own no-replace contract.
-func TestRestoreLiveLockFastPathOverwritesCompetingFile(t *testing.T) {
-	dir := t.TempDir()
-	reclaimed := filepath.Join(dir, "lock.stale.tok")
-	path := filepath.Join(dir, "lock")
-
-	if err := os.WriteFile(reclaimed, []byte("original-holder"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	if err := os.WriteFile(path, []byte("new-claimant"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	if err := restoreLiveLock(reclaimed, path); err != nil {
-		t.Fatalf("restoreLiveLock failed: %v", err)
-	}
-	data, err := os.ReadFile(path)
-	if err != nil || string(data) != "original-holder" {
-		t.Fatalf("path = %q, err %v; want the original holder's content restored", data, err)
-	}
-	if _, err := os.Stat(reclaimed); !errors.Is(err, os.ErrNotExist) {
-		t.Fatalf("expected reclaimed to be consumed by the rename: %v", err)
-	}
-}
-
-func TestReclaimStaleLockFailsClosedOnRestoreError(t *testing.T) {
-	// When both the no-replace restore and its copy fallback fail (only
-	// provokable via the seam; a healthy filesystem cannot produce it), the
-	// caller must receive an error so it fails closed instead of re-acquiring a
-	// missing lock path, and the sidelined file must not leak.
-	restoreLockFile = func(reclaimed, path string) error { return errors.New("restore failed") }
-	defer func() { restoreLockFile = restoreLiveLock }()
-
-	lockPath := filepath.Join(t.TempDir(), "lock")
-	if err := os.WriteFile(lockPath, []byte("live-holder"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	ok, err := ReclaimStaleLock(lockPath, "tok", func(string) bool { return true })
-	if err == nil || ok {
-		t.Fatalf("a failed restore must surface an error (ok=%v err=%v)", ok, err)
-	}
-	if matches, _ := filepath.Glob(lockPath + ".stale.*"); len(matches) != 0 {
-		t.Fatalf("a failed restore must not leak sidelined files: %v", matches)
-	}
-}
-
-func TestReclaimStaleLockDropsSidelinedWhenNewHolderWins(t *testing.T) {
-	// An os.ErrExist restore failure means a new holder recreated the lock
-	// path; that is not an error for the caller, and the sidelined file is
-	// dropped rather than leaked.
-	restoreLockFile = func(reclaimed, path string) error { return os.ErrExist }
-	defer func() { restoreLockFile = restoreLiveLock }()
-
-	lockPath := filepath.Join(t.TempDir(), "lock")
-	if err := os.WriteFile(lockPath, []byte("live-holder"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	ok, err := ReclaimStaleLock(lockPath, "tok", func(string) bool { return true })
-	if err != nil || ok {
-		t.Fatalf("losing to a new holder is not an error (ok=%v err=%v)", ok, err)
-	}
-	if matches, _ := filepath.Glob(lockPath + ".stale.*"); len(matches) != 0 {
-		t.Fatalf("the sidelined file must be dropped when a new holder wins: %v", matches)
-	}
-}
@@ -1,50 +0,0 @@
-//go:build windows
-
-package lockutil
-
-import (
-	"os"
-	"path/filepath"
-	"testing"
-)
-
-// TestReclaimStaleLockTreatsSharingViolationAsLostRace pins the errno
-// classification the Windows acquire loops depend on: a rename aside that
-// fails because the lock file is concurrently open (Go opens files without
-// FILE_SHARE_DELETE, so the rename fails with ERROR_SHARING_VIOLATION or
-// ERROR_ACCESS_DENIED) is contention, not a hard failure, and must report a
-// benign lost race so the caller keeps waiting.
-func TestReclaimStaleLockTreatsSharingViolationAsLostRace(t *testing.T) {
-	lockPath := filepath.Join(t.TempDir(), "lock")
-	if err := os.WriteFile(lockPath, []byte("held"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	f, err := os.Open(lockPath)
-	if err != nil {
-		t.Fatal(err)
-	}
-	defer f.Close()
-	if ok, rerr := ReclaimStaleLock(lockPath, "tok", func(string) bool { return true }); rerr != nil || ok {
-		t.Fatalf("a sharing-violation rename must report a benign lost race (ok=%v err=%v)", ok, rerr)
-	}
-	if _, err := os.Stat(lockPath); err != nil {
-		t.Fatalf("the lock file must be left in place: %v", err)
-	}
-}
-
-// TestReclaimStaleLockPropagatesRenameFailure pins the fail-fast contract of
-// the rename aside on Windows: a failure that is not contention must reach
-// the caller instead of masquerading as a lost race. A quote is an invalid
-// filename character, so the sidelined name fails with ERROR_INVALID_NAME.
-func TestReclaimStaleLockPropagatesRenameFailure(t *testing.T) {
-	lockPath := filepath.Join(t.TempDir(), "lock")
-	if err := os.WriteFile(lockPath, []byte("stale-holder"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	if ok, err := ReclaimStaleLock(lockPath, `bad"name`, func(string) bool { return false }); err == nil || ok {
-		t.Fatalf("a hard rename failure must surface an error (ok=%v err=%v)", ok, err)
-	}
-	if _, err := os.Stat(lockPath); err != nil {
-		t.Fatalf("the lock file must be left in place on a failed rename: %v", err)
-	}
-}
@@ -35,7 +35,7 @@ type Server struct {
 	// credential lookup uses it to avoid reusing legacy user tokens by name.
 	ProjectConfigured bool
 	// UnconfiguredDefault is true when this server is one of Zero's built-in
-	// defaults (e.g. keyless Firecrawl) that the user never touched in their
+	// defaults (e.g. keyless Exa) that the user never touched in their
 	// config — no credentials, no overrides. Callers use it to avoid warning
 	// loudly when a server nobody configured fails to connect.
 	UnconfiguredDefault bool
@@ -1,6 +1,8 @@
 package mcp

 import (
+	"os"
+	"path/filepath"
 	"strings"
 	"testing"

@@ -90,7 +92,7 @@ func TestNormalizeConfigValidatesTransportBoundaries(t *testing.T) {

 func TestNormalizeConfigFlagsUnconfiguredDefault(t *testing.T) {
 	cfg := config.MCPConfig{Servers: map[string]config.MCPServerConfig{
-		"firecrawl": config.DefaultMCPServers()["firecrawl"],
+		"exa": config.DefaultMCPServers()["exa"],
 		"web": {
 			Type: "http",
 			URL:  "https://example.com/mcp",
@@ -107,8 +109,8 @@ func TestNormalizeConfigFlagsUnconfiguredDefault(t *testing.T) {
 		byName[server.Name] = server
 	}

-	if !byName["firecrawl"].UnconfiguredDefault {
-		t.Fatal("an untouched firecrawl default should be flagged UnconfiguredDefault")
+	if !byName["exa"].UnconfiguredDefault {
+		t.Fatal("an untouched exa default should be flagged UnconfiguredDefault")
 	}
 	if byName["web"].UnconfiguredDefault {
 		t.Fatal("a server the user configured must not be flagged UnconfiguredDefault")
@@ -240,3 +242,116 @@ func TestCopyStringMapTrimsKeysAndPreservesValues(t *testing.T) {
 		t.Fatalf("copied[TOKEN] = %q, want value preserved verbatim", copied["TOKEN"])
 	}
 }
+
+// Startup behavior for the firecrawl -> exa default migration: a user who
+// disabled the retired default must end up with no Exa server to connect to,
+// not merely a disabled entry in the resolved config.
+func TestNormalizeConfigSkipsExaAfterLegacyFirecrawlDisable(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "config.json")
+	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"firecrawl":{"disabled":true}}}}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	cfg, err := config.ResolveMCP(config.ResolveOptions{UserConfigPath: path})
+	if err != nil {
+		t.Fatalf("ResolveMCP: %v", err)
+	}
+	servers, err := NormalizeConfig(cfg)
+	if err != nil {
+		t.Fatalf("NormalizeConfig: %v", err)
+	}
+	for _, server := range servers {
+		if server.Name == "exa" {
+			t.Fatalf("exa must not be started after the user disabled the default it replaced: %#v", server)
+		}
+	}
+}
+
+// The same path with no legacy disable still starts Exa, so the migration
+// cannot quietly switch off the default for everyone else.
+func TestNormalizeConfigStartsExaWithoutLegacyDisable(t *testing.T) {
+	cfg, err := config.ResolveMCP(config.ResolveOptions{})
+	if err != nil {
+		t.Fatalf("ResolveMCP: %v", err)
+	}
+	servers, err := NormalizeConfig(cfg)
+	if err != nil {
+		t.Fatalf("NormalizeConfig: %v", err)
+	}
+	for _, server := range servers {
+		if server.Name == "exa" {
+			if !server.UnconfiguredDefault {
+				t.Fatalf("an untouched exa default should be flagged unconfigured: %#v", server)
+			}
+			return
+		}
+	}
+	t.Fatal("expected the exa default to be started out of the box")
+}
+
+// The failure path CodeRabbit flagged: a firecrawl entry that named only a
+// header relied on the retired default for its transport. Resolving it must
+// still produce a complete server — an incomplete one fails NormalizeConfig,
+// which takes down every other server's startup with it, not just this one.
+func TestNormalizeConfigResolvesPartialRetiredDefaultEntry(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "config.json")
+	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"firecrawl":{"headers":{"Authorization":"Bearer k"}}}}}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	cfg, err := config.ResolveMCP(config.ResolveOptions{UserConfigPath: path})
+	if err != nil {
+		t.Fatalf("ResolveMCP: %v", err)
+	}
+	servers, err := NormalizeConfig(cfg)
+	if err != nil {
+		t.Fatalf("a header-only legacy entry must not break startup: %v", err)
+	}
+	var firecrawl *Server
+	var sawExa bool
+	for i := range servers {
+		switch servers[i].Name {
+		case "firecrawl":
+			firecrawl = &servers[i]
+		case "exa":
+			sawExa = true
+		}
+	}
+	if firecrawl == nil {
+		t.Fatalf("expected the customized firecrawl server to survive: %#v", servers)
+	}
+	if firecrawl.Type != ServerTypeHTTP || firecrawl.URL != "https://mcp.firecrawl.dev/v2/mcp" {
+		t.Fatalf("firecrawl lost the transport its entry relied on: %#v", *firecrawl)
+	}
+	if firecrawl.Headers["Authorization"] != "Bearer k" {
+		t.Fatalf("firecrawl lost the user's header: %#v", *firecrawl)
+	}
+	if !sawExa {
+		t.Fatal("the new exa default should still start alongside it")
+	}
+}
+
+// The mirror case: an entry that names its own stdio transport must not have
+// the retired http default grafted onto it, which would be rejected outright.
+func TestNormalizeConfigLeavesRetiredEntryWithOwnTransportAlone(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "config.json")
+	if err := os.WriteFile(path, []byte(`{"mcp":{"servers":{"firecrawl":{"command":"firecrawl-mcp"}}}}`), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	cfg, err := config.ResolveMCP(config.ResolveOptions{UserConfigPath: path})
+	if err != nil {
+		t.Fatalf("ResolveMCP: %v", err)
+	}
+	servers, err := NormalizeConfig(cfg)
+	if err != nil {
+		t.Fatalf("a self-hosted stdio entry must keep working: %v", err)
+	}
+	for _, server := range servers {
+		if server.Name != "firecrawl" {
+			continue
+		}
+		if server.Type != ServerTypeStdio || server.Command != "firecrawl-mcp" {
+			t.Fatalf("the user's own stdio transport was corrupted: %#v", server)
+		}
+		return
+	}
+	t.Fatalf("expected the self-hosted firecrawl server to survive: %#v", servers)
+}
@@ -176,9 +176,11 @@ func RegisterTools(ctx context.Context, registry *tools.Registry, cfg config.MCP
 			staged = append(staged, tool)
 		}
 	}
-	for _, tool := range staged {
-		registry.Register(tool)
+	registered := make([]tools.Tool, 0, len(staged))
+	for index := range staged {
+		registered = append(registered, staged[index])
 	}
+	registry.RegisterBatch(registered)
 	return runtime, nil
 }

@@ -70,6 +70,62 @@ func TestRegisterToolsAddsPromptGatedMCPTools(t *testing.T) {
 	}
 }

+func TestRegisterToolsPublishesServerToolsInOneGeneration(t *testing.T) {
+	registry := tools.NewRegistry()
+	before := registry.Snapshot().Generation
+	client := &fakeToolClient{listed: []RemoteTool{
+		{Name: "lookup", Description: "Lookup documentation"},
+		{Name: "search", Description: "Search documentation"},
+	}}
+	runtime, err := RegisterTools(context.Background(), registry, config.MCPConfig{Servers: map[string]config.MCPServerConfig{
+		"docs": {Type: "stdio", Command: "docs-mcp"},
+	}}, RegisterOptions{ClientFactory: func(context.Context, Server) (ToolClient, error) {
+		return client, nil
+	}})
+	if err != nil {
+		t.Fatalf("RegisterTools() error = %v", err)
+	}
+	defer runtime.Close()
+
+	after := registry.Snapshot()
+	if after.Generation != before+1 {
+		t.Fatalf("registry generation = %d, want %d", after.Generation, before+1)
+	}
+	for _, name := range []string{"mcp_docs_lookup", "mcp_docs_search"} {
+		if _, ok := registry.Get(name); !ok {
+			t.Fatalf("expected %s to be published in the batch", name)
+		}
+	}
+}
+
+func TestRegisterToolsPublishesNoneWhenServerToolValidationFails(t *testing.T) {
+	registry := tools.NewRegistry()
+	before := registry.Snapshot().Generation
+	client := &fakeToolClient{listed: []RemoteTool{
+		{Name: "lookup", Description: "Lookup documentation"},
+		{Name: "", Description: "Invalid nameless tool"},
+	}}
+	runtime, err := RegisterTools(context.Background(), registry, config.MCPConfig{Servers: map[string]config.MCPServerConfig{
+		"docs": {Type: "stdio", Command: "docs-mcp"},
+	}}, RegisterOptions{ClientFactory: func(context.Context, Server) (ToolClient, error) {
+		return client, nil
+	}})
+	if err != nil {
+		t.Fatalf("RegisterTools() error = %v", err)
+	}
+	defer runtime.Close()
+
+	if got := registry.Snapshot().Generation; got != before {
+		t.Fatalf("registry generation = %d, want unchanged %d", got, before)
+	}
+	if _, ok := registry.Get("mcp_docs_lookup"); ok {
+		t.Fatal("valid prefix of rejected server batch was published")
+	}
+	if skipped := runtime.Skipped(); len(skipped) != 1 || skipped[0].Name != "docs" || skipped[0].Err == nil {
+		t.Fatalf("Skipped() = %#v, want one validation failure for docs", skipped)
+	}
+}
+
 func TestRegisterToolsMarksPersistentlyApprovedToolsAllow(t *testing.T) {
 	store, err := NewPermissionStore(StoreOptions{
 		FilePath: filepath.Join(t.TempDir(), "permissions.json"),
@@ -153,16 +209,16 @@ func TestRegisterToolsSkipsUnreachableServerAndKeepsOthers(t *testing.T) {
 }

 func TestRegisterToolsFlagsUnconfiguredDefaultOnSkip(t *testing.T) {
-	// firecrawl is seeded by config.DefaultMCPServers with no credentials; when a
-	// user never configures it, a connect failure (e.g. the real HTTP 401 from
-	// issue #552) must be recorded as UnconfiguredDefault so callers can avoid
+	// Exa is seeded by config.DefaultMCPServers with no credentials; when a
+	// user never configures it, a connect failure must be recorded as
+	// UnconfiguredDefault so callers can avoid
 	// warning about a server the user never asked for. "custom" is configured by
 	// the user and must NOT be flagged even though it also fails to connect.
 	registry := tools.NewRegistry()

 	runtime, err := RegisterTools(context.Background(), registry, config.MCPConfig{Servers: map[string]config.MCPServerConfig{
-		"firecrawl": config.DefaultMCPServers()["firecrawl"],
-		"custom":    {Type: "stdio", Command: "custom-mcp"},
+		"exa":    config.DefaultMCPServers()["exa"],
+		"custom": {Type: "stdio", Command: "custom-mcp"},
 	}}, RegisterOptions{
 		ClientFactory: func(_ context.Context, server Server) (ToolClient, error) {
 			return nil, errors.New(server.Name + " connect failed")
@@ -177,12 +233,12 @@ func TestRegisterToolsFlagsUnconfiguredDefaultOnSkip(t *testing.T) {
 	for _, skipped := range runtime.Skipped() {
 		byName[skipped.Name] = skipped
 	}
-	firecrawl, ok := byName["firecrawl"]
+	exa, ok := byName["exa"]
 	if !ok {
-		t.Fatalf("Skipped() = %#v, want an entry for firecrawl", runtime.Skipped())
+		t.Fatalf("Skipped() = %#v, want an entry for exa", runtime.Skipped())
 	}
-	if !firecrawl.UnconfiguredDefault {
-		t.Fatalf("Skipped()[firecrawl] = %#v, want UnconfiguredDefault", firecrawl)
+	if !exa.UnconfiguredDefault {
+		t.Fatalf("Skipped()[exa] = %#v, want UnconfiguredDefault", exa)
 	}
 	custom, ok := byName["custom"]
 	if !ok {
@@ -231,6 +231,12 @@ func reasoningEffortsForModelName(name string) []ReasoningEffort {
 		// the gateway's translation concern — unknown fields are ignored, so the
 		// worst case is a silent no-op rather than a 400.
 		return []ReasoningEffort{ReasoningEffortLow, ReasoningEffortMedium, ReasoningEffortHigh}
+	case strings.Contains(n, "deepseek"):
+		// DeepSeek V4 (deepseek-v4-flash / deepseek-v4-pro) exposes thinking-mode
+		// effort control through the OpenAI-compatible reasoning_effort parameter.
+		// The API accepts low/high/max and maps medium/xhigh onto high, so only
+		// the three distinct tiers are advertised.
+		return []ReasoningEffort{ReasoningEffortLow, ReasoningEffortHigh, ReasoningEffortMax}
 	default:
 		return nil
 	}
@@ -20,6 +20,10 @@ func TestReasoningEffortsFallbackForGPT5AndOSeries(t *testing.T) {
 		{"hy3", []ReasoningEffort{ReasoningEffortLow, ReasoningEffortMedium, ReasoningEffortHigh}},
 		{"hunyuan-t1", []ReasoningEffort{ReasoningEffortLow, ReasoningEffortMedium, ReasoningEffortHigh}},
 		{"openai/o3-mini", []ReasoningEffort{ReasoningEffortLow, ReasoningEffortMedium, ReasoningEffortHigh}}, // github-style vendor/ id
+		{"deepseek-v4-flash", []ReasoningEffort{ReasoningEffortLow, ReasoningEffortHigh, ReasoningEffortMax}},
+		{"deepseek-v4-pro", []ReasoningEffort{ReasoningEffortLow, ReasoningEffortHigh, ReasoningEffortMax}},
+		{"deepseek-reasoner", []ReasoningEffort{ReasoningEffortLow, ReasoningEffortHigh, ReasoningEffortMax}},
+		{"deepseek-chat", []ReasoningEffort{ReasoningEffortLow, ReasoningEffortHigh, ReasoningEffortMax}},
 		{"gpt-4.1", nil}, // non-reasoning, registered: stays empty
 		{"gpt-4o-mini", nil},
 		{"ollama/llama3.1", nil},
@@ -5,24 +5,16 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
-	"sync/atomic"
 	"time"

 	"github.com/Gitlawb/zero/internal/lockutil"
 )

