test(acp): require nullable diff fields on wire

docs/HOW_ZERO_WORKS.md

@@ -302,9 +302,8 @@ Conceptually, one requested tool goes through these phases:
    the model can inspect it and decide what to do next.
 6. **Render and persist** — the result is surfaced to the TUI, stream-JSON
    writer, or ACP client. TUI and exec record rich tool/session events for
-   resume/history; ACP persists conversational messages and completed tool-call
-   starts/results for load replay. Live streaming details and permission
-   exchanges remain client notifications rather than durable history.
+   resume/history; ACP currently persists conversational messages and streams
+   tool/permission updates to the client.
 
 Tool success and failure are both informative context. A successful `read_file`
 result gives the model file contents; a failed `edit_file` result gives the model

internal/acp/agent.go

@@ -2,14 +2,10 @@ package acp
 
 import (
 	"context"
-	"crypto/sha256"
 	"encoding/base64"
 	"encoding/json"
 	"errors"
-	"fmt"
 	"log"
-	"os"
-	"path/filepath"
 	"strings"
 	"sync"
 
@@ -44,12 +40,8 @@ type Deps struct {
 	// ResolveWorkspaceRoot validates + normalizes a client-supplied cwd (must be an
 	// existing directory; never the bare root). It is the file-tool confinement root.
 	ResolveWorkspaceRoot func(cwd string) (string, error)
-	// PersistEvents is an optional test seam for injecting event-store failures.
-	// It receives a COMPLETED TURN as one batch, never one event at a time: the
-	// batch is the unit the shared store keeps contiguous (see persistTurn).
-	PersistEvents func(sessionID string, inputs []sessions.AppendEventInput) error
-	Store         *sessions.Store
-	AgentInfo     Implementation
+	Store                *sessions.Store
+	AgentInfo            Implementation
 }
 
 // Workspace is the per-turn execution environment passed to the agent. ACP does
@@ -114,8 +106,6 @@ func NewAgent(conn *Conn, deps Deps) *Agent {
 	conn.Handle(MethodInitialize, a.handleInitialize)
 	conn.Handle(MethodSessionNew, a.handleSessionNew)
 	conn.Handle(MethodSessionLoad, a.handleSessionLoad)
-	conn.Handle(MethodSessionList, a.handleSessionList)
-	conn.Handle(MethodSessionResume, a.handleSessionResume)
 	conn.Handle(MethodSessionPrompt, a.handleSessionPrompt)
 	conn.Handle(MethodSessionSetMode, a.handleSetMode)
 	conn.Handle(MethodSessionSetConfigOption, a.handleSetConfigOption)
@@ -144,11 +134,11 @@ func (a *Agent) handleInitialize(_ context.Context, params json.RawMessage) (any
 	return InitializeResult{
 		ProtocolVersion: negotiated,
 		AgentCapabilities: AgentCapabilities{
-			// ACP v1 optional methods are advertised as empty capability objects;
-			// clients must gate session/list and session/resume on their presence.
-			LoadSession:         true,
-			PromptCapabilities:  PromptCapabilities{Image: true},
-			SessionCapabilities: &SessionCapabilities{List: &struct{}{}, Resume: &struct{}{}},
+			// Only advertise what ZERO actually implements: session/load (loadSession)
+			// and image prompts. session/resume + the session-capability sub-object
+			// are intentionally omitted since there is no resume handler yet.
+			LoadSession:        true,
+			PromptCapabilities: PromptCapabilities{Image: true},
 		},
 		AgentInfo: &info,
 		// ZERO owns credentials (BYOK) and does not delegate auth to the editor.
@@ -158,41 +148,12 @@ func (a *Agent) handleInitialize(_ context.Context, params json.RawMessage) (any
 
 // ---- session lifecycle ----
 
-// requestedWorkspace is the single rule for a cwd that arrived from the client,
-// applied before the value can reach ResolveWorkspaceRoot.
-//
-// THE REQUEST'S OWN CWD IS THE ONLY THING ALLOWED TO PICK A ROOT. Every params
-// type spells cwd as a plain string, so an absent field and an empty one decode
-// to exactly the same "", and the resolver treats "" as "use the directory this
-// process was started in" and joins a relative cwd onto it. Those two defaults
-// meet in the middle: `{"sessionId":"known"}` used to activate a persisted
-// session, and `{}` used to create one, both rooted at wherever the editor
-// happened to spawn `zero acp` — which then becomes the sandbox and file-tool
-// confinement root. The client never named that directory, so it is a root the
-// server invented, and ACP requires an absolute cwd on every method carrying
-// one. Rejecting here is what keeps a missing field from being answered with a
-// guess.
-func requestedWorkspace(cwd string) (string, error) {
-	trimmed := strings.TrimSpace(cwd)
-	if trimmed == "" {
-		return "", RPCError(codeInvalidParams, "cwd is required and must be an absolute path")
-	}
-	if !filepath.IsAbs(trimmed) {
-		return "", RPCError(codeInvalidParams, "cwd must be an absolute path: "+trimmed)
-	}
-	return trimmed, nil
-}
-
 func (a *Agent) handleSessionNew(ctx context.Context, params json.RawMessage) (any, error) {
 	var p NewSessionParams
 	if err := json.Unmarshal(params, &p); err != nil {
 		return nil, RPCError(codeInvalidParams, "invalid session/new params")
 	}
-	cwd, err := requestedWorkspace(p.Cwd)
-	if err != nil {
-		return nil, err
-	}
-	root, err := a.deps.ResolveWorkspaceRoot(cwd)
+	root, err := a.deps.ResolveWorkspaceRoot(p.Cwd)
 	if err != nil {
 		return nil, RPCError(codeInvalidParams, err.Error())
 	}
@@ -204,7 +165,7 @@ func (a *Agent) handleSessionNew(ctx context.Context, params json.RawMessage) (a
 	if err != nil {
 		return nil, RPCError(codeInternalError, "create session: "+err.Error())
 	}
-	sess, _ := a.registerSession(meta.SessionID, root, nil, model, models, restrictModels)
+	sess := a.registerSession(meta.SessionID, root, nil, model, models, restrictModels)
 	return NewSessionResult{
 		SessionID:     sess.id,
 		ConfigOptions: a.configOptions(sess),
@@ -217,90 +178,22 @@ func (a *Agent) handleSessionLoad(ctx context.Context, params json.RawMessage) (
 	if err := json.Unmarshal(params, &p); err != nil {
 		return nil, RPCError(codeInvalidParams, "invalid session/load params")
 	}
-	return a.activatePersistedSession(ctx, p, persistedSessionLoad)
-}
-
-func (a *Agent) handleSessionResume(ctx context.Context, params json.RawMessage) (any, error) {
-	var p ResumeSessionParams
-	if err := json.Unmarshal(params, &p); err != nil {
-		return nil, RPCError(codeInvalidParams, "invalid session/resume params")
-	}
-	return a.activatePersistedSession(ctx, p, persistedSessionResume)
-}
-
-type persistedSessionOperation uint8
-
-const (
-	persistedSessionLoad persistedSessionOperation = iota
-	persistedSessionResume
-)
-
-// activatePersistedSession restores the agent's internal conversation context
-// for both lifecycle methods. session/load additionally replays user-visible
-// history as ordered session/update notifications; session/resume deliberately
-// does not, which makes it safe for an already-rendered desktop reconnect.
-func (a *Agent) activatePersistedSession(ctx context.Context, p LoadSessionParams, operation persistedSessionOperation) (any, error) {
-	// BOTH METHODS, BEFORE ANYTHING IS LOOKED UP. session/resume shares this
-	// params type with session/load, so the wire cannot tell an omitted cwd from
-	// an empty one; the blank case used to be answered with the persisted cwd,
-	// which made {"sessionId":"known"} a complete, successful activation request.
-	// Validating here rather than in one handler is what keeps the two entry
-	// points from drifting apart.
-	cwd, err := requestedWorkspace(p.Cwd)
-	if err != nil {
-		return nil, err
-	}
 	meta, err := a.deps.Store.Get(p.SessionID)
 	if err != nil || meta == nil {
 		return nil, RPCError(codeInvalidParams, "session not found: "+p.SessionID)
 	}
-	if operation == persistedSessionResume && !sessions.IsResumableKind(meta.SessionKind) {
-		return nil, RPCError(codeInvalidParams, "session is not resumable: "+p.SessionID)
+	cwdInput := p.Cwd
+	if strings.TrimSpace(cwdInput) == "" {
+		cwdInput = meta.Cwd
 	}
-	if strings.TrimSpace(meta.Cwd) == "" {
-		return nil, RPCError(codeInvalidParams, "session has no persisted workspace: "+p.SessionID)
-	}
-	// SAME RULE ON THE WAY IN. Omitting a relative entry from the listing is not
-	// enough: a stored "." still resolves against this process's directory, so a
-	// client that hands back that same directory as its cwd would be sold the
-	// invented root as a match. A workspace that cannot be identified is not one
-	// this session can be restored into.
-	if !filepath.IsAbs(meta.Cwd) {
-		return nil, RPCError(codeInvalidParams, "session workspace is not an absolute path, so it cannot be identified: "+p.SessionID)
-	}
-	persistedRoot, err := a.deps.ResolveWorkspaceRoot(meta.Cwd)
-	if err != nil {
-		return nil, RPCError(codeInvalidParams, "persisted session workspace is unavailable: "+err.Error())
-	}
-	root, err := a.deps.ResolveWorkspaceRoot(cwd)
+	root, err := a.deps.ResolveWorkspaceRoot(cwdInput)
 	if err != nil {
 		return nil, RPCError(codeInvalidParams, err.Error())
 	}
-	// ACP session cwd is immutable. Loading history under a different root
-	// would give a conversation from one workspace access to another
-	// workspace's configuration, files, and tools.
-	if !sameWorkspace(root, persistedRoot) {
-		return nil, RPCError(codeInvalidParams, "session cwd does not match its persisted workspace")
-	}
 	// Load history BEFORE publishing the session so no concurrent prompt observes
 	// a half-initialized session (registerSession sets history under the lock and
 	// reuses an already-live session rather than orphaning its in-flight turn).
-	requireHistoryLog := operation == persistedSessionResume && meta.EventCount > 0
-	history, messages, historyWarning, historyErr := a.loadHistory(meta.SessionID, requireHistoryLog)
-	// RESUME PROMISES RESTORED CONTEXT, SO A FAILED RESTORATION IS A FAILED
-	// RESUME. historyErr used to do nothing but suppress replay and raise a
-	// warning: the session was registered and reported ready regardless, so a
-	// corrupt record or an unreadable events file left the caller holding a live,
-	// promptable session ID whose next prompt ran as a brand-new conversation
-	// under the old identity. Nothing in the response said so.
-	//
-	// Publication is now gated on restoration for resume. LOAD keeps the
-	// best-effort policy deliberately rather than by inheriting this helper: it
-	// replays what it has and warns about the rest, which is the right trade for
-	// a client rebuilding a transcript it can still scroll. Reported by @jatmn.
-	if operation == persistedSessionResume && historyErr != nil {
-		return nil, RPCError(codeInternalError, "restore session history: "+historyErr.Error())
-	}
+	history, historyErr := a.loadHistory(meta.SessionID)
 	model, models, restrictModels, err := a.resolveModelChoices(ctx, root)
 	if err != nil {
 		return nil, RPCError(codeInternalError, "config: "+err.Error())
@@ -311,36 +204,12 @@ func (a *Agent) activatePersistedSession(ctx context.Context, p LoadSessionParam
 			models = append(models, SessionConfigOptionValue{Value: persistedModel, Name: persistedModel})
 		}
 	}
-	sess, existed := a.registerSession(meta.SessionID, root, history, model, models, restrictModels)
-	if existed {
-		_, messages, historyWarning, historyErr = a.refreshSessionHistory(sess, requireHistoryLog)
-		if operation == persistedSessionResume && historyErr != nil {
-			return nil, RPCError(codeInternalError, "restore session history: "+historyErr.Error())
-		}
-	}
-	note := &notifier{conn: a.conn, sessionID: sess.id}
-	if operation == persistedSessionLoad && historyErr == nil {
-		for _, message := range messages {
-			if message.tool != nil {
-				note.send(*message.tool)
-				continue
-			}
-			note.send(replayMessageChunk(message.role, replayMessageID(message.eventID), message.content))
-		}
-	}
+	sess := a.registerSession(meta.SessionID, root, history, model, models, restrictModels)
 	a.warnPersistence(
-		note,
-		"rehydrate session compaction",
-		"Could not apply session compaction. Raw session history was restored instead.",
-		historyWarning,
-		operation == persistedSessionLoad,
-	)
-	a.warnPersistence(
-		note,
+		&notifier{conn: a.conn, sessionID: sess.id},
 		"load session history",
 		"Could not load session history. The session is open, but earlier turns may be missing until storage recovers.",
 		historyErr,
-		operation == persistedSessionLoad,
 	)
 	return LoadSessionResult{
 		ConfigOptions: a.configOptions(sess),
@@ -348,80 +217,6 @@ func (a *Agent) activatePersistedSession(ctx context.Context, p LoadSessionParam
 	}, nil
 }
 
-func (a *Agent) handleSessionList(_ context.Context, params json.RawMessage) (any, error) {
-	var p ListSessionsParams
-	if len(params) > 0 {
-		if err := json.Unmarshal(params, &p); err != nil {
-			return nil, RPCError(codeInvalidParams, "invalid session/list params")
-		}
-	}
-	if p.Cursor != "" {
-		return nil, RPCError(codeInvalidParams, "invalid session/list cursor")
-	}
-	items, err := a.deps.Store.ListResumable()
-	if err != nil {
-		return nil, RPCError(codeInternalError, "list sessions: "+err.Error())
-	}
-	// The filter is the one cwd ACP leaves optional, so a blank one means "no
-	// filter" rather than an error — but a relative one is rebased onto this
-	// process's directory exactly like the others, and would then silently answer
-	// about a workspace the client never named.
-	var cwd string
-	if strings.TrimSpace(p.Cwd) != "" {
-		filter, err := requestedWorkspace(p.Cwd)
-		if err != nil {
-			return nil, err
-		}
-		cwd, err = a.deps.ResolveWorkspaceRoot(filter)
-		if err != nil {
-			return nil, RPCError(codeInvalidParams, err.Error())
-		}
-	}
-	result := ListSessionsResult{Sessions: make([]SessionInfo, 0, len(items))}
-	for _, item := range items {
-		// EVERY ENTRY IS RESOLVED, FILTER OR NO FILTER. Listing is a menu, and
-		// every item on it has to be orderable: activatePersistedSession
-		// resolves the persisted workspace and refuses what it cannot reach, so
-		// anything this loop cannot resolve is something the client would be
-		// offered and then denied.
-		//
-		// Resolving only when a cwd filter was supplied left two shapes through —
-		// a session whose workspace has since been deleted, and a legacy entry
-		// holding a relative path, which was then reported as cwd "." even though
-		// ACP requires SessionInfo.cwd to be absolute.
-		if strings.TrimSpace(item.Cwd) == "" {
-			continue
-		}
-		// A RELATIVE PERSISTED CWD HAS NO RECOVERABLE IDENTITY. Resolving one
-		// rebases it onto wherever this ACP server happens to be running and
-		// advertises that invented absolute path as the session's workspace — so a
-		// conversation created for one project could be resumed against another
-		// project's configuration, files and tools. The original base is not
-		// knowable from the metadata, so the honest answer is to omit the entry
-		// rather than to guess at it.
-		if !filepath.IsAbs(item.Cwd) {
-			continue
-		}
-		itemRoot, err := a.deps.ResolveWorkspaceRoot(item.Cwd)
-		if err != nil {
-			continue
-		}
-		if cwd != "" && !sameWorkspace(itemRoot, cwd) {
-			continue
-		}
-		result.Sessions = append(result.Sessions, SessionInfo{
-			SessionID: item.SessionID,
-			Title:     item.Title,
-			// The RESOLVED root, not the stored string: absolute as ACP
-			// requires, and the same value the client will hand back on resume.
-			Cwd:       itemRoot,
-			UpdatedAt: item.UpdatedAt,
-			Meta:      &SessionInfoMeta{ModelID: item.ModelID, CreatedAt: item.CreatedAt},
-		})
-	}
-	return result, nil
-}
-
 // ---- prompt turn ----
 
 func (a *Agent) handleSessionPrompt(ctx context.Context, params json.RawMessage) (any, error) {
@@ -498,15 +293,6 @@ func (a *Agent) runTurn(ctx context.Context, sess *acpSession, userText string,
 			note.text("\n\n[zero warning] " + text + "\n")
 		}
 	}
-	// Buffer the complete turn until RunAgent has a valid ACP outcome. A hard run
-	// failure is an aborted turn: neither live history nor durable history may
-	// retain its user/tool prefix under an RPC error. StopCancelled is a valid
-	// outcome and commits through the same boundary below.
-	pendingEvents := make([]sessions.AppendEventInput, 0, 4)
-	queue := func(input sessions.AppendEventInput) {
-		pendingEvents = append(pendingEvents, input)
-	}
-	queue(messageEvent("user", userText))
 
 	opts := agent.Options{
 		Cwd:            sess.cwd,
@@ -521,12 +307,8 @@ func (a *Agent) runTurn(ctx context.Context, sess *acpSession, userText string,
 		Images:         images,
 		OnText:         note.text,
 		OnReasoning:    note.thought,
-		OnToolCall: func(call agent.ToolCall) {
-			queue(toolCallEvent(call))
-			note.toolCall(call)
-		},
+		OnToolCall:     note.toolCall,
 		OnToolResult: func(result agent.ToolResult) {
-			queue(toolResultEvent(result))
 			note.toolResult(result)
 			if result.Name == "update_plan" {
 				a.emitPlan(registry, note)
@@ -539,36 +321,19 @@ func (a *Agent) runTurn(ctx context.Context, sess *acpSession, userText string,
 
 	agentPrompt := buildPrompt(sess.snapshotHistory(), userText)
 	result, runErr := a.deps.RunAgent(ctx, agentPrompt, provider, opts)
-	if result.FinalAnswer != "" {
-		queue(messageEvent("assistant", result.FinalAnswer))
-	}
+
 	reason, stopErr := stopReasonFor(result, runErr)
 	if stopErr != nil {
 		return "", RPCError(codeInternalError, stopErr.Error())
 	}
-	// ONE BATCH, ONE LOCK. The outcome gate above decides WHETHER the turn is
-	// committed; the store batch decides WHICH RECORDS STAY TOGETHER relative to
-	// other writers, and these are different guarantees. Persisting the buffer
-	// one event per call took and released the store's session lock between
-	// events, so a second ACP instance holding the same session — its turnMu is
-	// its own, only the store is shared — could append its whole turn in the
-	// gap: user A, user B, answer B, answer A. Every write was individually
-	// locked and the log was valid, but a fresh load pairs prose by order and
-	// reconstructed three wrong turns from two right ones. Before this branch,
-	// persistTurn handed the user and assistant events to AppendEvents together;
-	// buffering until the outcome is known was correct, splitting the commit
-	// into singleton writes was not. The store writes a batch under one lock and
-	// one file write, which is the contiguity restored here — not a disk
-	// transaction, and not a promise about crashes mid-fsync. Reported by @jatmn.
-	persistenceErr := a.persistTurn(sess.id, pendingEvents)
-	sess.appendHistory(turnRecord{user: userText, assistant: result.FinalAnswer})
-	a.warnPersistence(
-		note,
-		"save session history",
-		"Could not save session history. This turn is available in memory, but future resume may miss it until storage recovers.",
-		persistenceErr,
-		true,
-	)
+	if err := a.persistTurn(sess, userText, result.FinalAnswer); err != nil {
+		a.warnPersistence(
+			note,
+			"save session history",
+			"Could not save session history. This turn is available in memory, but future resume may miss it until storage recovers.",
+			err,
+		)
+	}
 	return reason, nil
 }
 
@@ -827,159 +592,39 @@ func (a *Agent) configOptions(s *acpSession) []SessionConfigOption {
 
 // ---- persistence + continuity ----
 
-// persistTurn commits a completed turn's buffered events as one store batch, so
-// no other writer's records can land between them. A failure is the failure of
-// the whole batch: nothing after a failed prerequisite is appended on its own.
-func (a *Agent) persistTurn(sessionID string, inputs []sessions.AppendEventInput) error {
-	if len(inputs) == 0 {
-		return nil
-	}
-	if a.deps.PersistEvents != nil {
-		return a.deps.PersistEvents(sessionID, inputs)
-	}
+func (a *Agent) persistTurn(sess *acpSession, user, assistant string) error {
+	defer sess.appendHistory(turnRecord{user: user, assistant: assistant})
 	if a.deps.Store == nil {
 		return nil
 	}
-	_, err := a.deps.Store.AppendEvents(sessionID, inputs)
+	events := []sessions.AppendEventInput{
+		{
+			Type:    sessions.EventMessage,
+			Payload: map[string]any{"role": "user", "content": user},
+		},
+	}
+	if assistant != "" {
+		events = append(events, sessions.AppendEventInput{
+			Type:    sessions.EventMessage,
+			Payload: map[string]any{"role": "assistant", "content": assistant},
+		})
+	}
+	_, err := a.deps.Store.AppendEvents(sess.id, events)
 	return err
 }
 
-func messageEvent(role, content string) sessions.AppendEventInput {
-	return sessions.AppendEventInput{
-		Type:    sessions.EventMessage,
-		Payload: map[string]any{"role": role, "content": content},
-	}
-}
-
-func toolCallEvent(call agent.ToolCall) sessions.AppendEventInput {
-	return sessions.AppendEventInput{
-		Type: sessions.EventToolCall,
-		Payload: map[string]any{
-			"toolCallId": call.ID,
-			"name":       call.Name,
-			"arguments":  call.Arguments,
-		},
-	}
-}
-
-func toolResultEvent(result agent.ToolResult) sessions.AppendEventInput {
-	return sessions.AppendEventInput{
-		Type: sessions.EventToolResult,
-		Payload: map[string]any{
-			"toolCallId":   result.ToolCallID,
-			"name":         result.Name,
-			"status":       result.Status,
-			"output":       result.Output,
-			"changedFiles": append([]string(nil), result.ChangedFiles...),
-		},
-	}
-}
-
-// persistedMessage is one entry of the restored transcript in stored order. It
-// is either a message (role/content) or a tool-call notification (tool), never
-// both: keeping them in ONE ordered slice is what preserves the interleaving a
-// client needs to redraw the conversation as it originally happened.
-type persistedMessage struct {
-	eventID string
-	role    string
-	content string
-	// tool is set for a replayed tool call or its result, and is already in wire
-	// shape — it comes from the same toolCallStart/toolCallResult mapping the
-	// live turn uses, so a replayed tool call renders identically to a fresh one
-	// and there is no second mapping to drift out of sync.
-	tool *ToolCallUpdate
-}
-
-func (a *Agent) loadHistory(sessionID string, requireHistoryLog bool) ([]turnRecord, []persistedMessage, error, error) {
+func (a *Agent) loadHistory(sessionID string) ([]turnRecord, error) {
 	if a.deps.Store == nil {
-		return nil, nil, nil, nil
+		return nil, nil
 	}
-	// THE EFFECTIVE CONVERSATION, NOT THE RAW LOG. A compacted session keeps its
-	// original prefix on disk alongside an EventCompaction that names the events
-	// it replaced and carries their durable summary. ReadEvents hands back both,
-	// so restoring from it replayed superseded turns AND dropped the summary that
-	// replaced them — resume then seeded the next turn with context the
-	// conversation had already moved past, and load visibly resurrected
-	// transcript entries the user had seen compacted away.
-	//
-	// ReadRehydratedEvents is the projection the TUI and exec paths already use
-	// (internal/tui/session.go, internal/sessions/exec_session.go), so all three
-	// now agree on what the conversation IS. Switching readers alone is not
-	// enough: rehydration substitutes the compaction event in place of the events
-	// it replaced, so a loop that skips everything but EventMessage would drop the
-	// summary exactly as before. It is projected below. Reported by @jatmn.
-	events, eventLogPresent, err := a.deps.Store.ReadRehydratedEventsWithPresence(sessionID)
-	var rehydrateWarning error
+	events, err := a.deps.Store.ReadEvents(sessionID)
 	if err != nil {
-		rehydrateWarning = err
-		events, eventLogPresent, err = a.deps.Store.ReadEventsWithPresence(sessionID)
-		if err != nil {
-			return nil, nil, nil, err
-		}
-	}
-	if requireHistoryLog && !eventLogPresent {
-		return nil, nil, nil, fmt.Errorf("zero session %s event log is missing", sessionID)
+		return nil, err
 	}
 	var records []turnRecord
-	var messages []persistedMessage
-	activeToolCalls := make(map[string]string)
 	var pendingUser string
 	havePending := false
 	for _, e := range events {
-		if e.Type == sessions.EventCompaction {
-			// The summary stands in for the turns it replaced, so it enters the
-			// history as an assistant message: it is prior context the next turn
-			// must see, and the wire has no separate role for it.
-			raw, marshalErr := json.Marshal(e.Payload)
-			if marshalErr != nil {
-				continue
-			}
-			var payload struct {
-				Summary string `json:"summary"`
-			}
-			if json.Unmarshal(raw, &payload) != nil || strings.TrimSpace(payload.Summary) == "" {
-				continue
-			}
-			messages = append(messages, persistedMessage{
-				eventID: persistedMessageIdentity(sessionID, e),
-				role:    "assistant",
-				content: payload.Summary,
-			})
-			records = append(records, turnRecord{user: pendingUser, assistant: payload.Summary})
-			pendingUser = ""
-			havePending = false
-			continue
-		}
-		// TOOL ACTIVITY IS PART OF THE TRANSCRIPT, NOT DECORATION. A restored
-		// conversation that shows only the prose reads as if the agent asserted
-		// its edits and command output from nowhere: the user sees "I updated
-		// scope.go" with no record that any tool ran. These are collected for
-		// replay only. They deliberately do NOT enter turnRecord, so the prompt
-		// context a resumed turn receives stays byte-identical to what it was —
-		// load and resume continue to consume the SAME effective history, and
-		// only the wire rendering differs. Reported by @jatmn.
-		if e.Type == sessions.EventToolCall || e.Type == sessions.EventToolResult {
-			if upd := replayToolUpdate(e); upd != nil {
-				rawID := upd.ToolCallID
-				if e.Type == sessions.EventToolResult {
-					replayID, ok := activeToolCalls[rawID]
-					if !ok {
-						continue
-					}
-					upd.ToolCallID = replayID
-					delete(activeToolCalls, rawID)
-				} else {
-					replayID := replayToolCallID(persistedMessageIdentity(sessionID, e))
-					activeToolCalls[rawID] = replayID
-					upd.ToolCallID = replayID
-				}
-				messages = append(messages, persistedMessage{
-					eventID: persistedMessageIdentity(sessionID, e),
-					tool:    upd,
-				})
-			}
-			continue
-		}
 		if e.Type != sessions.EventMessage {
 			continue
 		}
@@ -996,14 +641,12 @@ func (a *Agent) loadHistory(sessionID string, requireHistoryLog bool) ([]turnRec
 		}
 		switch msg.Role {
 		case "user":
-			messages = append(messages, persistedMessage{eventID: persistedMessageIdentity(sessionID, e), role: msg.Role, content: msg.Content})
 			if havePending {
 				records = append(records, turnRecord{user: pendingUser})
 			}
 			pendingUser = msg.Content
 			havePending = true
 		case "assistant":
-			messages = append(messages, persistedMessage{eventID: persistedMessageIdentity(sessionID, e), role: msg.Role, content: msg.Content})
 			records = append(records, turnRecord{user: pendingUser, assistant: msg.Content})
 			pendingUser = ""
 			havePending = false
@@ -1012,89 +655,10 @@ func (a *Agent) loadHistory(sessionID string, requireHistoryLog bool) ([]turnRec
 	if havePending {
 		records = append(records, turnRecord{user: pendingUser})
 	}
-	return records, messages, rehydrateWarning, nil
+	return records, nil
 }
 