-const (
-	fileLockTimeout    = 5 * time.Second
-	fileLockStaleAfter = 30 * time.Second
-)
+const fileLockTimeout = 5 * time.Second

-var lockSeq atomic.Uint64
-
-// acquireFileLock takes a cross-process exclusive lock by creating lockPath with
-// O_EXCL. It retries with a short backoff until a timeout, breaking a lock whose
-// file is older than fileLockStaleAfter (so a crashed holder cannot deadlock the
-// store). Release is ownership-aware: it removes the lock only if it still holds
-// our token, so a stale-broken holder cannot delete a newer holder's lock.
+// acquireFileLock takes a cross-process advisory lock through a stable lock
+// file. It retries with a short backoff until a timeout. Kernel lock lifetime
+// provides crash recovery, so the path is never renamed or removed.
 func acquireFileLock(lockPath string, now func() time.Time) (func(), error) {
 	if now == nil {
 		now = time.Now
@@ -30,64 +22,15 @@ func acquireFileLock(lockPath string, now func() time.Time) (func(), error) {
 	if err := os.MkdirAll(filepath.Dir(lockPath), 0o700); err != nil {
 		return nil, err
 	}
-	token := fmt.Sprintf("%d-%d-%d", os.Getpid(), now().UnixNano(), lockSeq.Add(1))
 	deadline := now().Add(fileLockTimeout)
 	for {
-		f, err := os.OpenFile(lockPath, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0o600)
+		lock, err := lockutil.TryAcquireFileLock(lockPath)
 		if err == nil {
-			// A partial/failed write would leave a lock file without our token, so
-			// the releaser below could never delete it — stranding the lock for
-			// other processes. Fail closed: remove the file and surface the error.
-			if _, werr := f.WriteString(token); werr != nil {
-				_ = f.Close()
-				_ = lockutil.RemoveLockFile(lockPath)
-				return nil, fmt.Errorf("oauth: write token lock: %w", werr)
-			}
-			if cerr := f.Close(); cerr != nil {
-				_ = lockutil.RemoveLockFile(lockPath)
-				return nil, fmt.Errorf("oauth: close token lock: %w", cerr)
-			}
-			var released bool
-			return func() {
-				if released {
-					return
-				}
-				released = true
-				if data, rerr := os.ReadFile(lockPath); rerr == nil && string(data) == token {
-					_ = lockutil.RemoveLockFile(lockPath)
-				}
-			}, nil
+			return func() { _ = lock.Release() }, nil
 		}
-		// On Windows a concurrent holder's os.Remove leaves the lock file in a
-		// "delete pending" state, so an O_EXCL create races it with
-		// ERROR_ACCESS_DENIED (os.ErrPermission) rather than ErrExist. Treat that
-		// as contention and retry, exactly like ErrExist — otherwise the lock
-		// spuriously fails under concurrency on Windows.
-		if !errors.Is(err, os.ErrExist) && !errors.Is(err, os.ErrPermission) {
+		if !errors.Is(err, lockutil.ErrLockHeld) {
 			return nil, fmt.Errorf("oauth: acquire token lock: %w", err)
 		}
-		// Reclaim a stale lock left by a crashed holder — atomically (H3). A blind
-		// Remove lets two racers both reclaim + recreate and so both hold the lock;
-		// reclaimStaleLock renames the file aside (only one rename wins) and restores
-		// it if it turns out fresh, so a live lock is never deleted out from under it.
-		if info, statErr := os.Stat(lockPath); statErr == nil && time.Since(info.ModTime()) > fileLockStaleAfter {
-			cleared, rerr := lockutil.ReclaimStaleLock(lockPath, token, func(reclaimedPath string) bool {
-				info, err := os.Stat(reclaimedPath)
-				return err == nil && time.Since(info.ModTime()) <= fileLockStaleAfter
-			})
-			if rerr != nil {
-				// Reclaim hit a hard failure: the rename aside failed outright, or a
-				// live holder's lock could not be put back (the lock path may be
-				// missing, so re-acquiring would break mutual exclusion). Fail closed
-				// instead of spinning to the deadline.
-				return nil, fmt.Errorf("oauth: reclaim stale token lock: %w", rerr)
-			}
-			if cleared {
-				continue
-			}
-			// Lost the reclaim race (or it was actually fresh) — fall through to the
-			// bounded wait rather than hot-spinning on a reclaim that never wins.
-		}
 		if now().After(deadline) {
 			return nil, fmt.Errorf("oauth: timed out acquiring token lock %s", filepath.Base(lockPath))
 		}
@@ -104,7 +104,7 @@ func windowsTokenOwner(token windows.Token) (*windows.SID, error) {
 	}
 	owner := (*windowsTokenOwnerInfo)(unsafe.Pointer(&buffer[0])).owner
 	if owner == nil {
-		return nil, errors.New("Windows access token has no default owner")
+		return nil, errors.New("windows access token has no default owner")
 	}
 	return owner.Copy()
 }
@@ -191,6 +191,7 @@ type TurnBenchResult struct {
 type TurnBenchTotals struct {
 	InputTokens       int64 `json:"inputTokens"`
 	CachedInputTokens int64 `json:"cachedInputTokens"`
+	CacheWriteTokens  int64 `json:"cacheWriteTokens"`
 	OutputTokens      int64 `json:"outputTokens"`
 	ModelRequests     int64 `json:"modelRequests"`
 	ToolCalls         int64 `json:"toolCalls"`
@@ -479,6 +480,7 @@ func topLatencySources(perSpan map[string]SpanStats, top int) []LatencySource {
 func aggregateTotals(totals *TurnBenchTotals, tr *trace.TurnTrace) {
 	totals.InputTokens += tr.Counter(trace.CounterInputTokens)
 	totals.CachedInputTokens += tr.Counter(trace.CounterCachedInputTokens)
+	totals.CacheWriteTokens += tr.Counter(trace.CounterCacheWriteTokens)
 	totals.OutputTokens += tr.Counter(trace.CounterOutputTokens)
 	totals.ModelRequests += tr.Counter(trace.CounterModelRequests)
 	totals.ToolCalls += tr.Counter(trace.CounterToolCalls)
@@ -531,8 +533,9 @@ func FormatTurnBenchSummary(result TurnBenchResult) string {
 			lines = append(lines, fmt.Sprintf("  %-18s %10s  %5.1f%%", src.Span, FormatMetric(src.TotalMs, "ms"), src.Share*100))
 		}
 	}
-	lines = append(lines, fmt.Sprintf("totals: in=%d (cached %d) out=%d | requests=%d tools=%d retries=%d reconnects=%d compactions=%d",
-		result.Totals.InputTokens, result.Totals.CachedInputTokens, result.Totals.OutputTokens,
+	lines = append(lines, fmt.Sprintf("totals: in=%d (cache-read %d, cache-write %d, uncached %d) out=%d | requests=%d tools=%d retries=%d reconnects=%d compactions=%d",
+		result.Totals.InputTokens, result.Totals.CachedInputTokens, result.Totals.CacheWriteTokens,
+		uncachedInputTokens(result.Totals), result.Totals.OutputTokens,
 		result.Totals.ModelRequests, result.Totals.ToolCalls, result.Totals.Retries,
 		result.Totals.Reconnects, result.Totals.Compactions))
 	for _, class := range sortedClasses(result.PerClass) {
@@ -545,6 +548,23 @@ func FormatTurnBenchSummary(result TurnBenchResult) string {
 	return strings.Join(lines, "\n")
 }

+func uncachedInputTokens(totals TurnBenchTotals) int64 {
+	remaining := totals.InputTokens
+	if remaining <= 0 {
+		return 0
+	}
+	for _, cached := range []int64{totals.CachedInputTokens, totals.CacheWriteTokens} {
+		if cached <= 0 {
+			continue
+		}
+		if cached >= remaining {
+			return 0
+		}
+		remaining -= cached
+	}
+	return remaining
+}
+
 // classTier returns the oracle tier label a class was classified into, so the
 // per-class roll-up states explicitly which oracle (if any) its "passed" count
 // is measured against.
@@ -74,6 +74,7 @@ func TestRunTurnBenchAggregation(t *testing.T) {
 		"t3": cannedTrace(150, 20, 1500),
 		"t4": cannedTrace(300, 10, 1000),
 	}
+	canned["t1"].Counters = append(canned["t1"].Counters, trace.Counter{Name: trace.CounterCacheWriteTokens, Value: 125})
 	cfg := TurnBenchConfig{
 		Model:      "fake-model",
 		Iterations: 1,
@@ -155,6 +156,9 @@ func TestRunTurnBenchAggregation(t *testing.T) {
 	if result.Totals.InputTokens != 5500 {
 		t.Fatalf("inputTokens = %d, want 5500", result.Totals.InputTokens)
 	}
+	if result.Totals.CacheWriteTokens != 125 {
+		t.Fatalf("cacheWriteTokens = %d, want 125", result.Totals.CacheWriteTokens)
+	}
 	if result.Totals.OutputTokens != 2750 {
 		t.Fatalf("outputTokens = %d, want 2750", result.Totals.OutputTokens)
 	}
@@ -334,6 +338,35 @@ func TestFormatTurnBenchSummaryNamesTopSources(t *testing.T) {
 	}
 }

+func TestUncachedInputTokensClampsInconsistentTotals(t *testing.T) {
+	tests := []struct {
+		name   string
+		totals TurnBenchTotals
+		want   int64
+	}{
+		{name: "normal", totals: TurnBenchTotals{InputTokens: 100, CachedInputTokens: 30, CacheWriteTokens: 20}, want: 50},
+		{name: "cached exceeds input", totals: TurnBenchTotals{InputTokens: 100, CachedInputTokens: 120}, want: 0},
+		{name: "write exceeds remainder", totals: TurnBenchTotals{InputTokens: 100, CachedInputTokens: 20, CacheWriteTokens: 90}, want: 0},
+		{name: "overflowing inconsistent counters", totals: TurnBenchTotals{CachedInputTokens: 1<<63 - 1, CacheWriteTokens: 1<<63 - 1}, want: 0},
+		{name: "overflowing counters with input", totals: TurnBenchTotals{InputTokens: 100, CachedInputTokens: 1<<63 - 1, CacheWriteTokens: 1<<63 - 1}, want: 0},
+		{name: "negative cache counters ignored", totals: TurnBenchTotals{InputTokens: 100, CachedInputTokens: -20, CacheWriteTokens: -10}, want: 100},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			if got := uncachedInputTokens(test.totals); got != test.want {
+				t.Fatalf("uncachedInputTokens(%+v) = %d, want %d", test.totals, got, test.want)
+			}
+		})
+	}
+	summary := FormatTurnBenchSummary(TurnBenchResult{Totals: TurnBenchTotals{
+		CachedInputTokens: 1<<63 - 1,
+		CacheWriteTokens:  1<<63 - 1,
+	}})
+	if !strings.Contains(summary, "uncached 0") {
+		t.Fatalf("summary did not clamp inconsistent cache totals:\n%s", summary)
+	}
+}
+
 func TestLoadBaselineManifest(t *testing.T) {
 	path := filepath.Join("manifests", "baseline.json")
 	set, err := LoadTaskSet(path)
@@ -184,6 +184,10 @@ func parseOpenAIStyleModelList(body []byte) ([]remoteModel, error) {

 func ModelsDevProviderID(provider providercatalog.Descriptor) string {
 	switch strings.TrimSpace(provider.ID) {
+	case "chatgpt":
+		// ChatGPT authenticates against the Codex backend, while its public
+		// model metadata is published under the OpenAI provider on models.dev.
+		return "openai"
 	case "dashscope":
 		return "alibaba"
 	case "github":
@@ -241,6 +241,7 @@ func TestPublicLiveCatalog(t *testing.T) {

 func TestModelsDevProviderIDMapsZeroAliases(t *testing.T) {
 	tests := map[string]string{
+		"chatgpt":      "openai",
 		"github":       "github-models",
 		"moonshot":     "moonshotai",
 		"nvidia-nim":   "nvidia",
@@ -539,7 +539,8 @@ func mergeLiveModels(provider providercatalog.Descriptor, liveModels []Model, ca
 	hasCatalog := len(byID) > 0
 	// Aggregators publish the live list as the source of truth. Keep live-only
 	// ids even when a remote catalog also loaded, instead of intersecting.
-	preferLive := providermodelcatalog.PublicLiveCatalog(provider.ID) ||
+	preferLive := provider.Local ||
+		providermodelcatalog.PublicLiveCatalog(provider.ID) ||
 		providercatalog.NormalizeID(provider.ID) == "chatgpt"
 	result := make([]Model, 0, len(liveModels))
 	for _, live := range liveModels {
@@ -139,6 +139,68 @@ func TestMergeChatGPTModelsKeepsLiveOnlyEntries(t *testing.T) {
 	}
 }

+func TestDiscoverCatalogChatGPTMergesOpenAIModelsDevMetadata(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch r.URL.Path {
+		case "/api.json":
+			_, _ = w.Write([]byte(`{
+				"openai": {"models": {
+					"gpt-5.6-sol": {
+						"id": "gpt-5.6-sol",
+						"name": "GPT-5.6 Sol",
+						"description": "Frontier coding model",
+						"tool_call": true,
+						"reasoning": true,
+						"reasoning_efforts": ["low", "high", "max"],
+						"limit": {"context": 1050000},
+						"modalities": {"input": ["text", "image", "pdf"], "output": ["text"]}
+					}
+				}}
+			}`))
+		case "/backend-api/codex/models":
+			_, _ = w.Write([]byte(`{"data":[{"id":"gpt-5.6-sol"}]}`))
+		default:
+			t.Errorf("unexpected request path %q", r.URL.Path)
+			http.NotFound(w, r)
+			return
+		}
+	}))
+	defer server.Close()
+
+	provider, ok := providercatalog.Get("chatgpt")
+	if !ok {
+		t.Fatal("ChatGPT provider missing from catalog")
+	}
+	models, err := DiscoverCatalog(context.Background(), provider, config.ProviderProfile{
+		Name:         "chatgpt",
+		CatalogID:    "chatgpt",
+		ProviderKind: config.ProviderKindOpenAICompatible,
+		BaseURL:      server.URL + "/backend-api/codex",
+	}, Options{
+		HTTPClient:   server.Client(),
+		ModelsDevURL: server.URL + "/api.json",
+		OAuthResolver: func(context.Context, bool) (string, string, bool, error) {
+			return "Authorization", "Bearer test", true, nil
+		},
+	})
+	if err != nil {
+		t.Fatalf("DiscoverCatalog returned error: %v", err)
+	}
+	if len(models) != 1 {
+		t.Fatalf("models = %#v, want one ChatGPT live model", models)
+	}
+	model := models[0]
+	if model.ID != "gpt-5.6-sol" || model.ContextWindow != 1050000 || !model.ToolCall || !model.Reasoning {
+		t.Fatalf("merged ChatGPT model = %#v, want models.dev metadata", model)
+	}
+	if got := strings.Join(model.InputModalities, ","); got != "text,image,pdf" {
+		t.Fatalf("input modalities = %q, want text,image,pdf", got)
+	}
+	if got := strings.Join(model.ReasoningEfforts, ","); got != "low,high,max" {
+		t.Fatalf("reasoning efforts = %q, want low,high,max", got)
+	}
+}
+
 func TestMergeLiveModelsUsesLiveDefaultsAndReasoningCapability(t *testing.T) {
 	models := mergeLiveModels(
 		providercatalog.Descriptor{ID: "chatgpt"},
@@ -164,6 +226,29 @@ func TestMergeLiveModelsUsesLiveDefaultsAndReasoningCapability(t *testing.T) {
 	}
 }

+func TestMergeLocalModelsKeepsLiveOnlyEntries(t *testing.T) {
+	models := mergeLiveModels(
+		providercatalog.Descriptor{ID: "lmstudio", Local: true},
+		[]Model{
+			{ID: "qwen3-coder-30b", ContextWindow: 32768},
+			{ID: "text-embedding-local"},
+			{ID: "qwen2.5-coder-32b-instruct", Description: "live description"},
+		},
+		[]Model{{ID: "qwen2.5-coder-32b-instruct", Description: "catalog description", ToolCall: true}},
+	)
+
+	if got, want := strings.Join(modelIDs(models), ","), "qwen3-coder-30b,qwen2.5-coder-32b-instruct"; got != want {
+		t.Fatalf("models = %q, want %q", got, want)
+	}
+	for _, model := range models {
+		if model.ID == "qwen2.5-coder-32b-instruct" {
+			if model.Description != "catalog description" || !model.ToolCall {
+				t.Fatalf("merged catalog metadata = %#v", model)
+			}
+		}
+	}
+}
+
 func TestDiscoverCatalogOpenGatewayUsesLiveListWithoutKey(t *testing.T) {
 	// Catalog and live endpoints return distinct payloads so the merge must keep
 	// live-only ids that are absent from the remote catalog response.
@@ -0,0 +1,108 @@
+package providers
+
+import (
+	"context"
+	"os"
+	"strings"
+
+	"github.com/Gitlawb/zero/internal/config"
+	"github.com/Gitlawb/zero/internal/zeroruntime"
+)
+
+// Compaction summarization model selection.
+//
+// Compaction summaries used to run on the session's main model — near a 200k
+// window one summarization is a ~100k-token input call at full price, the
+// single most expensive recurring event in a long run. A cheap model handles
+// the "dense factual summary" task fine, so summarization is routed to one
+// whenever the target is knowable.
+//
+// Resolution order: ZERO_COMPACTION_MODEL env > preferences.compactionModel
+// config > a curated per-kind default (OFFICIAL endpoints only) > "" (use the
+// main model). The literal value "main" at any level forces the main model.
+// A wrong choice is never fatal: the agent falls back to the main provider on
+// the first summarizer failure for the rest of the run.
+
+// CompactionModelEnv overrides the compaction summarization model.
+const CompactionModelEnv = "ZERO_COMPACTION_MODEL"
+
+// compactionMainSentinel disables the dedicated summarizer explicitly.
+const compactionMainSentinel = "main"
+
+// Curated cheap summarizer defaults, applied only for provider kinds whose
+// model catalog is guaranteed (official endpoints). Custom / *-compatible
+// endpoints get NO default — their catalogs are unknowable, and a guaranteed
+// failed call per run is worse than main-model prices.
+const (
+	defaultAnthropicCompactionModel = "claude-haiku-4-5-20251001"
+	defaultGoogleCompactionModel    = "gemini-2.5-flash-lite"
+	defaultOpenAICompactionModel    = "gpt-4.1-mini"
+)
+
+// CompactionModelID returns the model that compaction summarization calls
+// should use for the given profile, or "" to use the session's main model.
+// preference is the resolved config value (preferences.compactionModel).
+func CompactionModelID(profile config.ProviderProfile, preference string) string {
+	value := strings.TrimSpace(os.Getenv(CompactionModelEnv))
+	if value == "" {
+		value = strings.TrimSpace(preference)
+	}
+	if value != "" {
+		if strings.EqualFold(value, compactionMainSentinel) {
+			return ""
+		}
+		return value
+	}
+	return defaultCompactionModel(profile)
+}
+
+func defaultCompactionModel(profile config.ProviderProfile) string {
+	metadata, err := ResolveRuntimeMetadata(profile, Options{})
+	if err != nil {
+		return ""
+	}
+	var candidate string
+	switch metadata.ProviderKind {
+	case config.ProviderKindAnthropic:
+		candidate = defaultAnthropicCompactionModel
+	case config.ProviderKindGoogle:
+		candidate = defaultGoogleCompactionModel
+	case config.ProviderKindOpenAI:
+		candidate = defaultOpenAICompactionModel
+	default:
+		return ""
+	}
+	// Session already runs on the cheap model: a dedicated summarizer buys
+	// nothing and would only add a second provider instance.
+	if strings.EqualFold(strings.TrimSpace(metadata.APIModel), candidate) {
+		return ""
+	}
+	return candidate
+}
+
+// CompactionSummarizerFactory returns the lazy constructor the agent loop
+// calls for its dedicated compaction summarizer (agent.Options.Summarizer).
+// The compactor passes the main model in force at that moment — on the first
+// paid compaction and again after a mid-run model switch — so the choice
+// tracks escalations: a run that starts on the cheap model gets no dedicated
+// summarizer, and gains one once it escalates to a pricier main model.
+// Returning (nil, nil) means "summarize on the main provider". The factory
+// itself is nil only when no provider builder exists. Shared by the exec and
+// TUI front ends so the selection rules cannot drift between them.
+func CompactionSummarizerFactory(base config.ProviderProfile, preference string, newProvider func(config.ProviderProfile) (zeroruntime.Provider, error)) func(context.Context, string) (zeroruntime.Provider, error) {
+	if newProvider == nil {
+		return nil
+	}
+	return func(_ context.Context, mainModelID string) (zeroruntime.Provider, error) {
+		profile := base
+		if strings.TrimSpace(mainModelID) != "" {
+			profile.Model = mainModelID
+		}
+		modelID := CompactionModelID(profile, preference)
+		if modelID == "" {
+			return nil, nil
+		}
+		profile.Model = modelID
+		return newProvider(profile)
+	}
+}
@@ -0,0 +1,113 @@
+package providers
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/Gitlawb/zero/internal/config"
+	"github.com/Gitlawb/zero/internal/zeroruntime"
+)
+
+func TestCompactionModelIDResolutionOrder(t *testing.T) {
+	anthropic := config.ProviderProfile{
+		Name:         "anthropic",
+		ProviderKind: config.ProviderKindAnthropic,
+		Model:        "claude-sonnet-4.5",
+	}
+
+	t.Setenv(CompactionModelEnv, "my-env-model")
+	if got := CompactionModelID(anthropic, "my-config-model"); got != "my-env-model" {
+		t.Fatalf("env must win, got %q", got)
+	}
+
+	t.Setenv(CompactionModelEnv, "main")
+	if got := CompactionModelID(anthropic, "my-config-model"); got != "" {
+		t.Fatalf("env 'main' must force the main model, got %q", got)
+	}
+
+	t.Setenv(CompactionModelEnv, "")
+	if got := CompactionModelID(anthropic, "my-config-model"); got != "my-config-model" {
+		t.Fatalf("config preference must apply when env unset, got %q", got)
+	}
+	if got := CompactionModelID(anthropic, "main"); got != "" {
+		t.Fatalf("config 'main' must force the main model, got %q", got)
+	}
+}
+
+func TestCompactionModelIDCuratedDefaults(t *testing.T) {
+	t.Setenv(CompactionModelEnv, "")
+
+	anthropic := config.ProviderProfile{Name: "anthropic", ProviderKind: config.ProviderKindAnthropic, Model: "claude-sonnet-4.5"}
+	if got := CompactionModelID(anthropic, ""); got != defaultAnthropicCompactionModel {
+		t.Fatalf("anthropic default = %q, want %q", got, defaultAnthropicCompactionModel)
+	}
+
+	google := config.ProviderProfile{Name: "google", ProviderKind: config.ProviderKindGoogle, Model: "gemini-2.5-pro"}
+	if got := CompactionModelID(google, ""); got != defaultGoogleCompactionModel {
+		t.Fatalf("google default = %q, want %q", got, defaultGoogleCompactionModel)
+	}
+
+	openai := config.ProviderProfile{Name: "openai", ProviderKind: config.ProviderKindOpenAI, Model: "gpt-4.1"}
+	if got := CompactionModelID(openai, ""); got != defaultOpenAICompactionModel {
+		t.Fatalf("openai default = %q, want %q", got, defaultOpenAICompactionModel)
+	}
+
+	// Custom/compatible endpoints: catalog unknowable, no default.
+	compatible := config.ProviderProfile{
+		Name:         "opengateway",
+		ProviderKind: config.ProviderKindOpenAICompatible,
+		BaseURL:      "https://opengateway.gitlawb.com/v1",
+		Model:        "some-model",
+	}
+	if got := CompactionModelID(compatible, ""); got != "" {
+		t.Fatalf("openai-compatible must have no default, got %q", got)
+	}
+}
+
+func TestCompactionModelIDSkipsWhenMainIsAlreadyCheap(t *testing.T) {
+	t.Setenv(CompactionModelEnv, "")
+	haiku := config.ProviderProfile{
+		Name:         "anthropic",
+		ProviderKind: config.ProviderKindAnthropic,
+		Model:        defaultAnthropicCompactionModel,
+	}
+	if got := CompactionModelID(haiku, ""); got != "" {
+		t.Fatalf("already-cheap session must not get a dedicated summarizer, got %q", got)
+	}
+}
+
+func TestCompactionSummarizerFactoryTracksMainModel(t *testing.T) {
+	t.Setenv(CompactionModelEnv, "")
+	base := config.ProviderProfile{Name: "anthropic", ProviderKind: config.ProviderKindAnthropic, Model: defaultAnthropicCompactionModel}
+	var built []string
+	newProvider := func(profile config.ProviderProfile) (zeroruntime.Provider, error) {
+		built = append(built, profile.Model)
+		return nil, errors.New("not needed")
+	}
+	factory := CompactionSummarizerFactory(base, "", newProvider)
+	if factory == nil {
+		t.Fatal("factory must exist when a provider builder exists")
+	}
+	// Main model is the cheap default: no dedicated summarizer, nothing built.
+	if provider, err := factory(context.Background(), defaultAnthropicCompactionModel); provider != nil || err != nil || len(built) != 0 {
+		t.Fatalf("cheap main model must yield (nil, nil) without building, got %v %v built=%v", provider, err, built)
+	}
+	// After escalating to an expensive model the cheap default is built.
+	if _, err := factory(context.Background(), "claude-sonnet-4-5"); err == nil || len(built) != 1 || built[0] != defaultAnthropicCompactionModel {
+		t.Fatalf("escalated main model must build the cheap summarizer, built=%v err=%v", built, err)
+	}
+	// An empty main model falls back to the base profile's model — the cheap
+	// default here, so again nothing is built.
+	built = nil
+	if provider, err := factory(context.Background(), ""); provider != nil || err != nil || len(built) != 0 {
+		t.Fatalf("empty main model must use the base profile, got %v %v built=%v", provider, err, built)
+	}
+	// The explicit "main" preference disables the dedicated summarizer.
+	if provider, err := CompactionSummarizerFactory(base, "main", newProvider)(context.Background(), "claude-sonnet-4-5"); provider != nil || err != nil {
+		t.Fatalf("preference main must disable the summarizer, got %v %v", provider, err)
+	}
+	if CompactionSummarizerFactory(base, "", nil) != nil {
+		t.Fatal("no provider builder means no factory")
+	}
+}
@@ -62,6 +62,7 @@ const (
 	responsesEventReasoningDelta    = "response.reasoning_summary_text.delta"
 	responsesEventOutputTextDone    = "response.output_text.done"
 	responsesEventFunctionArgsDelta = "response.function_call_arguments.delta"
+	responsesEventCustomInputDelta  = "response.custom_tool_call_input.delta"
 	responsesEventContentPartDone   = "response.content_part.done"
 	responsesEventOutputItemDone    = "response.output_item.done"
 	responsesEventCompleted         = "response.completed"
@@ -70,17 +71,37 @@ const (
 	responsesEventIncomplete        = "response.incomplete"
 )

+const applyPatchLarkGrammar = `start: begin_patch hunk+ end_patch
+begin_patch: "*** Begin Patch" LF
+end_patch: "*** End Patch" LF?
+hunk: add_hunk | delete_hunk | update_hunk
+add_hunk: "*** Add File: " filename LF add_line+
+delete_hunk: "*** Delete File: " filename LF
+update_hunk: "*** Update File: " filename LF change_move? change?
+filename: /(.+)/
+add_line: "+" /(.*)/ LF -> line
+change_move: "*** Move to: " filename LF
+change: (change_context | change_line)+ eof_line?
+change_context: ("@@" | "@@ " /(.+)/) LF
+change_line: ("+" | "-" | " ") /(.*)/ LF
+eof_line: "*** End of File" LF
+%import common.LF`
+
 // responsesRequest is the wire shape POSTed to {baseURL}/responses.
 type responsesRequest struct {
-	Model           string              `json:"model"`
-	Instructions    string              `json:"instructions"`
-	Input           []inputItem         `json:"input"`
-	Stream          bool                `json:"stream"`
-	Store           bool                `json:"store"`
-	MaxOutputTokens int                 `json:"max_output_tokens,omitempty"`
-	Tools           []responsesTool     `json:"tools,omitempty"`
-	Reasoning       *responsesReasoning `json:"reasoning,omitempty"`
-	ServiceTier     string              `json:"service_tier,omitempty"`
+	Type               string              `json:"type,omitempty"`
+	Model              string              `json:"model"`
+	Instructions       string              `json:"instructions"`
+	PreviousResponseID string              `json:"previous_response_id,omitempty"`
+	Input              []inputItem         `json:"input"`
+	Stream             bool                `json:"stream"`
+	Store              bool                `json:"store"`
+	ParallelToolCalls  bool                `json:"parallel_tool_calls"`
+	MaxOutputTokens    int                 `json:"max_output_tokens,omitempty"`
+	Tools              []responsesTool     `json:"tools,omitempty"`
+	Reasoning          *responsesReasoning `json:"reasoning,omitempty"`
+	ServiceTier        string              `json:"service_tier,omitempty"`
+	PromptCacheKey     string              `json:"prompt_cache_key,omitempty"`
 }

 // responsesReasoning carries the reasoning controls for the Responses API. The
@@ -105,6 +126,7 @@ type inputItem struct {
 	CallID    string `json:"call_id,omitempty"`
 	Name      string `json:"name,omitempty"`
 	Arguments string `json:"arguments,omitempty"`
+	Input     string `json:"input,omitempty"`
 	// function_call_output fields
 	Output any `json:"output,omitempty"`
 }
@@ -118,10 +140,11 @@ type contentItem struct {
 }

 type responsesTool struct {
-	Type        string         `json:"type"`
-	Name        string         `json:"name"`
-	Description string         `json:"description,omitempty"`
-	Parameters  map[string]any `json:"parameters,omitempty"`
+	Type        string                            `json:"type"`
+	Name        string                            `json:"name"`
+	Description string                            `json:"description,omitempty"`
+	Parameters  map[string]any                    `json:"parameters,omitempty"`
+	Format      *zeroruntime.ToolDefinitionFormat `json:"format,omitempty"`
 }

 // responsesEvent is the decoded form of one Responses SSE data payload.
@@ -132,6 +155,7 @@ type responsesEvent struct {
 	Delta string `json:"delta,omitempty"`
 	// item payloads (response.output_item.added / done)
 	ItemID string `json:"item_id,omitempty"`
+	CallID string `json:"call_id,omitempty"`
 	// OutputIndex is a *int so a real 0 (the first output) is distinguishable from
 	// "absent" — a plain int defaulting to 0 dropped a no-item_id call's args (M1).
 	OutputIndex *int         `json:"output_index,omitempty"`
@@ -150,6 +174,7 @@ type itemPayload struct {
 	CallID    string `json:"call_id,omitempty"`
 	Name      string `json:"name,omitempty"`
 	Arguments string `json:"arguments,omitempty"`
+	Input     string `json:"input,omitempty"`
 	Status    string `json:"status,omitempty"`
 }

@@ -173,7 +198,8 @@ type outputDetails struct {
 }

 type inputDetails struct {
-	CachedTokens int `json:"cached_tokens"`
+	CachedTokens     int `json:"cached_tokens"`
+	CacheWriteTokens int `json:"cache_write_tokens"`
 }

 type errorPayload struct {
@@ -187,8 +213,10 @@ type errorPayload struct {
 // response.output_item.done.
 type toolCallBuilder struct {
 	ID        string
+	CallID    string
 	Name      string
 	Arguments strings.Builder
+	Freeform  bool
 	started   bool
 	ended     bool
 }
@@ -197,15 +225,57 @@ type toolCallBuilder struct {
 // event has been emitted. It is the Responses-API equivalent of the
 // chat-completions toolState in provider.go.
 type responsesState struct {
-	toolCalls map[string]*toolCallBuilder
-	usage     *usagePayload
-	done      bool
+	toolCalls  map[string]*toolCallBuilder
+	toolOrder  []string
+	text       strings.Builder
+	responseID string
+	usage      *usagePayload
+	emitted    bool
+	done       bool
 }

 func newResponsesState() *responsesState {
 	return &responsesState{toolCalls: map[string]*toolCallBuilder{}}
 }

+func (state *responsesState) outputInputItems() []inputItem {
+	items := make([]inputItem, 0, len(state.toolOrder)+1)
+	if state.text.Len() > 0 {
+		items = append(items, inputItem{
+			Type:    "message",
+			Role:    "assistant",
+			Content: []contentItem{{Type: "output_text", Text: state.text.String()}},
+		})
+	}
+	for _, key := range state.toolOrder {
+		builder := state.toolCalls[key]
+		if builder == nil || builder.ID == "" || builder.Name == "" {
+			continue
+		}
+		callID := builder.CallID
+		if callID == "" {
+			callID = builder.ID
+		}
+		itemType := "function_call"
+		if builder.Freeform {
+			itemType = "custom_tool_call"
+		}
+		item := inputItem{
+			Type:   itemType,
+			ID:     builder.ID,
+			CallID: callID,
+			Name:   builder.Name,
+		}
+		if builder.Freeform {
+			item.Input = builder.Arguments.String()
+		} else {
+			item.Arguments = builder.Arguments.String()
+		}
+		items = append(items, item)
+	}
+	return items
+}
+
 // buildResponsesRequest converts a runtime CompletionRequest into the
 // Responses API wire format. System messages fold into a top-level
 // `instructions` field; everything else (user/assistant turns, tool
@@ -215,11 +285,14 @@ func (p *CodexProvider) buildResponsesRequest(request zeroruntime.CompletionRequ
 		return nil, errors.New("codex provider: model is required")
 	}
 	req := &responsesRequest{
-		Model:           p.inner.model,
-		Stream:          true,
-		MaxOutputTokens: p.inner.maxTokens,
+		Model:             p.inner.model,
+		Stream:            true,
+		ParallelToolCalls: true,
+		MaxOutputTokens:   p.inner.maxTokens,
+		PromptCacheKey:    request.PromptCacheKey,
 	}
 	instructions := []string{}
+	customCallIDs := map[string]string{}
 	for _, msg := range request.Messages {
 		switch msg.Role {
 		case zeroruntime.MessageRoleSystem:
@@ -234,13 +307,31 @@ func (p *CodexProvider) buildResponsesRequest(request zeroruntime.CompletionRequ
 				return nil, err
 			}
 			req.Input = append(req.Input, items...)
+			for _, call := range msg.ToolCalls {
+				if call.Freeform && call.ID != "" {
+					callID := call.ProviderCallID
+					if callID == "" {
+						callID = call.ID
+					}
+					customCallIDs[call.ID] = callID
+				}
+			}
 		case zeroruntime.MessageRoleTool:
 			if msg.ToolCallID == "" {
 				return nil, fmt.Errorf("codex provider: tool message missing tool call id")
 			}
+			outputType := "function_call_output"
+			callID := msg.ToolCallProviderID
+			if callID == "" {
+				callID = msg.ToolCallID
+			}
+			if customID, custom := customCallIDs[msg.ToolCallID]; custom {
+				outputType = "custom_tool_call_output"
+				callID = customID
+			}
 			req.Input = append(req.Input, inputItem{
-				Type:   "function_call_output",
-				CallID: msg.ToolCallID,
+				Type:   outputType,
+				CallID: callID,
 				Output: msg.Content,
 			})
 		default:
@@ -249,12 +340,25 @@ func (p *CodexProvider) buildResponsesRequest(request zeroruntime.CompletionRequ
 	}
 	req.Instructions = strings.Join(instructions, "\n\n")
 	for _, tool := range request.Tools {
-		req.Tools = append(req.Tools, responsesTool{
-			Type:        "function",
-			Name:        tool.Name,
-			Description: tool.Description,
-			Parameters:  tool.Parameters,
-		})
+		definition := tool
+		if definition.Name == "apply_patch" && definition.Type == zeroruntime.ToolDefinitionFreeform {
+			definition.Description = "The apply_patch tool edits files from a raw structured patch. Use absolute file paths in patch headers to target a granted extra write root. Do not wrap the patch in JSON."
+			definition.Format = &zeroruntime.ToolDefinitionFormat{Type: "grammar", Syntax: "lark", Definition: applyPatchLarkGrammar}
+		}
+		wireTool := responsesTool{
+			Type:        string(definition.Type),
+			Name:        definition.Name,
+			Description: definition.Description,
+			Parameters:  definition.Parameters,
+			Format:      definition.Format,
+		}
+		if wireTool.Type == "" {
+			wireTool.Type = string(zeroruntime.ToolDefinitionFunction)
+		}
+		if wireTool.Type == string(zeroruntime.ToolDefinitionFreeform) {
+			wireTool.Parameters = nil
+		}
+		req.Tools = append(req.Tools, wireTool)
 	}
 	// Codex / o-series reasoning models take the effort tier nested under
 	// `reasoning` on the Responses API (the chat-completions `reasoning_effort`
@@ -312,13 +416,26 @@ func (p *CodexProvider) assistantInputItems(msg zeroruntime.Message) ([]inputIte
 		if tc.Name == "" {
 			return nil, errors.New("codex provider: assistant tool call missing name")
 		}
-		items = append(items, inputItem{
-			Type:      "function_call",
-			ID:        tc.ID,
-			CallID:    tc.ID,
-			Name:      tc.Name,
-			Arguments: tc.Arguments,
-		})
+		callID := tc.ProviderCallID
+		if callID == "" {
+			callID = tc.ID
+		}
+		itemType := "function_call"
+		if tc.Freeform {
+			itemType = "custom_tool_call"
+		}
+		item := inputItem{
+			Type:   itemType,
+			ID:     tc.ID,
+			CallID: callID,
+			Name:   tc.Name,
+		}
+		if tc.Freeform {
+			item.Input = tc.Arguments
+		} else {
+			item.Arguments = tc.Arguments
+		}
+		items = append(items, item)
 	}
 	return items, nil
 }
@@ -479,6 +596,18 @@ func (p *CodexProvider) emitResponsesEvent(
 		state.done = true
 		return false
 	}
+	return p.emitParsedResponsesEvent(ctx, &event, state, events)
+}
+
+// emitParsedResponsesEvent converts one already-decoded Responses event into
+// zero or more runtime events. WebSocket sessions use this path to avoid
+// decoding each frame twice; the SSE path retains emitResponsesEvent above.
+func (p *CodexProvider) emitParsedResponsesEvent(
+	ctx context.Context,
+	event *responsesEvent,
+	state *responsesState,
+	events chan<- zeroruntime.StreamEvent,
+) bool {
 	if event.Type == "" {
 		// A payload that parses as JSON but carries no `type` field is a
 		// malformed Responses event — the type is the discriminator that
@@ -500,12 +629,17 @@ func (p *CodexProvider) emitResponsesEvent(
 		// the runtime. response.incomplete is folded into a length finish at
 		// scan-end (state.done stays false so the wrapper emits the
 		// StreamEventDone with FinishReasonLength).
+		if event.Response != nil && event.Response.ID != "" {
+			state.responseID = event.Response.ID
+		}
 		return true
 	case responsesEventOutputItemAdded:
-		p.handleOutputItemAdded(ctx, &event, state, events)
+		p.handleOutputItemAdded(ctx, event, state, events)
 		return true
 	case responsesEventOutputTextDelta:
 		if event.Delta != "" {
+			state.emitted = true
+			state.text.WriteString(event.Delta)
 			providerio.SendEvent(ctx, events, zeroruntime.StreamEvent{
 				Type:    zeroruntime.StreamEventText,
 				Content: event.Delta,
@@ -517,6 +651,7 @@ func (p *CodexProvider) emitResponsesEvent(
 		// phase shows progress (and keeps the activity clock fresh) instead of
 		// looking like a hang. Requested via reasoning.summary="auto".
 		if event.Delta != "" {
+			state.emitted = true
 			providerio.SendEvent(ctx, events, zeroruntime.StreamEvent{
 				Type:    zeroruntime.StreamEventReasoning,
 				Content: event.Delta,
@@ -524,13 +659,16 @@ func (p *CodexProvider) emitResponsesEvent(
 		}
 		return true
 	case responsesEventFunctionArgsDelta:
-		p.handleFunctionArgsDelta(ctx, &event, state, events)
+		p.handleToolInputDelta(ctx, event, state, events, false)
+		return true
+	case responsesEventCustomInputDelta:
+		p.handleToolInputDelta(ctx, event, state, events, true)
 		return true
 	case responsesEventOutputItemDone:
-		p.handleOutputItemDone(ctx, &event, state, events)
+		p.handleOutputItemDone(ctx, event, state, events)
 		return true
 	case responsesEventCompleted, responsesEventFailed:
-		return p.handleTerminalResponse(ctx, &event, state, events)
+		return p.handleTerminalResponse(ctx, event, state, events)
 	case responsesEventError:
 		message := event.Message
 		if event.Code != "" {
@@ -570,22 +708,38 @@ func (p *CodexProvider) handleOutputItemAdded(
 		return
 	}
 	switch event.Item.Type {
-	case "function_call":
+	case "function_call", "custom_tool_call":
 		key := p.toolCallKey(event)
 		if key == "" {
 			return
 		}
-		builder := &toolCallBuilder{
-			ID:   key,
-			Name: event.Item.Name,
+		builder, exists := state.toolCalls[key]
+		if !exists {
+			builder = &toolCallBuilder{ID: key, Freeform: event.Item.Type == "custom_tool_call"}
+			state.toolCalls[key] = builder
+			state.toolOrder = append(state.toolOrder, key)
+		}
+		if event.Item.CallID != "" {
+			builder.CallID = event.Item.CallID
+		}
+		if event.Item.Name != "" {
+			builder.Name = event.Item.Name
+		}
+		builder.Freeform = builder.Freeform || event.Item.Type == "custom_tool_call"
+		if builder.Freeform && event.Item.Input != "" && builder.Arguments.Len() == 0 {
+			builder.Arguments.WriteString(event.Item.Input)
+		}
+		state.emitted = true
+		if !builder.started {
+			providerio.SendEvent(ctx, events, zeroruntime.StreamEvent{
+				Type:               zeroruntime.StreamEventToolCallStart,
+				ToolCallID:         key,
+				ToolCallProviderID: builder.CallID,
+				ToolName:           builder.Name,
+				ToolCallFreeform:   builder.Freeform,
+			})
+			builder.started = true
 		}
-		state.toolCalls[key] = builder
-		providerio.SendEvent(ctx, events, zeroruntime.StreamEvent{
-			Type:       zeroruntime.StreamEventToolCallStart,
-			ToolCallID: key,
-			ToolName:   event.Item.Name,
-		})
-		builder.started = true
 	}
 }