-// replayToolUpdate rebuilds the ACP notification for one stored tool event.
-//
-// The stored toolCallId is returned here as a correlation key. loadHistory maps
-// each call occurrence to a stable session-wide replay identity and applies that
-// identity to its result. Older records wrote the field as "id", so both
-// spellings are accepted — the TUI projection already does the same
-// (internal/tui/session.go).
-//
-// A record that carries no usable id is skipped rather than replayed under a
-// synthesized one: an unpairable update is worse than a missing row.
-func replayToolUpdate(event sessions.Event) *ToolCallUpdate {
-	raw, err := json.Marshal(event.Payload)
-	if err != nil {
-		return nil
-	}
-	var payload struct {
-		Name         string   `json:"name"`
-		ToolCallID   string   `json:"toolCallId"`
-		ID           string   `json:"id"`
-		Arguments    string   `json:"arguments"`
-		Status       string   `json:"status"`
-		Output       string   `json:"output"`
-		ChangedFiles []string `json:"changedFiles"`
-	}
-	if json.Unmarshal(raw, &payload) != nil {
-		return nil
-	}
-	id := payload.ToolCallID
-	if id == "" {
-		id = payload.ID
-	}
-	if id == "" {
-		return nil
-	}
-	if event.Type == sessions.EventToolCall {
-		upd := toolCallStart(agent.ToolCall{ID: id, Name: payload.Name, Arguments: payload.Arguments})
-		return &upd
-	}
-	status := tools.Status(payload.Status)
-	if status == "" {
-		status = tools.StatusOK
-	}
-	upd := toolCallResult(agent.ToolResult{
-		ToolCallID:   id,
-		Name:         payload.Name,
-		Status:       status,
-		Output:       payload.Output,
-		ChangedFiles: append([]string(nil), payload.ChangedFiles...),
-	})
-	return &upd
-}
-
-func persistedMessageIdentity(sessionID string, event sessions.Event) string {
-	if event.ID != "" {
-		return event.ID
-	}
-	return fmt.Sprintf("%s:%d", sessionID, event.Sequence)
-}
-
-// replayMessageID maps ZERO's stable event identity to a standards-shaped UUID
-// without leaking or parsing the event id on the wire. The same stored message
-// receives the same opaque id across loads, which also gives clients an exact
-// chunk boundary when two adjacent persisted messages have the same role.
-func replayMessageID(eventID string) string {
-	return replayOpaqueID("message", eventID)
-}
-
-func replayToolCallID(eventID string) string {
-	return replayOpaqueID("tool-call", eventID)
-}
-
-func replayOpaqueID(kind, eventID string) string {
-	sum := sha256.Sum256([]byte("zero-acp-" + kind + ":" + eventID))
-	b := sum[:16]
-	b[6] = (b[6] & 0x0f) | 0x50
-	b[8] = (b[8] & 0x3f) | 0x80
-	return fmt.Sprintf("%x-%x-%x-%x-%x", b[:4], b[4:6], b[6:8], b[8:10], b[10:16])
-}
-
-func (a *Agent) warnPersistence(note *notifier, action string, message string, err error, notify bool) {
+func (a *Agent) warnPersistence(note *notifier, action string, message string, err error) {
 	if err == nil {
 		return
 	}
@@ -1103,7 +667,7 @@ func (a *Agent) warnPersistence(note *notifier, action string, message string, e
 		sessionID = note.sessionID
 	}
 	log.Printf("zero acp: failed to %s for session %s: %v", action, sessionID, err)
-	if note != nil && notify {
+	if note != nil {
 		note.text("\n\n[zero warning] " + message + "\n")
 	}
 }
@@ -1150,34 +714,18 @@ func promptImages(blocks []ContentBlock) []zeroruntime.ImageBlock {
 
 // registerSession publishes a session under the agent's lock. If one is already
 // registered for id (e.g. a re-load of an in-flight session) the existing live
-// session is returned rather than orphaning its turn or resetting its mode/model.
-// The bool reports that case so persisted activation can re-read and apply disk
-// history under turnMu. history is set BEFORE first publication so no concurrent
-// prompt can read a half-initialized session.
-func (a *Agent) registerSession(id, cwd string, history []turnRecord, model string, models []SessionConfigOptionValue, restrictModels bool) (*acpSession, bool) {
+// session is returned unchanged rather than orphaning its turn or resetting its
+// mode/model. history is set BEFORE publishing so no concurrent prompt can read a
+// half-initialized session.
+func (a *Agent) registerSession(id, cwd string, history []turnRecord, model string, models []SessionConfigOptionValue, restrictModels bool) *acpSession {
 	a.mu.Lock()
 	defer a.mu.Unlock()
 	if existing := a.sessions[id]; existing != nil {
-		return existing, true
+		return existing
 	}
 	sess := &acpSession{id: id, cwd: cwd, mode: agent.PermissionModeAuto, model: model, models: models, restrictModels: restrictModels, history: history}
 	a.sessions[id] = sess
-	return sess, false
-}
-
-// refreshSessionHistory is the activation apply boundary for an already-live
-// session. The history is read while prompts are excluded, then applied to the
-// same object the prompt path uses. Re-reading here avoids overwriting a turn
-// that committed between activatePersistedSession's pre-publication read and
-// discovering that another activation had already registered the session.
-func (a *Agent) refreshSessionHistory(sess *acpSession, requireHistoryLog bool) ([]turnRecord, []persistedMessage, error, error) {
-	sess.turnMu.Lock()
-	defer sess.turnMu.Unlock()
-	history, messages, warning, err := a.loadHistory(sess.id, requireHistoryLog)
-	if err == nil {
-		sess.setHistory(history)
-	}
-	return history, messages, warning, err
+	return sess
 }
 
 func (a *Agent) session(id string) *acpSession {
@@ -1260,48 +808,8 @@ func (s *acpSession) appendHistory(rec turnRecord) {
 	s.mu.Unlock()
 }
 
-func (s *acpSession) setHistory(history []turnRecord) {
-	s.mu.Lock()
-	s.history = append([]turnRecord(nil), history...)
-	s.mu.Unlock()
-}
-
 func (s *acpSession) snapshotHistory() []turnRecord {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 	return append([]turnRecord(nil), s.history...)
 }
-
-// sameWorkspace reports whether two resolved roots name the same directory.
-//
-// STRING EQUALITY IS NOT DIRECTORY IDENTITY. ResolveWorkspaceRoot is abs plus
-// filepath.Clean plus a stat: it does not fold case and does not resolve
-// junctions, so one directory reached by two spellings produces two different
-// roots. A session persisted from the TUI was then unresumable from an editor
-// holding a different spelling of the same project folder, and session/list
-// filtered by the other spelling returned nothing — not a failed resume but an
-// invisible one, on exactly the case this feature exists for.
-//
-// filepath.EvalSymlinks is NOT the fix on Windows: it normalises a drive letter
-// but returns a junction path unchanged, so the alias survives it. Junctions need
-// no privilege, so this is ordinary rather than exotic. os.SameFile compares the
-// filesystem's own identity for the two directories, which is the question being
-// asked.
-//
-// The string comparison stays as the fast path, and a stat failure falls back to
-// it rather than widening the match — this gate refuses access to another
-// workspace's files and configuration, so an unanswerable comparison denies.
-func sameWorkspace(left, right string) bool {
-	if left == right {
-		return true
-	}
-	leftInfo, err := os.Stat(left)
-	if err != nil {
-		return false
-	}
-	rightInfo, err := os.Stat(right)
-	if err != nil {
-		return false
-	}
-	return os.SameFile(leftInfo, rightInfo)
-}

internal/acp/jsonrpc.go

@@ -89,13 +89,6 @@ type Conn struct {
 
 	handlers  map[string]HandlerFunc
 	notifiers map[string]NotifyFunc
-	// Notifications for one method are an ordered stream: session/update in
-	// particular is stateful, so dispatching every frame in an unrelated
-	// goroutine can make a later chunk overtake an earlier one. Different
-	// methods retain independent tails, keeping session/cancel responsive while
-	// an update handler is busy.
-	notifyMu    sync.Mutex
-	notifyTails map[string]chan struct{}
 
 	mu      sync.Mutex
 	nextID  int64
@@ -113,12 +106,11 @@ type Conn struct {
 // lifetime.
 func NewConn(r io.Reader, w io.Writer) *Conn {
 	return &Conn{
-		rawReader:   r,
-		w:           w,
-		handlers:    make(map[string]HandlerFunc),
-		notifiers:   make(map[string]NotifyFunc),
-		notifyTails: make(map[string]chan struct{}),
-		pending:     make(map[int64]chan rpcMessage),
+		rawReader: r,
+		w:         w,
+		handlers:  make(map[string]HandlerFunc),
+		notifiers: make(map[string]NotifyFunc),
+		pending:   make(map[int64]chan rpcMessage),
 	}
 }
 
@@ -311,7 +303,11 @@ func (c *Conn) handleLine(ctx context.Context, line []byte) {
 		}(msg)
 	case msg.isNotify():
 		if fn := c.notifiers[msg.Method]; fn != nil {
-			c.dispatchNotification(ctx, msg, fn)
+			c.wg.Add(1)
+			go func(m rpcMessage) {
+				defer c.wg.Done()
+				fn(ctx, m.Params)
+			}(msg)
 		}
 	default:
 		// Malformed frame; reply only if we can identify a request id.
@@ -321,35 +317,6 @@ func (c *Conn) handleLine(ctx context.Context, line []byte) {
 	}
 }
 
-// dispatchNotification preserves wire order within one method without making
-// unrelated notification methods wait for each other. The read loop installs
-// each tail before starting its goroutine, so goroutine scheduling cannot
-// reorder the chain it observes.
-func (c *Conn) dispatchNotification(ctx context.Context, msg rpcMessage, fn NotifyFunc) {
-	c.notifyMu.Lock()
-	previous := c.notifyTails[msg.Method]
-	done := make(chan struct{})
-	c.notifyTails[msg.Method] = done
-	c.notifyMu.Unlock()
-
-	c.wg.Add(1)
-	go func() {
-		defer c.wg.Done()
-		defer func() {
-			close(done)
-			c.notifyMu.Lock()
-			if c.notifyTails[msg.Method] == done {
-				delete(c.notifyTails, msg.Method)
-			}
-			c.notifyMu.Unlock()
-		}()
-		if previous != nil {
-			<-previous
-		}
-		fn(ctx, msg.Params)
-	}()
-}
-
 func (c *Conn) dispatchRequest(ctx context.Context, msg rpcMessage) {
 	fn := c.handlers[msg.Method]
 	if fn == nil {

internal/acp/jsonrpc_test.go

@@ -360,86 +360,6 @@ func TestConnNotification(t *testing.T) {
 	}
 }
 
-func TestConnNotificationsForOneMethodStayInWireOrder(t *testing.T) {
-	a, b, stop := connPair(t)
-	defer stop()
-
-	firstStarted := make(chan struct{})
-	releaseFirst := make(chan struct{})
-	delivered := make(chan int, 2)
-	b.HandleNotify("update", func(_ context.Context, params json.RawMessage) {
-		var in struct{ Sequence int }
-		_ = json.Unmarshal(params, &in)
-		if in.Sequence == 1 {
-			close(firstStarted)
-			<-releaseFirst
-		}
-		delivered <- in.Sequence
-	})
-
-	if err := a.Notify("update", map[string]int{"Sequence": 1}); err != nil {
-		t.Fatalf("first notify: %v", err)
-	}
-	select {
-	case <-firstStarted:
-	case <-time.After(2 * time.Second):
-		t.Fatal("first notification did not start")
-	}
-	if err := a.Notify("update", map[string]int{"Sequence": 2}); err != nil {
-		t.Fatalf("second notify: %v", err)
-	}
-	select {
-	case sequence := <-delivered:
-		t.Fatalf("notification %d overtook the blocked first notification", sequence)
-	case <-time.After(25 * time.Millisecond):
-	}
-	close(releaseFirst)
-	for want := 1; want <= 2; want++ {
-		select {
-		case got := <-delivered:
-			if got != want {
-				t.Fatalf("notification order = ...,%d; want %d", got, want)
-			}
-		case <-time.After(2 * time.Second):
-			t.Fatalf("notification %d was not delivered", want)
-		}
-	}
-}
-
-func TestConnDifferentNotificationMethodsStayConcurrent(t *testing.T) {
-	a, b, stop := connPair(t)
-	defer stop()
-
-	updateStarted := make(chan struct{})
-	releaseUpdate := make(chan struct{})
-	cancelDelivered := make(chan struct{})
-	b.HandleNotify("update", func(context.Context, json.RawMessage) {
-		close(updateStarted)
-		<-releaseUpdate
-	})
-	b.HandleNotify("cancel", func(context.Context, json.RawMessage) {
-		close(cancelDelivered)
-	})
-
-	if err := a.Notify("update", nil); err != nil {
-		t.Fatalf("update notify: %v", err)
-	}
-	select {
-	case <-updateStarted:
-	case <-time.After(2 * time.Second):
-		t.Fatal("update notification did not start")
-	}
-	if err := a.Notify("cancel", nil); err != nil {
-		t.Fatalf("cancel notify: %v", err)
-	}
-	select {
-	case <-cancelDelivered:
-	case <-time.After(2 * time.Second):
-		t.Fatal("different notification method was blocked behind update")
-	}
-	close(releaseUpdate)
-}
-
 func TestConnMethodNotFound(t *testing.T) {
 	a, _, stop := connPair(t)
 	defer stop()

internal/acp/translate.go

@@ -3,6 +3,7 @@ package acp
 import (
 	"encoding/json"
 	"net/url"
+	"path/filepath"
 	"strings"
 	"unicode"
 	"unicode/utf8"
@@ -19,14 +20,6 @@ func agentMessageChunk(delta string) ContentChunk {
 	return ContentChunk{SessionUpdate: UpdateAgentMessageChunk, Content: TextBlock(delta)}
 }
 
-func replayMessageChunk(role, messageID, text string) ContentChunk {
-	update := UpdateAgentMessageChunk
-	if role == "user" {
-		update = UpdateUserMessageChunk
-	}
-	return ContentChunk{SessionUpdate: update, MessageID: messageID, Content: TextBlock(text)}
-}
-
 func agentThoughtChunk(delta string) ContentChunk {
 	return ContentChunk{SessionUpdate: UpdateAgentThoughtChunk, Content: TextBlock(delta)}
 }
@@ -246,22 +239,59 @@ func toolCallResult(result agent.ToolResult) ToolCallUpdate {
 }
 
 func toolResultContent(result agent.ToolResult) []ToolCallContent {
+	content := make([]ToolCallContent, 0, 1+len(result.FileDiffs))
 	text := strings.TrimRight(result.Output, "\n")
 	if text == "" {
 		text = result.Display.Summary
 	}
 	if text == "" {
-		return nil
+		return appendToolResultDiffs(content, result.FileDiffs)
 	}
-	return []ToolCallContent{ToolContent(TextBlock(text))}
+	content = append(content, ToolContent(TextBlock(text)))
+	return appendToolResultDiffs(content, result.FileDiffs)
+}
+
+func appendToolResultDiffs(content []ToolCallContent, diffs []tools.FileDiff) []ToolCallContent {
+	for _, diff := range diffs {
+		if !filepath.IsAbs(diff.Path) || (!diff.OldExists && !diff.NewExists) {
+			continue
+		}
+		var oldText *string
+		if diff.OldExists {
+			old := diff.OldText
+			oldText = &old
+		}
+		var newText *string
+		if diff.NewExists {
+			updated := diff.NewText
+			newText = &updated
+		}
+		content = append(content, ToolCallContent{Type: "diff", Path: diff.Path, OldText: oldText, NewText: newText})
+	}
+	return content
 }
 
 func toolResultLocations(result agent.ToolResult) []ToolCallLocation {
-	locs := make([]ToolCallLocation, 0, len(result.ChangedFiles))
-	for _, f := range result.ChangedFiles {
-		if strings.TrimSpace(f) == "" {
+	locs := make([]ToolCallLocation, 0, len(result.FileDiffs)+len(result.ChangedFiles))
+	seen := make(map[string]bool, len(result.FileDiffs)+len(result.ChangedFiles))
+	for _, diff := range result.FileDiffs {
+		path := diff.Path
+		if path == "" || seen[path] {
 			continue
 		}
+		seen[path] = true
+		locs = append(locs, ToolCallLocation{Path: path})
+	}
+	// FileDiff.Path is canonical absolute path data while ChangedFiles is
+	// normally workspace-relative. Without the trusted workspace root these
+	// coordinate systems cannot be correlated safely: a suffix match would let
+	// /workspace/sub/a.go consume the fallback for a distinct root a.go. The
+	// shared seen set deduplicates only identities already exactly comparable.
+	for _, f := range result.ChangedFiles {
+		if f == "" || seen[f] {
+			continue
+		}
+		seen[f] = true
 		locs = append(locs, ToolCallLocation{Path: f})
 	}
 	return locs

internal/acp/translate_test.go

@@ -2,6 +2,7 @@ package acp
 
 import (
 	"encoding/json"
+	"path/filepath"
 	"strings"
 	"testing"
 	"unicode"
@@ -300,21 +301,26 @@ func TestToolCallStart(t *testing.T) {
 }
 
 func TestToolCallResult(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "a.go")
 	ok := toolCallResult(agent.ToolResult{
 		ToolCallID:   "tc1",
 		Name:         "edit_file",
 		Status:       tools.StatusOK,
 		Output:       "applied\n",
 		ChangedFiles: []string{"a.go", ""},
+		FileDiffs:    []tools.FileDiff{{Path: path, OldExists: true, NewExists: true, OldText: "before\n", NewText: "after\n"}},
 	})
 	if ok.SessionUpdate != UpdateToolCallUpdate || ok.Status != ToolStatusCompleted {
 		t.Fatalf("unexpected ok result: %+v", ok)
 	}
-	if len(ok.Content) != 1 || ok.Content[0].Type != "content" || ok.Content[0].Content.Text != "applied" {
+	if len(ok.Content) != 2 || ok.Content[0].Type != "content" || ok.Content[0].Content.Text != "applied" {
 		t.Fatalf("unexpected content: %+v", ok.Content)
 	}
-	if len(ok.Locations) != 1 || ok.Locations[0].Path != "a.go" {
-		t.Fatalf("blank changed files should be dropped, got %+v", ok.Locations)
+	if diff := ok.Content[1]; diff.Type != "diff" || diff.Path != path || diff.OldText == nil || *diff.OldText != "before\n" || diff.NewText == nil || *diff.NewText != "after\n" {
+		t.Fatalf("unexpected diff content: %+v", diff)
+	}
+	if len(ok.Locations) != 2 || ok.Locations[0].Path != path || ok.Locations[1].Path != "a.go" {
+		t.Fatalf("unproven absolute/relative aliases must both remain visible, got %+v", ok.Locations)
 	}
 
 	failed := toolCallResult(agent.ToolResult{ToolCallID: "tc2", Status: tools.StatusError, Output: "boom"})
@@ -323,6 +329,190 @@ func TestToolCallResult(t *testing.T) {
 	}
 }
 
+func TestToolCallDiffJSONDistinguishesEmptyFilesAndDeletion(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "empty.txt")
+	content := appendToolResultDiffs(nil, []tools.FileDiff{
+		{Path: path, OldExists: false, NewExists: true, NewText: ""},
+		{Path: path, OldExists: true, NewExists: true, OldText: "before", NewText: ""},
+		{Path: path, OldExists: true, NewExists: false, OldText: "before"},
+	})
+	if len(content) != 3 {
+		t.Fatalf("diff content = %#v", content)
+	}
+	for index, diff := range content {
+		encoded, err := json.Marshal(diff)
+		if err != nil {
+			t.Fatal(err)
+		}
+		var wire map[string]any
+		if err := json.Unmarshal(encoded, &wire); err != nil {
+			t.Fatal(err)
+		}
+		if wire["path"] != path {
+			t.Fatalf("wire diff %d = %s", index, encoded)
+		}
+		switch index {
+		case 0:
+			oldText, present := wire["oldText"]
+			if !present || oldText != nil || wire["newText"] != "" {
+				t.Fatalf("create diff = %s, want null oldText and empty newText", encoded)
+			}
+		case 1:
+			if wire["oldText"] != "before" || wire["newText"] != "" {
+				t.Fatalf("empty replacement diff = %s", encoded)
+			}
+		case 2:
+			newText, present := wire["newText"]
+			if wire["oldText"] != "before" || !present || newText != nil {
+				t.Fatalf("deletion diff = %s, want oldText and null newText", encoded)
+			}
+		}
+	}
+}
+
+func TestToolResultLocationsPreserveDistinctPathIdentities(t *testing.T) {
+	root := t.TempDir()
+	rootPath := filepath.Join(root, "a.go")
+	nestedPath := filepath.Join(root, "sub", "a.go")
+	diff := func(path string) tools.FileDiff {
+		return tools.FileDiff{Path: path, OldExists: true, NewExists: true, OldText: "before", NewText: "after"}
+	}
+	for _, tc := range []struct {
+		name  string
+		diffs []tools.FileDiff
+		want  []string
+	}{
+		{name: "both rich", diffs: []tools.FileDiff{diff(rootPath), diff(nestedPath)}, want: []string{rootPath, nestedPath, "a.go", filepath.Join("sub", "a.go")}},
+		{name: "root rich", diffs: []tools.FileDiff{diff(rootPath)}, want: []string{rootPath, "a.go", filepath.Join("sub", "a.go")}},
+		{name: "nested rich", diffs: []tools.FileDiff{diff(nestedPath)}, want: []string{nestedPath, "a.go", filepath.Join("sub", "a.go")}},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			locations := toolResultLocations(agent.ToolResult{
+				ChangedFiles: []string{"a.go", filepath.Join("sub", "a.go")},
+				FileDiffs:    tc.diffs,
+			})
+			if len(locations) != len(tc.want) {
+				t.Fatalf("locations = %#v, want %#v", locations, tc.want)
+			}
+			for index := range tc.want {
+				if locations[index].Path != tc.want[index] {
+					t.Fatalf("locations = %#v, want %#v", locations, tc.want)
+				}
+			}
+		})
+	}
+}
+
+func TestToolCallResultPreservesWhitespaceInFilePaths(t *testing.T) {
+	relativePath := " report.txt "
+	absolutePath := filepath.Join(t.TempDir(), relativePath)
+	update := toolCallResult(agent.ToolResult{
+		ChangedFiles: []string{relativePath},
+		FileDiffs: []tools.FileDiff{{
+			Path: absolutePath, OldExists: true, NewExists: true, OldText: "before", NewText: "after",
+		}},
+	})
+	if len(update.Content) != 1 || update.Content[0].Path != absolutePath {
+		t.Fatalf("diff content path = %#v, want %q", update.Content, absolutePath)
+	}
+	if len(update.Locations) != 2 || update.Locations[0].Path != absolutePath || update.Locations[1].Path != relativePath {
+		t.Fatalf("locations = %#v, want exact paths %q and %q", update.Locations, absolutePath, relativePath)
+	}
+}
+
+func TestToolResultLocationsDeduplicateOnlyExactPaths(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "a.go")
+	locations := toolResultLocations(agent.ToolResult{
+		ChangedFiles: []string{path, path},
+		FileDiffs:    []tools.FileDiff{{Path: path, OldExists: true, NewExists: true, OldText: "before", NewText: "after"}},
+	})
+	if len(locations) != 1 || locations[0].Path != path {
+		t.Fatalf("exact duplicate locations = %#v", locations)
+	}
+}
+
+func TestDeletedFileEmitsDiffAndKeepsLocations(t *testing.T) {
+	relativePath := "deleted.go"
+	absolutePath := filepath.Join(t.TempDir(), relativePath)
+	update := toolCallResult(agent.ToolResult{
+		ChangedFiles: []string{relativePath},
+		FileDiffs: []tools.FileDiff{{
+			Path: absolutePath, OldExists: true, NewExists: false, OldText: "before",
+		}},
+	})
+	if len(update.Content) != 1 || update.Content[0].OldText == nil || *update.Content[0].OldText != "before" || update.Content[0].NewText != nil {
+		t.Fatalf("deleted file diff = %#v, want oldText with null newText", update.Content)
+	}
+	if len(update.Locations) != 2 || update.Locations[0].Path != absolutePath || update.Locations[1].Path != relativePath {
+		t.Fatalf("deleted file locations = %#v", update.Locations)
+	}
+}
+
+func TestToolCallResultEmitsOnlyRedactedFileDiffs(t *testing.T) {
+	secret := "sk-proj-abcdefghijklmnopqrstuvwxyz"
+	path := filepath.Join(t.TempDir(), "secret.txt")
+	scrubbed := tools.ScrubResultSecrets(tools.Result{FileDiffs: []tools.FileDiff{{
+		Path: path, OldExists: true, NewExists: true, OldText: "token=" + secret, NewText: "safe",
+	}}})
+	update := toolCallResult(agent.ToolResult{ToolCallID: "call", Status: tools.StatusError, FileDiffs: scrubbed.FileDiffs})
+	if len(update.Content) != 1 || update.Content[0].OldText == nil || strings.Contains(*update.Content[0].OldText, secret) {
+		t.Fatalf("ACP content leaked unredacted diff: %#v", update.Content)
+	}
+}
+
+func TestToolCallResultOmitsSemanticallyUnchangedRedactedDiff(t *testing.T) {
+	oldSecret := "ghp_ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
+	newSecret := "ghp_9876543210ZYXWVUTSRQPONMLKJIHGFEDCBA"
+	scrubbed := tools.ScrubResultSecrets(tools.Result{
+		ChangedFiles: []string{"credentials.txt"},
+		FileDiffs: []tools.FileDiff{{
+			Path: filepath.Join(t.TempDir(), "credentials.txt"), OldExists: true, NewExists: true,
+			OldText: "token=" + oldSecret, NewText: "token=" + newSecret,
+		}},
+	})
+	update := toolCallResult(agent.ToolResult{
+		ToolCallID: "call", Status: tools.StatusOK,
+		ChangedFiles: scrubbed.ChangedFiles, FileDiffs: scrubbed.FileDiffs,
+	})
+	if len(update.Content) != 0 {
+		t.Fatalf("ACP emitted semantically unchanged redacted diff: %#v", update.Content)
+	}
+	if len(update.Locations) != 1 || update.Locations[0].Path != "credentials.txt" {
+		t.Fatalf("ACP path fallback = %#v", update.Locations)
+	}
+}
+
+func TestToolCallResultOmitsDefaultIgnorableSplitSecretsOnEitherSide(t *testing.T) {
+	secret := "sk-ant-api03-AAAABBBBCCCCDDDDEEEEFFFFGGGG"
+	for name, separator := range map[string]string{
+		"combining grapheme joiner": "\u034f",
+		"variation selector":        "\ufe0f",
+	} {
+		for _, side := range []string{"old", "new"} {
+			t.Run(name+" "+side, func(t *testing.T) {
+				obfuscated := secret[:20] + separator + secret[20:]
+				diff := tools.FileDiff{
+					Path: filepath.Join(t.TempDir(), "secret.txt"), OldExists: true, NewExists: true,
+					OldText: "safe old", NewText: "safe new",
+				}
+				if side == "old" {
+					diff.OldText = obfuscated
+				} else {
+					diff.NewText = obfuscated
+				}
+				scrubbed := tools.ScrubResultSecrets(tools.Result{FileDiffs: []tools.FileDiff{diff}})
+				if !scrubbed.Redacted || len(scrubbed.FileDiffs) != 0 {
+					t.Fatalf("registry boundary retained an obfuscated secret: %#v", scrubbed)
+				}
+				update := toolCallResult(agent.ToolResult{ToolCallID: "call", Status: tools.StatusOK, FileDiffs: scrubbed.FileDiffs})
+				if len(update.Content) != 0 {
+					t.Fatalf("ACP content retained an obfuscated secret: %#v", update.Content)
+				}
+			})
+		}
+	}
+}
+
 func TestPlanUpdateAndStatus(t *testing.T) {
 	upd := planUpdate([]tools.PlanItem{
 		{Content: "step a", Status: "completed"},