@@ -593,11 +747,12 @@ func (p *CodexProvider) handleOutputItemAdded(
 // to the in-flight builder and emits StreamEventToolCallDelta. The
 // Codex backend uses either `item_id` or `output_index` to attribute
 // the delta; we honor both.
-func (p *CodexProvider) handleFunctionArgsDelta(
+func (p *CodexProvider) handleToolInputDelta(
 	ctx context.Context,
 	event *responsesEvent,
 	state *responsesState,
 	events chan<- zeroruntime.StreamEvent,
+	freeform bool,
 ) {
 	key := p.toolCallKey(event)
 	if key == "" {
@@ -610,10 +765,16 @@ func (p *CodexProvider) handleFunctionArgsDelta(
 		// an intermediate proxy). Treat the delta as the start of a new
 		// tool call with no known name yet — the eventual
 		// response.output_item.done carries the final name.
-		builder = &toolCallBuilder{ID: key}
+		builder = &toolCallBuilder{ID: key, Freeform: freeform}
 		state.toolCalls[key] = builder
+		state.toolOrder = append(state.toolOrder, key)
+	}
+	builder.Freeform = builder.Freeform || freeform
+	if event.CallID != "" && builder.CallID == "" {
+		builder.CallID = event.CallID
 	}
 	builder.Arguments.WriteString(event.Delta)
+	state.emitted = true
 	providerio.SendEvent(ctx, events, zeroruntime.StreamEvent{
 		Type:              zeroruntime.StreamEventToolCallDelta,
 		ToolCallID:        key,
@@ -632,7 +793,7 @@ func (p *CodexProvider) handleOutputItemDone(
 	state *responsesState,
 	events chan<- zeroruntime.StreamEvent,
 ) {
-	if event.Item == nil || event.Item.Type != "function_call" {
+	if event.Item == nil || (event.Item.Type != "function_call" && event.Item.Type != "custom_tool_call") {
 		return
 	}
 	key := p.toolCallKey(event)
@@ -641,20 +802,31 @@ func (p *CodexProvider) handleOutputItemDone(
 	}
 	builder, ok := state.toolCalls[key]
 	if !ok {
-		builder = &toolCallBuilder{ID: key}
+		builder = &toolCallBuilder{ID: key, Freeform: event.Item.Type == "custom_tool_call"}
 		state.toolCalls[key] = builder
+		state.toolOrder = append(state.toolOrder, key)
 	}
 	if event.Item.Name != "" {
 		builder.Name = event.Item.Name
 	}
-	if event.Item.Arguments != "" && builder.Arguments.Len() == 0 {
-		builder.Arguments.WriteString(event.Item.Arguments)
+	if event.Item.CallID != "" {
+		builder.CallID = event.Item.CallID
+	}
+	builder.Freeform = builder.Freeform || event.Item.Type == "custom_tool_call"
+	finalInput := event.Item.Arguments
+	if builder.Freeform {
+		finalInput = event.Item.Input
+	}
+	if finalInput != "" && builder.Arguments.Len() == 0 {
+		builder.Arguments.WriteString(finalInput)
 	}
 	if !builder.started {
 		providerio.SendEvent(ctx, events, zeroruntime.StreamEvent{
-			Type:       zeroruntime.StreamEventToolCallStart,
-			ToolCallID: key,
-			ToolName:   builder.Name,
+			Type:               zeroruntime.StreamEventToolCallStart,
+			ToolCallID:         key,
+			ToolCallProviderID: builder.CallID,
+			ToolName:           builder.Name,
+			ToolCallFreeform:   builder.Freeform,
 		})
 		builder.started = true
 	}
@@ -664,6 +836,7 @@ func (p *CodexProvider) handleOutputItemDone(
 		ToolName:   builder.Name,
 	})
 	builder.ended = true
+	state.emitted = true
 }