internal/acp/types.go

@@ -12,8 +12,6 @@ const (
 	MethodAuthenticate           = "authenticate"
 	MethodSessionNew             = "session/new"
 	MethodSessionLoad            = "session/load"
-	MethodSessionList            = "session/list"
-	MethodSessionResume          = "session/resume"
 	MethodSessionPrompt          = "session/prompt"
 	MethodSessionCancel          = "session/cancel" // notification
 	MethodSessionUpdate          = "session/update" // notification (agent -> client)
@@ -64,16 +62,8 @@ type PromptCapabilities struct {
 }
 
 type AgentCapabilities struct {
-	LoadSession         bool                 `json:"loadSession"`
-	PromptCapabilities  PromptCapabilities   `json:"promptCapabilities"`
-	SessionCapabilities *SessionCapabilities `json:"sessionCapabilities,omitempty"`
-}
-
-// Empty capability objects are presence flags in ACP v1. Pointers preserve
-// the wire distinction between an advertised `{}` and an omitted capability.
-type SessionCapabilities struct {
-	List   *struct{} `json:"list,omitempty"`
-	Resume *struct{} `json:"resume,omitempty"`
+	LoadSession        bool               `json:"loadSession"`
+	PromptCapabilities PromptCapabilities `json:"promptCapabilities"`
 }
 
 type AuthMethod struct {
@@ -127,14 +117,9 @@ type McpServer struct {
 }
 
 type NewSessionParams struct {
-	Cwd        string      `json:"cwd"`
-	McpServers []McpServer `json:"mcpServers"`
-	// AdditionalDirectories is declared by the protocol and consumed nowhere in
-	// this repo yet. When it is wired up it must go through requestedWorkspace
-	// like Cwd does: these are client-supplied paths with no absoluteness rule of
-	// their own, which is the same shape as the resume-cwd hole that made
-	// {"sessionId":"known"} activate a session against this process's directory.
-	AdditionalDirectories []string `json:"additionalDirectories,omitempty"`
+	Cwd                   string      `json:"cwd"`
+	McpServers            []McpServer `json:"mcpServers"`
+	AdditionalDirectories []string    `json:"additionalDirectories,omitempty"`
 }
 
 type NewSessionResult struct {
@@ -155,39 +140,6 @@ type LoadSessionResult struct {
 	Modes         *SessionModeState     `json:"modes,omitempty"`
 }
 
-// ListSessionsParams and the following types implement ACP v1 session/list.
-// Transcript contents stay behind session/load; this method returns metadata
-// only and leaves the optional pagination cursor opaque.
-type ListSessionsParams struct {
-	Cwd    string `json:"cwd,omitempty"`
-	Cursor string `json:"cursor,omitempty"`
-}
-
-type SessionInfoMeta struct {
-	ModelID   string `json:"modelId,omitempty"`
-	CreatedAt string `json:"createdAt,omitempty"`
-}
-
-type SessionInfo struct {
-	SessionID string           `json:"sessionId"`
-	Cwd       string           `json:"cwd"`
-	Title     string           `json:"title,omitempty"`
-	UpdatedAt string           `json:"updatedAt,omitempty"`
-	Meta      *SessionInfoMeta `json:"_meta,omitempty"`
-}
-
-type ListSessionsResult struct {
-	Sessions   []SessionInfo `json:"sessions"`
-	NextCursor string        `json:"nextCursor,omitempty"`
-}
-
-// session/resume takes session/load's wire shape, so its cwd is a plain string
-// too and an omitted one decodes exactly like an empty one. Sharing the type is
-// safe only because activatePersistedSession requires an absolute cwd from the
-// request itself — nothing downstream may supply a default for either method.
-type ResumeSessionParams = LoadSessionParams
-type ResumeSessionResult = LoadSessionResult
-
 // ---- prompt turn ----
 
 type PromptParams struct {
@@ -222,7 +174,6 @@ type SessionNotification struct {
 // ContentBlock under "content"; the variant is set via SessionUpdate.
 type ContentChunk struct {
 	SessionUpdate string       `json:"sessionUpdate"`
-	MessageID     string       `json:"messageId,omitempty"`
 	Content       ContentBlock `json:"content"`
 }
 
@@ -284,9 +235,30 @@ type ToolCallContent struct {
 	// type == "content"
 	Content *ContentBlock `json:"content,omitempty"`
 	// type == "diff"
-	Path    string `json:"path,omitempty"`
-	OldText string `json:"oldText,omitempty"`
-	NewText string `json:"newText,omitempty"`
+	Path    string  `json:"path,omitempty"`
+	OldText *string `json:"oldText,omitempty"`
+	NewText *string `json:"newText,omitempty"`
+}
+
+// MarshalJSON preserves ACP's discriminated content union. A diff always has
+// path, while nullable oldText/newText distinguish creation, deletion, and an
+// existing file replaced with empty content. Other content variants omit all
+// diff fields rather than serializing irrelevant nulls.
+func (content ToolCallContent) MarshalJSON() ([]byte, error) {
+	if content.Type == "diff" {
+		return json.Marshal(struct {
+			Type    string  `json:"type"`
+			Path    string  `json:"path"`
+			OldText *string `json:"oldText"`
+			NewText *string `json:"newText"`
+		}{
+			Type: content.Type, Path: content.Path, OldText: content.OldText, NewText: content.NewText,
+		})
+	}
+	return json.Marshal(struct {
+		Type    string        `json:"type"`
+		Content *ContentBlock `json:"content,omitempty"`
+	}{Type: content.Type, Content: content.Content})
 }
 
 func ToolContent(block ContentBlock) ToolCallContent {

internal/agent/loop.go

@@ -1527,6 +1527,7 @@ func executeToolCall(ctx context.Context, registry *tools.Registry, call ToolCal
 		Images:          result.Images,
 		Redacted:        result.Redacted,
 		ChangedFiles:    result.ChangedFiles,
+		FileDiffs:       result.FileDiffs,
 		ChangeSummaries: result.ChangeSummaries,
 		Display:         result.HumanDisplay(),
 		Outcome:         result.Outcome,
@@ -1833,6 +1834,10 @@ func runToolForUnsandboxedRetry(ctx context.Context, registry *tools.Registry, n
 }
 
 func toolResultFromPrePermissionReject(call ToolCall, result tools.Result) ToolResult {
+	// PrePermissionRejecter runs before Registry.RunWithOptions, so it must
+	// explicitly cross the same transcript/redaction boundary before its result
+	// can be forwarded through ACP.
+	result = tools.ScrubResultSecrets(result)
 	output, outputRedacted := scrubInterceptedOutput(result.Output)
 	display := result.Display
 	summary, summaryRedacted := scrubInterceptedOutput(display.Summary)
@@ -1860,6 +1865,7 @@ func toolResultFromPrePermissionReject(call ToolCall, result tools.Result) ToolR
 		Meta:            meta,
 		Redacted:        result.Redacted || outputRedacted || summaryRedacted || metaRedacted,
 		ChangedFiles:    result.ChangedFiles,
+		FileDiffs:       result.FileDiffs,
 		ChangeSummaries: result.ChangeSummaries,
 		Display:         display,
 		LoadedTools:     loadedToolsFromResult(meta),
@@ -2153,6 +2159,7 @@ func askUserFallbackResult(ctx context.Context, registry *tools.Registry, call T
 			Meta:            result.Meta,
 			Redacted:        result.Redacted,
 			ChangedFiles:    result.ChangedFiles,
+			FileDiffs:       result.FileDiffs,
 			ChangeSummaries: result.ChangeSummaries,
 			Display:         result.HumanDisplay(),
 			Outcome:         result.Outcome,

internal/agent/loop_test.go

@@ -27,6 +27,23 @@ type mockProvider struct {
 	requests []zeroruntime.CompletionRequest
 }
 
+func TestPrePermissionRejectScrubsFileDiffs(t *testing.T) {
+	secret := "sk-proj-abcdefghijklmnopqrstuvwxyz"
+	result := toolResultFromPrePermissionReject(ToolCall{ID: "call", Name: "test"}, tools.Result{
+		Status: tools.StatusError,
+		FileDiffs: []tools.FileDiff{{
+			Path:      filepath.Join(t.TempDir(), "secret.txt"),
+			OldExists: true,
+			NewExists: true,
+			OldText:   "token=" + secret,
+			NewText:   "safe",
+		}},
+	})
+	if len(result.FileDiffs) != 1 || strings.Contains(result.FileDiffs[0].OldText, secret) || !result.Redacted {
+		t.Fatalf("pre-permission FileDiff = %#v, redacted = %t", result.FileDiffs, result.Redacted)
+	}
+}
+
 func TestTypedExecutionOutcomeOverridesLegacySandboxHeuristics(t *testing.T) {
 	engine := sandbox.NewEngine(sandbox.EngineOptions{WorkspaceRoot: t.TempDir(), Policy: sandbox.DefaultPolicy()})
 	call := ToolCall{Name: tools.ExecCommandToolName}

internal/agent/types.go

@@ -84,6 +84,7 @@ type ToolResult struct {
 	Images       []zeroruntime.ImageBlock
 	Redacted     bool
 	ChangedFiles []string
+	FileDiffs    []tools.FileDiff
 	// ChangeSummaries are non-selectable generated-tree summaries emitted by
 	// command execution; callers must not schedule per-file work from them.
 	ChangeSummaries []execution.Change

internal/cli/daemon.go

@@ -7,6 +7,7 @@ import (
 	"os"
 	"os/exec"
 	"os/signal"
+	"path/filepath"
 	"strings"
 	"syscall"
 	"time"
@@ -146,7 +147,11 @@ func runDaemonStartDetached(paths daemon.Paths, stdout io.Writer, stderr io.Writ
 	if err != nil {
 		return writeAppError(stderr, err.Error(), exitCrash)
 	}
-	logFile, logPath, err := daemon.OpenRuntimeLog(paths)
+	if err := os.MkdirAll(filepath.Dir(paths.Socket), 0o700); err != nil {
+		return writeAppError(stderr, err.Error(), exitCrash)
+	}
+	logPath := filepath.Join(filepath.Dir(paths.Socket), "daemon.log")
+	logFile, err := os.OpenFile(logPath, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o600)
 	if err != nil {
 		return writeAppError(stderr, err.Error(), exitCrash)
 	}

internal/cli/exec.go

@@ -49,14 +49,6 @@ const (
 	exitInterrupted = 130
 )
 
-// defaultExecMaxTurns is the headless tool-turn budget when no source sets one.
-// An interactive run can be continued past the shared interactive default by the
-// user; an exec run has nobody to unstick it, so evals and automation would
-// truncate mid-task at 80 turns. The ceiling is the already-justified bound —
-// still finite against a genuinely runaway loop, which the loop's empty-turn
-// guard also cuts independently of this budget.
-const defaultExecMaxTurns = config.MaxTurnsCeiling
-
 type execOutputFormat string
 type execInputFormat string
 
@@ -328,7 +320,6 @@ func runExec(args []string, stdout io.Writer, stderr io.Writer, deps appDeps) in
 		}
 		return writeExecProviderError(stdout, stderr, options.outputFormat, "provider_error", err.Error())
 	}
-	resolved.MaxTurns = execTurnBudget(resolved)
 	var displacedMaxTurns int
 	resolved.MaxTurns, displacedMaxTurns = applyProfileTurnBudget(execProfile, options.maxTurns, resolved.MaxTurns)
 	execScope, err := sandbox.NewScope(workspaceRoot, append(append([]string{}, resolved.Sandbox.AdditionalWriteRoots...), options.addDirs...))
@@ -1231,20 +1222,6 @@ func specProfileEffortFilled(effortFilled bool, specReasoningEffort string) bool
 	return effortFilled && strings.TrimSpace(specReasoningEffort) == ""
 }
 
-// execTurnBudget applies the headless default to the resolved turn budget: an
-// interactive run can be continued past the shared default by the user, but an
-// exec run has nobody to unstick it, so an unconfigured budget starts at the
-// documented ceiling instead of truncating mid-task. Explicit sources
-// (--max-turns, mode presets, ZERO_MAX_TURNS, config files) resolve as
-// MaxTurnsSet and pass through; an exec-profile budget still wins via
-// applyProfileTurnBudget afterward.
-func execTurnBudget(resolved config.ResolvedConfig) int {
-	if resolved.MaxTurnsSet {
-		return resolved.MaxTurns
-	}
-	return defaultExecMaxTurns
-}
-
 // applyProfileTurnBudget decides the run's turn budget once config is resolved.
 // The profile displaces the RESOLVED value, not the flag: a pinned budget
 // always wins and the profile backs off entirely, while an env/config budget

internal/cli/exec_test.go

@@ -1975,23 +1975,3 @@ func TestRunExecTopTierDeclineNoSwitch(t *testing.T) {
 		t.Fatalf("provider model = %q, want claude-opus-4.1", providerModels[0])
 	}
 }
-
-func TestExecTurnBudgetDefaultsToCeilingUnlessSet(t *testing.T) {
-	cases := []struct {
-		name     string
-		resolved config.ResolvedConfig
-		want     int
-	}{
-		// A headless run has no user to continue past the shared interactive
-		// default, so an unconfigured budget starts at the ceiling.
-		{"unconfigured default", config.ResolvedConfig{MaxTurns: 80, MaxTurnsSet: false}, config.MaxTurnsCeiling},
-		// A user who configured 80 on purpose (e.g. cost control in CI) keeps 80.
-		{"explicit default value", config.ResolvedConfig{MaxTurns: 80, MaxTurnsSet: true}, 80},
-		{"configured value passes through", config.ResolvedConfig{MaxTurns: 42, MaxTurnsSet: true}, 42},
-	}
-	for _, tc := range cases {
-		if got := execTurnBudget(tc.resolved); got != tc.want {
-			t.Fatalf("%s: execTurnBudget = %d, want %d", tc.name, got, tc.want)
-		}
-	}
-}

internal/config/resolver.go

@@ -166,7 +166,6 @@ func Resolve(options ResolveOptions) (ResolvedConfig, error) {
 		Providers:           providers,
 		Provider:            active,
 		MaxTurns:            cfg.MaxTurns,
-		MaxTurnsSet:         cfg.maxTurnsSet,
 		MCP:                 cfg.MCP,
 		Sandbox:             cfg.Sandbox,
 		Notify:              cfg.Notify,
@@ -235,7 +234,6 @@ func mergeConfig(dst *FileConfig, src FileConfig) {
 	}
 	if src.MaxTurns > 0 {
 		dst.MaxTurns = src.MaxTurns
-		dst.maxTurnsSet = true
 	}
 	for _, provider := range src.Providers {
 		mergeProvider(dst, provider)
@@ -296,7 +294,6 @@ func mergeProjectConfig(dst *FileConfig, src FileConfig) error {
 	}
 	if src.MaxTurns > 0 {
 		dst.MaxTurns = src.MaxTurns
-		dst.maxTurnsSet = true
 	}
 	for _, provider := range src.Providers {
 		candidate := providerMergeCandidate(*dst, provider)
@@ -609,7 +606,6 @@ func applyEnv(cfg *FileConfig, env map[string]string) {
 				n = MaxTurnsCeiling
 			}
 			cfg.MaxTurns = n
-			cfg.maxTurnsSet = true
 		}
 	}
 
@@ -730,7 +726,6 @@ func applyOverrides(cfg *FileConfig, overrides Overrides) {
 	}
 	if overrides.MaxTurns > 0 {
 		cfg.MaxTurns = overrides.MaxTurns
-		cfg.maxTurnsSet = true
 	}
 	if overrides.Sandbox.Enabled != nil {
 		cfg.Sandbox.Enabled = overrides.Sandbox.Enabled

internal/config/resolver_test.go

@@ -2252,45 +2252,3 @@ func TestResolveRejectsInvalidCrossSessionInbound(t *testing.T) {
 		t.Fatalf("error = %v", err)
 	}
 }
-
-func TestResolveReportsExplicitMaxTurns(t *testing.T) {
-	const providerJSON = `{
-		"activeProvider": "p",
-		"providers": [{"name": "p", "provider_kind": "openai-compatible", "base_url": "https://x.example/v1", "apiKey": "k", "model": "m"}]
-	}`
-	providerWithTurns := strings.Replace(providerJSON, `"activeProvider": "p"`, `"activeProvider": "p", "maxTurns": 40`, 1)
-
-	cases := []struct {
-		name string
-		opts ResolveOptions
-		set  bool
-	}{
-		{"built-in default only", ResolveOptions{
-			Overrides: Overrides{Provider: ProviderProfile{Name: "p", ProviderKind: "openai-compatible", BaseURL: "https://x.example/v1", APIKey: "k", Model: "m"}},
-		}, false},
-		{"user config", ResolveOptions{UserConfigPath: writeConfig(t, providerWithTurns)}, true},
-		{"project config", ResolveOptions{
-			UserConfigPath:    writeConfig(t, providerJSON),
-			ProjectConfigPath: writeConfig(t, `{"maxTurns": 40}`),
-		}, true},
-		{"env", ResolveOptions{
-			Env:       map[string]string{MaxTurnsEnv: "120"},
-			Overrides: Overrides{Provider: ProviderProfile{Name: "p", ProviderKind: "openai-compatible", BaseURL: "https://x.example/v1", APIKey: "k", Model: "m"}},
-		}, true},
-		{"cli override", ResolveOptions{
-			Overrides: Overrides{
-				MaxTurns: 42,
-				Provider: ProviderProfile{Name: "p", ProviderKind: "openai-compatible", BaseURL: "https://x.example/v1", APIKey: "k", Model: "m"},
-			},
-		}, true},
-	}
-	for _, tc := range cases {
-		resolved, err := Resolve(tc.opts)
-		if err != nil {
-			t.Fatalf("%s: Resolve() error = %v", tc.name, err)
-		}
-		if resolved.MaxTurnsSet != tc.set {
-			t.Fatalf("%s: MaxTurnsSet = %v, want %v (MaxTurns=%d)", tc.name, resolved.MaxTurnsSet, tc.set, resolved.MaxTurns)
-		}
-	}
-}

internal/config/types.go

@@ -364,10 +364,6 @@ type FileConfig struct {
 	LocalControl        LocalControlConfig `json:"localControl,omitempty"`
 	STT                 STTConfig          `json:"stt,omitempty"`
 	CrossSessionInbound string             `json:"crossSessionInbound,omitempty"`
-	// maxTurnsSet records that some merge source supplied a positive maxTurns —
-	// i.e. the value is configured, not the built-in default. Unexported like
-	// Tools.deferThresholdSet: merge bookkeeping, not a config key.
-	maxTurnsSet bool
 	// Extra preserves top-level fields written by newer Zero versions or
 	// extensions so a read-modify-write through this version is non-destructive.
 	Extra map[string]json.RawMessage `json:"-"`
@@ -465,15 +461,10 @@ type Overrides struct {
 }
 
 type ResolvedConfig struct {
-	ActiveProvider string
-	Providers      []ProviderProfile
-	Provider       ProviderProfile
-	MaxTurns       int
-	// MaxTurnsSet reports whether MaxTurns came from an explicit source (a
-	// config file, a provider command, ZERO_MAX_TURNS, or CLI overrides) rather
-	// than the built-in default — callers that need a different default can
-	// tell the two apart.
-	MaxTurnsSet         bool
+	ActiveProvider      string
+	Providers           []ProviderProfile
+	Provider            ProviderProfile
+	MaxTurns            int
 	MCP                 MCPConfig
 	Sandbox             SandboxConfig
 	Notify              NotifyConfig

internal/daemon/lock.go

@@ -30,35 +30,15 @@ var processAlive = osProcessAlive
 // 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) {
-	return acquireLockWith(isAlive, func() (*lockutil.FileLock, error) {
-		return lockutil.TryAcquireFileLock(path)
-	}, func() (int, error) {
-		return readPidFile(path)
-	})
-}
-
-func acquireLockRoot(root *os.Root, name, displayPath string, isAlive func(pid int) bool) (*fileLock, error) {
-	return acquireLockWith(isAlive, func() (*lockutil.FileLock, error) {
-		return lockutil.TryAcquireFileLockRoot(root, name, displayPath)
-	}, func() (int, error) {
-		return readPidFileRoot(root, name)
-	})
-}
-
-func acquireLockWith(
-	isAlive func(pid int) bool,
-	acquire func() (*lockutil.FileLock, error),
-	readPID func() (int, error),
-) (*fileLock, error) {
 	if isAlive == nil {
 		isAlive = processAlive
 	}
-	lock, err := acquire()
+	lock, err := lockutil.TryAcquireFileLock(path)
 	if err != nil {
 		if !errors.Is(err, lockutil.ErrLockHeld) {
 			return nil, err
 		}
-		pid, perr := readPID()
+		pid, perr := readPidFile(path)
 		if perr == nil && pid > 0 && isAlive(pid) {
 			return nil, fmt.Errorf("%w (pid %d)", ErrAlreadyRunning, pid)
 		}
@@ -82,15 +62,6 @@ func (l *fileLock) release() error {
 // readPidFile reads and parses the PID recorded in a lock file.
 func readPidFile(path string) (int, error) {
 	data, err := os.ReadFile(path)
-	return parsePidFile(data, err)
-}
-
-func readPidFileRoot(root *os.Root, name string) (int, error) {
-	data, err := root.ReadFile(name)
-	return parsePidFile(data, err)
-}
-
-func parsePidFile(data []byte, err error) (int, error) {
 	if err != nil {
 		return 0, err
 	}

internal/daemon/server.go

@@ -7,7 +7,6 @@ import (
 	"fmt"
 	"net"
 	"os"
-	"path/filepath"
 	"sync"
 	"time"
 )
@@ -24,23 +23,6 @@ type Server struct {
 	listener net.Listener
 	conns    map[net.Conn]struct{} // open connections, closed on Shutdown so blocked reads return
 	lock     *fileLock
-	// runtimeRoot is retained for the full default-daemon lifecycle. Every file
-	// child is addressed relative to this capability; runtimeDir is used only to
-	// verify the unavoidable AF_UNIX pathname bind still names the same object.
-	runtimeRoot *os.Root
-	runtimeDir  string
-	// socketRoot captures the directory that actually received the pathname
-	// bind. It can differ from runtimeRoot only when the configured directory is
-	// exchanged in the final pre-bind window; retaining it makes rollback target
-	// the socket that was really created rather than re-resolving the pathname.
-	socketRoot *os.Root
-	socketName string
-	// statusRoot binds status publication and shutdown cleanup to the same
-	// directory object. statusCommitted is set only after this server publishes
-	// its document, so a failed startup never removes a previous daemon's status.
-	statusRoot      *os.Root
-	statusName      string
-	statusCommitted bool
 
 	ctx    context.Context
 	cancel context.CancelFunc
@@ -59,14 +41,6 @@ type ServerOptions struct {
 	Now     func() time.Time
 	Log     func(string)
 	isAlive func(int) bool // test hook for the single-instance lock
-	// beforeStatusReplace, replaceStatusFile, and syncStatusParent are test hooks
-	// for the status-file commit boundary. nil selects production behavior.
-	beforeStatusReplace  func()
-	replaceStatusFile    func(root *os.Root, src, dst string) error
-	syncStatusParent     func(root *os.Root) error
-	afterRuntimeRootOpen func() // test hook at the default-root trust boundary
-	beforeSocketBind     func() // test hook before the final root verification
-	afterSocketPreflight func() // test hook in the unavoidable pathname-bind window
 }
 