 // handleTerminalResponse emits the final usage + done event for a
@@ -693,6 +866,7 @@ func (p *CodexProvider) handleTerminalResponse(
 		return false
 	}
 	state.usage = event.Response.Usage
+	state.responseID = event.Response.ID
 	if event.Response.Usage != nil {
 		usage := zeroruntime.Usage{
 			InputTokens:  event.Response.Usage.InputTokens,
@@ -700,6 +874,7 @@ func (p *CodexProvider) handleTerminalResponse(
 		}
 		if event.Response.Usage.InputTokensDetails != nil {
 			usage.CachedInputTokens = event.Response.Usage.InputTokensDetails.CachedTokens
+			usage.CacheWriteTokens = event.Response.Usage.InputTokensDetails.CacheWriteTokens
 		}
 		if event.Response.Usage.OutputTokensDetails != nil {
 			usage.ReasoningTokens = event.Response.Usage.OutputTokensDetails.ReasoningTokens
@@ -735,7 +910,7 @@ func (p *CodexProvider) handleTerminalResponse(
 		state.done = true
 		return false
 	}
-	providerio.SendEvent(ctx, events, zeroruntime.StreamEvent{Type: zeroruntime.StreamEventDone})
+	providerio.SendEvent(ctx, events, zeroruntime.StreamEvent{Type: zeroruntime.StreamEventDone, ResponseID: event.Response.ID})
 	state.done = true
 	return false
 }
@@ -754,6 +929,9 @@ func (p *CodexProvider) toolCallKey(event *responsesEvent) string {
 	if event.Item != nil && event.Item.CallID != "" {
 		return event.Item.CallID
 	}
+	if event.CallID != "" {
+		return event.CallID
+	}
 	if event.OutputIndex != nil {
 		// output_index is present (a *int distinguishes a real 0 — the first output
 		// in the response — from "absent"), so key on it even when 0 instead of
@@ -0,0 +1,421 @@
+package openai
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+	"net/url"
+	"reflect"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/coder/websocket"
+
+	"github.com/Gitlawb/zero/internal/providers/providerio"
+	"github.com/Gitlawb/zero/internal/trace"
+	"github.com/Gitlawb/zero/internal/zeroruntime"
+)
+
+const (
+	responsesWebSocketBetaHeader = "OpenAI-Beta"
+	responsesWebSocketBetaValue  = "responses_websockets=2026-02-06"
+	responsesWebSocketRequest    = "response.create"
+	previousResponseNotFoundCode = "previous_response_not_found"
+	webSocketConnectionLimitCode = "websocket_connection_limit_reached"
+	responsesWebSocketReadLimit  = 16 << 20
+)
+
+var errCodexTurnSessionBusy = errors.New("codex turn session already has an active stream")
+
+// NewCodexTurnSessionProvider enables one Responses WebSocket connection for
+// each agent run. The session falls back to the existing HTTP/SSE provider when
+// the endpoint cannot upgrade or loses its response chain.
+func NewCodexTurnSessionProvider(provider *CodexProvider, caps zeroruntime.ProviderCapabilities) zeroruntime.TurnSessionProvider {
+	return &codexTurnSessionProvider{provider: provider, caps: caps}
+}
+
+type codexTurnSessionProvider struct {
+	provider *CodexProvider
+	caps     zeroruntime.ProviderCapabilities
+}
+
+func (provider *codexTurnSessionProvider) OpenTurnSession(ctx context.Context) (zeroruntime.TurnSession, error) {
+	if provider == nil || provider.provider == nil || provider.provider.inner == nil {
+		return nil, errors.New("codex turn session requires a provider")
+	}
+	sessionCtx, cancel := context.WithCancel(ctx)
+	return &codexTurnSession{
+		ctx:         sessionCtx,
+		cancel:      cancel,
+		provider:    provider.provider,
+		prewarmDone: make(chan struct{}),
+	}, nil
+}
+
+func (provider *codexTurnSessionProvider) Capabilities() zeroruntime.ProviderCapabilities {
+	return provider.caps
+}
+
+type codexTurnSession struct {
+	ctx      context.Context
+	cancel   context.CancelFunc
+	provider *CodexProvider
+
+	mu             sync.Mutex
+	connection     *websocket.Conn
+	webSocketOff   bool
+	lastRequest    *responsesRequest
+	lastResponseID string
+	lastOutput     []inputItem
+	streamActive   bool
+
+	prewarmOnce sync.Once
+	prewarmDone chan struct{}
+	closeOnce   sync.Once
+}
+
+// Prewarm starts the WebSocket handshake without blocking prompt assembly. The
+// first Stream waits for this bounded attempt; failure simply selects HTTP/SSE.
+func (session *codexTurnSession) Prewarm(ctx context.Context) error {
+	session.prewarmOnce.Do(func() {
+		go func() {
+			defer close(session.prewarmDone)
+			prewarmCtx, cancel := context.WithTimeout(session.ctx, prewarmTimeout)
+			defer cancel()
+			recorder := trace.FromContext(ctx)
+			span := recorder.Span(trace.SpanProviderPrewarm)
+			defer span.End()
+			recorder.Counter(trace.CounterPrewarmAttempts, 1)
+			connection, err := session.provider.dialResponsesWebSocket(prewarmCtx)
+			session.mu.Lock()
+			defer session.mu.Unlock()
+			if err != nil {
+				session.webSocketOff = true
+				return
+			}
+			session.connection = connection
+		}()
+	})
+	return nil
+}
+
+func (session *codexTurnSession) Stream(ctx context.Context, request zeroruntime.CompletionRequest) (<-chan zeroruntime.StreamEvent, error) {
+	_ = session.Prewarm(ctx)
+	select {
+	case <-session.prewarmDone:
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	}
+
+	fullRequest, err := session.provider.buildResponsesRequest(request)
+	if err != nil {
+		return nil, err
+	}
+
+	session.mu.Lock()
+	if session.streamActive {
+		session.mu.Unlock()
+		return nil, errCodexTurnSessionBusy
+	}
+	if session.webSocketOff || session.connection == nil {
+		session.mu.Unlock()
+		trace.FromContext(ctx).Counter(trace.CounterResponsesHTTPFallback, 1)
+		return session.provider.StreamCompletion(ctx, request)
+	}
+	session.streamActive = true
+	connection := session.connection
+	wireRequest := *fullRequest
+	wireRequest.Type = responsesWebSocketRequest
+	if delta, ok := responseInputDelta(session.lastRequest, session.lastOutput, fullRequest); ok && session.lastResponseID != "" {
+		wireRequest.PreviousResponseID = session.lastResponseID
+		wireRequest.Input = delta
+		trace.FromContext(ctx).Counter(trace.CounterResponseChainReused, 1)
+	} else if session.lastRequest != nil {
+		trace.FromContext(ctx).Counter(trace.CounterResponseChainReset, 1)
+		session.lastRequest = nil
+		session.lastResponseID = ""
+		session.lastOutput = nil
+	}
+	session.mu.Unlock()
+
+	body, err := json.Marshal(wireRequest)
+	if err != nil {
+		session.releaseStream()
+		return nil, fmt.Errorf("encode codex websocket request: %w", err)
+	}
+	events := make(chan zeroruntime.StreamEvent, 16)
+	go func() {
+		defer close(events)
+		defer session.releaseStream()
+		session.streamWebSocket(ctx, connection, body, fullRequest, request, events)
+	}()
+	return events, nil
+}
+
+func (session *codexTurnSession) releaseStream() {
+	session.mu.Lock()
+	session.streamActive = false
+	session.mu.Unlock()
+}
+
+func (session *codexTurnSession) Compact(context.Context, zeroruntime.CompletionRequest) ([]zeroruntime.Message, error) {
+	return nil, zeroruntime.ErrCompactionUnsupported
+}
+
+func (session *codexTurnSession) Close() error {
+	session.closeOnce.Do(func() {
+		session.cancel()
+		session.prewarmOnce.Do(func() { close(session.prewarmDone) })
+		select {
+		case <-session.prewarmDone:
+		case <-time.After(prewarmTimeout):
+		}
+		session.mu.Lock()
+		connection := session.connection
+		session.connection = nil
+		session.webSocketOff = true
+		session.mu.Unlock()
+		if connection != nil {
+			_ = connection.CloseNow()
+		}
+	})
+	return nil
+}
+
+func responseInputDelta(previous *responsesRequest, output []inputItem, current *responsesRequest) ([]inputItem, bool) {
+	if previous == nil || current == nil || !responsesRequestPropertiesEqual(previous, current) {
+		return nil, false
+	}
+	prefix := make([]inputItem, 0, len(previous.Input)+len(output))
+	prefix = append(prefix, previous.Input...)
+	prefix = append(prefix, output...)
+	if len(current.Input) <= len(prefix) || !reflect.DeepEqual(current.Input[:len(prefix)], prefix) {
+		return nil, false
+	}
+	return append([]inputItem(nil), current.Input[len(prefix):]...), true
+}
+
+func responsesRequestPropertiesEqual(left, right *responsesRequest) bool {
+	return left.Model == right.Model &&
+		left.Instructions == right.Instructions &&
+		left.Stream == right.Stream &&
+		left.Store == right.Store &&
+		left.ParallelToolCalls == right.ParallelToolCalls &&
+		left.MaxOutputTokens == right.MaxOutputTokens &&
+		reflect.DeepEqual(left.Tools, right.Tools) &&
+		reflect.DeepEqual(left.Reasoning, right.Reasoning) &&
+		left.ServiceTier == right.ServiceTier &&
+		left.PromptCacheKey == right.PromptCacheKey
+}
+
+func (session *codexTurnSession) streamWebSocket(
+	ctx context.Context,
+	connection *websocket.Conn,
+	body []byte,
+	fullRequest *responsesRequest,
+	runtimeRequest zeroruntime.CompletionRequest,
+	events chan<- zeroruntime.StreamEvent,
+) {
+	if err := connection.Write(ctx, websocket.MessageText, body); err != nil {
+		session.disableWebSocket(connection)
+		session.forwardHTTP(ctx, runtimeRequest, events)
+		return
+	}
+
+	state := newResponsesState()
+	for {
+		readCtx := ctx
+		cancel := func() {}
+		idleTimeout := session.provider.inner.streamIdleTimeout
+		if idleTimeout > 0 {
+			readCtx, cancel = context.WithTimeout(ctx, idleTimeout)
+		}
+		messageType, data, err := connection.Read(readCtx)
+		readTimedOut := errors.Is(readCtx.Err(), context.DeadlineExceeded) && ctx.Err() == nil
+		cancel()
+		if err != nil {
+			session.disableWebSocket(connection)
+			if ctx.Err() != nil {
+				return
+			}
+			if !state.emitted {
+				session.forwardHTTP(ctx, runtimeRequest, events)
+				return
+			}
+			errorMessage := err.Error()
+			if readTimedOut {
+				errorMessage = providerio.StreamTimeoutMessage(providerio.ErrStreamIdle, idleTimeout)
+			}
+			providerio.SendEvent(ctx, events, zeroruntime.StreamEvent{
+				Type:  zeroruntime.StreamEventError,
+				Error: session.provider.redact("provider stream error: " + errorMessage),
+			})
+			return
+		}
+		if messageType != websocket.MessageText {
+			continue
+		}
+
+		var responseEvent responsesEvent
+		decodeErr := json.Unmarshal(data, &responseEvent)
+		if decodeErr == nil {
+			if (responseEvent.Code == previousResponseNotFoundCode || responseEvent.Code == webSocketConnectionLimitCode) &&
+				!state.emitted {
+				session.disableWebSocket(connection)
+				session.forwardHTTP(ctx, runtimeRequest, events)
+				return
+			}
+			if responseEvent.Type == responsesEventIncomplete {
+				session.resetResponseChain(connection)
+				providerio.SendEvent(ctx, events, zeroruntime.StreamEvent{
+					Type:         zeroruntime.StreamEventDone,
+					FinishReason: zeroruntime.FinishReasonLength,
+				})
+				return
+			}
+		}
+
+		keepReading := false
+		if decodeErr == nil {
+			keepReading = session.provider.emitParsedResponsesEvent(ctx, &responseEvent, state, events)
+		} else {
+			keepReading = session.provider.emitResponsesEvent(ctx, string(data), state, events)
+		}
+		if keepReading {
+			continue
+		}
+		if responseEvent.Type == responsesEventCompleted && responseEvent.Response != nil &&
+			responseEvent.Response.Error == nil && responseEvent.Response.Status != "failed" && state.responseID != "" {
+			session.mu.Lock()
+			if session.connection == connection && !session.webSocketOff {
+				requestCopy := *fullRequest
+				requestCopy.Input = append([]inputItem(nil), fullRequest.Input...)
+				session.lastRequest = &requestCopy
+				session.lastResponseID = state.responseID
+				session.lastOutput = state.outputInputItems()
+			}
+			session.mu.Unlock()
+		}
+		return
+	}
+}
+
+func (session *codexTurnSession) resetResponseChain(connection *websocket.Conn) {
+	session.mu.Lock()
+	defer session.mu.Unlock()
+	if session.connection != connection {
+		return
+	}
+	session.lastRequest = nil
+	session.lastResponseID = ""
+	session.lastOutput = nil
+}
+
+func (session *codexTurnSession) forwardHTTP(ctx context.Context, request zeroruntime.CompletionRequest, events chan<- zeroruntime.StreamEvent) {
+	trace.FromContext(ctx).Counter(trace.CounterResponsesHTTPFallback, 1)
+	stream, err := session.provider.StreamCompletion(ctx, request)
+	if err != nil {
+		providerio.SendEvent(ctx, events, zeroruntime.StreamEvent{
+			Type:  zeroruntime.StreamEventError,
+			Error: session.provider.redact(err.Error()),
+		})
+		return
+	}
+	for event := range stream {
+		providerio.SendEvent(ctx, events, event)
+	}
+}
+
+func (session *codexTurnSession) disableWebSocket(connection *websocket.Conn) {
+	session.mu.Lock()
+	if session.connection == connection {
+		session.connection = nil
+		session.webSocketOff = true
+		session.lastRequest = nil
+		session.lastResponseID = ""
+		session.lastOutput = nil
+	}
+	session.mu.Unlock()
+	_ = connection.CloseNow()
+}
+
+func (provider *CodexProvider) dialResponsesWebSocket(ctx context.Context) (*websocket.Conn, error) {
+	endpoint, err := responsesWebSocketURL(provider.inner.endpoint)
+	if err != nil {
+		return nil, err
+	}
+	for authTry := 0; authTry < 2; authTry++ {
+		headers, err := provider.responsesWebSocketHeaders(ctx, authTry == 1)
+		if err != nil {
+			return nil, err
+		}
+		connection, response, err := websocket.Dial(ctx, endpoint, &websocket.DialOptions{
+			HTTPClient:      provider.inner.httpClient,
+			HTTPHeader:      headers,
+			CompressionMode: websocket.CompressionNoContextTakeover,
+		})
+		if err == nil {
+			connection.SetReadLimit(responsesWebSocketReadLimit)
+			return connection, nil
+		}
+		if response == nil || response.StatusCode != http.StatusUnauthorized || provider.inner.oauthResolver == nil || authTry == 1 {
+			return nil, err
+		}
+	}
+	return nil, errors.New("codex websocket authentication failed")
+}
+
+func (provider *CodexProvider) responsesWebSocketHeaders(ctx context.Context, forceRefresh bool) (http.Header, error) {
+	request, err := http.NewRequestWithContext(ctx, http.MethodGet, provider.inner.endpoint, nil)
+	if err != nil {
+		return nil, err
+	}
+	base := providerio.AuthHeaders{
+		APIKey:            provider.inner.apiKey,
+		DefaultAuthHeader: "Authorization",
+		DefaultAuthScheme: "Bearer",
+		AuthHeader:        provider.inner.authHeader,
+		AuthScheme:        provider.inner.authScheme,
+		AuthHeaderValue:   provider.inner.authHeaderValue,
+		CustomHeaders:     provider.inner.customHeaders,
+	}
+	if resolver := provider.inner.oauthResolver; resolver != nil {
+		header, value, ok, err := resolver(ctx, forceRefresh)
+		if err != nil {
+			return nil, err
+		}
+		if ok {
+			providerio.ApplyAuthHeaders(request, providerio.AuthHeaders{CustomHeaders: provider.inner.customHeaders})
+			if strings.TrimSpace(header) == "" {
+				header = "Authorization"
+			}
+			request.Header.Set(header, value)
+		} else {
+			providerio.ApplyAuthHeaders(request, base)
+		}
+	} else {
+		providerio.ApplyAuthHeaders(request, base)
+	}
+	provider.injectCodexHeaders(request)
+	request.Header.Set(responsesWebSocketBetaHeader, responsesWebSocketBetaValue)
+	return request.Header.Clone(), nil
+}
+
+func responsesWebSocketURL(endpoint string) (string, error) {
+	parsed, err := url.Parse(strings.TrimSpace(endpoint))
+	if err != nil {
+		return "", err
+	}
+	switch parsed.Scheme {
+	case "http":
+		parsed.Scheme = "ws"
+	case "https":
+		parsed.Scheme = "wss"
+	default:
+		return "", fmt.Errorf("unsupported Responses websocket URL scheme %q", parsed.Scheme)
+	}
+	return parsed.String(), nil
+}
@@ -0,0 +1,590 @@
+package openai
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/coder/websocket"
+
+	"github.com/Gitlawb/zero/internal/trace"
+	"github.com/Gitlawb/zero/internal/zeroruntime"
+)
+
+func TestCodexTurnSessionChainsOnlyAppendOnlyRequests(t *testing.T) {
+	var mu sync.Mutex
+	requests := []map[string]any{}
+	betaHeader := ""
+	server := httptest.NewServer(http.HandlerFunc(func(writer http.ResponseWriter, request *http.Request) {
+		if !strings.EqualFold(request.Header.Get("Upgrade"), "websocket") {
+			http.Error(writer, "websocket required", http.StatusUpgradeRequired)
+			return
+		}
+		mu.Lock()
+		betaHeader = request.Header.Get(responsesWebSocketBetaHeader)
+		mu.Unlock()
+		connection, err := websocket.Accept(writer, request, nil)
+		if err != nil {
+			return
+		}
+		defer connection.CloseNow()
+		for index := 0; index < 3; index++ {
+			_, body, err := connection.Read(request.Context())
+			if err != nil {
+				return
+			}
+			var payload map[string]any
+			if err := json.Unmarshal(body, &payload); err != nil {
+				return
+			}
+			mu.Lock()
+			requests = append(requests, payload)
+			mu.Unlock()
+			switch index {
+			case 0:
+				writeWebSocketEvents(request.Context(), connection,
+					`{"type":"response.created","response":{"id":"resp-1","status":"in_progress"}}`,
+					`{"type":"response.output_item.added","item_id":"call-1","item":{"type":"function_call","id":"call-1","call_id":"call-1","name":"read_file"}}`,
+					`{"type":"response.function_call_arguments.delta","item_id":"call-1","delta":"{}"}`,
+					`{"type":"response.output_item.done","item_id":"call-1","item":{"type":"function_call","id":"call-1","call_id":"call-1","name":"read_file","arguments":"{}"}}`,
+					`{"type":"response.completed","response":{"id":"resp-1","status":"completed"}}`,
+				)
+			case 1:
+				writeWebSocketEvents(request.Context(), connection,
+					`{"type":"response.output_text.delta","delta":"done"}`,
+					`{"type":"response.completed","response":{"id":"resp-2","status":"completed"}}`,
+				)
+			case 2:
+				writeWebSocketEvents(request.Context(), connection,
+					`{"type":"response.completed","response":{"id":"resp-3","status":"completed"}}`,
+				)
+			}
+		}
+	}))
+	defer server.Close()
+
+	provider := newCodexSessionTestProvider(t, server)
+	// A disabled stream watchdog must use the parent context rather than creating
+	// an immediately-expired read deadline.
+	provider.inner.streamIdleTimeout = 0
+	session := openCodexSession(t, provider)
+	defer session.Close()
+	recorder := trace.NewRecorder("session-1", "run-1", "test")
+	recorder.Start()
+	streamContext := trace.WithContext(t.Context(), recorder)
+
+	base := zeroruntime.CompletionRequest{
+		Messages: []zeroruntime.Message{
+			{Role: zeroruntime.MessageRoleSystem, Content: "Use tools carefully."},
+			{Role: zeroruntime.MessageRoleUser, Content: "Read the file."},
+		},
+		Tools:          []zeroruntime.ToolDefinition{{Name: "read_file", Parameters: map[string]any{"type": "object"}}},
+		PromptCacheKey: "session-1",
+	}
+	first := collectCodexSessionEvents(t, session, base)
+	if !hasToolCallEnd(first, "call-1") {
+		t.Fatalf("first stream did not produce the tool call: %#v", first)
+	}
+
+	second := base
+	second.Messages = append(append([]zeroruntime.Message(nil), base.Messages...),
+		zeroruntime.Message{Role: zeroruntime.MessageRoleAssistant, ToolCalls: []zeroruntime.ToolCall{{ID: "call-1", Name: "read_file", Arguments: "{}"}}},
+		zeroruntime.Message{Role: zeroruntime.MessageRoleTool, ToolCallID: "call-1", Content: "contents"},
+	)
+	secondEvents := collectCodexSessionEventsContext(t, streamContext, session, second)
+	if got := joinedText(secondEvents); got != "done" {
+		t.Fatalf("second stream text = %q, want done", got)
+	}
+
+	third := second
+	third.ReasoningEffort = "high"
+	third.Messages = append(append([]zeroruntime.Message(nil), second.Messages...),
+		zeroruntime.Message{Role: zeroruntime.MessageRoleAssistant, Content: "done"},
+		zeroruntime.Message{Role: zeroruntime.MessageRoleUser, Content: "Continue."},
+	)
+	collectCodexSessionEventsContext(t, streamContext, session, third)
+	finishedTrace := recorder.Finish()
+	if got := finishedTrace.Counter(trace.CounterResponseChainReused); got != 1 {
+		t.Fatalf("response-chain reuse count = %d, want 1", got)
+	}
+	if got := finishedTrace.Counter(trace.CounterResponseChainReset); got != 1 {
+		t.Fatalf("response-chain reset count = %d, want 1", got)
+	}
+
+	mu.Lock()
+	defer mu.Unlock()
+	if len(requests) != 3 {
+		t.Fatalf("websocket requests = %d, want 3", len(requests))
+	}
+	if betaHeader != responsesWebSocketBetaValue {
+		t.Fatalf("OpenAI-Beta = %q, want %q", betaHeader, responsesWebSocketBetaValue)
+	}
+	if requests[0]["type"] != responsesWebSocketRequest || requests[0]["previous_response_id"] != nil {
+		t.Fatalf("first request chaining fields = %#v", requests[0])
+	}
+	if requests[0]["parallel_tool_calls"] != true || requests[0]["prompt_cache_key"] != "session-1" {
+		t.Fatalf("first request stable fields = %#v", requests[0])
+	}
+	if requests[1]["previous_response_id"] != "resp-1" {
+		t.Fatalf("second previous_response_id = %#v", requests[1]["previous_response_id"])
+	}
+	secondInput, _ := requests[1]["input"].([]any)
+	if len(secondInput) != 1 || secondInput[0].(map[string]any)["type"] != "function_call_output" {
+		t.Fatalf("second incremental input = %#v", requests[1]["input"])
+	}
+	if requests[2]["previous_response_id"] != nil {
+		t.Fatalf("incompatible request reused response chain: %#v", requests[2])
+	}
+	thirdInput, _ := requests[2]["input"].([]any)
+	if len(thirdInput) <= 1 {
+		t.Fatalf("incompatible request did not send full input: %#v", thirdInput)
+	}
+}
+
+func TestCodexTurnSessionFallsBackWhenPreviousResponseIsMissing(t *testing.T) {
+	var mu sync.Mutex
+	webSocketRequests := 0
+	httpRequests := 0
+	server := httptest.NewServer(http.HandlerFunc(func(writer http.ResponseWriter, request *http.Request) {
+		if strings.EqualFold(request.Header.Get("Upgrade"), "websocket") {
+			connection, err := websocket.Accept(writer, request, nil)
+			if err != nil {
+				return
+			}
+			defer connection.CloseNow()
+			for index := 0; index < 2; index++ {
+				if _, _, err := connection.Read(request.Context()); err != nil {
+					return
+				}
+				mu.Lock()
+				webSocketRequests++
+				mu.Unlock()
+				if index == 0 {
+					writeWebSocketEvents(request.Context(), connection,
+						`{"type":"response.output_item.added","item_id":"call-1","item":{"type":"function_call","id":"call-1","call_id":"call-1","name":"read_file"}}`,
+						`{"type":"response.output_item.done","item_id":"call-1","item":{"type":"function_call","id":"call-1","call_id":"call-1","name":"read_file","arguments":"{}"}}`,
+						`{"type":"response.completed","response":{"id":"resp-1","status":"completed"}}`,
+					)
+					continue
+				}
+				writeWebSocketEvents(request.Context(), connection,
+					`{"type":"response.error","code":"previous_response_not_found","message":"missing"}`,
+				)
+			}
+			return
+		}
+
+		mu.Lock()
+		httpRequests++
+		mu.Unlock()
+		writer.Header().Set("Content-Type", "text/event-stream")
+		_, _ = fmt.Fprint(writer, "data: {\"type\":\"response.output_text.delta\",\"delta\":\"fallback\"}\n\n")
+		_, _ = fmt.Fprint(writer, "data: {\"type\":\"response.completed\",\"response\":{\"id\":\"resp-http\",\"status\":\"completed\"}}\n\n")
+	}))
+	defer server.Close()
+
+	provider := newCodexSessionTestProvider(t, server)
+	session := openCodexSession(t, provider)
+	defer session.Close()
+	base := zeroruntime.CompletionRequest{
+		Messages: []zeroruntime.Message{{Role: zeroruntime.MessageRoleUser, Content: "Read it."}},
+		Tools:    []zeroruntime.ToolDefinition{{Name: "read_file", Parameters: map[string]any{"type": "object"}}},
+	}
+	collectCodexSessionEvents(t, session, base)
+	second := base
+	second.Messages = append(append([]zeroruntime.Message(nil), base.Messages...),
+		zeroruntime.Message{Role: zeroruntime.MessageRoleAssistant, ToolCalls: []zeroruntime.ToolCall{{ID: "call-1", Name: "read_file", Arguments: "{}"}}},
+		zeroruntime.Message{Role: zeroruntime.MessageRoleTool, ToolCallID: "call-1", Content: "contents"},
+	)
+	events := collectCodexSessionEvents(t, session, second)
+	if got := joinedText(events); got != "fallback" {
+		t.Fatalf("fallback stream text = %q, want fallback; events=%#v", got, events)
+	}
+	for _, event := range events {
+		if event.Type == zeroruntime.StreamEventError {
+			t.Fatalf("response-chain recovery leaked an error: %#v", event)
+		}
+	}
+	mu.Lock()
+	defer mu.Unlock()
+	if webSocketRequests != 2 || httpRequests != 1 {
+		t.Fatalf("requests = websocket:%d http:%d, want 2/1", webSocketRequests, httpRequests)
+	}
+}
+
+func TestCodexTurnSessionFallsBackWhenSocketClosesBeforeOutput(t *testing.T) {
+	var mu sync.Mutex
+	httpRequests := 0
+	server := httptest.NewServer(http.HandlerFunc(func(writer http.ResponseWriter, request *http.Request) {
+		if strings.EqualFold(request.Header.Get("Upgrade"), "websocket") {
+			connection, err := websocket.Accept(writer, request, nil)
+			if err != nil {
+				return
+			}
+			if _, _, err := connection.Read(request.Context()); err == nil {
+				_ = connection.CloseNow()
+			}
+			return
+		}
+		mu.Lock()
+		httpRequests++
+		mu.Unlock()
+		writer.Header().Set("Content-Type", "text/event-stream")
+		_, _ = fmt.Fprint(writer, "data: {\"type\":\"response.output_text.delta\",\"delta\":\"recovered\"}\n\n")
+		_, _ = fmt.Fprint(writer, "data: {\"type\":\"response.completed\",\"response\":{\"id\":\"resp-http\",\"status\":\"completed\"}}\n\n")
+	}))
+	defer server.Close()
+
+	provider := newCodexSessionTestProvider(t, server)
+	session := openCodexSession(t, provider)
+	defer session.Close()
+	recorder := trace.NewRecorder("session-fallback", "run-fallback", "test")
+	recorder.Start()
+	events := collectCodexSessionEventsContext(t, trace.WithContext(t.Context(), recorder), session, zeroruntime.CompletionRequest{
+		Messages: []zeroruntime.Message{{Role: zeroruntime.MessageRoleUser, Content: "Hello"}},
+	})
+	if got := joinedText(events); got != "recovered" {
+		t.Fatalf("fallback text = %q, want recovered", got)
+	}
+	mu.Lock()
+	defer mu.Unlock()
+	if httpRequests != 1 {
+		t.Fatalf("HTTP fallback requests = %d, want 1", httpRequests)
+	}
+	if got := recorder.Finish().Counter(trace.CounterResponsesHTTPFallback); got != 1 {
+		t.Fatalf("responses HTTP fallback counter = %d, want 1", got)
+	}
+}
+
+func TestCodexTurnSessionKeepsWebSocketAfterIncompleteResponse(t *testing.T) {
+	var mu sync.Mutex
+	webSocketRequests := 0
+	httpRequests := 0
+	server := httptest.NewServer(http.HandlerFunc(func(writer http.ResponseWriter, request *http.Request) {
+		if strings.EqualFold(request.Header.Get("Upgrade"), "websocket") {
+			connection, err := websocket.Accept(writer, request, nil)
+			if err != nil {
+				return
+			}
+			defer connection.CloseNow()
+			for index := 0; index < 2; index++ {
+				if _, _, err := connection.Read(request.Context()); err != nil {
+					return
+				}
+				mu.Lock()
+				webSocketRequests++
+				mu.Unlock()
+				if index == 0 {
+					writeWebSocketEvents(request.Context(), connection,
+						`{"type":"response.incomplete","response":{"id":"resp-1","status":"incomplete"}}`,
+					)
+					continue
+				}
+				writeWebSocketEvents(request.Context(), connection,
+					`{"type":"response.output_text.delta","delta":"websocket"}`,
+					`{"type":"response.completed","response":{"id":"resp-2","status":"completed"}}`,
+				)
+			}
+			return
+		}
+
+		mu.Lock()
+		httpRequests++
+		mu.Unlock()
+		writer.Header().Set("Content-Type", "text/event-stream")
+		_, _ = fmt.Fprint(writer, "data: {\"type\":\"response.output_text.delta\",\"delta\":\"fallback\"}\n\n")
+		_, _ = fmt.Fprint(writer, "data: {\"type\":\"response.completed\",\"response\":{\"id\":\"resp-http\",\"status\":\"completed\"}}\n\n")
+	}))
+	defer server.Close()
+
+	provider := newCodexSessionTestProvider(t, server)
+	session := openCodexSession(t, provider)
+	defer session.Close()
+	request := zeroruntime.CompletionRequest{
+		Messages: []zeroruntime.Message{{Role: zeroruntime.MessageRoleUser, Content: "Continue."}},
+	}
+	first := collectCodexSessionEvents(t, session, request)
+	if len(first) != 1 || first[0].Type != zeroruntime.StreamEventDone || first[0].FinishReason != zeroruntime.FinishReasonLength {
+		t.Fatalf("incomplete response events = %#v, want length completion", first)
+	}
+	second := collectCodexSessionEvents(t, session, request)
+	if got := joinedText(second); got != "websocket" {
+		t.Fatalf("second turn text = %q, want websocket; events=%#v", got, second)
+	}
+	mu.Lock()
+	defer mu.Unlock()
+	if webSocketRequests != 2 || httpRequests != 0 {
+		t.Fatalf("requests = websocket:%d http:%d, want 2/0", webSocketRequests, httpRequests)
+	}
+}
+
+func TestCodexTurnSessionDoesNotReplayAfterVisibleOutput(t *testing.T) {
+	var mu sync.Mutex
+	httpRequests := 0
+	server := httptest.NewServer(http.HandlerFunc(func(writer http.ResponseWriter, request *http.Request) {
+		if strings.EqualFold(request.Header.Get("Upgrade"), "websocket") {
+			connection, err := websocket.Accept(writer, request, nil)
+			if err != nil {
+				return
+			}
+			if _, _, err := connection.Read(request.Context()); err == nil {
+				writeWebSocketEvents(request.Context(), connection,
+					`{"type":"response.output_text.delta","delta":"visible"}`,
+				)
+			}
+			_ = connection.Close(websocket.StatusInternalError, "interrupted")
+			return
+		}
+		mu.Lock()
+		httpRequests++
+		mu.Unlock()
+	}))
+	defer server.Close()
+
+	provider := newCodexSessionTestProvider(t, server)
+	session := openCodexSession(t, provider)
+	defer session.Close()
+	stream, err := session.Stream(t.Context(), zeroruntime.CompletionRequest{
+		Messages: []zeroruntime.Message{{Role: zeroruntime.MessageRoleUser, Content: "Hello"}},
+	})
+	if err != nil {
+		t.Fatalf("Stream: %v", err)
+	}
+	sawText, sawError := false, false
+	for event := range stream {
+		sawText = sawText || event.Type == zeroruntime.StreamEventText
+		sawError = sawError || event.Type == zeroruntime.StreamEventError
+	}
+	if !sawText || !sawError {
+		t.Fatalf("visible interrupted stream = text:%v error:%v", sawText, sawError)
+	}
+	mu.Lock()
+	defer mu.Unlock()
+	if httpRequests != 0 {
+		t.Fatalf("visible interrupted stream was replayed over HTTP %d time(s)", httpRequests)
+	}
+}
+
+func TestCodexTurnSessionReportsWebSocketIdleTimeout(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(writer http.ResponseWriter, request *http.Request) {
+		connection, err := websocket.Accept(writer, request, nil)
+		if err != nil {
+			return
+		}
+		defer connection.CloseNow()
+		if _, _, err := connection.Read(request.Context()); err != nil {
+			return
+		}
+		writeWebSocketEvents(request.Context(), connection,
+			`{"type":"response.output_text.delta","delta":"visible"}`,
+		)
+		<-request.Context().Done()
+	}))
+	defer server.Close()
+
+	provider := newCodexSessionTestProvider(t, server)
+	provider.inner.streamIdleTimeout = 200 * time.Millisecond
+	session := openCodexSession(t, provider)
+	defer session.Close()
+	stream, err := session.Stream(t.Context(), zeroruntime.CompletionRequest{
+		Messages: []zeroruntime.Message{{Role: zeroruntime.MessageRoleUser, Content: "Hello"}},
+	})
+	if err != nil {
+		t.Fatalf("Stream: %v", err)
+	}
+
+	var streamError string
+	for event := range stream {
+		if event.Type == zeroruntime.StreamEventError {
+			streamError = event.Error
+			break
+		}
+	}
+	if !strings.Contains(streamError, "idle timeout after 200ms") {
+		t.Fatalf("stream error = %q, want idle-timeout detail", streamError)
+	}
+}
+
+func TestCodexTurnSessionRejectsOverlappingStreams(t *testing.T) {
+	started := make(chan struct{})
+	release := make(chan struct{})
+	var releaseOnce sync.Once
+	releaseStream := func() { releaseOnce.Do(func() { close(release) }) }
+	t.Cleanup(releaseStream)
+	server := httptest.NewServer(http.HandlerFunc(func(writer http.ResponseWriter, request *http.Request) {
+		connection, err := websocket.Accept(writer, request, nil)
+		if err != nil {
+			return
+		}
+		defer connection.CloseNow()
+		if _, _, err := connection.Read(request.Context()); err != nil {
+			return
+		}
+		close(started)
+		<-release
+		writeWebSocketEvents(request.Context(), connection,
+			`{"type":"response.completed","response":{"id":"resp-1","status":"completed"}}`,
+		)
+	}))
+	defer server.Close()
+
+	provider := newCodexSessionTestProvider(t, server)
+	session := openCodexSession(t, provider)
+	defer session.Close()
+	request := zeroruntime.CompletionRequest{
+		Messages: []zeroruntime.Message{{Role: zeroruntime.MessageRoleUser, Content: "Hello"}},
+	}
+	first, err := session.Stream(t.Context(), request)
+	if err != nil {
+		t.Fatalf("first Stream: %v", err)
+	}
+	select {
+	case <-started:
+	case <-time.After(time.Second):
+		t.Fatal("first WebSocket stream did not start")
+	}
+	if _, err := session.Stream(t.Context(), request); !errors.Is(err, errCodexTurnSessionBusy) {
+		t.Fatalf("overlapping Stream error = %v, want %v", err, errCodexTurnSessionBusy)
+	}
+	releaseStream()
+	for range first {
+	}
+}
+
+func TestCodexTurnSessionHTTPFallbackRedactsSetupError(t *testing.T) {
+	const secret = "sk-secret-fallback"
+	provider, err := NewCodexProvider(CodexOptions{Options: Options{
+		APIKey:  secret,
+		BaseURL: "https://chatgpt.example/backend-api/codex",
+		Model:   "gpt-test",
+	}})
+	if err != nil {
+		t.Fatalf("NewCodexProvider: %v", err)
+	}
+	session := &codexTurnSession{provider: provider}
+	events := make(chan zeroruntime.StreamEvent, 1)
+	session.forwardHTTP(t.Context(), zeroruntime.CompletionRequest{
+		Messages: []zeroruntime.Message{{Role: zeroruntime.MessageRole(secret), Content: "invalid"}},
+	}, events)
+
+	select {
+	case event := <-events:
+		if event.Type != zeroruntime.StreamEventError {
+			t.Fatalf("fallback event type = %s, want error", event.Type)
+		}
+		if strings.Contains(event.Error, secret) {
+			t.Fatalf("fallback error leaked credential: %q", event.Error)
+		}
+	case <-time.After(time.Second):
+		t.Fatal("fallback did not emit setup error")
+	}
+}
+
+func TestCodexTurnSessionCloseDoesNotStartPrewarm(t *testing.T) {
+	provider, err := NewCodexProvider(CodexOptions{Options: Options{
+		APIKey:  "test-token",
+		BaseURL: "https://chatgpt.example/backend-api/codex",
+		Model:   "gpt-test",
+	}})
+	if err != nil {
+		t.Fatalf("NewCodexProvider: %v", err)
+	}
+	session, err := NewCodexTurnSessionProvider(provider, zeroruntime.ProviderCapabilities{}).OpenTurnSession(t.Context())
+	if err != nil {
+		t.Fatalf("OpenTurnSession: %v", err)
+	}
+	done := make(chan error, 1)
+	go func() { done <- session.Close() }()
+	select {
+	case err := <-done:
+		if err != nil {
+			t.Fatalf("Close() error = %v", err)
+		}
+	case <-time.After(200 * time.Millisecond):
+		t.Fatal("Close blocked without a prewarm attempt")
+	}
+}
+
+func newCodexSessionTestProvider(t *testing.T, server *httptest.Server) *CodexProvider {
+	t.Helper()
+	provider, err := NewCodexProvider(CodexOptions{
+		Options: Options{
+			APIKey:     "test-token",
+			BaseURL:    server.URL,
+			Model:      "gpt-test",
+			HTTPClient: server.Client(),
+		},
+		AccountID: "account-test",
+	})
+	if err != nil {
+		t.Fatalf("NewCodexProvider: %v", err)
+	}
+	return provider
+}
+
+func openCodexSession(t *testing.T, provider *CodexProvider) zeroruntime.TurnSession {
+	t.Helper()
+	session, err := NewCodexTurnSessionProvider(provider, zeroruntime.ProviderCapabilities{}).OpenTurnSession(t.Context())
+	if err != nil {
+		t.Fatalf("OpenTurnSession: %v", err)
+	}
+	if err := session.Prewarm(t.Context()); err != nil {
+		t.Fatalf("Prewarm: %v", err)
+	}
+	return session
+}
+
+func collectCodexSessionEvents(t *testing.T, session zeroruntime.TurnSession, request zeroruntime.CompletionRequest) []zeroruntime.StreamEvent {
+	t.Helper()
+	return collectCodexSessionEventsContext(t, t.Context(), session, request)
+}
+
+func collectCodexSessionEventsContext(t *testing.T, ctx context.Context, session zeroruntime.TurnSession, request zeroruntime.CompletionRequest) []zeroruntime.StreamEvent {
+	t.Helper()
+	stream, err := session.Stream(ctx, request)
+	if err != nil {
+		t.Fatalf("Stream: %v", err)
+	}
+	events := []zeroruntime.StreamEvent{}
+	for event := range stream {
+		events = append(events, event)
+		if event.Type == zeroruntime.StreamEventError {
+			t.Fatalf("stream error: %s", event.Error)
+		}
+	}
+	return events
+}
+
+func writeWebSocketEvents(ctx context.Context, connection *websocket.Conn, events ...string) {
+	for _, event := range events {
+		if err := connection.Write(ctx, websocket.MessageText, []byte(event)); err != nil {
+			return
+		}
+	}
+}
+
+func hasToolCallEnd(events []zeroruntime.StreamEvent, id string) bool {
+	for _, event := range events {
+		if event.Type == zeroruntime.StreamEventToolCallEnd && event.ToolCallID == id {
+			return true
+		}
+	}
+	return false
+}
+
+func joinedText(events []zeroruntime.StreamEvent) string {
+	var builder strings.Builder
+	for _, event := range events {
+		if event.Type == zeroruntime.StreamEventText {
+			builder.WriteString(event.Content)
+		}
+	}
+	return builder.String()
+}
@@ -2,6 +2,8 @@ package openai

 import (
 	"context"
+	"reflect"
+	"strings"
 	"testing"

 	"github.com/Gitlawb/zero/internal/zeroruntime"
@@ -25,6 +27,126 @@ func TestToolCallKeyOutputIndexZero(t *testing.T) {
 	}
 }

+func TestResponsesStatePreservesDistinctCallID(t *testing.T) {
+	provider := &CodexProvider{}
+	state := newResponsesState()
+	events := make(chan zeroruntime.StreamEvent, 4)
+	provider.handleOutputItemAdded(context.Background(), &responsesEvent{
+		ItemID: "item-1",
+		Item: &itemPayload{
+			Type:   "function_call",
+			ID:     "item-1",
+			CallID: "call-1",
+			Name:   "read_file",
+		},
+	}, state, events)
+	items := state.outputInputItems()
+	if len(items) != 1 || items[0].ID != "item-1" || items[0].CallID != "call-1" {
+		t.Fatalf("captured function call = %#v, want item id item-1 and call id call-1", items)
+	}
+}
+
+func TestCodexCustomApplyPatchStreamProducesFreeformCall(t *testing.T) {
+	provider := &CodexProvider{}
+	state := newResponsesState()
+	events := make(chan zeroruntime.StreamEvent, 16)
+	patch := "*** Begin Patch\n*** Add File: hello.txt\n+hello\n*** End Patch\n"
+	for _, payload := range []string{
+		`{"type":"response.output_item.added","item_id":"item-1","item":{"type":"custom_tool_call","call_id":"call-1","name":"apply_patch"}}`,
+		`{"type":"response.custom_tool_call_input.delta","item_id":"item-1","call_id":"call-1","delta":"*** Begin Patch\n*** Add File: hello.txt\n"}`,
+		`{"type":"response.custom_tool_call_input.delta","item_id":"item-1","call_id":"call-1","delta":"+hello\n*** End Patch\n"}`,
+		`{"type":"response.output_item.done","item_id":"item-1","item":{"type":"custom_tool_call","call_id":"call-1","name":"apply_patch","input":"*** Begin Patch\n*** Add File: hello.txt\n+hello\n*** End Patch\n"}}`,
+		`{"type":"response.completed","response":{"id":"resp-1","status":"completed"}}`,
+	} {
+		if keepReading := provider.emitResponsesEvent(context.Background(), payload, state, events); !keepReading && !state.done {
+			t.Fatalf("stream stopped before terminal event for %s", payload)
+		}
+	}
+	close(events)
+	collected := zeroruntime.CollectStream(context.Background(), events)
+	if len(collected.ToolCalls) != 1 {
+		t.Fatalf("tool calls = %#v, want one", collected.ToolCalls)
+	}
+	call := collected.ToolCalls[0]
+	if call.ID != "item-1" || call.ProviderCallID != "call-1" || call.Name != "apply_patch" || !call.Freeform || call.Arguments != patch {
+		t.Fatalf("custom apply_patch call = %#v", call)
+	}
+}
+
+func TestCodexApplyPatchUsesFreeformWireContract(t *testing.T) {
+	provider, err := NewCodexProvider(CodexOptions{Options: Options{
+		APIKey:  "test-token",
+		BaseURL: "https://chatgpt.example/backend-api/codex",
+		Model:   "gpt-test",
+	}})
+	if err != nil {
+		t.Fatalf("NewCodexProvider: %v", err)
+	}
+	patch := "*** Begin Patch\n*** Add File: hello.txt\n+hello\n*** End Patch\n"
+	request, err := provider.buildResponsesRequest(zeroruntime.CompletionRequest{
+		Messages: []zeroruntime.Message{
+			{Role: zeroruntime.MessageRoleUser, Content: "Add the file."},
+			{Role: zeroruntime.MessageRoleAssistant, ToolCalls: []zeroruntime.ToolCall{{
+				ID: "item-1", ProviderCallID: "call-1", Name: "apply_patch", Arguments: patch, Freeform: true,
+			}}},
+			{Role: zeroruntime.MessageRoleTool, ToolCallID: "item-1", ToolCallProviderID: "call-1", Content: "Done!"},
+		},
+		Tools: []zeroruntime.ToolDefinition{{
+			Name: "apply_patch", Description: "Apply a patch.", Type: zeroruntime.ToolDefinitionFreeform,
+		}},
+	})
+	if err != nil {
+		t.Fatalf("buildResponsesRequest: %v", err)
+	}
+	if len(request.Tools) != 1 || request.Tools[0].Type != string(zeroruntime.ToolDefinitionFreeform) ||
+		request.Tools[0].Format == nil || request.Tools[0].Format.Syntax != "lark" || request.Tools[0].Parameters != nil {
+		t.Fatalf("apply_patch tool wire shape = %#v", request.Tools)
+	}
+	if !strings.Contains(request.Tools[0].Format.Definition, "*** Begin Patch") {
+		t.Fatalf("apply_patch grammar = %q", request.Tools[0].Format.Definition)
+	}
+	if !strings.Contains(request.Tools[0].Description, "absolute file paths") || !strings.Contains(request.Tools[0].Description, "granted extra write root") {
+		t.Fatalf("apply_patch description does not explain extra-root paths: %q", request.Tools[0].Description)
+	}
+	if len(request.Input) != 3 || request.Input[1].Type != "custom_tool_call" || request.Input[1].ID != "item-1" ||
+		request.Input[1].CallID != "call-1" || request.Input[1].Input != patch ||
+		request.Input[2].Type != "custom_tool_call_output" || request.Input[2].CallID != "call-1" {
+		t.Fatalf("custom apply_patch replay input = %#v", request.Input)
+	}
+}
+
+func TestCodexPreservesCustomApplyPatchFunction(t *testing.T) {
+	provider, err := NewCodexProvider(CodexOptions{Options: Options{
+		APIKey:  "test-token",
+		BaseURL: "https://chatgpt.example/backend-api/codex",
+		Model:   "gpt-test",
+	}})
+	if err != nil {
+		t.Fatalf("NewCodexProvider: %v", err)
+	}
+	parameters := map[string]any{
+		"type":       "object",
+		"properties": map[string]any{"value": map[string]any{"type": "string"}},
+	}
+	request, err := provider.buildResponsesRequest(zeroruntime.CompletionRequest{
+		Messages: []zeroruntime.Message{{Role: zeroruntime.MessageRoleUser, Content: "Call the custom tool."}},
+		Tools: []zeroruntime.ToolDefinition{{
+			Name: "apply_patch", Description: "Custom integration tool.", Parameters: parameters,
+		}},
+	})
+	if err != nil {
+		t.Fatalf("buildResponsesRequest: %v", err)
+	}
+	if len(request.Tools) != 1 {
+		t.Fatalf("tools = %#v, want one", request.Tools)
+	}
+	tool := request.Tools[0]
+	if tool.Type != string(zeroruntime.ToolDefinitionFunction) || tool.Format != nil ||
+		tool.Description != "Custom integration tool." || !reflect.DeepEqual(tool.Parameters, parameters) {
+		t.Fatalf("custom apply_patch function was rewritten: %#v", tool)
+	}
+}
+
 func TestHandleTerminalResponseNilPayload(t *testing.T) {
 	p := &CodexProvider{}

@@ -90,11 +212,14 @@ func TestHandleTerminalResponseFailedPayloadWithoutError(t *testing.T) {
 	// A response.completed with a payload and no error remains a clean done.
 	ok := make(chan zeroruntime.StreamEvent, 8)
 	p.handleTerminalResponse(context.Background(),
-		&responsesEvent{Type: responsesEventCompleted, Response: &responsePayload{Status: "completed"}}, &responsesState{}, ok)
+		&responsesEvent{Type: responsesEventCompleted, Response: &responsePayload{ID: "resp-1", Status: "completed"}}, &responsesState{}, ok)
 	close(ok)
 	for ev := range ok {
 		if ev.Type == zeroruntime.StreamEventError {
 			t.Error("response.completed with a non-error payload must NOT emit an error")
 		}
+		if ev.Type == zeroruntime.StreamEventDone && ev.ResponseID != "resp-1" {
+			t.Errorf("done response id = %q, want resp-1", ev.ResponseID)
+		}
 	}
 }
@@ -771,7 +771,7 @@ func TestCodexProviderParsesResponsesTextDeltas(t *testing.T) {
 		`{"type":"response.output_text.delta","delta":"hello "}`,
 		`{"type":"response.output_text.delta","delta":"world"}`,
 		`{"type":"response.output_text.delta","delta":"!"}`,
-		`{"type":"response.completed","response":{"id":"resp-1","status":"completed","usage":{"input_tokens":7,"output_tokens":3,"output_tokens_details":{"reasoning_tokens":1},"input_tokens_details":{"cached_tokens":2}}}}`,
+		`{"type":"response.completed","response":{"id":"resp-1","status":"completed","usage":{"input_tokens":7,"output_tokens":3,"output_tokens_details":{"reasoning_tokens":1},"input_tokens_details":{"cached_tokens":2,"cache_write_tokens":1}}}}`,
 	)
 	defer srv.Close()