 // NewServer validates options and builds a Server.
@@ -106,41 +80,11 @@ func (s *Server) Serve() error {
 	if err := checkSocketPathLength(s.opts.Paths.Socket); err != nil {
 		return err
 	}
-	defaultRoot, isDefault, err := openDefaultRuntimeRoot(s.opts.Paths)
-	if err != nil {
+	if err := secureSocketParent(s.opts.Paths.Socket); err != nil {
 		return err
 	}
-	if isDefault {
-		s.runtimeRoot = defaultRoot
-		s.runtimeDir = filepath.Dir(s.opts.Paths.Socket)
-		s.statusRoot = defaultRoot
-		s.statusName = filepath.Base(s.opts.Paths.Status)
-		if s.opts.afterRuntimeRootOpen != nil {
-			s.opts.afterRuntimeRootOpen()
-		}
-		if err := runtimeRootStillNamesPath(defaultRoot, s.runtimeDir); err != nil {
-			s.closeRuntimeRoots()
-			return err
-		}
-	} else {
-		if err := secureCustomRuntimeParents(s.opts.Paths); err != nil {
-			return err
-		}
-		statusRoot, err := openStatusRoot(s.opts.Paths.Status)
-		if err != nil {
-			return fmt.Errorf("daemon: open status directory: %w", err)
-		}
-		s.statusRoot = statusRoot
-		s.statusName = filepath.Base(s.opts.Paths.Status)
-	}
-	var lock *fileLock
-	if s.runtimeRoot != nil {
-		lock, err = acquireLockRoot(s.runtimeRoot, filepath.Base(s.opts.Paths.Lock), s.opts.Paths.Lock, s.opts.isAlive)
-	} else {
-		lock, err = acquireLock(s.opts.Paths.Lock, s.opts.isAlive)
-	}
+	lock, err := acquireLock(s.opts.Paths.Lock, s.opts.isAlive)
 	if err != nil {
-		s.closeRuntimeRoots()
 		return err
 	}
 	s.lock = lock
@@ -148,22 +92,7 @@ func (s *Server) Serve() error {
 
 	// A leftover socket file from an unclean exit would make Listen fail with
 	// "address already in use"; we hold the lock, so any socket here is stale.
-	if s.runtimeRoot != nil {
-		if err := s.runtimeRoot.Remove(filepath.Base(s.opts.Paths.Socket)); err != nil && !errors.Is(err, os.ErrNotExist) {
-			return fmt.Errorf("daemon: remove stale control socket: %w", err)
-		}
-		if s.opts.beforeSocketBind != nil {
-			s.opts.beforeSocketBind()
-		}
-		if err := runtimeRootStillNamesPath(s.runtimeRoot, s.runtimeDir); err != nil {
-			return err
-		}
-		if s.opts.afterSocketPreflight != nil {
-			s.opts.afterSocketPreflight()
-		}
-	} else {
-		_ = os.Remove(s.opts.Paths.Socket)
-	}
+	_ = os.Remove(s.opts.Paths.Socket)
 
 	listener, err := net.Listen("unix", s.opts.Paths.Socket)
 	if err != nil {
@@ -172,22 +101,6 @@ func (s *Server) Serve() error {
 	s.mu.Lock()
 	s.listener = listener
 	s.mu.Unlock()
-	if s.runtimeRoot != nil {
-		boundRoot, boundName, err := captureBoundSocketRoot(s.opts.Paths.Socket)
-		if err != nil {
-			_ = listener.Close()
-			return fmt.Errorf("daemon: capture bound control socket: %w", err)
-		}
-		s.socketRoot = boundRoot
-		s.socketName = boundName
-		if err := runtimeRootStillNamesPath(s.runtimeRoot, s.runtimeDir); err != nil {
-			return err
-		}
-		info, err := s.runtimeRoot.Lstat(filepath.Base(s.opts.Paths.Socket))
-		if err != nil || info.Mode()&os.ModeSocket == 0 {
-			return fmt.Errorf("daemon: bound control socket is outside the secured runtime directory")
-		}
-	}
 	// If Shutdown already fired during the bind window, close now and bail so a
 	// shutdown requested at startup is never lost (the accept loop would otherwise
 	// block forever waiting for a connection that never comes) (D4).
@@ -198,7 +111,7 @@ func (s *Server) Serve() error {
 		return nil
 	default:
 	}
-	if err := s.hardenSocket(); err != nil {
+	if err := hardenSocketFile(s.opts.Paths.Socket); err != nil {
 		return fmt.Errorf("daemon: harden control socket: %w", err)
 	}
 	s.startedAt = s.opts.Now()
@@ -277,56 +190,11 @@ func (s *Server) cleanup() {
 	if s.listener != nil {
 		_ = s.listener.Close()
 	}
-	if s.socketRoot != nil {
-		if err := s.socketRoot.Remove(s.socketName); err != nil && !errors.Is(err, os.ErrNotExist) {
-			s.logf("daemon: remove control socket: %v", err)
-		}
-	} else if s.runtimeRoot != nil {
-		if err := s.runtimeRoot.Remove(filepath.Base(s.opts.Paths.Socket)); err != nil && !errors.Is(err, os.ErrNotExist) {
-			s.logf("daemon: remove control socket: %v", err)
-		}
-	} else {
-		_ = os.Remove(s.opts.Paths.Socket)
-	}
-	if s.statusRoot != nil {
-		if s.statusCommitted {
-			if err := s.statusRoot.Remove(s.statusName); err != nil && !errors.Is(err, os.ErrNotExist) {
-				s.logf("daemon: remove status file: %v", err)
-			}
-		}
-	}
+	_ = os.Remove(s.opts.Paths.Socket)
+	_ = os.Remove(s.opts.Paths.Status)
 	if s.lock != nil {
 		_ = s.lock.release()
 	}
-	s.closeRuntimeRoots()
-}
-
-func (s *Server) hardenSocket() error {
-	if s.runtimeRoot != nil {
-		return hardenSocketFileRoot(s.runtimeRoot, filepath.Base(s.opts.Paths.Socket))
-	}
-	return hardenSocketFile(s.opts.Paths.Socket)
-}
-
-func (s *Server) closeRuntimeRoots() {
-	if s.socketRoot != nil {
-		if err := s.socketRoot.Close(); err != nil {
-			s.logf("daemon: close bound socket directory: %v", err)
-		}
-	}
-	s.socketRoot = nil
-	if s.statusRoot != nil && s.statusRoot != s.runtimeRoot {
-		if err := s.statusRoot.Close(); err != nil {
-			s.logf("daemon: close status directory: %v", err)
-		}
-	}
-	s.statusRoot = nil
-	if s.runtimeRoot != nil {
-		if err := s.runtimeRoot.Close(); err != nil {
-			s.logf("daemon: close runtime directory: %v", err)
-		}
-	}
-	s.runtimeRoot = nil
 }
 
 func (s *Server) writeStatusFile() error {
@@ -340,30 +208,7 @@ func (s *Server) writeStatusFile() error {
 	if err != nil {
 		return err
 	}
-	root := s.statusRoot
-	ownedRoot := false
-	if root == nil {
-		var err error
-		root, err = openStatusRoot(s.opts.Paths.Status)
-		if err != nil {
-			return fmt.Errorf("daemon: write status file: %w", err)
-		}
-		ownedRoot = true
-	}
-	committed, err := writeStatusFileAtomicallyRoot(root, filepath.Base(s.opts.Paths.Status), data, 0o600, s.opts.beforeStatusReplace, s.opts.replaceStatusFile, s.opts.syncStatusParent)
-	if ownedRoot {
-		if closeErr := root.Close(); closeErr != nil {
-			err = errors.Join(err, fmt.Errorf("close status directory: %w", closeErr))
-		}
-	}
-	if committed {
-		s.statusCommitted = true
-	}
-	if err != nil {
-		if committed {
-			s.logf("daemon: status file publication committed with warning: %v", err)
-			return nil
-		}
+	if err := os.WriteFile(s.opts.Paths.Status, data, 0o600); err != nil {
 		return fmt.Errorf("daemon: write status file: %w", err)
 	}
 	return nil

internal/daemon/server_test.go

@@ -2,201 +2,20 @@ package daemon
 
 import (
 	"errors"
-	"net"
 	"os"
 	"path/filepath"
-	"runtime"
-	"strings"
 	"testing"
 	"time"
-
-	"github.com/Gitlawb/zero/internal/observability"
 )
 
-func TestServeSupportsReadOnlyCustomRuntimeDirectory(t *testing.T) {
-	if runtime.GOOS == "windows" {
-		t.Skip("Unix permission compatibility regression")
-	}
-	dir, err := os.MkdirTemp("/tmp", "zero-serve-")
-	if err != nil {
-		t.Fatal(err)
-	}
-	t.Cleanup(func() { _ = os.RemoveAll(dir) })
-	if err := os.Chmod(dir, 0o755); err != nil {
-		t.Fatal(err)
-	}
-	paths := Paths{
-		Socket: filepath.Join(dir, "daemon.sock"),
-		Lock:   filepath.Join(dir, "daemon.lock"),
-		Status: filepath.Join(dir, "daemon.status"),
-	}
-	launcher, _ := seqLauncher(&fakeWorker{pid: 1})
-	srv := newTestServerWithPaths(t, launcher, paths)
-	serveErr := make(chan error, 1)
-	go func() { serveErr <- srv.Serve() }()
-	waitForFile(t, paths.Status)
-	srv.Shutdown()
-	if err := <-serveErr; err != nil {
-		t.Fatalf("Serve with 0755 custom runtime directory: %v", err)
-	}
-	info, err := os.Stat(dir)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if got := info.Mode().Perm(); got != 0o755 {
-		t.Fatalf("custom runtime directory permissions = %04o, want unchanged 0755", got)
-	}
-}
-
-func TestServeKeepsDefaultRootBoundAcrossCoordination(t *testing.T) {
-	if runtime.GOOS == "windows" {
-		t.Skip("Windows may deny renaming a directory with an open AF_UNIX lifecycle handle")
-	}
-	home, err := os.MkdirTemp("/tmp", "zero-root-")
-	if err != nil {
-		t.Fatal(err)
-	}
-	t.Cleanup(func() { _ = os.RemoveAll(home) })
-	t.Setenv("HOME", home)
-	t.Setenv("USERPROFILE", home)
-	t.Setenv("XDG_RUNTIME_DIR", "")
-	paths, err := DefaultPaths()
-	if err != nil {
-		t.Fatal(err)
-	}
-	dir := filepath.Dir(paths.Socket)
-	moved := filepath.Join(home, "bound-runtime")
-	if err := os.Mkdir(dir, 0o700); err != nil {
-		t.Fatal(err)
-	}
-	launcher, _ := seqLauncher(&fakeWorker{pid: 1})
-	srv := newTestServerWithPaths(t, launcher, paths)
-	srv.opts.beforeSocketBind = func() {
-		if err := os.Rename(dir, moved); err != nil {
-			t.Fatal(err)
-		}
-		if err := os.Mkdir(dir, 0o700); err != nil {
-			t.Fatal(err)
-		}
-	}
-
-	err = srv.Serve()
-	if err == nil || !strings.Contains(err.Error(), "changed after it was secured") {
-		t.Fatalf("Serve error = %v, want replaced-runtime rejection", err)
-	}
-	if _, err := os.Stat(filepath.Join(moved, filepath.Base(paths.Lock))); err != nil {
-		t.Fatalf("rooted lock was not created in the bound directory: %v", err)
-	}
-	for _, path := range []string{paths.Lock, paths.Socket, paths.Status} {
-		if _, err := os.Lstat(path); !errors.Is(err, os.ErrNotExist) {
-			t.Fatalf("substitute runtime entry %s was touched: %v", path, err)
-		}
-	}
-}
-
-func TestServeRemovesSocketBoundAfterFinalRuntimeSwap(t *testing.T) {
-	if runtime.GOOS == "windows" {
-		t.Skip("Windows may deny renaming a directory with an open AF_UNIX lifecycle handle")
-	}
-	home, err := os.MkdirTemp("/tmp", "zero-bind-swap-")
-	if err != nil {
-		t.Fatal(err)
-	}
-	t.Cleanup(func() { _ = os.RemoveAll(home) })
-	t.Setenv("HOME", home)
-	t.Setenv("USERPROFILE", home)
-	t.Setenv("XDG_RUNTIME_DIR", "")
-	paths, err := DefaultPaths()
-	if err != nil {
-		t.Fatal(err)
-	}
-	dir := filepath.Dir(paths.Socket)
-	moved := filepath.Join(home, "trusted-runtime")
-	if err := os.Mkdir(dir, 0o700); err != nil {
-		t.Fatal(err)
-	}
-	launcher, _ := seqLauncher(&fakeWorker{pid: 1})
-	srv := newTestServerWithPaths(t, launcher, paths)
-	srv.opts.afterSocketPreflight = func() {
-		if err := os.Rename(dir, moved); err != nil {
-			t.Fatal(err)
-		}
-		if err := os.Mkdir(dir, 0o700); err != nil {
-			t.Fatal(err)
-		}
-	}
-
-	err = srv.Serve()
-	if err == nil || !strings.Contains(err.Error(), "changed after it was secured") {
-		t.Fatalf("Serve error = %v, want post-bind runtime replacement rejection", err)
-	}
-	if _, err := os.Stat(filepath.Join(moved, filepath.Base(paths.Lock))); err != nil {
-		t.Fatalf("rooted lock was not retained in the trusted directory: %v", err)
-	}
-	if _, err := os.Lstat(paths.Socket); !errors.Is(err, os.ErrNotExist) {
-		t.Fatalf("substitute runtime retained stale socket: %v", err)
-	}
-	listener, err := net.Listen("unix", paths.Socket)
-	if err != nil {
-		t.Fatalf("substitute runtime remained unbindable after rollback: %v", err)
-	}
-	if err := listener.Close(); err != nil {
-		t.Fatal(err)
-	}
-}
-
-func TestOpenRuntimeLogHardensDefaultRootBeforeOpen(t *testing.T) {
-	if runtime.GOOS == "windows" {
-		t.Skip("Windows DACL hardening has platform-specific coverage")
-	}
-	home := t.TempDir()
-	t.Setenv("HOME", home)
-	t.Setenv("USERPROFILE", home)
-	t.Setenv("XDG_RUNTIME_DIR", "")
-	paths, err := DefaultPaths()
-	if err != nil {
-		t.Fatal(err)
-	}
-	dir := filepath.Dir(paths.Socket)
-	if err := os.MkdirAll(dir, 0o777); err != nil {
-		t.Fatal(err)
-	}
-	if err := os.Chmod(dir, 0o777); err != nil {
-		t.Fatal(err)
-	}
-	file, logPath, err := OpenRuntimeLog(paths)
-	if err != nil {
-		t.Fatalf("OpenRuntimeLog: %v", err)
-	}
-	if err := file.Close(); err != nil {
-		t.Fatal(err)
-	}
-	if logPath != filepath.Join(dir, "daemon.log") {
-		t.Fatalf("log path = %q", logPath)
-	}
-	info, err := os.Stat(dir)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if got := info.Mode().Perm(); got&0o077 != 0 {
-		t.Fatalf("default runtime directory permissions = %04o, want owner-only", got)
-	}
-}
-
 func newTestServer(t *testing.T, launcher Launcher) (*Server, Paths) {
 	t.Helper()
 	dir := t.TempDir()
-	secureStatusTestDir(t, dir)
 	paths := Paths{
 		Socket: filepath.Join(dir, "d.sock"),
 		Lock:   filepath.Join(dir, "d.lock"),
 		Status: filepath.Join(dir, "d.status"),
 	}
-	return newTestServerWithPaths(t, launcher, paths), paths
-}
-
-func newTestServerWithPaths(t *testing.T, launcher Launcher, paths Paths) *Server {
-	t.Helper()
 	pool, err := NewPool(PoolOptions{Size: 2, Launcher: launcher, KillTimeout: 200 * time.Millisecond})
 	if err != nil {
 		t.Fatalf("NewPool: %v", err)
@@ -209,7 +28,7 @@ func newTestServerWithPaths(t *testing.T, launcher Launcher, paths Paths) *Serve
 	if err != nil {
 		t.Fatalf("NewServer: %v", err)
 	}
-	return srv
+	return srv, paths
 }
 
 func waitForFile(t *testing.T, path string) {
@@ -317,153 +136,6 @@ func TestServerEndToEnd(t *testing.T) {
 	}
 }
 
-func TestServePreservesPreviousStatusWhenReplacementFails(t *testing.T) {
-	launcher, _ := seqLauncher(&fakeWorker{pid: 1, exitCode: 0})
-	dir, err := os.MkdirTemp("", "zero-daemon-status-")
-	if err != nil {
-		t.Fatal(err)
-	}
-	t.Cleanup(func() { _ = os.RemoveAll(dir) })
-	secureStatusTestDir(t, dir)
-	paths := Paths{Socket: filepath.Join(dir, "d.sock"), Lock: filepath.Join(dir, "d.lock"), Status: filepath.Join(dir, "d.status")}
-	srv := newTestServerWithPaths(t, launcher, paths)
-	previous := []byte(`{"pid":7,"socket":"previous","version":1}`)
-	if err := os.WriteFile(paths.Status, previous, 0o600); err != nil {
-		t.Fatal(err)
-	}
-	srv.opts.replaceStatusFile = func(*os.Root, string, string) error {
-		return errors.New("injected replacement failure")
-	}
-
-	if err := srv.Serve(); err == nil || !strings.Contains(err.Error(), "injected replacement failure") {
-		t.Fatal("Serve succeeded despite injected status replacement failure")
-	}
-	got, err := os.ReadFile(paths.Status)
-	if err != nil {
-		t.Fatalf("previous status was removed after failed publication: %v", err)
-	}
-	if string(got) != string(previous) {
-		t.Fatalf("previous status changed after failed publication: %q", got)
-	}
-}
-
-func TestServeCleansStatusThroughBoundDirectoryAfterSwap(t *testing.T) {
-	if runtime.GOOS == "windows" {
-		t.Skip("Windows does not permit renaming the directory containing the live socket")
-	}
-	parent, err := os.MkdirTemp("", "zero-daemon-swap-")
-	if err != nil {
-		t.Fatal(err)
-	}
-	t.Cleanup(func() { _ = os.RemoveAll(parent) })
-	dir := filepath.Join(parent, "live")
-	movedDir := filepath.Join(parent, "moved")
-	if err := os.Mkdir(dir, 0o700); err != nil {
-		t.Fatal(err)
-	}
-	secureStatusTestDir(t, dir)
-	paths := Paths{
-		Socket: filepath.Join(dir, "d.sock"),
-		Lock:   filepath.Join(dir, "d.lock"),
-		Status: filepath.Join(dir, "d.status"),
-	}
-	launcher, _ := seqLauncher(&fakeWorker{pid: 1, exitCode: 0})
-	srv := newTestServerWithPaths(t, launcher, paths)
-	substitute := []byte(`{"pid":999,"socket":"substitute"}`)
-	srv.opts.beforeStatusReplace = func() {
-		if err := os.Rename(dir, movedDir); err != nil {
-			t.Fatalf("move status directory: %v", err)
-		}
-		if err := os.Mkdir(dir, 0o700); err != nil {
-			t.Fatalf("create substitute directory: %v", err)
-		}
-		if err := os.WriteFile(paths.Status, substitute, 0o600); err != nil {
-			t.Fatalf("write substitute status: %v", err)
-		}
-	}
-
-	serveErr := make(chan error, 1)
-	go func() { serveErr <- srv.Serve() }()
-	waitForFile(t, filepath.Join(movedDir, "d.status"))
-	srv.Shutdown()
-	select {
-	case err := <-serveErr:
-		if err != nil {
-			t.Fatalf("Serve: %v", err)
-		}
-	case <-time.After(3 * time.Second):
-		t.Fatal("Serve did not return after shutdown")
-	}
-	if _, err := os.Stat(filepath.Join(movedDir, "d.status")); !errors.Is(err, os.ErrNotExist) {
-		t.Fatalf("bound status survived cleanup: %v", err)
-	}
-	got, err := os.ReadFile(paths.Status)
-	if err != nil {
-		t.Fatalf("substitute status was removed by pathname cleanup: %v", err)
-	}
-	if string(got) != string(substitute) {
-		t.Fatalf("substitute status changed during cleanup: %q", got)
-	}
-}
-
-func TestServerPublishesDefaultStatusAfterCrashReportCreatesRuntimeDirectory(t *testing.T) {
-	home, err := os.MkdirTemp("", "zero-home-")
-	if err != nil {
-		t.Fatal(err)
-	}
-	t.Cleanup(func() { _ = os.RemoveAll(home) })
-	t.Setenv("HOME", home)
-	t.Setenv("USERPROFILE", home)
-	t.Setenv("XDG_RUNTIME_DIR", "")
-
-	if _, err := observability.WriteCrashReport(
-		observability.DefaultCrashDir(),
-		"cli",
-		"boom",
-		[]byte("stack"),
-		time.Now(),
-	); err != nil {
-		t.Fatalf("WriteCrashReport: %v", err)
-	}
-	paths, err := DefaultPaths()
-	if err != nil {
-		t.Fatalf("DefaultPaths: %v", err)
-	}
-	if paths.Status != filepath.Join(home, ".zero", "daemon.status") {
-		t.Fatalf("default status path = %q, want path beneath temporary home", paths.Status)
-	}
-
-	launcher, _ := seqLauncher(&fakeWorker{pid: 1})
-	srv := newTestServerWithPaths(t, launcher, paths)
-	serveErr := make(chan error, 1)
-	go func() { serveErr <- srv.Serve() }()
-
-	deadline := time.NewTimer(3 * time.Second)
-	defer deadline.Stop()
-	for {
-		if _, err := os.Stat(paths.Status); err == nil {
-			break
-		}
-		select {
-		case err := <-serveErr:
-			t.Fatalf("Serve returned before publishing status: %v", err)
-		case <-deadline.C:
-			t.Fatal("daemon did not publish its default status file")
-		case <-time.After(2 * time.Millisecond):
-		}
-	}
-
-	srv.Shutdown()
-	select {
-	case err := <-serveErr:
-		if err != nil {
-			t.Fatalf("Serve returned error: %v", err)
-		}
-	case <-time.After(3 * time.Second):
-		t.Fatal("Serve did not return after shutdown")
-	}
-}
-
 func TestServerSecondInstanceFails(t *testing.T) {
 	block := make(chan struct{})
 	defer close(block)

internal/daemon/socket.go

@@ -1,12 +1,9 @@
 package daemon
 
 import (
-	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
-
-	"github.com/Gitlawb/zero/internal/privatedir"
 )
 
 // maxUnixSocketPath bounds the socket path to the smallest platform sun_path
@@ -15,182 +12,10 @@ import (
 // safe cross-platform ceiling.
 const maxUnixSocketPath = 103
 