@@ -809,8 +809,8 @@ func TestCodexProviderParsesResponsesTextDeltas(t *testing.T) {
 	if usage == nil {
 		t.Fatal("expected a usage event, got none")
 	}
-	if usage.InputTokens != 7 || usage.OutputTokens != 3 || usage.CachedInputTokens != 2 || usage.ReasoningTokens != 1 {
-		t.Fatalf("usage = %+v, want input=7 output=3 cached=2 reasoning=1", *usage)
+	if usage.InputTokens != 7 || usage.OutputTokens != 3 || usage.CachedInputTokens != 2 || usage.CacheWriteTokens != 1 || usage.ReasoningTokens != 1 {
+		t.Fatalf("usage = %+v, want input=7 output=3 cached=2 cache-write=1 reasoning=1", *usage)
 	}
 	if !gotDone {
 		t.Fatal("expected a done event, got none")
@@ -357,6 +357,7 @@ func (provider *Provider) emitChunk(
 				PromptTokens:      chunk.Usage.PromptTokens,
 				CompletionTokens:  chunk.Usage.CompletionTokens,
 				CachedInputTokens: chunk.Usage.PromptTokensDetails.CachedTokens,
+				CacheWriteTokens:  chunk.Usage.PromptTokensDetails.CacheWriteTokens,
 				ReasoningTokens:   chunk.Usage.CompletionTokensDetails.ReasoningTokens,
 			},
 		})
@@ -486,7 +487,7 @@ func (provider *Provider) openAIRequest(request zeroruntime.CompletionRequest) c
 				Function: toolFunction{
 					Name:        tool.Name,
 					Description: tool.Description,
-					Parameters:  tool.Parameters,
+					Parameters:  normalizeToolParameters(tool.Parameters),
 				},
 			})
 		}
@@ -494,6 +495,21 @@ func (provider *Provider) openAIRequest(request zeroruntime.CompletionRequest) c
 	return mapped
 }

+// normalizeToolParameters keeps schemas accepted by strict OpenAI-compatible
+// servers such as LM Studio. No-argument tools still need an object-valued
+// parameters.properties field instead of an omitted field.
+func normalizeToolParameters(parameters map[string]any) map[string]any {
+	normalized := make(map[string]any, len(parameters)+1)
+	for key, value := range parameters {
+		normalized[key] = value
+	}
+	properties, ok := normalized["properties"].(map[string]any)
+	if !ok || properties == nil {
+		normalized["properties"] = map[string]any{}
+	}
+	return normalized
+}
+
 // promptCacheKeyDisabled reports whether the ZERO_DISABLE_PROMPT_CACHE_KEY
 // kill switch is set to a truthy value. "0" and "false" (any case) are
 // no-ops, matching how ZERO_FORMAT_ON_WRITE parses boolean flags, so an
@@ -3,6 +3,7 @@ package openai
 import (
 	"context"
 	"encoding/json"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"reflect"
@@ -105,6 +106,72 @@ func TestStreamCompletionPostsChatCompletionRequest(t *testing.T) {
 	if tool["type"] != "function" {
 		t.Fatalf("unexpected tool wrapper: %#v", tool)
 	}
+	functionDefinition := tool["function"].(map[string]any)
+	parameters := functionDefinition["parameters"].(map[string]any)
+	properties, ok := parameters["properties"].(map[string]any)
+	if !ok || len(properties) != 0 {
+		t.Fatalf("parameters.properties = %#v, want empty object", parameters["properties"])
+	}
+}
+
+// TestStreamCompletionSerializesTypedNilPropertiesAsEmptyObject locks in the
+// normalizeToolParameters fix: a tool whose parameters carry a typed-nil
+// properties map must serialize "properties":{} on the wire, never
+// "properties":null, because strict OpenAI-compatible servers (LM Studio)
+// reject the null form.
+func TestStreamCompletionSerializesTypedNilPropertiesAsEmptyObject(t *testing.T) {
+	var gotBody map[string]any
+	var gotRaw []byte
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		raw, err := io.ReadAll(r.Body)
+		if err != nil {
+			t.Fatalf("read request body: %v", err)
+		}
+		gotRaw = raw
+		if err := json.Unmarshal(raw, &gotBody); err != nil {
+			t.Fatalf("decode request body: %v", err)
+		}
+		writeSSE(w, `{"choices":[]}`)
+		writeSSE(w, `[DONE]`)
+	}))
+	defer server.Close()
+
+	provider, err := New(Options{
+		APIKey:  "sk-secret",
+		BaseURL: server.URL + "/",
+		Model:   "gpt-test",
+	})
+	if err != nil {
+		t.Fatalf("New returned error: %v", err)
+	}
+
+	stream, err := provider.StreamCompletion(context.Background(), zeroruntime.CompletionRequest{
+		Messages: []zeroruntime.Message{{Role: zeroruntime.MessageRoleUser, Content: "hi"}},
+		Tools: []zeroruntime.ToolDefinition{{
+			Name:        "no_args",
+			Description: "Takes no arguments",
+			Parameters:  map[string]any{"type": "object", "properties": map[string]any(nil)},
+		}},
+	})
+	if err != nil {
+		t.Fatalf("StreamCompletion returned error: %v", err)
+	}
+	drain(stream)
+
+	if !strings.Contains(string(gotRaw), `"properties":{}`) {
+		t.Fatalf("request body must serialize properties as an empty object, got: %s", gotRaw)
+	}
+	if strings.Contains(string(gotRaw), `"properties":null`) {
+		t.Fatalf("request body must not serialize properties as null, got: %s", gotRaw)
+	}
+	tools := gotBody["tools"].([]any)
+	tool := tools[0].(map[string]any)
+	functionDefinition := tool["function"].(map[string]any)
+	parameters := functionDefinition["parameters"].(map[string]any)
+	properties, ok := parameters["properties"].(map[string]any)
+	if !ok || len(properties) != 0 {
+		t.Fatalf("parameters.properties = %#v, want empty object", parameters["properties"])
+	}
 }

 func TestNewRequiresModelButNotAPIKey(t *testing.T) {
@@ -193,14 +260,14 @@ func TestStreamCompletionAppliesCustomAuthAndHeaders(t *testing.T) {
 func TestStreamCompletionEmitsTextUsageAndDone(t *testing.T) {
 	provider := newTestProvider(t, func(w http.ResponseWriter, r *http.Request) {
 		writeSSE(w, `{"choices":[{"delta":{"content":"hello "}}]}`)
-		writeSSE(w, `{"choices":[{"delta":{"content":"zero"}}],"usage":{"prompt_tokens":12,"completion_tokens":5,"prompt_tokens_details":{"cached_tokens":3}}}`)
+		writeSSE(w, `{"choices":[{"delta":{"content":"zero"}}],"usage":{"prompt_tokens":12,"completion_tokens":5,"prompt_tokens_details":{"cached_tokens":3,"cache_write_tokens":2}}}`)
 		writeSSE(w, `[DONE]`)
 	})

 	events := collectProviderEvents(t, provider)
 	assertEvent(t, events[0], zeroruntime.StreamEventText, "hello ")
 	assertEvent(t, events[1], zeroruntime.StreamEventText, "zero")
-	if events[2].Type != zeroruntime.StreamEventUsage || events[2].Usage.PromptTokens != 12 || events[2].Usage.CompletionTokens != 5 || events[2].Usage.CachedInputTokens != 3 {
+	if events[2].Type != zeroruntime.StreamEventUsage || events[2].Usage.PromptTokens != 12 || events[2].Usage.CompletionTokens != 5 || events[2].Usage.CachedInputTokens != 3 || events[2].Usage.CacheWriteTokens != 2 {
 		t.Fatalf("unexpected usage event: %#v", events[2])
 	}
 	if events[3].Type != zeroruntime.StreamEventDone {
@@ -1479,3 +1546,66 @@ func TestOpenAIRequestPreservesCacheablePrefixAcrossTurns(t *testing.T) {
 		t.Fatalf("wire prompt cache key must remain stable: first=%#v second=%#v", first["prompt_cache_key"], second["prompt_cache_key"])
 	}
 }
+
+// TestStreamCompletionSerializesNonMapPropertiesAsEmptyObject locks in the
+// normalizeToolParameters type-assert branch: when a tool's parameters carry a
+// `properties` field whose value is a non-map (e.g., an empty slice), it must
+// be normalized to "properties":{} on the wire, never "properties":[] or
+// "properties":null.
+func TestStreamCompletionSerializesNonMapPropertiesAsEmptyObject(t *testing.T) {
+	var gotBody map[string]any
+	var gotRaw []byte
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		raw, err := io.ReadAll(r.Body)
+		if err != nil {
+			t.Fatalf("read request body: %v", err)
+		}
+		gotRaw = raw
+		if err := json.Unmarshal(raw, &gotBody); err != nil {
+			t.Fatalf("decode request body: %v", err)
+		}
+		writeSSE(w, `{"choices":[]}`)
+		writeSSE(w, `[DONE]`)
+	}))
+	defer server.Close()
+
+	provider, err := New(Options{
+		APIKey:  "sk-secret",
+		BaseURL: server.URL + "/",
+		Model:   "gpt-test",
+	})
+	if err != nil {
+		t.Fatalf("New returned error: %v", err)
+	}
+
+	stream, err := provider.StreamCompletion(context.Background(), zeroruntime.CompletionRequest{
+		Messages: []zeroruntime.Message{{Role: zeroruntime.MessageRoleUser, Content: "hi"}},
+		Tools: []zeroruntime.ToolDefinition{{
+			Name:        "no_args",
+			Description: "Takes no arguments",
+			Parameters:  map[string]any{"type": "object", "properties": []any{}},
+		}},
+	})
+	if err != nil {
+		t.Fatalf("StreamCompletion returned error: %v", err)
+	}
+	drain(stream)
+
+	if !strings.Contains(string(gotRaw), `"properties":{}`) {
+		t.Fatalf("request body must serialize properties as an empty object, got: %s", gotRaw)
+	}
+	if strings.Contains(string(gotRaw), `"properties":null`) {
+		t.Fatalf("request body must not serialize properties as null, got: %s", gotRaw)
+	}
+	if strings.Contains(string(gotRaw), `"properties":[]`) {
+		t.Fatalf("request body must not serialize properties as an empty array, got: %s", gotRaw)
+	}
+	tools := gotBody["tools"].([]any)
+	tool := tools[0].(map[string]any)
+	functionDefinition := tool["function"].(map[string]any)
+	parameters := functionDefinition["parameters"].(map[string]any)
+	properties, ok := parameters["properties"].(map[string]any)
+	if !ok || len(properties) != 0 {
+		t.Fatalf("parameters.properties = %#v, want empty object", parameters["properties"])
+	}
+}
@@ -195,7 +195,12 @@ func (s *turnSession) computeFingerprint(request zeroruntime.CompletionRequest)
 func wireToolsDigest(tools []zeroruntime.ToolDefinition) string {
 	rendered := make([]string, 0, len(tools))
 	for _, tool := range tools {
-		schema, err := json.Marshal(tool.Parameters)
+		wireShape := struct {
+			Type       zeroruntime.ToolDefinitionType    `json:"type,omitempty"`
+			Parameters map[string]any                    `json:"parameters,omitempty"`
+			Format     *zeroruntime.ToolDefinitionFormat `json:"format,omitempty"`
+		}{Type: tool.Type, Parameters: tool.Parameters, Format: tool.Format}
+		schema, err := json.Marshal(wireShape)
 		if err != nil {
 			rendered = append(rendered, tool.Name+"\n"+tool.Description+"\n__non_json:"+tool.Name)
 			continue
@@ -109,7 +109,8 @@ type usage struct {
 }

 type promptTokenDetails struct {
-	CachedTokens int `json:"cached_tokens"`
+	CachedTokens     int `json:"cached_tokens"`
+	CacheWriteTokens int `json:"cache_write_tokens"`
 }

 type completionTokenDetails struct {
@@ -15,9 +15,27 @@ import (
 // value (e.g. "1") to enable — the same boolean idiom as ZERO_FORMAT_ON_WRITE.
 const openaiTurnSessionEnv = "ZERO_OPENAI_TURN_SESSION"

+// ChatGPT Responses sessions are enabled by default for their native provider.
+// Setting this to 0/false/off restores the stateless HTTP/SSE transport.
+const chatGPTTurnSessionEnv = "ZERO_CHATGPT_TURN_SESSION"
+
 func openaiTurnSessionEnabled() bool {
 	value := strings.TrimSpace(os.Getenv(openaiTurnSessionEnv))
-	return value != "" && value != "0" && !strings.EqualFold(value, "false")
+	return value != "" && !explicitEnvFalse(value)
+}
+
+func chatGPTTurnSessionEnabled() bool {
+	value := strings.TrimSpace(os.Getenv(chatGPTTurnSessionEnv))
+	return value == "" || !explicitEnvFalse(value)
+}
+
+func explicitEnvFalse(value string) bool {
+	switch strings.ToLower(strings.TrimSpace(value)) {
+	case "0", "false", "off":
+		return true
+	default:
+		return false
+	}
 }

 // OptimizedTurnSessions returns the gated optimized TurnSessionProvider for an
@@ -25,20 +43,33 @@ func openaiTurnSessionEnabled() bool {
 // is ineligible. Callers leave agent Options.TurnSessionProvider nil on false,
 // so the loop's default wrap keeps today's behavior byte-identical.
 //
-// Eligibility is deliberately narrow: the resolved provider kind must be
-// official OpenAI (NOT openai-compatible gateways — the constructor merges the
-// two, so this branches on the resolved kind explicitly), not the ChatGPT
-// Codex catalog, and the provider value must be the concrete *openai.Provider
-// (a fake, a Codex provider, or nil falls back to the default path safely).
-// No base-URL check on top of the kind: prewarm and fingerprint telemetry are
-// harmless against any host, and kind==openai mirrors the existing
-// official-OpenAI precedent used for prompt_cache_key.
+// Eligibility is deliberately narrow: native ChatGPT Responses uses its
+// concrete Codex provider and defaults on with a kill switch; official OpenAI
+// chat-completions keeps its existing opt-in prewarm session. Compatible
+// gateways and foreign provider values always retain the default adapter.
 func OptimizedTurnSessions(profile config.ProviderProfile, provider zeroruntime.Provider, options Options) (zeroruntime.TurnSessionProvider, bool) {
-	if !openaiTurnSessionEnabled() {
+	resolved, err := resolveProfile(profile, options)
+	if err != nil {
 		return nil, false
 	}
-	resolved, err := resolveProfile(profile, options)
-	if err != nil || resolved.providerKind != config.ProviderKindOpenAI || isCodexCatalog(profile, resolved) {
+	if isCodexCatalog(profile, resolved) {
+		if !chatGPTTurnSessionEnabled() {
+			return nil, false
+		}
+		concrete, ok := provider.(*openai.CodexProvider)
+		if !ok {
+			return nil, false
+		}
+		caps, err := resolveCapabilities(profile, options)
+		if err != nil {
+			return nil, false
+		}
+		return openai.NewCodexTurnSessionProvider(concrete, caps), true
+	}
+	if resolved.providerKind != config.ProviderKindOpenAI {
+		return nil, false
+	}
+	if !openaiTurnSessionEnabled() {
 		return nil, false
 	}
 	concrete, ok := provider.(*openai.Provider)
@@ -5,6 +5,7 @@ import (
 	"testing"

 	"github.com/Gitlawb/zero/internal/config"
+	"github.com/Gitlawb/zero/internal/providers/openai"
 	"github.com/Gitlawb/zero/internal/zeroruntime"
 )

@@ -45,7 +46,7 @@ func TestOptimizedTurnSessionsDefaultOff(t *testing.T) {
 func TestOptimizedTurnSessionsFalseyValues(t *testing.T) {
 	profile := openaiEligibleProfile()
 	provider := buildGateProvider(t, profile)
-	for _, value := range []string{"0", "false", "FALSE", "False", " ", ""} {
+	for _, value := range []string{"0", "false", "FALSE", "False", "off", "OFF", " ", ""} {
 		t.Setenv(openaiTurnSessionEnv, value)
 		if _, ok := OptimizedTurnSessions(profile, provider, Options{}); ok {
 			t.Fatalf("gate enabled for falsey value %q", value)
@@ -59,6 +60,21 @@ func TestOptimizedTurnSessionsFalseyValues(t *testing.T) {
 	}
 }

+func TestChatGPTTurnSessionGateValues(t *testing.T) {
+	for _, value := range []string{"0", "false", "FALSE", "off", "OFF"} {
+		t.Setenv(chatGPTTurnSessionEnv, value)
+		if chatGPTTurnSessionEnabled() {
+			t.Fatalf("ChatGPT gate enabled for falsey value %q", value)
+		}
+	}
+	for _, value := range []string{"", " ", "1", "true", "on"} {
+		t.Setenv(chatGPTTurnSessionEnv, value)
+		if !chatGPTTurnSessionEnabled() {
+			t.Fatalf("ChatGPT gate disabled for default/truthy value %q", value)
+		}
+	}
+}
+
 func TestOptimizedTurnSessionsOpenAIEligible(t *testing.T) {
 	t.Setenv(openaiTurnSessionEnv, "1")
 	profile := openaiEligibleProfile()
@@ -88,13 +104,64 @@ func TestOptimizedTurnSessionsRejectsCompatible(t *testing.T) {
 }

 func TestOptimizedTurnSessionsRejectsCodexCatalog(t *testing.T) {
-	t.Setenv(openaiTurnSessionEnv, "1")
+	t.Setenv(chatGPTTurnSessionEnv, "0")
+	profile := openaiEligibleProfile()
+	profile.Name = "chatgpt"
+	profile.CatalogID = "chatgpt"
+	if _, ok := OptimizedTurnSessions(profile, buildChatGPTGateProvider(t, profile), Options{}); ok {
+		t.Fatal("the ChatGPT Codex catalog must honor the turn-session kill switch")
+	}
+}
+
+func TestOptimizedTurnSessionsEnablesChatGPTResponsesByDefault(t *testing.T) {
+	t.Setenv(chatGPTTurnSessionEnv, "")
+	profile := openaiEligibleProfile()
+	profile.Name = "chatgpt"
+	profile.CatalogID = "chatgpt"
+	provider := buildChatGPTGateProvider(t, profile)
+
+	turnSessions, ok := OptimizedTurnSessions(profile, provider, Options{})
+	if !ok || turnSessions == nil {
+		t.Fatal("ChatGPT Responses provider did not receive its default turn session")
+	}
+	if got := turnSessions.Capabilities().Model; got != profile.Model {
+		t.Fatalf("Capabilities().Model = %q, want %q", got, profile.Model)
+	}
+}
+
+func TestOptimizedTurnSessionsRecognizesCompatibleLabeledChatGPTProfile(t *testing.T) {
+	t.Setenv(chatGPTTurnSessionEnv, "")
+	profile := openaiEligibleProfile()
+	profile.Name = "chatgpt"
+	profile.CatalogID = "chatgpt"
+	profile.ProviderKind = config.ProviderKindOpenAICompatible
+	if turnSessions, ok := OptimizedTurnSessions(profile, buildChatGPTGateProvider(t, profile), Options{}); !ok || turnSessions == nil {
+		t.Fatal("ChatGPT catalog profile must use its native session regardless of the stored compatibility label")
+	}
+}
+
+func buildChatGPTGateProvider(t *testing.T, profile config.ProviderProfile) *openai.CodexProvider {
+	t.Helper()
+	provider, err := openai.NewCodexProvider(openai.CodexOptions{
+		Options: openai.Options{
+			APIKey:  "test-token",
+			BaseURL: "https://chatgpt.example/backend-api/codex",
+			Model:   profile.Model,
+		},
+		AccountID: "account-test",
+	})
+	if err != nil {
+		t.Fatalf("NewCodexProvider: %v", err)
+	}
+	return provider
+}
+
+func TestOptimizedTurnSessionsRejectsNonCodexProviderForChatGPT(t *testing.T) {
+	t.Setenv(chatGPTTurnSessionEnv, "1")
 	profile := openaiEligibleProfile()
 	profile.CatalogID = "chatgpt"
-	// Build the provider from the base profile: the point under test is the
-	// catalog check, not Codex construction (which needs OAuth wiring).
 	if _, ok := OptimizedTurnSessions(profile, buildGateProvider(t, openaiEligibleProfile()), Options{}); ok {
-		t.Fatal("the ChatGPT Codex catalog must not get the optimized session")
+		t.Fatal("a ChatGPT catalog profile with a non-Codex provider must use the default session")
 	}
 }