-func secureCustomRuntimeParents(paths Paths) error {
-	parents := []struct {
-		name string
-		path string
-	}{
-		{name: "socket", path: filepath.Dir(paths.Socket)},
-		{name: "lock", path: filepath.Dir(paths.Lock)},
-		{name: "status", path: filepath.Dir(paths.Status)},
-	}
-	seen := make(map[string]struct{}, len(parents))
-	for _, parent := range parents {
-		absolute, err := filepath.Abs(parent.path)
-		if err != nil {
-			return fmt.Errorf("daemon: resolve %s directory: %w", parent.name, err)
-		}
-		if _, ok := seen[absolute]; ok {
-			continue
-		}
-		seen[absolute] = struct{}{}
-		if err := os.MkdirAll(absolute, 0o700); err != nil {
-			return fmt.Errorf("daemon: create %s directory: %w", parent.name, err)
-		}
-		root, err := os.OpenRoot(absolute)
-		if err != nil {
-			return fmt.Errorf("daemon: open custom %s directory: %w", parent.name, err)
-		}
-		validateErr := validateStatusRoot(root)
-		closeErr := root.Close()
-		if validateErr != nil {
-			return fmt.Errorf("daemon: validate custom %s directory: %w", parent.name, validateErr)
-		}
-		if closeErr != nil {
-			return fmt.Errorf("daemon: close custom %s directory: %w", parent.name, closeErr)
-		}
-	}
-	return nil
-}
-
-// OpenRuntimeLog secures the default runtime root before acquiring the
-// detached daemon's log descriptor. Custom endpoint layouts remain supported,
-// but their existing parent permissions are caller-owned and left untouched.
-func OpenRuntimeLog(paths Paths) (*os.File, string, error) {
-	logPath := filepath.Join(filepath.Dir(paths.Socket), "daemon.log")
-	root, isDefault, err := openDefaultRuntimeRoot(paths)
-	if err != nil {
-		return nil, logPath, err
-	}
-	if isDefault {
-		defer root.Close()
-		file, err := openRootAppendRegular(root, filepath.Base(logPath))
-		if err != nil {
-			return nil, logPath, fmt.Errorf("daemon: open runtime log: %w", err)
-		}
-		return file, logPath, nil
-	}
-
-	parent := filepath.Dir(logPath)
-	if err := os.MkdirAll(parent, 0o700); err != nil {
-		return nil, logPath, fmt.Errorf("daemon: create custom log directory: %w", err)
-	}
-	info, err := os.Lstat(logPath)
-	if err == nil && !info.Mode().IsRegular() {
-		return nil, logPath, fmt.Errorf("daemon: custom runtime log is not a regular file")
-	}
-	if err != nil && !errors.Is(err, os.ErrNotExist) {
-		return nil, logPath, fmt.Errorf("daemon: inspect custom runtime log: %w", err)
-	}
-	file, err := os.OpenFile(logPath, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o600)
-	if err != nil {
-		return nil, logPath, fmt.Errorf("daemon: open custom runtime log: %w", err)
-	}
-	return file, logPath, nil
-}
-
-func openDefaultRuntimeRoot(paths Paths) (*os.Root, bool, error) {
-	defaults, err := DefaultPaths()
-	if err != nil {
-		// A caller-supplied layout remains usable even when the process has no
-		// resolvable home directory. Production default paths can only reach this
-		// helper after DefaultPaths has already succeeded.
-		return nil, false, nil
-	}
-	matches, err := samePaths(paths, defaults)
-	if err != nil {
-		return nil, false, err
-	}
-	if !matches {
-		return nil, false, nil
-	}
-	root, err := privatedir.Open(filepath.Dir(defaults.Socket))
-	if err != nil {
-		return nil, false, fmt.Errorf("daemon: secure default runtime directory: %w", err)
-	}
-	return root, true, nil
-}
-
-func samePaths(left, right Paths) (bool, error) {
-	pairs := [][2]string{
-		{left.Socket, right.Socket},
-		{left.Lock, right.Lock},
-		{left.Status, right.Status},
-	}
-	for _, pair := range pairs {
-		leftAbs, err := filepath.Abs(pair[0])
-		if err != nil {
-			return false, fmt.Errorf("daemon: resolve runtime path: %w", err)
-		}
-		rightAbs, err := filepath.Abs(pair[1])
-		if err != nil {
-			return false, fmt.Errorf("daemon: resolve default runtime path: %w", err)
-		}
-		if filepath.Clean(leftAbs) != filepath.Clean(rightAbs) {
-			return false, nil
-		}
-	}
-	return true, nil
-}
-
-func runtimeRootStillNamesPath(root *os.Root, path string) error {
-	opened, err := root.Stat(".")
-	if err != nil {
-		return fmt.Errorf("inspect bound runtime directory: %w", err)
-	}
-	current, err := os.Lstat(path)
-	if err != nil {
-		return fmt.Errorf("inspect runtime directory entry: %w", err)
-	}
-	if current.Mode()&os.ModeSymlink != 0 || !os.SameFile(opened, current) {
-		return fmt.Errorf("daemon: default runtime directory changed after it was secured")
-	}
-	return nil
-}
-
-func captureBoundSocketRoot(path string) (*os.Root, string, error) {
-	root, err := os.OpenRoot(filepath.Dir(path))
-	if err != nil {
-		return nil, "", fmt.Errorf("open bound socket directory: %w", err)
-	}
-	name := filepath.Base(path)
-	info, err := root.Lstat(name)
-	if err != nil {
-		_ = root.Close()
-		return nil, "", fmt.Errorf("inspect bound socket: %w", err)
-	}
-	if info.Mode()&os.ModeSocket == 0 {
-		_ = root.Close()
-		return nil, "", fmt.Errorf("bound socket path is not a socket")
-	}
-	return root, name, nil
-}
-
-func openRootAppendRegular(root *os.Root, name string) (*os.File, error) {
-	info, err := root.Lstat(name)
-	if errors.Is(err, os.ErrNotExist) {
-		return root.OpenFile(name, os.O_CREATE|os.O_EXCL|os.O_WRONLY|os.O_APPEND, 0o600)
-	}
-	if err != nil {
-		return nil, err
-	}
-	if !info.Mode().IsRegular() {
-		return nil, fmt.Errorf("runtime log is not a regular file")
-	}
-	file, err := root.OpenFile(name, os.O_WRONLY|os.O_APPEND, 0o600)
-	if err != nil {
-		return nil, err
-	}
-	opened, err := file.Stat()
-	if err != nil {
-		_ = file.Close()
-		return nil, err
-	}
-	if !opened.Mode().IsRegular() {
-		_ = file.Close()
-		return nil, fmt.Errorf("runtime log changed while opening")
-	}
-	return file, nil
+// secureSocketParent creates the socket's parent directory owner-only (0700 on
+// POSIX; on Windows the per-user profile directory is already ACL-restricted).
+func secureSocketParent(socketPath string) error {
+	return os.MkdirAll(filepath.Dir(socketPath), 0o700)
 }
 
 // checkSocketPathLength rejects an over-long unix socket path before bind.

internal/daemon/socket_posix.go

@@ -10,7 +10,3 @@ import "os"
 func hardenSocketFile(path string) error {
 	return os.Chmod(path, 0o600)
 }
-
-func hardenSocketFileRoot(root *os.Root, name string) error {
-	return root.Chmod(name, 0o600)
-}

internal/daemon/socket_windows.go

@@ -2,12 +2,8 @@
 
 package daemon
 
-import "os"
-
 // hardenSocketFile is a no-op on Windows: AF_UNIX socket files do not honor POSIX
 // mode bits, and the daemon places the socket under the per-user profile
 // directory, which is already ACL-restricted to the owner. A dedicated restricted
 // ACL (or a named pipe with an explicit DACL) is a documented follow-up.
 func hardenSocketFile(string) error { return nil }
-
-func hardenSocketFileRoot(*os.Root, string) error { return nil }

internal/daemon/status_dir_owner_unix.go

@@ -1,20 +0,0 @@
-//go:build !windows
-
-package daemon
-
-import (
-	"fmt"
-	"os"
-	"syscall"
-)
-
-func checkStatusDirOwner(_ *os.Root, info os.FileInfo) error {
-	stat, ok := info.Sys().(*syscall.Stat_t)
-	if !ok {
-		return fmt.Errorf("status directory ownership metadata is unavailable")
-	}
-	if int(stat.Uid) != os.Geteuid() {
-		return fmt.Errorf("status directory is owned by uid %d, not the current user", stat.Uid)
-	}
-	return nil
-}

internal/daemon/status_dir_owner_unix_test.go

@@ -1,51 +0,0 @@
-//go:build !windows
-
-package daemon
-
-import (
-	"os"
-	"strings"
-	"syscall"
-	"testing"
-	"time"
-)
-
-func secureStatusTestDirPlatform(t *testing.T, dir string) {
-	t.Helper()
-	if err := os.Chmod(dir, 0o700); err != nil {
-		t.Fatal(err)
-	}
-}
-
-func broadenStatusTestDirPlatform(t *testing.T, dir string) {
-	t.Helper()
-	if err := os.Chmod(dir, 0o755); err != nil {
-		t.Fatal(err)
-	}
-}
-
-func TestCheckStatusDirOwnerRejectsMissingMetadata(t *testing.T) {
-	err := checkStatusDirOwner(nil, statusDirOwnerTestInfo{})
-	if err == nil || !strings.Contains(err.Error(), "metadata is unavailable") {
-		t.Fatalf("checkStatusDirOwner error = %v, want unavailable metadata rejection", err)
-	}
-}
-
-func TestCheckStatusDirOwnerRejectsDifferentUser(t *testing.T) {
-	info := statusDirOwnerTestInfo{sys: &syscall.Stat_t{Uid: uint32(os.Geteuid() + 1)}}
-	err := checkStatusDirOwner(nil, info)
-	if err == nil || !strings.Contains(err.Error(), "not the current user") {
-		t.Fatalf("checkStatusDirOwner error = %v, want owner mismatch rejection", err)
-	}
-}
-
-type statusDirOwnerTestInfo struct {
-	sys any
-}
-
-func (statusDirOwnerTestInfo) Name() string       { return "." }
-func (statusDirOwnerTestInfo) Size() int64        { return 0 }
-func (statusDirOwnerTestInfo) Mode() os.FileMode  { return os.ModeDir | 0o700 }
-func (statusDirOwnerTestInfo) ModTime() time.Time { return time.Time{} }
-func (statusDirOwnerTestInfo) IsDir() bool        { return true }
-func (info statusDirOwnerTestInfo) Sys() any      { return info.sys }

internal/daemon/status_dir_owner_windows.go

@@ -1,137 +0,0 @@
-//go:build windows
-
-package daemon
-
-import (
-	"errors"
-	"fmt"
-	"os"
-	"unsafe"
-
-	"golang.org/x/sys/windows"
-)
-
-const statusDirectoryWriteAccess = windows.ACCESS_MASK(
-	windows.GENERIC_ALL |
-		windows.GENERIC_WRITE |
-		windows.DELETE |
-		windows.WRITE_DAC |
-		windows.WRITE_OWNER |
-		windows.FILE_WRITE_DATA |
-		windows.FILE_APPEND_DATA |
-		windows.FILE_WRITE_ATTRIBUTES |
-		windows.FILE_WRITE_EA |
-		0x40, // FILE_DELETE_CHILD
-)
-
-// checkStatusDirOwner validates ownership and write access through a handle
-// opened beneath root. Path-based ACL inspection would recreate the ancestor
-// swap race that Root is intended to close.
-func checkStatusDirOwner(root *os.Root, _ os.FileInfo) (returnErr error) {
-	directory, err := root.Open(".")
-	if err != nil {
-		return fmt.Errorf("open status directory for access validation: %w", err)
-	}
-	defer func() {
-		if err := directory.Close(); err != nil {
-			returnErr = errors.Join(returnErr, fmt.Errorf("close status directory access handle: %w", err))
-		}
-	}()
-
-	raw, err := directory.SyscallConn()
-	if err != nil {
-		return fmt.Errorf("access status directory handle: %w", err)
-	}
-	var descriptor *windows.SECURITY_DESCRIPTOR
-	var queryErr error
-	if err := raw.Control(func(handle uintptr) {
-		descriptor, queryErr = windows.GetSecurityInfo(
-			windows.Handle(handle),
-			windows.SE_FILE_OBJECT,
-			windows.OWNER_SECURITY_INFORMATION|windows.DACL_SECURITY_INFORMATION,
-		)
-	}); err != nil {
-		return fmt.Errorf("inspect status directory access: %w", err)
-	}
-	if queryErr != nil {
-		return fmt.Errorf("inspect status directory owner and DACL: %w", queryErr)
-	}
-	if descriptor == nil {
-		return fmt.Errorf("status directory security descriptor is unavailable")
-	}
-
-	token := windows.GetCurrentProcessToken()
-	user, err := token.GetTokenUser()
-	if err != nil {
-		return fmt.Errorf("resolve current Windows user: %w", err)
-	}
-	tokenOwner, err := currentWindowsTokenOwner(token)
-	if err != nil {
-		return fmt.Errorf("resolve current Windows token owner: %w", err)
-	}
-	owner, _, err := descriptor.Owner()
-	if err != nil {
-		return fmt.Errorf("read status directory owner: %w", err)
-	}
-	if owner == nil || (!owner.Equals(user.User.Sid) && !owner.Equals(tokenOwner)) {
-		return fmt.Errorf("status directory is not owned by the current Windows token")
-	}
-
-	dacl, _, err := descriptor.DACL()
-	if err != nil {
-		return fmt.Errorf("read status directory DACL: %w", err)
-	}
-	if dacl == nil {
-		return fmt.Errorf("status directory has an unrestricted Windows DACL")
-	}
-	for index := uint16(0); index < dacl.AceCount; index++ {
-		var ace *windows.ACCESS_ALLOWED_ACE
-		if err := windows.GetAce(dacl, uint32(index), &ace); err != nil {
-			return fmt.Errorf("read status directory DACL entry %d: %w", index, err)
-		}
-		switch ace.Header.AceType {
-		case windows.ACCESS_DENIED_ACE_TYPE:
-			continue
-		case windows.ACCESS_ALLOWED_ACE_TYPE:
-		default:
-			return fmt.Errorf("status directory DACL entry %d has unsupported type %d", index, ace.Header.AceType)
-		}
-		if ace.Mask&statusDirectoryWriteAccess == 0 {
-			continue
-		}
-		trustee := (*windows.SID)(unsafe.Pointer(&ace.SidStart))
-		if !allowedStatusDirectoryTrustee(trustee, user.User.Sid) {
-			return fmt.Errorf("status directory DACL grants write access to unexpected trustee %s", trustee.String())
-		}
-	}
-	return nil
-}
-
-type statusDirectoryTokenOwner struct {
-	owner *windows.SID
-}
-
-func currentWindowsTokenOwner(token windows.Token) (*windows.SID, error) {
-	var size uint32
-	err := windows.GetTokenInformation(token, windows.TokenOwner, nil, 0, &size)
-	if err != windows.ERROR_INSUFFICIENT_BUFFER {
-		return nil, err
-	}
-	buffer := make([]byte, size)
-	if err := windows.GetTokenInformation(token, windows.TokenOwner, &buffer[0], size, &size); err != nil {
-		return nil, err
-	}
-	owner := (*statusDirectoryTokenOwner)(unsafe.Pointer(&buffer[0])).owner
-	if owner == nil {
-		return nil, errors.New("windows access token has no default owner")
-	}
-	return owner.Copy()
-}
-
-func allowedStatusDirectoryTrustee(trustee, user *windows.SID) bool {
-	return trustee != nil && (trustee.Equals(user) ||
-		trustee.IsWellKnown(windows.WinLocalSystemSid) ||
-		trustee.IsWellKnown(windows.WinBuiltinAdministratorsSid) ||
-		trustee.IsWellKnown(windows.WinCreatorOwnerSid) ||
-		trustee.IsWellKnown(windows.WinCreatorOwnerRightsSid))
-}

internal/daemon/status_dir_owner_windows_test.go

@@ -1,97 +0,0 @@
-//go:build windows
-
-package daemon
-
-import (
-	"fmt"
-	"os"
-	"runtime"
-	"strings"
-	"testing"
-
-	"golang.org/x/sys/windows"
-)
-
-func secureStatusTestDirPlatform(t *testing.T, dir string) {
-	t.Helper()
-	user, err := windows.GetCurrentProcessToken().GetTokenUser()
-	if err != nil {
-		t.Fatal(err)
-	}
-	descriptor, err := windows.SecurityDescriptorFromString(
-		fmt.Sprintf("O:%sD:P(A;OICI;GA;;;%s)(A;OICI;GA;;;SY)", user.User.Sid.String(), user.User.Sid.String()),
-	)
-	if err != nil {
-		t.Fatal(err)
-	}
-	dacl, _, err := descriptor.DACL()
-	if err != nil {
-		t.Fatal(err)
-	}
-	if err := windows.SetNamedSecurityInfo(
-		dir,
-		windows.SE_FILE_OBJECT,
-		windows.DACL_SECURITY_INFORMATION|windows.PROTECTED_DACL_SECURITY_INFORMATION,
-		nil,
-		nil,
-		dacl,
-		nil,
-	); err != nil {
-		t.Fatal(err)
-	}
-}
-
-func broadenStatusTestDirPlatform(t *testing.T, dir string) {
-	t.Helper()
-	worldSID, err := windows.CreateWellKnownSid(windows.WinWorldSid)
-	if err != nil {
-		t.Fatal(err)
-	}
-	var pinner runtime.Pinner
-	pinner.Pin(worldSID)
-	defer pinner.Unpin()
-	broadDACL, err := windows.ACLFromEntries([]windows.EXPLICIT_ACCESS{{
-		AccessPermissions: windows.GENERIC_ALL,
-		AccessMode:        windows.GRANT_ACCESS,
-		Inheritance:       windows.SUB_CONTAINERS_AND_OBJECTS_INHERIT,
-		Trustee: windows.TRUSTEE{
-			TrusteeForm:  windows.TRUSTEE_IS_SID,
-			TrusteeType:  windows.TRUSTEE_IS_WELL_KNOWN_GROUP,
-			TrusteeValue: windows.TrusteeValueFromSID(worldSID),
-		},
-	}}, nil)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if err := windows.SetNamedSecurityInfo(
-		dir,
-		windows.SE_FILE_OBJECT,
-		windows.DACL_SECURITY_INFORMATION|windows.PROTECTED_DACL_SECURITY_INFORMATION,
-		nil,
-		nil,
-		broadDACL,
-		nil,
-	); err != nil {
-		t.Fatal(err)
-	}
-}
-
-func TestCheckStatusDirOwnerRejectsBroadDACL(t *testing.T) {
-	dir := t.TempDir()
-	secureStatusTestDirPlatform(t, dir)
-	broadenStatusTestDirPlatform(t, dir)
-
-	root, err := os.OpenRoot(dir)
-	if err != nil {
-		t.Fatal(err)
-	}
-	defer root.Close()
-	info, err := root.Stat(".")
-	if err != nil {
-		t.Fatal(err)
-	}
-	err = checkStatusDirOwner(root, info)
-	if err == nil || !strings.Contains(err.Error(), "unexpected trustee") {
-		t.Fatalf("checkStatusDirOwner error = %v, want broad DACL rejection", err)
-	}
-}

internal/daemon/status_file.go

@@ -1,169 +0,0 @@
-package daemon
-
-import (
-	"crypto/rand"
-	"encoding/hex"
-	"errors"
-	"fmt"
-	"os"
-	"path/filepath"
-	"runtime"
-
-	"github.com/Gitlawb/zero/internal/fsutil"
-)
-
-const (
-	statusTempPrefix  = ".daemon-status-"
-	statusTempPattern = statusTempPrefix + "*"
-)
-
-func openStatusRoot(path string) (*os.Root, error) {
-	root, err := os.OpenRoot(filepath.Dir(path))
-	if err != nil {
-		return nil, fmt.Errorf("open status directory: %w", err)
-	}
-	if err := validateStatusRoot(root); err != nil {
-		_ = root.Close()
-		return nil, err
-	}
-	return root, nil
-}
-
-// writeStatusFileAtomicallyRoot publishes through a caller-owned, already
-// bound directory root. The returned boolean crosses the commit boundary: once
-// true, err is a durability/cleanup warning and the complete document is live.
-func writeStatusFileAtomicallyRoot(
-	root *os.Root,
-	statusName string,
-	data []byte,
-	perm os.FileMode,
-	beforeReplace func(),
-	replace func(root *os.Root, src, dst string) error,
-	syncParent func(root *os.Root) error,
-) (committed bool, returnErr error) {
-	if err := validateStatusRoot(root); err != nil {
-		return false, err
-	}
-
-	temp, tempName, err := createStatusTemp(root, perm)
-	if err != nil {
-		return false, err
-	}
-	closed := false
-	defer func() {
-		if !closed {
-			if err := temp.Close(); err != nil {
-				returnErr = errors.Join(returnErr, fmt.Errorf("close temporary status file during cleanup: %w", err))
-			}
-			closed = true
-		}
-		if err := root.Remove(tempName); err != nil && !errors.Is(err, os.ErrNotExist) {
-			returnErr = errors.Join(returnErr, fmt.Errorf("remove temporary status file: %w", err))
-		}
-	}()
-
-	if err := temp.Chmod(perm); err != nil {
-		return false, fmt.Errorf("set temporary status file permissions: %w", err)
-	}
-	if _, err := temp.Write(data); err != nil {
-		return false, fmt.Errorf("write temporary status file: %w", err)
-	}
-	if err := temp.Sync(); err != nil {
-		return false, fmt.Errorf("sync temporary status file: %w", err)
-	}
-	closeErr := temp.Close()
-	closed = true
-	if closeErr != nil {
-		return false, fmt.Errorf("close temporary status file: %w", closeErr)
-	}
-	if beforeReplace != nil {
-		beforeReplace()
-	}
-	if err := prepareStatusReplacement(root, tempName, statusName); err != nil {
-		return false, fmt.Errorf("prepare status replacement: %w", err)
-	}
-
-	rename := root.Rename
-	if replace != nil {
-		rename = func(src, dst string) error { return replace(root, src, dst) }
-	}
-	// On Windows an existing reader that omitted FILE_SHARE_DELETE can block
-	// this replacement even though an in-place write would succeed. Keep the
-	// atomic publication boundary: RenameWithRetry bounds transient sharing
-	// failures to ten short attempts, and a persistent failure leaves the old
-	// status document intact instead of exposing a partially written one.
-	var committedWarning error
-	if err := fsutil.RenameWithRetry(tempName, statusName, rename); err != nil {
-		var committedReplacement *fsutil.CommittedReplacementCleanupError
-		if !errors.As(err, &committedReplacement) {
-			return false, fmt.Errorf("replace status file: %w", err)
-		}
-		committedWarning = fmt.Errorf("clean up replaced status file: %w", err)
-	}
-	committed = true
-	if syncParent == nil {
-		syncParent = syncStatusRoot
-	}
-	if err := syncParent(root); err != nil {
-		committedWarning = errors.Join(committedWarning, fmt.Errorf("sync status directory: %w", err))
-	}
-	if committedWarning != nil {
-		return committed, committedWarning
-	}
-	return committed, nil
-}
-
-func validateStatusRoot(root *os.Root) error {
-	info, err := root.Stat(".")
-	if err != nil {
-		return fmt.Errorf("inspect status directory: %w", err)
-	}
-	if !info.IsDir() {
-		return fmt.Errorf("status directory is not a directory")
-	}
-	if runtime.GOOS != "windows" && info.Mode().Perm()&0o022 != 0 {
-		return fmt.Errorf("status directory permissions are %04o, want no group/other write access", info.Mode().Perm())
-	}
-	if err := checkStatusDirOwner(root, info); err != nil {
-		return err
-	}
-	return nil
-}
-
-func createStatusTemp(root *os.Root, perm os.FileMode) (*os.File, string, error) {
-	for range 100 {
-		var suffix [16]byte
-		if _, err := rand.Read(suffix[:]); err != nil {
-			return nil, "", fmt.Errorf("generate temporary status file name: %w", err)
-		}
-		name := statusTempPrefix + hex.EncodeToString(suffix[:])
-		file, err := root.OpenFile(name, os.O_WRONLY|os.O_CREATE|os.O_EXCL, perm)
-		if err == nil {
-			return file, name, nil
-		}
-		if errors.Is(err, os.ErrExist) {
-			continue
-		}
-		return nil, "", fmt.Errorf("create temporary status file: %w", err)
-	}
-	return nil, "", fmt.Errorf("create temporary status file: exhausted unique names")
-}
-
-// syncStatusRoot makes the replacement directory entry durable through the
-// same bound root used for creation and replacement. Windows directory sync is
-// best-effort because Go cannot fsync a directory there.
-func syncStatusRoot(root *os.Root) error {
-	if runtime.GOOS == "windows" {
-		return nil
-	}
-	directory, err := root.Open(".")
-	if err != nil {
-		return err
-	}
-	syncErr := directory.Sync()
-	closeErr := directory.Close()
-	if syncErr != nil {
-		return syncErr
-	}
-	return closeErr
-}