@@ -7,6 +7,7 @@ import (
 type BackendOptions struct {
 	GOOS             string
 	LookupExecutable func(string) (string, error)
+	DetectWSL        func() WSLInfo
 }

 type Backend struct {
@@ -53,6 +54,7 @@ func SelectBackend(options BackendOptions) Backend {
 	return NewSandboxManager(SandboxManagerOptions{
 		GOOS:             options.GOOS,
 		LookupExecutable: options.LookupExecutable,
+		DetectWSL:        options.DetectWSL,
 	}).Backend()
 }

@@ -45,6 +45,7 @@ func TestSelectBackendChoosesPlatformAdapterWithFallback(t *testing.T) {
 				}
 				return "", errors.New("missing")
 			},
+			DetectWSL: func() WSLInfo { return WSLInfo{} },
 		})
 		if backend.Name != BackendUnavailable || backend.Available {
 			t.Fatalf("linux backend = %#v, want native sandbox unavailable without Linux helper", backend)
@@ -54,6 +55,20 @@ func TestSelectBackendChoosesPlatformAdapterWithFallback(t *testing.T) {
 		}
 	})

+	t.Run("linux helper missing under WSL reports WSL fallback", func(t *testing.T) {
+		backend := SelectBackend(BackendOptions{
+			GOOS:             "linux",
+			LookupExecutable: func(string) (string, error) { return "", errors.New("missing") },
+			DetectWSL:        func() WSLInfo { return WSLInfo{IsWSL: true, IsWSL2: true} },
+		})
+		if backend.Name != BackendWSL || backend.Available || !backend.Fallback {
+			t.Fatalf("linux backend = %#v, want explicit WSL fallback", backend)
+		}
+		if !strings.Contains(backend.Message, "WSL2") {
+			t.Fatalf("linux fallback message = %q, want WSL2 diagnostic", backend.Message)
+		}
+	})
+
 	t.Run("darwin sandbox exec available", func(t *testing.T) {
 		backend := SelectBackend(BackendOptions{
 			GOOS: "darwin",
@@ -0,0 +1,96 @@
+package sandbox
+
+import (
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestApplyPatchPathBlockOnlyRejectsRelativeTraversal(t *testing.T) {
+	root := t.TempDir()
+	inside := filepath.Join(root, "main.js")
+	structured := func(path string) string {
+		return strings.Join([]string{"*** Begin Patch", "*** Update File: " + path, "@@", "-a", "+b", "*** End Patch"}, "\n")
+	}
+	for name, patch := range map[string]string{
+		"absolute inside workspace": structured(inside),
+		"relative":                  structured("main.js"),
+		"decorated markers":         "*** Begin Patch ***\n*** Update File: main.js\n@@\n-a\n+b\n*** End Patch ***",
+		"no-space marker":           "***Begin Patch\n*** Update File: main.js\n@@\n-a\n+b\n***End Patch",
+	} {
+		request := Request{ToolName: "apply_patch", WorkspaceRoot: root, SideEffect: SideEffectWrite, Args: map[string]any{"patch": patch}}
+		if block := applyPatchPathBlock(request); block != nil {
+			t.Fatalf("%s: unexpected block %+v", name, block)
+		}
+	}
+	for _, path := range []string{"../escape.js", ".."} {
+		for name, patch := range map[string]string{"canonical": structured(path), "no-space": "***Begin Patch\n*** Update File: " + path + "\n@@\n-a\n+b\n***End Patch"} {
+			request := Request{ToolName: "apply_patch", WorkspaceRoot: root, SideEffect: SideEffectWrite, Args: map[string]any{"patch": patch}}
+			block := applyPatchPathBlock(request)
+			if block == nil || block.Code != BlockOutsideWorkspace {
+				t.Fatalf("%s %q must be blocked as traversal, got %+v", name, path, block)
+			}
+		}
+	}
+}
+
+// Every marker spelling the tool applies must be classified as structured at
+// the sandbox boundary too; otherwise the boundary scans the patch as a unified
+// diff, extracts no targets, and validates nothing (fail-open).
+func TestStructuredPatchClassifierMatchesToolSpellings(t *testing.T) {
+	for _, header := range []string{"*** Begin Patch", "*** Begin Patch ***", "***Begin Patch", "  *** Begin Patch  ", "\ufeff*** Begin Patch"} {
+		patch := header + "\n*** Update File: main.js\n@@\n-a\n+b\n*** End Patch"
+		if !IsStructuredPatch(patch) {
+			t.Fatalf("%q must classify as a structured patch", header)
+		}
+		if paths := applyPatchPaths(patch); len(paths) != 1 || paths[0] != "main.js" {
+			t.Fatalf("%q: sandbox must extract the structured target, got %v", header, paths)
+		}
+	}
+	for _, header := range []string{"--- a/x", "Begin Patch", "*** Begin Patchwork", "*** Update File: x"} {
+		if IsStructuredPatch(header + "\n-a\n+b") {
+			t.Fatalf("%q must not classify as a structured patch", header)
+		}
+	}
+	if StructuredPatchMarker("*** End Patch ***") != "end" || StructuredPatchMarker("***End Patch") != "end" {
+		t.Fatal("decorated end markers must classify as end")
+	}
+}
+
+func TestApplyPatchRequestPathsCarryAbsolutePathsToScopeValidation(t *testing.T) {
+	root := t.TempDir()
+	// NewScope also grants the system temp dir, so a sibling t.TempDir() is
+	// legitimately in scope; pick a path under the filesystem root instead.
+	outside, err := filepath.Abs(filepath.Join(string(filepath.Separator), "zero-outside-workspace-test", "escape.js"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	scope, err := NewScope(root, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	inside := filepath.Join(root, "main.js")
+	structured := func(header, footer, path string) string {
+		return strings.Join([]string{header, "*** Update File: " + path, "@@", "-a", "+b", footer}, "\n")
+	}
+	for name, spelling := range map[string][2]string{"canonical": {"*** Begin Patch", "*** End Patch"}, "no-space": {"***Begin Patch", "***End Patch"}} {
+		// Failure path: the exact path the boundary parsed must be denied by the
+		// scope. structuredPatchHeaderPaths normalises separators to "/", so the
+		// parsed form is compared in slash form and then validated as-is.
+		paths := applyPatchRequestPaths(map[string]any{"patch": structured(spelling[0], spelling[1], outside)})
+		if len(paths) != 1 || paths[0] != filepath.ToSlash(outside) {
+			t.Fatalf("%s: absolute patch path must reach scope validation unchanged, got %v", name, paths)
+		}
+		if block := scope.validate(paths[0]); block == nil || block.Code != BlockOutsideWorkspace {
+			t.Fatalf("%s: scope must deny the parsed outside path %q, got %+v", name, paths[0], block)
+		}
+		// Success path: the parsed inside path must be accepted by the scope.
+		paths = applyPatchRequestPaths(map[string]any{"patch": structured(spelling[0], spelling[1], inside)})
+		if len(paths) != 1 || paths[0] != filepath.ToSlash(inside) {
+			t.Fatalf("%s: inside patch path must reach scope validation unchanged, got %v", name, paths)
+		}
+		if block := scope.validate(paths[0]); block != nil {
+			t.Fatalf("%s: scope must accept the parsed inside path %q, got %+v", name, paths[0], block)
+		}
+	}
+}
@@ -148,8 +148,10 @@ func unsafeCommandPrefix(prefix []string) bool {
 			return true
 		}
 	}
+	normalized := append([]string(nil), prefix...)
+	normalized[0] = normalizeLauncherName(normalized[0])
 	for _, banned := range bannedCommandPrefixSuggestions {
-		if sameStringSlice(prefix, banned) {
+		if sameStringSlice(prefix, banned) || sameStringSlice(normalized, banned) {
 			return true
 		}
 	}
@@ -165,25 +167,118 @@ func unsafeCommandPrefixPart(part string) bool {
 }

 func unsafeCommandPrefixLauncher(program string) bool {
-	program = strings.ToLower(strings.TrimSpace(program))
-	if strings.ContainsAny(program, `/\`) {
+	// A path is already refused. ":" and "~" are refused for the same reason:
+	// on Windows they introduce names that resolve to a different file than the
+	// one matched here, and no list can keep up with them. "PYTHON~1.EXE" is
+	// python.exe under an 8.3 short name, and 8.3 truncates the stem, so
+	// "POWERS~1.EXE" cannot be recognized by name at all; "python.exe::$DATA"
+	// names the same executable through its default stream. Refusing the shape
+	// costs a permission prompt on names no real command uses.
+	if strings.ContainsAny(program, `/\:~`) {
 		return true
 	}
-	switch program {
-	case "bash", "sh", "zsh", "/bin/bash", "/bin/zsh",
-		"pwsh", "powershell", "powershell.exe",
-		"env", "sudo", "doas", "su", "run0", "osascript",
+	name := normalizeLauncherName(program)
+	return bannedLauncherName(name) || bannedLauncherName(strings.TrimRight(name, "0123456789"))
+}
+
+func bannedLauncherName(name string) bool {
+	switch name {
+	case "bash", "sh", "zsh", "dash", "ash", "ksh", "csh", "tcsh", "fish", "busybox",
+		"pwsh", "powershell", "cmd", "wsl",
+		"env", "sudo", "sudoedit", "doas", "su", "run0", "osascript",
 		"command", "eval", "exec", "time",
 		"find", "xargs", "timeout", "nice", "nohup", "watch", "setsid", "stdbuf", "ionice",
-		"ssh", "make", "npm", "npx",
-		"python", "python3", "py", "pythonw", "pyw", "pypy", "pypy3",
-		"node", "perl", "ruby", "php", "lua", "deno", "bun":
+		"ssh", "make", "npm", "npx", "pnpm", "yarn", "bunx",
+		"python", "py", "pythonw", "pyw", "pypy", "uv", "uvx",
+		"node", "nodejs", "perl", "ruby", "php", "lua", "deno", "bun":
 		return true
 	default:
 		return false
 	}
 }

+// normalizeLauncherName reduces a program name to the launcher it actually runs
+// so the list above cannot be stepped around by spelling the same interpreter
+// differently: "python3.11", "python.exe" and "PYTHON3" all reach it as a name
+// the list matches. internal/agent's commandName already normalizes case and
+// Windows executable extensions on the allow side; this side matched raw, so
+// every versioned or .exe-suffixed launcher validated as an ordinary command
+// and persisted as a prefix grant that auto-allows every later invocation.
+//
+// A name is only ever narrowed toward an existing entry, so the failure
+// direction is an extra permission prompt, never a silent grant.
+func normalizeLauncherName(program string) string {
+	name := strings.ToLower(strings.TrimSpace(program))
+	// Windows discards trailing dots and spaces when resolving a filename, so
+	// "python." starts python.exe. Drop them before anything matches on the
+	// result, on every platform: the deny side must not depend on which OS is
+	// reading the grant, since the grants file travels with a synced home
+	// directory.
+	name = strings.TrimRight(name, ". ")
+	for _, suffix := range []string{".exe", ".cmd", ".bat", ".com", ".ps1"} {
+		if strings.HasSuffix(name, suffix) {
+			name = strings.TrimSuffix(name, suffix)
+			name = strings.TrimRight(name, ". ")
+			break
+		}
+	}
+	return trimLauncherVersion(trimLauncherABISuffix(trimLauncherBuildSuffix(name)))
+}
+
+// trimLauncherBuildSuffix drops the build-channel suffixes distributions and
+// upstreams append to an otherwise unchanged interpreter, so "python3.11-dbg",
+// "bash-static" and "pwsh-preview" are the launchers they say they are. The set
+// is closed on purpose: a general "-word" strip would also swallow
+// "node-gyp", "python3-config" and "ruby-lsp", which are ordinary tools a user
+// should still be able to approve.
+func trimLauncherBuildSuffix(name string) string {
+	for _, suffix := range []string{"-dbg", "-debug", "-static", "-nightly", "-preview", "-beta"} {
+		if strings.HasSuffix(name, suffix) {
+			return strings.TrimSuffix(name, suffix)
+		}
+	}
+	return name
+}
+
+// trimLauncherABISuffix drops CPython's ABI flags from a versioned interpreter
+// name, so "python3.7m" and "python3.6dm" reduce to their version, and the
+// free-threaded builds "python3.13t" and "python3.13td" reduce to theirs. The
+// flags are only removed when a digit sits underneath them, which leaves
+// ordinary names that happen to end in those letters alone: "sha256sum" keeps
+// its "sum", "zstd" its "td", "cat" its "t".
+func trimLauncherABISuffix(name string) string {
+	trimmed := strings.TrimRight(name, "dmut")
+	if trimmed == name || trimmed == "" {
+		return name
+	}
+	if last := trimmed[len(trimmed)-1]; last < '0' || last > '9' {
+		return name
+	}
+	return trimmed
+}
+
+// trimLauncherVersion drops a trailing "<separator><digits>" version from a
+// program name, so "python3.11" becomes "python3" and "python2.7" becomes
+// "python2". Digits without a separator are part of the name, which keeps
+// "base64", "7z" and "sha256sum" intact; the caller handles the "python3" shape
+// by also testing the digit-stripped form.
+func trimLauncherVersion(name string) string {
+	for {
+		trimmed := strings.TrimRight(name, "0123456789")
+		if trimmed == name || trimmed == "" {
+			return name
+		}
+		if !strings.HasSuffix(trimmed, ".") && !strings.HasSuffix(trimmed, "-") {
+			return name
+		}
+		next := trimmed[:len(trimmed)-1]
+		if next == "" {
+			return name
+		}
+		name = next
+	}
+}
+
 func sameStringSlice(left []string, right []string) bool {
 	if len(left) != len(right) {
 		return false
@@ -0,0 +1,115 @@
+package sandbox
+
+import "testing"
+
+func TestUnsafeCommandPrefixLauncherIgnoresVersionAndExtension(t *testing.T) {
+	for _, program := range []string{
+		"python3", "python", "node", "git", "sh", "bash", "sudo",
+		"python3.11", "python3.12", "python2.7", "python3.13.1",
+		"python.exe", "python3.exe", "node.exe", "git.exe", "bash.exe",
+		"PYTHON3.11", "Node.EXE",
+		"cmd", "cmd.exe", "wsl", "wsl.exe",
+		// Windows resolves these to the same executable.
+		"python.", "python3.", "python3.11.", "python.exe.", "PYTHON.",
+		"python.cmd", "python.bat", "python.com", "python.ps1",
+		"PYTHON~1.EXE", "POWERS~1.EXE", "python.exe::$DATA",
+		// Versioned and ABI-suffixed interpreters.
+		"python3.7m", "python3.6dm", "pythonw3.11", "python-3.11",
+		// Free-threaded CPython (PEP 703) ships beside the GIL build.
+		"python3.13t", "python3.13t.exe", "python3.14t", "python3.13td",
+		// Distribution and build-channel spellings of the same interpreter.
+		"nodejs", "nodejs.exe", "node-nightly", "python3-dbg", "python3.11-dbg",
+		"python3.13t-dbg", "python3-debug", "python3.11-debug", "node-beta",
+		"pwsh-preview", "bash-static", "sudoedit",
+		// Twins of npm and npx, which the list already refuses.
+		"pnpm", "yarn", "bunx", "pnpm.cmd", "yarn.exe",
+		"perl5.36", "ruby3.2", "php8", "lua5.4", "node22.exe", "bash5",
+	} {
+		if !unsafeCommandPrefix([]string{program}) {
+			t.Errorf("unsafeCommandPrefix([%q]) = false, want true", program)
+		}
+	}
+}
+
+func TestUnsafeCommandPrefixKeepsOrdinaryCommandsGrantable(t *testing.T) {
+	for _, prefix := range [][]string{
+		{"cargo", "build"},
+		{"go", "test"},
+		{"ls", "-la"},
+		{"rg", "--json"},
+		{"7z", "l"},
+		{"base64", "-d"},
+		{"kubectl", "get", "pods"},
+		{"docker", "ps"},
+		{"sha256sum", "file"},
+		{"gcc-13", "-c"},
+		{"node-gyp", "build"},
+		{"python3-config", "--includes"},
+		{"s3cmd", "ls"},
+		{"cat", "file"},
+		{"zstd", "-d"},
+		{"sqlite3", "db"},
+		{"yt-dlp", "url"},
+		{"perl-doc", "-h"},
+		{"php-fpm", "-t"},
+		{"ruby-lsp", "--version"},
+		{"lua-language-server", "--check"},
+		{"nodemon", "app.js"},
+	} {
+		if unsafeCommandPrefix(prefix) {
+			t.Errorf("unsafeCommandPrefix(%q) = true, want false", prefix)
+		}
+	}
+}
+func TestNormalizeLauncherName(t *testing.T) {
+	for _, testCase := range []struct{ in, want string }{
+		{"python3.11", "python3"},
+		{"python2.7", "python2"},
+		{"pypy3", "pypy3"},
+		{"node.exe", "node"},
+		{"POWERSHELL.EXE", "powershell"},
+		{"7z", "7z"},
+		{"base64", "base64"},
+		{"sha256sum", "sha256sum"},
+		{"python.", "python"},
+		{"python3.11.exe.", "python3"},
+		{"python3.7m", "python3"},
+		{"python3.6dm", "python3"},
+		{"python3.13t", "python3"},
+		{"python3.13td", "python3"},
+		{"python3.11-dbg", "python3"},
+		{"node-nightly", "node"},
+		{"node-gyp", "node-gyp"},
+		{"python3-config", "python3-config"},
+		{"zstd", "zstd"},
+		{"cat", "cat"},
+		{"cargo", "cargo"},
+		{"", ""},
+	} {
+		if got := normalizeLauncherName(testCase.in); got != testCase.want {
+			t.Errorf("normalizeLauncherName(%q) = %q, want %q", testCase.in, got, testCase.want)
+		}
+	}
+}
+
+// Session-scoped grants are the agent's other entry point (loop.go grants them
+// for a single turn without touching the store), so they must refuse the same
+// launcher spellings the persisted path does.
+func TestGrantCommandPrefixForSessionRefusesLauncherVariants(t *testing.T) {
+	engine := &Engine{commandPrefixes: newCommandPrefixGrantSet()}
+	engine.GrantCommandPrefixForSession("bash", []string{"cargo", "build"})
+	if _, ok := engine.LookupCommandPrefixForSession("bash", []string{"cargo", "build", "--release"}); !ok {
+		t.Fatal("CONTROL BROKEN: an ordinary session prefix grant did not match")
+	}
+	for _, prefix := range [][]string{
+		{"python3.11", "-c"},
+		{"python.exe", "-c"},
+		{"cmd", "/c"},
+	} {
+		engine.GrantCommandPrefixForSession("bash", prefix)
+		command := append(append([]string(nil), prefix...), "whatever")
+		if _, ok := engine.LookupCommandPrefixForSession("bash", command); ok {
+			t.Errorf("session grant %q matched %q, want refused", prefix, command)
+		}
+	}
+}