internal/daemon/status_file_test.go

@@ -1,476 +0,0 @@
-package daemon
-
-import (
-	"encoding/json"
-	"errors"
-	"os"
-	"path/filepath"
-	"runtime"
-	"strings"
-	"testing"
-	"time"
-
-	"github.com/Gitlawb/zero/internal/fsutil"
-	"github.com/Gitlawb/zero/internal/privatedir"
-)
-
-func TestWriteStatusFilePreservesPreviousDocumentWhenReplaceFails(t *testing.T) {
-	dir := t.TempDir()
-	secureStatusTestDir(t, dir)
-	path := filepath.Join(dir, "daemon.status")
-	previous := []byte(`{"pid":7,"socket":"old.sock","version":1,"startedAt":"2026-08-01T00:00:00Z"}`)
-	if err := os.WriteFile(path, previous, 0o600); err != nil {
-		t.Fatal(err)
-	}
-
-	replaceErr := errors.New("injected replacement failure")
-	server := &Server{
-		startedAt: time.Date(2026, 8, 24, 12, 0, 0, 0, time.UTC),
-		opts: ServerOptions{
-			Paths:   Paths{Status: path},
-			Version: 2,
-			replaceStatusFile: func(root *os.Root, src, dst string) error {
-				staged, err := root.ReadFile(src)
-				if err != nil {
-					t.Fatalf("read staged status: %v", err)
-				}
-				var decoded StatusFile
-				if err := json.Unmarshal(staged, &decoded); err != nil {
-					t.Fatalf("staged status is incomplete JSON: %v", err)
-				}
-				current, err := root.ReadFile(dst)
-				if err != nil {
-					t.Fatalf("read previous status at commit boundary: %v", err)
-				}
-				if string(current) != string(previous) {
-					t.Fatalf("previous status changed before commit: %q", current)
-				}
-				return replaceErr
-			},
-		},
-	}
-
-	err := server.writeStatusFile()
-	if !errors.Is(err, replaceErr) {
-		t.Fatalf("writeStatusFile error = %v, want injected replacement failure", err)
-	}
-	current, err := os.ReadFile(path)
-	if err != nil {
-		t.Fatalf("read preserved status: %v", err)
-	}
-	if string(current) != string(previous) {
-		t.Fatalf("status after failed publication = %q, want previous document", current)
-	}
-	assertNoStatusTemps(t, dir)
-}
-
-func TestWriteStatusFilePublishesCompleteRestrictedDocument(t *testing.T) {
-	dir := t.TempDir()
-	secureStatusTestDir(t, dir)
-	path := filepath.Join(dir, "daemon.status")
-	if err := os.WriteFile(path, []byte(`{"pid":7}`), 0o644); err != nil {
-		t.Fatal(err)
-	}
-
-	startedAt := time.Date(2026, 8, 24, 12, 0, 0, 0, time.UTC)
-	parentSynced := false
-	server := &Server{
-		startedAt: startedAt,
-		opts: ServerOptions{
-			Paths:   Paths{Socket: filepath.Join(dir, "daemon.sock"), Status: path},
-			Version: 3,
-			syncStatusParent: func(root *os.Root) error {
-				if _, err := root.Stat("."); err != nil {
-					t.Fatalf("stat bound status parent: %v", err)
-				}
-				parentSynced = true
-				return nil
-			},
-		},
-	}
-
-	if err := server.writeStatusFile(); err != nil {
-		t.Fatalf("writeStatusFile: %v", err)
-	}
-	data, err := os.ReadFile(path)
-	if err != nil {
-		t.Fatal(err)
-	}
-	var status StatusFile
-	if err := json.Unmarshal(data, &status); err != nil {
-		t.Fatalf("published status is invalid JSON: %v", err)
-	}
-	if status.PID != os.Getpid() || status.Socket != server.opts.Paths.Socket || status.Version != 3 || !status.StartedAt.Equal(startedAt) {
-		t.Fatalf("published status = %+v", status)
-	}
-	if !parentSynced {
-		t.Fatal("status parent directory was not synced")
-	}
-	if runtime.GOOS != "windows" {
-		info, err := os.Stat(path)
-		if err != nil {
-			t.Fatal(err)
-		}
-		if got := info.Mode().Perm(); got != 0o600 {
-			t.Fatalf("status mode = %04o, want 0600", got)
-		}
-	}
-	assertNoStatusTemps(t, dir)
-}
-
-func TestWriteStatusFileReaderSeesCompleteDocumentsDuringPublication(t *testing.T) {
-	dir := t.TempDir()
-	secureStatusTestDir(t, dir)
-	path := filepath.Join(dir, "daemon.status")
-	previous := StatusFile{
-		PID:       7,
-		Socket:    filepath.Join(dir, "old.sock"),
-		Version:   1,
-		StartedAt: time.Date(2026, 8, 1, 0, 0, 0, 0, time.UTC),
-	}
-	previousData, err := json.Marshal(previous)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if err := os.WriteFile(path, previousData, 0o600); err != nil {
-		t.Fatal(err)
-	}
-
-	replacementReady := make(chan struct{})
-	publish := make(chan struct{})
-	writeDone := make(chan error, 1)
-	server := &Server{
-		startedAt: time.Date(2026, 8, 24, 12, 0, 0, 0, time.UTC),
-		opts: ServerOptions{
-			Paths:   Paths{Socket: filepath.Join(dir, "new.sock"), Status: path},
-			Version: 2,
-			replaceStatusFile: func(root *os.Root, src, dst string) error {
-				close(replacementReady)
-				<-publish
-				return fsutil.RenameWithRetry(src, dst, root.Rename)
-			},
-		},
-	}
-	go func() {
-		writeDone <- server.writeStatusFile()
-	}()
-
-	<-replacementReady
-	for range 100 {
-		status := readStatusDocument(t, path)
-		if status != previous {
-			t.Fatalf("status before commit = %+v, want previous document %+v", status, previous)
-		}
-	}
-	close(publish)
-	if err := <-writeDone; err != nil {
-		t.Fatalf("writeStatusFile: %v", err)
-	}
-
-	status := readStatusDocument(t, path)
-	if status.PID != os.Getpid() || status.Socket != server.opts.Paths.Socket || status.Version != 2 || !status.StartedAt.Equal(server.startedAt) {
-		t.Fatalf("status after commit = %+v", status)
-	}
-	assertNoStatusTemps(t, dir)
-}
-
-func TestWriteStatusFileContinuesAfterDirectorySyncWarning(t *testing.T) {
-	dir := t.TempDir()
-	secureStatusTestDir(t, dir)
-	path := filepath.Join(dir, "daemon.status")
-	if err := os.WriteFile(path, []byte(`{"pid":7}`), 0o600); err != nil {
-		t.Fatal(err)
-	}
-
-	syncErr := errors.New("injected directory sync failure")
-	var logs []string
-	server := &Server{
-		startedAt: time.Date(2026, 8, 24, 12, 0, 0, 0, time.UTC),
-		opts: ServerOptions{
-			Paths:            Paths{Socket: filepath.Join(dir, "daemon.sock"), Status: path},
-			Version:          4,
-			Log:              func(message string) { logs = append(logs, message) },
-			syncStatusParent: func(*os.Root) error { return syncErr },
-		},
-	}
-
-	if err := server.writeStatusFile(); err != nil {
-		t.Fatalf("writeStatusFile returned a post-commit warning as failure: %v", err)
-	}
-	status := readStatusDocument(t, path)
-	if status.Version != 4 {
-		t.Fatalf("published status = %+v, want version 4", status)
-	}
-	if len(logs) != 1 || !strings.Contains(logs[0], syncErr.Error()) {
-		t.Fatalf("logs = %q, want directory sync warning", logs)
-	}
-	assertNoStatusTemps(t, dir)
-}
-
-func TestWriteStatusFileContinuesAfterCommittedReplacementWarning(t *testing.T) {
-	dir := t.TempDir()
-	secureStatusTestDir(t, dir)
-	path := filepath.Join(dir, "daemon.status")
-	if err := os.WriteFile(path, []byte(`{"pid":7}`), 0o600); err != nil {
-		t.Fatal(err)
-	}
-
-	cleanupErr := errors.New("injected backup cleanup failure")
-	parentSynced := false
-	var logs []string
-	server := &Server{
-		startedAt: time.Date(2026, 8, 24, 12, 0, 0, 0, time.UTC),
-		opts: ServerOptions{
-			Paths:   Paths{Socket: filepath.Join(dir, "daemon.sock"), Status: path},
-			Version: 5,
-			Log:     func(message string) { logs = append(logs, message) },
-			replaceStatusFile: func(root *os.Root, src, dst string) error {
-				if err := fsutil.RenameWithRetry(src, dst, root.Rename); err != nil {
-					return err
-				}
-				return &fsutil.CommittedReplacementCleanupError{
-					BackupPath: filepath.Join(dir, ".zero-replace-backup"),
-					Cause:      cleanupErr,
-				}
-			},
-			syncStatusParent: func(*os.Root) error {
-				parentSynced = true
-				return nil
-			},
-		},
-	}
-
-	if err := server.writeStatusFile(); err != nil {
-		t.Fatalf("writeStatusFile returned a post-commit warning as failure: %v", err)
-	}
-	if !parentSynced {
-		t.Fatal("status directory was not synced after committed replacement warning")
-	}
-	status := readStatusDocument(t, path)
-	if status.Version != 5 {
-		t.Fatalf("published status = %+v, want version 5", status)
-	}
-	if len(logs) != 1 || !strings.Contains(logs[0], cleanupErr.Error()) {
-		t.Fatalf("logs = %q, want committed cleanup warning", logs)
-	}
-	assertNoStatusTemps(t, dir)
-}
-
-func TestWriteStatusFileContinuesAfterCommittedTempCleanupWarning(t *testing.T) {
-	dir := t.TempDir()
-	secureStatusTestDir(t, dir)
-	path := filepath.Join(dir, "daemon.status")
-	if err := os.WriteFile(path, []byte(`{"pid":7}`), 0o600); err != nil {
-		t.Fatal(err)
-	}
-
-	var tempName string
-	var logs []string
-	server := &Server{
-		startedAt: time.Date(2026, 8, 24, 12, 0, 0, 0, time.UTC),
-		opts: ServerOptions{
-			Paths:   Paths{Socket: filepath.Join(dir, "daemon.sock"), Status: path},
-			Version: 6,
-			Log:     func(message string) { logs = append(logs, message) },
-			replaceStatusFile: func(root *os.Root, src, dst string) error {
-				if err := fsutil.RenameWithRetry(src, dst, root.Rename); err != nil {
-					return err
-				}
-				tempName = src
-				if err := root.Mkdir(src, 0o700); err != nil {
-					t.Fatalf("recreate staged path as directory: %v", err)
-				}
-				keep, err := root.OpenFile(filepath.Join(src, "keep"), os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o600)
-				if err != nil {
-					t.Fatalf("make staged directory non-empty: %v", err)
-				}
-				if err := keep.Close(); err != nil {
-					t.Fatalf("close staged directory marker: %v", err)
-				}
-				return nil
-			},
-		},
-	}
-
-	if err := server.writeStatusFile(); err != nil {
-		t.Fatalf("writeStatusFile returned a post-commit warning as failure: %v", err)
-	}
-	status := readStatusDocument(t, path)
-	if status.Version != 6 {
-		t.Fatalf("published status = %+v, want version 6", status)
-	}
-	if len(logs) != 1 || !strings.Contains(logs[0], "remove temporary status file") {
-		t.Fatalf("logs = %q, want temporary cleanup warning", logs)
-	}
-	if err := os.Remove(filepath.Join(dir, tempName, "keep")); err != nil {
-		t.Fatal(err)
-	}
-	if err := os.Remove(filepath.Join(dir, tempName)); err != nil {
-		t.Fatal(err)
-	}
-	assertNoStatusTemps(t, dir)
-}
-
-func TestWriteStatusFileBindsDirectoryDuringAncestorSwap(t *testing.T) {
-	parent := t.TempDir()
-	dir := filepath.Join(parent, "live")
-	movedDir := filepath.Join(parent, "moved")
-	if err := os.Mkdir(dir, 0o700); err != nil {
-		t.Fatal(err)
-	}
-	secureStatusTestDir(t, dir)
-	path := filepath.Join(dir, "daemon.status")
-	if err := os.WriteFile(path, []byte(`{"pid":7}`), 0o600); err != nil {
-		t.Fatal(err)
-	}
-
-	substitute := []byte(`{"pid":999,"socket":"substitute"}`)
-	var swapErr error
-	server := &Server{
-		startedAt: time.Date(2026, 8, 24, 12, 0, 0, 0, time.UTC),
-		opts: ServerOptions{
-			Paths:   Paths{Socket: filepath.Join(dir, "daemon.sock"), Status: path},
-			Version: 6,
-			beforeStatusReplace: func() {
-				swapErr = os.Rename(dir, movedDir)
-				if swapErr != nil {
-					if runtime.GOOS == "windows" {
-						return
-					}
-					t.Fatalf("move bound status directory: %v", swapErr)
-				}
-				if err := os.Mkdir(dir, 0o700); err != nil {
-					t.Fatalf("create substitute status directory: %v", err)
-				}
-				if err := os.WriteFile(path, substitute, 0o600); err != nil {
-					t.Fatalf("write substitute status: %v", err)
-				}
-			},
-		},
-	}
-
-	if err := server.writeStatusFile(); err != nil {
-		t.Fatalf("writeStatusFile: %v", err)
-	}
-	if swapErr != nil {
-		if runtime.GOOS != "windows" {
-			t.Fatalf("unexpected directory-swap error: %v", swapErr)
-		}
-		status := readStatusDocument(t, path)
-		if status.Version != 6 {
-			t.Fatalf("status after blocked swap = %+v, want version 6", status)
-		}
-		if _, err := os.Lstat(movedDir); !os.IsNotExist(err) {
-			t.Fatalf("moved directory exists after blocked Windows swap: %v", err)
-		}
-		assertNoStatusTemps(t, dir)
-		return
-	}
-	if got, err := os.ReadFile(path); err != nil {
-		t.Fatal(err)
-	} else if string(got) != string(substitute) {
-		t.Fatalf("substitute destination changed: %q", got)
-	}
-	status := readStatusDocument(t, filepath.Join(movedDir, "daemon.status"))
-	if status.Version != 6 {
-		t.Fatalf("bound status = %+v, want version 6", status)
-	}
-	assertNoStatusTemps(t, dir)
-	assertNoStatusTemps(t, movedDir)
-}
-
-func TestWriteStatusFileAllowsReadOnlyCustomStatusDirectory(t *testing.T) {
-	if runtime.GOOS == "windows" {
-		t.Skip("Windows directory access is governed by DACLs, not Unix mode bits")
-	}
-	dir := t.TempDir()
-	if err := os.Chmod(dir, 0o755); err != nil {
-		t.Fatal(err)
-	}
-	path := filepath.Join(dir, "daemon.status")
-
-	server := &Server{
-		startedAt: time.Date(2026, 8, 24, 12, 0, 0, 0, time.UTC),
-		opts: ServerOptions{
-			Paths:   Paths{Status: path},
-			Version: 6,
-		},
-	}
-	err := server.writeStatusFile()
-	if err != nil {
-		t.Fatalf("writeStatusFile in 0755 directory: %v", err)
-	}
-	if _, err := os.Lstat(path); err != nil {
-		t.Fatalf("status file not created in read-only custom directory: %v", err)
-	}
-	assertNoStatusTemps(t, dir)
-}
-
-func TestWriteStatusFileRejectsWritableStatusDirectory(t *testing.T) {
-	if runtime.GOOS == "windows" {
-		t.Skip("Windows directory access is governed by DACLs, not Unix mode bits")
-	}
-	dir := t.TempDir()
-	if err := os.Chmod(dir, 0o777); err != nil {
-		t.Fatal(err)
-	}
-	path := filepath.Join(dir, "daemon.status")
-	server := &Server{
-		startedAt: time.Date(2026, 8, 24, 12, 0, 0, 0, time.UTC),
-		opts:      ServerOptions{Paths: Paths{Status: path}, Version: 6},
-	}
-	err := server.writeStatusFile()
-	if err == nil || !strings.Contains(err.Error(), "no group/other write access") {
-		t.Fatalf("writeStatusFile error = %v, want writable-directory rejection", err)
-	}
-	if _, err := os.Lstat(path); !os.IsNotExist(err) {
-		t.Fatalf("status file created in writable directory: %v", err)
-	}
-	assertNoStatusTemps(t, dir)
-}
-
-func TestPrivateDirHardensBroadCurrentUserStatusDirectory(t *testing.T) {
-	dir := t.TempDir()
-	broadenStatusTestDirPlatform(t, dir)
-	if err := privatedir.Ensure(dir); err != nil {
-		t.Fatalf("privatedir.Ensure: %v", err)
-	}
-	root, err := os.OpenRoot(dir)
-	if err != nil {
-		t.Fatal(err)
-	}
-	defer root.Close()
-
-	if err := validateStatusRoot(root); err != nil {
-		t.Fatalf("validate hardened status root: %v", err)
-	}
-}
-
-func readStatusDocument(t *testing.T, path string) StatusFile {
-	t.Helper()
-	data, err := os.ReadFile(path)
-	if err != nil {
-		t.Fatalf("read status: %v", err)
-	}
-	var status StatusFile
-	if err := json.Unmarshal(data, &status); err != nil {
-		t.Fatalf("status is incomplete JSON: %v (content %q)", err, data)
-	}
-	return status
-}
-
-func assertNoStatusTemps(t *testing.T, dir string) {
-	t.Helper()
-	matches, err := filepath.Glob(filepath.Join(dir, statusTempPattern))
-	if err != nil {
-		t.Fatal(err)
-	}
-	if len(matches) != 0 {
-		t.Fatalf("temporary status files remain: %v", matches)
-	}
-}
-
-func secureStatusTestDir(t *testing.T, dir string) {
-	t.Helper()
-	secureStatusTestDirPlatform(t, dir)
-}

internal/daemon/status_file_windows_test.go

@@ -1,63 +0,0 @@
-//go:build windows
-
-package daemon
-
-import (
-	"os"
-	"path/filepath"
-	"strings"
-	"testing"
-	"time"
-
-	"golang.org/x/sys/windows"
-)
-
-func TestWriteStatusFilePreservesExistingProtectedDACL(t *testing.T) {
-	dir := t.TempDir()
-	secureStatusTestDir(t, dir)
-	path := filepath.Join(dir, "daemon.status")
-	if err := os.WriteFile(path, []byte(`{"pid":7}`), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	restricted, err := windows.SecurityDescriptorFromString("D:P(A;;FA;;;OW)")
-	if err != nil {
-		t.Skipf("cannot build restrictive DACL: %v", err)
-	}
-	dacl, _, err := restricted.DACL()
-	if err != nil {
-		t.Skipf("cannot read restrictive DACL: %v", err)
-	}
-	if err := windows.SetNamedSecurityInfo(path, windows.SE_FILE_OBJECT,
-		windows.DACL_SECURITY_INFORMATION|windows.PROTECTED_DACL_SECURITY_INFORMATION,
-		nil, nil, dacl, nil); err != nil {
-		t.Skipf("cannot apply restrictive DACL: %v", err)
-	}
-	want := statusDACL(t, path)
-
-	server := &Server{
-		startedAt: time.Date(2026, 8, 30, 18, 0, 0, 0, time.UTC),
-		opts: ServerOptions{
-			Paths:   Paths{Socket: filepath.Join(dir, "daemon.sock"), Status: path},
-			Version: 2,
-		},
-	}
-	if err := server.writeStatusFile(); err != nil {
-		t.Fatalf("writeStatusFile: %v", err)
-	}
-	if got := statusDACL(t, path); got != want {
-		t.Fatalf("status DACL after replacement = %q, want %q", got, want)
-	}
-}
-
-func statusDACL(t *testing.T, path string) string {
-	t.Helper()
-	descriptor, err := windows.GetNamedSecurityInfo(path, windows.SE_FILE_OBJECT, windows.DACL_SECURITY_INFORMATION)
-	if err != nil {
-		t.Skipf("cannot read status DACL: %v", err)
-	}
-	text := descriptor.String()
-	if index := strings.Index(text, "D:"); index >= 0 {
-		return text[index:]
-	}
-	return text
-}

internal/daemon/status_replace_other.go

@@ -1,7 +0,0 @@
-//go:build !windows
-
-package daemon
-
-import "os"
-
-func prepareStatusReplacement(*os.Root, string, string) error { return nil }

internal/daemon/status_replace_windows.go

@@ -1,136 +0,0 @@
-//go:build windows
-
-package daemon
-
-import (
-	"errors"
-	"fmt"
-	"os"
-	"path/filepath"
-	"unsafe"
-
-	"golang.org/x/sys/windows"
-)
-
-// prepareStatusReplacement copies the existing status document's DACL to the
-// complete staging file before Root.Rename replaces it. Both files are opened
-// relative to the already-bound Root directory handle, so preserving Windows
-// security metadata does not reintroduce a pathname/ancestor-swap boundary.
-func prepareStatusReplacement(root *os.Root, src, dst string) (returnErr error) {
-	if filepath.Base(src) != src || filepath.Base(dst) != dst {
-		return fmt.Errorf("status replacement names must be root-relative base names")
-	}
-	directory, err := root.Open(".")
-	if err != nil {
-		return fmt.Errorf("open bound status directory for DACL preservation: %w", err)
-	}
-	defer func() {
-		if err := directory.Close(); err != nil {
-			returnErr = errors.Join(returnErr, fmt.Errorf("close bound status directory for DACL preservation: %w", err))
-		}
-	}()
-
-	raw, err := directory.SyscallConn()
-	if err != nil {
-		return fmt.Errorf("access bound status directory handle: %w", err)
-	}
-	var destination, source windows.Handle
-	var openErr error
-	if err := raw.Control(func(rootHandle uintptr) {
-		destination, openErr = openStatusSecurityHandle(windows.Handle(rootHandle), dst, windows.READ_CONTROL|windows.FILE_READ_ATTRIBUTES)
-		if isMissingStatusObject(openErr) {
-			openErr = nil // no destination descriptor exists to preserve
-			return
-		}
-		if openErr != nil {
-			return
-		}
-		source, openErr = openStatusSecurityHandle(windows.Handle(rootHandle), src, windows.READ_CONTROL|windows.WRITE_DAC|windows.FILE_READ_ATTRIBUTES)
-	}); err != nil {
-		return fmt.Errorf("open status files through bound directory: %w", err)
-	}
-	if destination != 0 {
-		defer windows.CloseHandle(destination)
-	}
-	if source != 0 {
-		defer windows.CloseHandle(source)
-	}
-	if openErr != nil {
-		return fmt.Errorf("open status files for DACL preservation: %w", openErr)
-	}
-	if destination == 0 {
-		return nil
-	}
-
-	descriptor, err := windows.GetSecurityInfo(destination, windows.SE_FILE_OBJECT, windows.DACL_SECURITY_INFORMATION)
-	if err != nil {
-		return fmt.Errorf("read existing status DACL: %w", err)
-	}
-	dacl, _, err := descriptor.DACL()
-	if err != nil {
-		return fmt.Errorf("decode existing status DACL: %w", err)
-	}
-	if dacl == nil {
-		return fmt.Errorf("existing status file has an unrestricted Windows DACL")
-	}
-	control, _, err := descriptor.Control()
-	if err != nil {
-		return fmt.Errorf("read existing status DACL control: %w", err)
-	}
-	securityInfo := windows.SECURITY_INFORMATION(windows.DACL_SECURITY_INFORMATION)
-	if control&windows.SE_DACL_PROTECTED != 0 {
-		securityInfo |= windows.SECURITY_INFORMATION(windows.PROTECTED_DACL_SECURITY_INFORMATION)
-	} else {
-		securityInfo |= windows.SECURITY_INFORMATION(windows.UNPROTECTED_DACL_SECURITY_INFORMATION)
-	}
-	if err := windows.SetSecurityInfo(source, windows.SE_FILE_OBJECT, securityInfo, nil, nil, dacl, nil); err != nil {
-		return fmt.Errorf("preserve existing status DACL on replacement: %w", err)
-	}
-	return nil
-}
-
-func openStatusSecurityHandle(root windows.Handle, name string, access uint32) (windows.Handle, error) {
-	objectName, err := windows.NewNTUnicodeString(name)
-	if err != nil {
-		return 0, err
-	}
-	attributes := &windows.OBJECT_ATTRIBUTES{
-		Length:        uint32(unsafe.Sizeof(windows.OBJECT_ATTRIBUTES{})),
-		RootDirectory: root,
-		ObjectName:    objectName,
-		Attributes:    windows.OBJ_CASE_INSENSITIVE | windows.OBJ_DONT_REPARSE,
-	}
-	var handle windows.Handle
-	var status windows.IO_STATUS_BLOCK
-	err = windows.NtCreateFile(
-		&handle,
-		access,
-		attributes,
-		&status,
-		nil,
-		0,
-		windows.FILE_SHARE_READ|windows.FILE_SHARE_WRITE|windows.FILE_SHARE_DELETE,
-		windows.FILE_OPEN,
-		windows.FILE_NON_DIRECTORY_FILE|windows.FILE_OPEN_REPARSE_POINT,
-		0,
-		0,
-	)
-	if err != nil {
-		return 0, err
-	}
-	var info windows.ByHandleFileInformation
-	if err := windows.GetFileInformationByHandle(handle, &info); err != nil {
-		windows.CloseHandle(handle)
-		return 0, err
-	}
-	if info.FileAttributes&windows.FILE_ATTRIBUTE_REPARSE_POINT != 0 {
-		windows.CloseHandle(handle)
-		return 0, fmt.Errorf("refusing status DACL operation on reparse point %q", name)
-	}
-	return handle, nil
-}
-
-func isMissingStatusObject(err error) bool {
-	return errors.Is(err, windows.STATUS_OBJECT_NAME_NOT_FOUND) ||
-		errors.Is(err, windows.STATUS_OBJECT_PATH_NOT_FOUND)
-}

internal/lockutil/lockutil.go

@@ -64,28 +64,6 @@ func TryAcquireFileLockAt(root, path string) (*FileLock, error) {
 	if err != nil {
 		return nil, fmt.Errorf("lockutil: open lock file: %w", err)
 	}
-	return acquireOpenedFileLock(file)
-}
-
-// TryAcquireFileLockRoot attempts to lock name relative to an already-bound
-// directory root. It is intended for lifecycle owners that must not resolve the
-// root pathname again between validation and lock acquisition.
-func TryAcquireFileLockRoot(root *os.Root, name, displayPath string) (*FileLock, error) {
-	if root == nil {
-		return nil, errors.New("lockutil: lock root is nil")
-	}
-	name = filepath.Clean(name)
-	if name == "." || name == ".." || filepath.IsAbs(name) || strings.HasPrefix(name, ".."+string(filepath.Separator)) {
-		return nil, fmt.Errorf("lockutil: lock name %q escapes root", name)
-	}
-	file, err := openLockFileRoot(root, name, displayPath)
-	if err != nil {
-		return nil, fmt.Errorf("lockutil: open rooted lock file: %w", err)
-	}
-	return acquireOpenedFileLock(file)
-}
-
-func acquireOpenedFileLock(file *os.File) (*FileLock, error) {
 	state, contended, err := tryLockFile(file)
 	if err != nil {
 		_ = file.Close()
@@ -104,41 +82,6 @@ func acquireOpenedFileLock(file *os.File) (*FileLock, error) {
 	return lock, nil
 }
 
-func openLockFileRoot(root *os.Root, name, displayPath string) (*os.File, error) {
-	info, err := root.Lstat(name)
-	if errors.Is(err, os.ErrNotExist) {
-		file, createErr := root.OpenFile(name, os.O_CREATE|os.O_EXCL|os.O_RDWR, 0o600)
-		if createErr != nil {
-			return nil, createErr
-		}
-		if err := validateRootLockFile(file); err != nil {
-			return nil, errors.Join(err, file.Close())
-		}
-		return file, nil
-	}
-	if err != nil {
-		return nil, err
-	}
-	if !info.Mode().IsRegular() {
-		return nil, errors.New("refusing non-regular rooted lock file")
-	}
-	file, err := root.OpenFile(name, os.O_RDWR, 0o600)
-	if err != nil {
-		return nil, err
-	}
-	opened, err := file.Stat()
-	if err != nil {
-		return nil, errors.Join(err, file.Close())
-	}
-	if !os.SameFile(info, opened) {
-		return nil, errors.Join(errors.New("rooted lock file changed while opening"), file.Close())
-	}
-	if err := validateRootLockFile(file); err != nil {
-		return nil, errors.Join(err, file.Close())
-	}
-	return file, 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 {

internal/lockutil/lockutil_other.go

@@ -76,20 +76,6 @@ func openLockFileAt(root, relative, displayPath string) (_ *os.File, resultErr e
 	return file, nil
 }
 
-func validateRootLockFile(file *os.File) error {
-	var stat unix.Stat_t
-	if err := unix.Fstat(int(file.Fd()), &stat); err != nil {
-		return fmt.Errorf("inspect rooted lock file: %w", err)
-	}
-	if stat.Mode&unix.S_IFMT != unix.S_IFREG {
-		return errors.New("refusing non-regular rooted lock file")
-	}
-	if stat.Nlink != 1 {
-		return errors.New("refusing multiply-linked rooted lock file")
-	}
-	return nil
-}
-
 func tryLockFile(file *os.File) (platformLockState, bool, error) {
 	err := unix.Flock(int(file.Fd()), unix.LOCK_EX|unix.LOCK_NB)
 	if err == nil {

internal/lockutil/lockutil_windows.go

@@ -73,10 +73,6 @@ func openLockFileAt(root, relative, displayPath string) (_ *os.File, resultErr e
 	return file, nil
 }
 
-func validateRootLockFile(file *os.File) error {
-	return validateWindowsLockHandle(windows.Handle(file.Fd()), false)
-}
-
 func openLockDirectoryAt(parent windows.Handle, name string) (windows.Handle, error) {
 	handle, err := openLockPathAt(
 		parent,

internal/observability/crash.go

@@ -7,50 +7,17 @@
 package observability
 
 import (
-	"crypto/rand"
-	"encoding/hex"
-	"errors"
 	"fmt"
 	"io"
 	"os"
 	"path/filepath"
 	"runtime/debug"
-	"strings"
 	"time"
-
-	"github.com/Gitlawb/zero/internal/privatedir"
 )
 
 // crashExitCode is returned when a top-level panic is recovered.
 const crashExitCode = 1
 
-const crashTempPrefix = ".crash-report-"
-
-// ErrCrashReportCommitted marks an error that happened after a complete crash
-// report was published. Callers may still use the returned path and should
-// surface the error as a cleanup warning rather than as a failed publication.
-var ErrCrashReportCommitted = errors.New("crash report publication committed")
-
-type crashReportCommittedError struct {
-	cause error
-}
-
-func (err *crashReportCommittedError) Error() string {
-	return fmt.Sprintf("%v with warning: %v", ErrCrashReportCommitted, err.cause)
-}
-
-func (err *crashReportCommittedError) Unwrap() []error {
-	return []error{ErrCrashReportCommitted, err.cause}
-}
-
-type crashReportHooks struct {
-	beforePublish   func()
-	write           func(*os.File, []byte) (int, error)
-	link            func(*os.Root, string, string) error
-	renameNoReplace func(*os.Root, string, string) error
-	remove          func(*os.Root, string) error
-}
-
 // FormatCrashReport renders a human-readable crash report.
 func FormatCrashReport(label string, recovered any, stack []byte, ts time.Time) string {
 	return fmt.Sprintf("zero crash report\ntime:  %s\nlabel: %s\npanic: %v\n\nstack:\n%s\n",
@@ -59,189 +26,16 @@ func FormatCrashReport(label string, recovered any, stack []byte, ts time.Time)
 
 // WriteCrashReport writes a crash report file into dir and returns its path.
 func WriteCrashReport(dir, label string, recovered any, stack []byte, ts time.Time) (string, error) {
-	return writeCrashReport(dir, label, recovered, stack, ts, crashReportHooks{})
-}
-
-func writeCrashReport(dir, label string, recovered any, stack []byte, ts time.Time, hooks crashReportHooks) (path string, returnErr error) {
-	absoluteDir, err := filepath.Abs(dir)
-	if err != nil {
-		return "", fmt.Errorf("resolve crash report directory: %w", err)
-	}
-	root, err := openCrashDirectory(dir)
-	if err != nil {
+	if err := os.MkdirAll(dir, 0o755); err != nil {
 		return "", err
 	}
-	committed := false
-	defer func() {
-		if err := root.Close(); err != nil {
-			returnErr = errors.Join(returnErr, fmt.Errorf("close crash report directory: %w", err))
-		}
-		if committed && returnErr != nil && !errors.Is(returnErr, ErrCrashReportCommitted) {
-			returnErr = &crashReportCommittedError{cause: returnErr}
-		}
-		if !committed && returnErr != nil {
-			path = ""
-		}
-	}()
-
-	name := "crash-" + ts.UTC().Format("20060102-150405") + ".log"
-	path = filepath.Join(dir, name)
-	report, tempName, err := createCrashTemp(root)
-	if err != nil {
+	path := filepath.Join(dir, "crash-"+ts.UTC().Format("20060102-150405")+".log")
+	if err := os.WriteFile(path, []byte(FormatCrashReport(label, recovered, stack, ts)), 0o600); err != nil {
 		return "", err
 	}
-	defer func() {
-		if tempName == "" {
-			return
-		}
-		if err := removeCrashTemp(hooks, root, tempName); err != nil && !errors.Is(err, os.ErrNotExist) {
-			returnErr = errors.Join(returnErr, fmt.Errorf("remove temporary crash report: %w", err))
-		}
-	}()
-
-	data := []byte(FormatCrashReport(label, recovered, stack, ts))
-	writeReport := hooks.write
-	if writeReport == nil {
-		writeReport = func(file *os.File, data []byte) (int, error) { return file.Write(data) }
-	}
-	written, err := writeReport(report, data)
-	if err == nil && written != len(data) {
-		err = io.ErrShortWrite
-	}
-	if err != nil {
-		closeErr := report.Close()
-		if closeErr != nil {
-			return "", errors.Join(fmt.Errorf("write crash report: %w", err), fmt.Errorf("close crash report: %w", closeErr))
-		}
-		return "", fmt.Errorf("write crash report: %w", err)
-	}
-	if err := report.Sync(); err != nil {
-		closeErr := report.Close()
-		if closeErr != nil {
-			return "", errors.Join(fmt.Errorf("sync crash report: %w", err), fmt.Errorf("close crash report: %w", closeErr))
-		}
-		return "", fmt.Errorf("sync crash report: %w", err)
-	}
-	if err := report.Close(); err != nil {
-		return "", fmt.Errorf("close crash report: %w", err)
-	}
-	if hooks.beforePublish != nil {
-		hooks.beforePublish()
-	}
-	publishName := name
-	link := root.Link
-	if hooks.link != nil {
-		link = func(oldname, newname string) error { return hooks.link(root, oldname, newname) }
-	}
-	if linkErr := link(tempName, name); linkErr != nil {
-		publishName, err = publishCrashFallback(root, name, tempName, hooks.renameNoReplace)
-		if err != nil {
-			return "", errors.Join(fmt.Errorf("publish crash report with hard link: %w", linkErr), err)
-		}
-		committed = true
-		tempName = ""
-	} else {
-		committed = true
-	}
-	path = filepath.Join(dir, publishName)
-	if !crashPathUsesRoot(root, absoluteDir) {
-		path = ""
-	}
-	if tempName != "" {
-		if err := removeCrashTemp(hooks, root, tempName); err != nil && !errors.Is(err, os.ErrNotExist) {
-			tempName = ""
-			return path, fmt.Errorf("remove temporary crash report: %w", err)
-		}
-		tempName = ""
-	}
 	return path, nil
 }
 
-// publishCrashFallback atomically renames the complete staging file to an
-// unpredictable unused name. The no-replace operation is the collision check;
-// there is no check-then-rename window in which another report can be replaced.
-func publishCrashFallback(root *os.Root, timestampName, tempName string, rename func(*os.Root, string, string) error) (string, error) {
-	if rename == nil {
-		rename = renameNoReplace
-	}
-	base := strings.TrimSuffix(timestampName, filepath.Ext(timestampName))
-	if suffix := strings.TrimPrefix(tempName, crashTempPrefix); suffix != "" && suffix != tempName {
-		candidate := base + "-" + suffix + filepath.Ext(timestampName)
-		if err := rename(root, tempName, candidate); err == nil {
-			return candidate, nil
-		} else if !errors.Is(err, os.ErrExist) {
-			return "", fmt.Errorf("publish fallback crash report: %w", err)
-		}
-	}
-	for range 100 {
-		var suffix [16]byte
-		if _, err := rand.Read(suffix[:]); err != nil {
-			return "", fmt.Errorf("generate fallback crash report name: %w", err)
-		}
-		candidate := base + "-" + hex.EncodeToString(suffix[:]) + filepath.Ext(timestampName)
-		if err := rename(root, tempName, candidate); err == nil {
-			return candidate, nil
-		} else if !errors.Is(err, os.ErrExist) {
-			return "", fmt.Errorf("publish fallback crash report: %w", err)
-		}
-	}
-	return "", fmt.Errorf("generate fallback crash report name: exhausted unique names")
-}
-
-func removeCrashTemp(hooks crashReportHooks, root *os.Root, name string) error {
-	if hooks.remove != nil {
-		return hooks.remove(root, name)
-	}
-	return root.Remove(name)
-}
-
-func createCrashTemp(root *os.Root) (*os.File, string, error) {
-	for range 100 {
-		var suffix [16]byte
-		if _, err := rand.Read(suffix[:]); err != nil {
-			return nil, "", fmt.Errorf("generate temporary crash report name: %w", err)
-		}
-		name := crashTempPrefix + hex.EncodeToString(suffix[:])
-		file, err := root.OpenFile(name, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o600)
-		if err == nil {
-			return file, name, nil
-		}
-		if errors.Is(err, os.ErrExist) {
-			continue
-		}
-		return nil, "", fmt.Errorf("create temporary crash report: %w", err)
-	}
-	return nil, "", fmt.Errorf("create temporary crash report: exhausted unique names")
-}
-
-func crashPathUsesRoot(root *os.Root, dir string) bool {
-	bound, err := root.Stat(".")
-	if err != nil {
-		return false
-	}
-	current, err := os.Stat(filepath.Clean(dir))
-	return err == nil && os.SameFile(bound, current)
-}
-
-func openCrashDirectory(dir string) (*os.Root, error) {
-	clean := filepath.Clean(dir)
-	defaultDir := filepath.Clean(DefaultCrashDir())
-	parent := filepath.Dir(clean)
-	// The default layout shares ~/.zero with the daemon runtime fallback. Keep
-	// both the shared parent and the crash-report child private. Custom crash
-	// destinations are hardened at the caller-supplied boundary only.
-	if clean == defaultDir && filepath.Base(clean) == "crashes" && filepath.Base(parent) == ".zero" {
-		if err := privatedir.Ensure(parent); err != nil {
-			return nil, fmt.Errorf("secure crash report parent: %w", err)
-		}
-	}
-	root, err := privatedir.Open(clean)
-	if err != nil {
-		return nil, fmt.Errorf("secure crash report directory: %w", err)
-	}
-	return root, nil
-}
-
 // DefaultCrashDir is where crash reports are written by default.
 func DefaultCrashDir() string {
 	if home, err := os.UserHomeDir(); err == nil && home != "" {
@@ -260,22 +54,8 @@ func Recover(dir, label string, stderr io.Writer, code *int) {
 		return
 	}
 	stack := debug.Stack()
-	reportRecoveredCrash(stderr, code, recovered, stack, func() (string, error) {
-		return WriteCrashReport(dir, label, recovered, stack, time.Now())
-	})
-}
-
-func reportRecoveredCrash(stderr io.Writer, code *int, recovered any, stack []byte, write func() (string, error)) {
-	path, err := write()
-	if err == nil || errors.Is(err, ErrCrashReportCommitted) {
-		if path != "" {
-			fmt.Fprintf(stderr, "zero crashed: %v\nA crash report was saved to %s\n", recovered, path)
-		} else {
-			fmt.Fprintf(stderr, "zero crashed: %v\nA crash report was saved, but its current path could not be determined\n", recovered)
-		}
-		if err != nil {
-			fmt.Fprintf(stderr, "Warning: %v\n", err)
-		}
+	if path, err := WriteCrashReport(dir, label, recovered, stack, time.Now()); err == nil {
+		fmt.Fprintf(stderr, "zero crashed: %v\nA crash report was saved to %s\n", recovered, path)
 	} else {
 		fmt.Fprintf(stderr, "zero crashed: %v\n%s\n", recovered, stack)
 	}

internal/observability/crash_test.go

@@ -2,10 +2,7 @@ package observability
 
 import (
 	"bytes"
-	"errors"
 	"os"
-	"path/filepath"
-	"runtime"
 	"strings"
 	"testing"
 	"time"
@@ -30,400 +27,6 @@ func TestWriteAndFormatCrashReport(t *testing.T) {
 	}
 }
 
-func TestWriteCrashReportKeepsTwoReportsFromTheSameSecond(t *testing.T) {
-	dir := t.TempDir()
-	ts := time.Date(2026, 8, 30, 18, 0, 0, 0, time.UTC)
-	first, err := WriteCrashReport(dir, "cli", "first panic", []byte("first stack"), ts)
-	if err != nil {
-		t.Fatal(err)
-	}
-	second, err := WriteCrashReport(dir, "cli", "second panic", []byte("second stack"), ts)
-	if err != nil {
-		t.Fatalf("second report in the same second: %v", err)
-	}
-	if first == second {
-		t.Fatalf("same-second reports shared path %q", first)
-	}
-	firstData, err := os.ReadFile(first)
-	if err != nil {
-		t.Fatal(err)
-	}
-	secondData, err := os.ReadFile(second)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if !strings.Contains(string(firstData), "first panic") || strings.Contains(string(firstData), "second panic") {
-		t.Fatalf("first report was replaced: %q", firstData)
-	}
-	if !strings.Contains(string(secondData), "second panic") {
-		t.Fatalf("second report was not persisted: %q", secondData)
-	}
-}
-
-func TestWriteCrashReportCreatesPrivateDefaultDirectories(t *testing.T) {
-	home := t.TempDir()
-	t.Setenv("HOME", home)
-	t.Setenv("USERPROFILE", home)
-
-	dir := DefaultCrashDir()
-	if dir != filepath.Join(home, ".zero", "crashes") {
-		t.Fatalf("DefaultCrashDir = %q, want path beneath temporary home", dir)
-	}
-	if _, err := WriteCrashReport(dir, "cli", "boom", []byte("stack"), time.Now()); err != nil {
-		t.Fatalf("WriteCrashReport: %v", err)
-	}
-	if runtime.GOOS == "windows" {
-		return
-	}
-	for _, path := range []string{filepath.Join(home, ".zero"), dir} {
-		info, err := os.Stat(path)
-		if err != nil {
-			t.Fatal(err)
-		}
-		if got := info.Mode().Perm(); got&0o077 != 0 {
-			t.Fatalf("directory %s permissions = %04o, want owner-only", path, got)
-		}
-	}
-}
-
-func TestWriteCrashReportHardensPreexistingDefaultDirectories(t *testing.T) {
-	if runtime.GOOS == "windows" {
-		t.Skip("Windows DACL migration is covered by the daemon integration test")
-	}
-	home := t.TempDir()
-	t.Setenv("HOME", home)
-	t.Setenv("USERPROFILE", home)
-	dir := DefaultCrashDir()
-	if err := os.MkdirAll(dir, 0o755); err != nil {
-		t.Fatal(err)
-	}
-	for _, path := range []string{filepath.Join(home, ".zero"), dir} {
-		if err := os.Chmod(path, 0o755); err != nil {
-			t.Fatal(err)
-		}
-	}
-
-	if _, err := WriteCrashReport(dir, "cli", "boom", []byte("stack"), time.Now()); err != nil {
-		t.Fatalf("WriteCrashReport: %v", err)
-	}
-	for _, path := range []string{filepath.Join(home, ".zero"), dir} {
-		info, err := os.Stat(path)
-		if err != nil {
-			t.Fatal(err)
-		}
-		if got := info.Mode().Perm(); got&0o077 != 0 {
-			t.Fatalf("directory %s permissions = %04o after migration, want owner-only", path, got)
-		}
-	}
-}
-
-func TestWriteCrashReportBindsDirectoryDuringSwap(t *testing.T) {
-	parent := t.TempDir()
-	dir := filepath.Join(parent, "live")
-	movedDir := filepath.Join(parent, "moved")
-	if err := os.Mkdir(dir, 0o700); err != nil {
-		t.Fatal(err)
-	}
-
-	ts := time.Date(2026, 8, 24, 12, 0, 0, 0, time.UTC)
-	var swapErr error
-	path, err := writeCrashReport(dir, "cli", "secret panic", []byte("secret stack"), ts, crashReportHooks{
-		beforePublish: func() {
-			swapErr = os.Rename(dir, movedDir)
-			if swapErr != nil {
-				return
-			}
-			if err := os.Mkdir(dir, 0o700); err != nil {
-				t.Fatalf("create substitute crash directory: %v", err)
-			}
-		},
-	})
-	if err != nil {
-		t.Fatalf("writeCrashReport: %v", err)
-	}
-	if swapErr != nil {
-		if runtime.GOOS != "windows" {
-			t.Fatalf("swap crash directory: %v", swapErr)
-		}
-		if _, err := os.Stat(path); err != nil {
-			t.Fatalf("report missing after Windows blocked directory swap: %v", err)
-		}
-		return
-	}
-
-	if path != "" {
-		t.Fatalf("writeCrashReport returned stale path %q after directory swap", path)
-	}
-	reportName := "crash-" + ts.UTC().Format("20060102-150405") + ".log"
-	data, err := os.ReadFile(filepath.Join(movedDir, reportName))
-	if err != nil {
-		t.Fatalf("read report through originally bound directory: %v", err)
-	}
-	if !strings.Contains(string(data), "secret panic") {
-		t.Fatalf("report in bound directory missing panic: %q", data)
-	}
-	if _, err := os.Stat(filepath.Join(dir, reportName)); !errors.Is(err, os.ErrNotExist) {
-		t.Fatalf("substitute directory received crash report: %v", err)
-	}
-}
-
-func TestWriteCrashReportPublishesOnlyCompleteContent(t *testing.T) {
-	dir := t.TempDir()
-	ts := time.Date(2026, 8, 24, 12, 0, 0, 0, time.UTC)
-	finalPath := filepath.Join(dir, "crash-20260824-120000.log")
-	staged := make(chan struct{})
-	release := make(chan struct{})
-	result := make(chan crashWriteResult, 1)
-	go func() {
-		path, err := writeCrashReport(dir, "cli", "boom", []byte("complete stack"), ts, crashReportHooks{
-			beforePublish: func() {
-				close(staged)
-				<-release
-			},
-		})
-		result <- crashWriteResult{path: path, err: err}
-	}()
-	select {
-	case <-staged:
-	case written := <-result:
-		t.Fatalf("writeCrashReport returned before publication hook: %v", written.err)
-	case <-time.After(time.Second):
-		t.Fatal("writeCrashReport did not reach publication hook")
-	}
-	defer func() {
-		select {
-		case <-release:
-		default:
-			close(release)
-		}
-	}()
-	if _, err := os.Stat(finalPath); !errors.Is(err, os.ErrNotExist) {
-		t.Fatalf("final report visible before complete publication: %v", err)
-	}
-	close(release)
-	written := <-result
-	if written.err != nil {
-		t.Fatalf("writeCrashReport: %v", written.err)
-	}
-	data, err := os.ReadFile(written.path)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if !strings.Contains(string(data), "complete stack") {
-		t.Fatalf("published report is incomplete: %q", data)
-	}
-}
-
-func TestWriteCrashReportRemovesTempAfterWriteFailure(t *testing.T) {
-	dir := t.TempDir()
-	injected := errors.New("injected write failure")
-	_, err := writeCrashReport(dir, "cli", "boom", []byte("stack"), time.Now(), crashReportHooks{
-		write: func(*os.File, []byte) (int, error) { return 0, injected },
-	})
-	if !errors.Is(err, injected) {
-		t.Fatalf("writeCrashReport error = %v, want injected failure", err)
-	}
-	entries, err := os.ReadDir(dir)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if len(entries) != 0 {
-		t.Fatalf("crash directory contains partial files after failure: %v", entries)
-	}
-}
-
-func TestWriteCrashReportDoesNotOverwriteExistingReport(t *testing.T) {
-	dir := t.TempDir()
-	ts := time.Date(2026, 8, 24, 12, 0, 0, 0, time.UTC)
-	path := filepath.Join(dir, "crash-20260824-120000.log")
-	if err := os.WriteFile(path, []byte("existing"), 0o600); err != nil {
-		t.Fatal(err)
-	}
-	published, err := WriteCrashReport(dir, "cli", "boom", []byte("stack"), ts)
-	if err != nil {
-		t.Fatalf("WriteCrashReport with existing timestamp: %v", err)
-	}
-	if published == path {
-		t.Fatal("new report reused the occupied timestamp path")
-	}
-	data, err := os.ReadFile(path)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if string(data) != "existing" {
-		t.Fatalf("existing report overwritten: %q", data)
-	}
-	entries, err := os.ReadDir(dir)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if len(entries) != 2 {
-		t.Fatalf("crash directory should contain existing and uniquely published reports: %v", entries)
-	}
-}
-
-func TestWriteCrashReportPreservesPathAfterCommittedCleanupWarning(t *testing.T) {
-	dir := t.TempDir()
-	ts := time.Date(2026, 8, 24, 12, 0, 0, 0, time.UTC)
-	injected := errors.New("injected cleanup failure")
-	path, err := writeCrashReport(dir, "cli", "boom", []byte("complete stack"), ts, crashReportHooks{
-		remove: func(*os.Root, string) error { return injected },
-	})
-	if !errors.Is(err, ErrCrashReportCommitted) || !errors.Is(err, injected) {
-		t.Fatalf("writeCrashReport error = %v, want committed cleanup warning", err)
-	}
-	wantPath := filepath.Join(dir, "crash-20260824-120000.log")
-	if path != wantPath {
-		t.Fatalf("writeCrashReport path = %q, want %q", path, wantPath)
-	}
-	data, readErr := os.ReadFile(path)
-	if readErr != nil {
-		t.Fatalf("read committed crash report: %v", readErr)
-	}
-	if !strings.Contains(string(data), "complete stack") {
-		t.Fatalf("committed crash report is incomplete: %q", data)
-	}
-}
-
-func TestWriteCrashReportDoesNotReturnStalePathWithCleanupWarning(t *testing.T) {
-	parent := t.TempDir()
-	dir := filepath.Join(parent, "live")
-	movedDir := filepath.Join(parent, "moved")
-	if err := os.Mkdir(dir, 0o700); err != nil {
-		t.Fatal(err)
-	}
-	injected := errors.New("injected cleanup failure")
-	ts := time.Date(2026, 8, 24, 12, 0, 0, 0, time.UTC)
-	var swapErr error
-	path, err := writeCrashReport(dir, "cli", "boom", []byte("complete stack"), ts, crashReportHooks{
-		beforePublish: func() {
-			swapErr = os.Rename(dir, movedDir)
-			if swapErr == nil {
-				if err := os.Mkdir(dir, 0o700); err != nil {
-					t.Fatalf("create substitute crash directory: %v", err)
-				}
-			}
-		},
-		remove: func(*os.Root, string) error { return injected },
-	})
-	if swapErr != nil {
-		if runtime.GOOS == "windows" {
-			t.Skipf("Windows kept the open crash directory from being renamed: %v", swapErr)
-		}
-		t.Fatalf("swap crash directory: %v", swapErr)
-	}
-	if !errors.Is(err, ErrCrashReportCommitted) || !errors.Is(err, injected) {
-		t.Fatalf("writeCrashReport error = %v, want committed cleanup warning", err)
-	}
-	if path != "" {
-		t.Fatalf("writeCrashReport returned stale path %q after directory swap", path)
-	}
-	report := filepath.Join(movedDir, "crash-20260824-120000.log")
-	data, readErr := os.ReadFile(report)
-	if readErr != nil {
-		t.Fatalf("read committed report through moved directory: %v", readErr)
-	}
-	if !strings.Contains(string(data), "complete stack") {
-		t.Fatalf("committed report is incomplete: %q", data)
-	}
-}
-
-func TestWriteCrashReportFallsBackWhenHardLinksAreUnavailable(t *testing.T) {
-	dir := t.TempDir()
-	ts := time.Date(2026, 8, 24, 12, 0, 0, 0, time.UTC)
-	unsupported := errors.New("hard links unavailable")
-	var collisionName string
-	path, err := writeCrashReport(dir, "cli", "boom", []byte("complete stack"), ts, crashReportHooks{
-		link: func(root *os.Root, oldname, _ string) error {
-			suffix := strings.TrimPrefix(oldname, crashTempPrefix)
-			collisionName = "crash-20260824-120000-" + suffix + ".log"
-			if err := root.WriteFile(collisionName, []byte("existing"), 0o600); err != nil {
-				t.Fatalf("create fallback-name collision: %v", err)
-			}
-			return unsupported
-		},
-	})
-	if err != nil {
-		t.Fatalf("writeCrashReport fallback: %v", err)
-	}
-	if path == filepath.Join(dir, collisionName) {
-		t.Fatalf("fallback replaced the existing report %q", collisionName)
-	}
-	if !strings.HasPrefix(filepath.Base(path), "crash-20260824-120000-") {
-		t.Fatalf("fallback path = %q, want timestamp and random suffix", path)
-	}
-	data, readErr := os.ReadFile(path)
-	if readErr != nil {
-		t.Fatalf("read fallback crash report: %v", readErr)
-	}
-	if !strings.Contains(string(data), "complete stack") {
-		t.Fatalf("fallback crash report is incomplete: %q", data)
-	}
-	existing, readErr := os.ReadFile(filepath.Join(dir, collisionName))
-	if readErr != nil {
-		t.Fatalf("read existing collision: %v", readErr)
-	}
-	if string(existing) != "existing" {
-		t.Fatalf("existing fallback collision was overwritten: %q", existing)
-	}
-	entries, readErr := os.ReadDir(dir)
-	if readErr != nil {
-		t.Fatal(readErr)
-	}
-	if len(entries) != 2 {
-		t.Fatalf("crash directory contains partial files after fallback: %v", entries)
-	}
-}
-
-func TestWriteCrashReportFallbackDoesNotReplaceCommitTimeCollision(t *testing.T) {
-	dir := t.TempDir()
-	ts := time.Date(2026, 8, 24, 12, 0, 0, 0, time.UTC)
-	unsupported := errors.New("hard links unavailable")
-	var collisionName string
-	attempts := 0
-	path, err := writeCrashReport(dir, "cli", "boom", []byte("complete stack"), ts, crashReportHooks{
-		link: func(*os.Root, string, string) error { return unsupported },
-		renameNoReplace: func(root *os.Root, oldname, newname string) error {
-			attempts++
-			if attempts == 1 {
-				collisionName = newname
-				if err := root.WriteFile(newname, []byte("concurrent report"), 0o600); err != nil {
-					t.Fatalf("create commit-time collision: %v", err)
-				}
-			}
-			return renameNoReplace(root, oldname, newname)
-		},
-	})
-	if err != nil {
-		t.Fatalf("writeCrashReport fallback: %v", err)
-	}
-	if attempts < 2 {
-		t.Fatalf("fallback rename attempts = %d, want collision retry", attempts)
-	}
-	if filepath.Base(path) == collisionName {
-		t.Fatalf("fallback replaced the concurrent report %q", collisionName)
-	}
-	existing, err := os.ReadFile(filepath.Join(dir, collisionName))
-	if err != nil {
-		t.Fatal(err)
-	}
-	if string(existing) != "concurrent report" {
-		t.Fatalf("concurrent report overwritten: %q", existing)
-	}
-	published, err := os.ReadFile(path)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if !strings.Contains(string(published), "complete stack") {
-		t.Fatalf("published fallback is incomplete: %q", published)
-	}
-}
-
-type crashWriteResult struct {
-	path string
-	err  error
-}
-
 func TestRecoverCapturesPanic(t *testing.T) {
 	dir := t.TempDir()
 	var stderr bytes.Buffer
@@ -460,25 +63,3 @@ func TestRecoverNoPanicIsNoop(t *testing.T) {
 		t.Fatalf("unexpected output without a panic: %q", stderr.String())
 	}
 }
-
-func TestReportRecoveredCrashReportsCommittedCleanupWarning(t *testing.T) {
-	var stderr bytes.Buffer
-	code := 0
-	injected := errors.New("injected cleanup failure")
-	reportRecoveredCrash(&stderr, &code, "kaboom", []byte("secret stack"), func() (string, error) {
-		return "/tmp/crash.log", &crashReportCommittedError{cause: injected}
-	})
-
-	if code != crashExitCode {
-		t.Fatalf("exit code = %d, want %d", code, crashExitCode)
-	}
-	output := stderr.String()
-	for _, want := range []string{"kaboom", "saved to /tmp/crash.log", "Warning:", injected.Error()} {
-		if !strings.Contains(output, want) {
-			t.Fatalf("crash notice missing %q: %q", want, output)
-		}
-	}
-	if strings.Contains(output, "secret stack") {
-		t.Fatalf("committed report warning fell back to inline stack: %q", output)
-	}
-}

internal/observability/rename_noreplace_darwin.go

@@ -1,19 +0,0 @@
-//go:build darwin
-
-package observability
-
-import (
-	"fmt"
-	"os"
-
-	"golang.org/x/sys/unix"
-)
-
-func renameNoReplace(root *os.Root, oldname, newname string) error {
-	directory, err := root.Open(".")
-	if err != nil {
-		return fmt.Errorf("open crash directory for publication: %w", err)
-	}
-	defer directory.Close()
-	return unix.RenameatxNp(int(directory.Fd()), oldname, int(directory.Fd()), newname, unix.RENAME_EXCL)
-}

internal/observability/rename_noreplace_linux.go

@@ -1,19 +0,0 @@
-//go:build linux
-
-package observability
-
-import (
-	"fmt"
-	"os"
-
-	"golang.org/x/sys/unix"
-)
-
-func renameNoReplace(root *os.Root, oldname, newname string) error {
-	directory, err := root.Open(".")
-	if err != nil {
-		return fmt.Errorf("open crash directory for publication: %w", err)
-	}
-	defer directory.Close()
-	return unix.Renameat2(int(directory.Fd()), oldname, int(directory.Fd()), newname, unix.RENAME_NOREPLACE)
-}

internal/observability/rename_noreplace_other.go

@@ -1,12 +0,0 @@
-//go:build !darwin && !linux && !windows
-
-package observability
-
-import (
-	"errors"
-	"os"
-)
-
-func renameNoReplace(*os.Root, string, string) error {
-	return errors.ErrUnsupported
-}

internal/observability/rename_noreplace_windows.go

@@ -1,84 +0,0 @@
-//go:build windows
-
-package observability
-
-import (
-	"errors"
-	"os"
-	"unsafe"
-
-	"golang.org/x/sys/windows"
-)
-
-type fileRenameInformation struct {
-	replaceIfExists uint32
-	rootDirectory   windows.Handle
-	fileNameLength  uint32
-	fileName        [1]uint16
-}
-
-func renameNoReplace(root *os.Root, oldname, newname string) (returnErr error) {
-	directory, err := root.Open(".")
-	if err != nil {
-		return err
-	}
-	defer directory.Close()
-	raw, err := directory.SyscallConn()
-	if err != nil {
-		return err
-	}
-	if err := raw.Control(func(rawHandle uintptr) {
-		rootHandle := windows.Handle(rawHandle)
-		oldObjectName, nameErr := windows.NewNTUnicodeString(oldname)
-		if nameErr != nil {
-			returnErr = nameErr
-			return
-		}
-		attributes := &windows.OBJECT_ATTRIBUTES{
-			Length:        uint32(unsafe.Sizeof(windows.OBJECT_ATTRIBUTES{})),
-			RootDirectory: rootHandle,
-			ObjectName:    oldObjectName,
-			Attributes:    windows.OBJ_CASE_INSENSITIVE | windows.OBJ_DONT_REPARSE,
-		}
-		var source windows.Handle
-		var status windows.IO_STATUS_BLOCK
-		returnErr = windows.NtCreateFile(
-			&source,
-			windows.DELETE|windows.SYNCHRONIZE,
-			attributes,
-			&status,
-			nil,
-			0,
-			windows.FILE_SHARE_READ|windows.FILE_SHARE_WRITE|windows.FILE_SHARE_DELETE,
-			windows.FILE_OPEN,
-			windows.FILE_NON_DIRECTORY_FILE|windows.FILE_SYNCHRONOUS_IO_NONALERT|windows.FILE_OPEN_REPARSE_POINT,
-			0,
-			0,
-		)
-		if returnErr != nil {
-			return
-		}
-		defer windows.CloseHandle(source)
-
-		newName, nameErr := windows.UTF16FromString(newname)
-		if nameErr != nil {
-			returnErr = nameErr
-			return
-		}
-		nameBytes := (len(newName) - 1) * 2
-		var layout fileRenameInformation
-		bufferSize := int(unsafe.Offsetof(layout.fileName)) + nameBytes
-		buffer := make([]byte, bufferSize)
-		info := (*fileRenameInformation)(unsafe.Pointer(&buffer[0]))
-		info.rootDirectory = rootHandle
-		info.fileNameLength = uint32(nameBytes)
-		copy((*[windows.MAX_LONG_PATH]uint16)(unsafe.Pointer(&info.fileName[0]))[:nameBytes/2:nameBytes/2], newName)
-		returnErr = windows.NtSetInformationFile(source, &status, &buffer[0], uint32(bufferSize), windows.FileRenameInformation)
-	}); err != nil {
-		return err
-	}
-	if errors.Is(returnErr, windows.STATUS_OBJECT_NAME_COLLISION) || errors.Is(returnErr, windows.STATUS_OBJECT_NAME_EXISTS) {
-		return os.ErrExist
-	}
-	return returnErr
-}

internal/privatedir/privatedir.go

@@ -1,85 +0,0 @@
-// Package privatedir creates and safely hardens current-user-owned state
-// directories without applying permission changes through a path-only check.
-package privatedir
-
-import (
-	"errors"
-	"fmt"
-	"os"
-	"path/filepath"
-)
-
-// Ensure creates path when needed and enforces owner-only access. Existing
-// directories are hardened only after ownership is verified through a bound
-// directory handle; foreign-owned paths fail closed.
-func Ensure(path string) error {
-	root, err := Open(path)
-	if err != nil {
-		return err
-	}
-	if err := root.Close(); err != nil {
-		return fmt.Errorf("close private directory: %w", err)
-	}
-	return nil
-}
-
-// Open creates path when needed, enforces owner-only access, and returns a
-// traversal-resistant handle that callers can retain across subsequent I/O.
-func Open(path string) (*os.Root, error) {
-	absolute, err := filepath.Abs(path)
-	if err != nil {
-		return nil, fmt.Errorf("resolve private directory: %w", err)
-	}
-	if err := os.MkdirAll(absolute, 0o700); err != nil {
-		return nil, fmt.Errorf("create private directory: %w", err)
-	}
-	before, err := os.Lstat(absolute)
-	if err != nil {
-		return nil, fmt.Errorf("inspect private directory entry: %w", err)
-	}
-	if before.Mode()&os.ModeSymlink != 0 {
-		return nil, fmt.Errorf("private directory entry is a symbolic link")
-	}
-	if !before.IsDir() {
-		return nil, fmt.Errorf("private directory path is not a directory")
-	}
-	root, err := os.OpenRoot(absolute)
-	if err != nil {
-		return nil, fmt.Errorf("open private directory: %w", err)
-	}
-	opened, err := root.Stat(".")
-	if err != nil {
-		_ = root.Close()
-		return nil, fmt.Errorf("inspect opened private directory: %w", err)
-	}
-	after, err := os.Lstat(absolute)
-	if err != nil {
-		_ = root.Close()
-		return nil, fmt.Errorf("reinspect private directory entry: %w", err)
-	}
-	if after.Mode()&os.ModeSymlink != 0 || !os.SameFile(opened, after) {
-		_ = root.Close()
-		return nil, fmt.Errorf("private directory entry changed while opening")
-	}
-	if err := harden(root); err != nil {
-		closeErr := root.Close()
-		if closeErr != nil {
-			return nil, errors.Join(err, fmt.Errorf("close private directory: %w", closeErr))
-		}
-		return nil, err
-	}
-	current, err := os.Lstat(absolute)
-	if err != nil || current.Mode()&os.ModeSymlink != 0 || !os.SameFile(opened, current) {
-		closeErr := root.Close()
-		if err == nil {
-			err = fmt.Errorf("private directory entry changed while hardening")
-		} else {
-			err = fmt.Errorf("verify private directory entry after hardening: %w", err)
-		}
-		if closeErr != nil {
-			err = errors.Join(err, fmt.Errorf("close private directory: %w", closeErr))
-		}
-		return nil, err
-	}
-	return root, nil
-}

internal/privatedir/privatedir_test.go

@@ -1,35 +0,0 @@
-package privatedir
-
-import (
-	"os"
-	"path/filepath"
-	"runtime"
-	"strings"
-	"testing"
-)
-
-func TestOpenRejectsFinalDirectorySymlinkWithoutHardeningTarget(t *testing.T) {
-	if runtime.GOOS == "windows" {
-		t.Skip("creating directory symlinks requires privileges on some Windows runners")
-	}
-	parent := t.TempDir()
-	target := filepath.Join(parent, "target")
-	if err := os.Mkdir(target, 0o755); err != nil {
-		t.Fatal(err)
-	}
-	link := filepath.Join(parent, "private")
-	if err := os.Symlink(target, link); err != nil {
-		t.Fatal(err)
-	}
-
-	if _, err := Open(link); err == nil || !strings.Contains(err.Error(), "symbolic link") {
-		t.Fatalf("Open symlink error = %v, want symbolic-link rejection", err)
-	}
-	info, err := os.Stat(target)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if got := info.Mode().Perm(); got != 0o755 {
-		t.Fatalf("symlink target permissions = %04o, want unchanged 0755", got)
-	}
-}

internal/privatedir/privatedir_unix.go

@@ -1,47 +0,0 @@
-//go:build !windows
-
-package privatedir
-
-import (
-	"errors"
-	"fmt"
-	"os"
-	"syscall"
-)
-
-func harden(root *os.Root) (returnErr error) {
-	directory, err := root.Open(".")
-	if err != nil {
-		return fmt.Errorf("open private directory hardening handle: %w", err)
-	}
-	defer func() {
-		if err := directory.Close(); err != nil {
-			returnErr = errors.Join(returnErr, fmt.Errorf("close private directory hardening handle: %w", err))
-		}
-	}()
-	info, err := directory.Stat()
-	if err != nil {
-		return fmt.Errorf("inspect private directory before hardening: %w", err)
-	}
-	if !info.IsDir() {
-		return fmt.Errorf("private directory path is not a directory")
-	}
-	stat, ok := info.Sys().(*syscall.Stat_t)
-	if !ok {
-		return fmt.Errorf("private directory ownership metadata is unavailable")
-	}
-	if int(stat.Uid) != os.Geteuid() {
-		return fmt.Errorf("private directory is owned by uid %d, not the current user", stat.Uid)
-	}
-	if err := directory.Chmod(0o700); err != nil {
-		return fmt.Errorf("harden private directory permissions: %w", err)
-	}
-	info, err = directory.Stat()
-	if err != nil {
-		return fmt.Errorf("verify private directory permissions: %w", err)
-	}
-	if info.Mode().Perm()&0o077 != 0 {
-		return fmt.Errorf("private directory permissions are %04o, want owner-only", info.Mode().Perm())
-	}
-	return nil
-}

internal/privatedir/privatedir_windows.go

@@ -1,135 +0,0 @@
-//go:build windows
-
-package privatedir
-
-import (
-	"errors"
-	"fmt"
-	"os"
-	"unsafe"
-
-	"golang.org/x/sys/windows"
-)
-
-func harden(root *os.Root) (returnErr error) {
-	directory, err := root.Open(".")
-	if err != nil {
-		return fmt.Errorf("open private directory hardening handle: %w", err)
-	}
-	defer func() {
-		if err := directory.Close(); err != nil {
-			returnErr = errors.Join(returnErr, fmt.Errorf("close private directory hardening handle: %w", err))
-		}
-	}()
-	raw, err := directory.SyscallConn()
-	if err != nil {
-		return fmt.Errorf("access private directory hardening handle: %w", err)
-	}
-	// Root.Open uses NtCreateFile, so ReOpenFile cannot accept its handle. An
-	// empty relative NT object name reopens the bound directory itself with the
-	// security rights needed for the DACL update and no pathname re-resolution.
-	var securityHandle windows.Handle
-	var openErr error
-	if err := raw.Control(func(rawHandle uintptr) {
-		objectName, nameErr := windows.NewNTUnicodeString("")
-		if nameErr != nil {
-			openErr = nameErr
-			return
-		}
-		openErr = windows.NtCreateFile(
-			&securityHandle,
-			windows.READ_CONTROL|windows.WRITE_DAC|windows.FILE_READ_ATTRIBUTES|windows.SYNCHRONIZE,
-			&windows.OBJECT_ATTRIBUTES{
-				Length:        uint32(unsafe.Sizeof(windows.OBJECT_ATTRIBUTES{})),
-				RootDirectory: windows.Handle(rawHandle),
-				ObjectName:    objectName,
-				Attributes:    windows.OBJ_CASE_INSENSITIVE | windows.OBJ_DONT_REPARSE,
-			},
-			&windows.IO_STATUS_BLOCK{},
-			nil,
-			windows.FILE_ATTRIBUTE_DIRECTORY,
-			windows.FILE_SHARE_READ|windows.FILE_SHARE_WRITE|windows.FILE_SHARE_DELETE,
-			windows.FILE_OPEN,
-			windows.FILE_DIRECTORY_FILE|windows.FILE_SYNCHRONOUS_IO_NONALERT|windows.FILE_OPEN_REPARSE_POINT|windows.FILE_OPEN_FOR_BACKUP_INTENT,
-			0,
-			0,
-		)
-	}); err != nil {
-		return fmt.Errorf("open private directory security handle: %w", err)
-	}
-	if openErr != nil {
-		return fmt.Errorf("open private directory with security access: %w", openErr)
-	}
-	if securityHandle == 0 || securityHandle == windows.InvalidHandle {
-		return fmt.Errorf("open private directory with security access: invalid handle")
-	}
-	defer func() {
-		if err := windows.CloseHandle(securityHandle); err != nil {
-			returnErr = errors.Join(returnErr, fmt.Errorf("close private directory security handle: %w", err))
-		}
-	}()
-
-	token := windows.GetCurrentProcessToken()
-	user, err := token.GetTokenUser()
-	if err != nil {
-		return fmt.Errorf("resolve current Windows user: %w", err)
-	}
-	tokenOwner, err := windowsTokenOwner(token)
-	if err != nil {
-		return fmt.Errorf("resolve current Windows token owner: %w", err)
-	}
-	current, err := windows.GetSecurityInfo(securityHandle, windows.SE_FILE_OBJECT, windows.OWNER_SECURITY_INFORMATION)
-	if err != nil {
-		return fmt.Errorf("read private directory owner before hardening: %w", err)
-	}
-	owner, _, err := current.Owner()
-	if err != nil {
-		return fmt.Errorf("read private directory owner before hardening: %w", err)
-	}
-	if owner == nil || (!owner.Equals(user.User.Sid) && !owner.Equals(tokenOwner)) {
-		return fmt.Errorf("private directory is not owned by the current Windows token")
-	}
-	desired, err := windows.SecurityDescriptorFromString(
-		fmt.Sprintf("O:%sD:P(A;OICI;GA;;;%s)(A;OICI;GA;;;SY)", user.User.Sid.String(), user.User.Sid.String()),
-	)
-	if err != nil {
-		return fmt.Errorf("build private Windows directory DACL: %w", err)
-	}
-	dacl, _, err := desired.DACL()
-	if err != nil {
-		return fmt.Errorf("read private Windows directory DACL: %w", err)
-	}
-	if err := windows.SetSecurityInfo(
-		securityHandle,
-		windows.SE_FILE_OBJECT,
-		windows.DACL_SECURITY_INFORMATION|windows.PROTECTED_DACL_SECURITY_INFORMATION,
-		nil,
-		nil,
-		dacl,
-		nil,
-	); err != nil {
-		return fmt.Errorf("harden private Windows directory DACL: %w", err)
-	}
-	return nil
-}
-
-type tokenOwnerInfo struct {
-	owner *windows.SID
-}
-
-func windowsTokenOwner(token windows.Token) (*windows.SID, error) {
-	var size uint32
-	err := windows.GetTokenInformation(token, windows.TokenOwner, nil, 0, &size)
-	if err != windows.ERROR_INSUFFICIENT_BUFFER {
-		return nil, err
-	}
-	buffer := make([]byte, size)
-	if err := windows.GetTokenInformation(token, windows.TokenOwner, &buffer[0], size, &size); err != nil {
-		return nil, err
-	}
-	owner := (*tokenOwnerInfo)(unsafe.Pointer(&buffer[0])).owner
-	if owner == nil {
-		return nil, errors.New("windows access token has no default owner")
-	}
-	return owner.Copy()
-}

internal/sessions/replay.go

@@ -226,20 +226,11 @@ func CompactionPayloadFromPlan(summary string, plan CompactionPlan) (CompactionP
 }
 
 func (store *Store) ReadRehydratedEvents(sessionID string) ([]Event, error) {
-	events, _, err := store.ReadRehydratedEventsWithPresence(sessionID)
-	return events, err
-}
-
-// ReadRehydratedEventsWithPresence carries the underlying event-log presence
-// through compaction projection without changing ReadRehydratedEvents' existing
-// empty-on-missing contract.
-func (store *Store) ReadRehydratedEventsWithPresence(sessionID string) ([]Event, bool, error) {
-	events, present, err := store.ReadEventsWithPresence(sessionID)
+	events, err := store.ReadEvents(sessionID)
 	if err != nil {
-		return nil, present, err
+		return nil, err
 	}
-	rehydrated, err := RehydrateEvents(events)
-	return rehydrated, present, err
+	return RehydrateEvents(events)
 }
 
 func (store *Store) ReadReplayEvents(sessionID string) ([]Event, error) {

internal/sessions/store.go

@@ -813,24 +813,15 @@ func (store *Store) UpdateModel(sessionID string, modelID string) (Metadata, err
 }
 
 func (store *Store) ReadEvents(sessionID string) ([]Event, error) {
-	events, _, err := store.ReadEventsWithPresence(sessionID)
-	return events, err
-}
-
-// ReadEventsWithPresence preserves the distinction between an intentionally
-// empty event log and a missing one. Most readers accept both as empty history,
-// but activation protocols that promise to restore previously populated
-// context need the stronger signal.
-func (store *Store) ReadEventsWithPresence(sessionID string) ([]Event, bool, error) {
 	if !ValidSessionID(sessionID) {
-		return nil, false, fmt.Errorf("invalid zero session id %q", sessionID)
+		return nil, fmt.Errorf("invalid zero session id %q", sessionID)
 	}
 	data, err := os.ReadFile(store.eventsPath(sessionID))
 	if err != nil {
 		if errors.Is(err, os.ErrNotExist) {
-			return []Event{}, false, nil
+			return []Event{}, nil
 		}
-		return nil, false, fmt.Errorf("read zero session events: %w", err)
+		return nil, fmt.Errorf("read zero session events: %w", err)
 	}
 	// A genuine torn tail is an INCOMPLETE final write — a crash mid-append leaves
 	// the last line without its terminating newline. If the file ends with a
@@ -860,11 +851,11 @@ func (store *Store) ReadEventsWithPresence(sessionID string) ([]Event, bool, err
 			if index == lastNonEmpty && tornTailPossible {
 				break
 			}
-			return nil, true, fmt.Errorf("invalid json in zero session %s %s at line %d: %w", sessionID, EventsFile, index+1, err)
+			return nil, fmt.Errorf("invalid json in zero session %s %s at line %d: %w", sessionID, EventsFile, index+1, err)
 		}
 		events = append(events, event)
 	}
-	return events, true, nil
+	return events, nil
 }
 
 func (store *Store) timestamp() string {

internal/tools/apply_patch_tolerance_test.go

@@ -2,8 +2,10 @@ package tools
 
 import (
 	"context"
+	"errors"
 	"os"
 	"path/filepath"
+	"slices"
 	"strconv"
 	"strings"
 	"testing"
@@ -363,7 +365,7 @@ func TestUnifiedPatchCopyOperation(t *testing.T) {
 	if content, _ := os.ReadFile(filepath.Join(root, "dst.txt")); string(content) != "hello\nnew\n" {
 		t.Fatalf("copy destination = %q", string(content))
 	}
-	if len(result.ChangedFiles) != 2 || result.ChangedFiles[0] != "src.txt" || result.ChangedFiles[1] != "dst.txt" {
+	if len(result.ChangedFiles) != 1 || result.ChangedFiles[0] != "dst.txt" {
 		t.Fatalf("changed files = %v", result.ChangedFiles)
 	}
 	destination, err := filepath.EvalSymlinks(filepath.Join(root, "dst.txt"))
@@ -571,9 +573,9 @@ func TestApplyStructuredPatchChangeRefusesSourceChangedAfterPlanning(t *testing.
 		"copy":   {kind: structuredPatchCopy, from: target, to: destination, before: "planned\n", after: "planned\n", mode: 0o644},
 	} {
 		writeTestFile(t, path, "changed after planning\n")
-		committed, err := applyStructuredPatchChange(workspace, change)
-		if err == nil || committed || !strings.Contains(err.Error(), "changed on disk between planning and commit") {
-			t.Fatalf("%s: expected a refusal, got committed=%v err=%v", name, committed, err)
+		outcome, err := applyStructuredPatchChange(workspace, change)
+		if err == nil || len(outcome.completed) != 0 || len(outcome.incompletePaths) != 0 || !strings.Contains(err.Error(), "changed on disk between planning and commit") {
+			t.Fatalf("%s: expected a refusal, got outcome=%#v err=%v", name, outcome, err)
 		}
 		if content, _ := os.ReadFile(path); string(content) != "changed after planning\n" {
 			t.Fatalf("%s: file must be untouched, got %q", name, string(content))
@@ -709,4 +711,158 @@ func TestApplyPatchOperationsReportsCommittedPrefixOnFailure(t *testing.T) {
 	if content, _ := os.ReadFile(filepath.Join(root, "third.txt")); string(content) != "three\n" {
 		t.Fatalf("third.txt must be untouched, got %q", string(content))
 	}
+	if got := result.ChangedFiles; len(got) != 1 || got[0] != "first.txt" {
+		t.Fatalf("partial patch ChangedFiles = %#v, want committed prefix only", got)
+	}
+	resolvedFirst, err := filepath.EvalSymlinks(filepath.Join(root, "first.txt"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := result.FileDiffs; len(got) != 1 || got[0] != (FileDiff{Path: resolvedFirst, OldExists: true, NewExists: true, OldText: "one\n", NewText: "ONE\n"}) {
+		t.Fatalf("partial patch FileDiffs = %#v", got)
+	}
+}
+
+func TestApplyPatchOperationsReportsWorkspaceRelativeCommittedPrefixUnderCwd(t *testing.T) {
+	root := t.TempDir()
+	applyRoot := filepath.Join(root, "sub", "dir")
+	if err := os.MkdirAll(applyRoot, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	writeTestFile(t, filepath.Join(applyRoot, "first.txt"), "one\n")
+	writeTestFile(t, filepath.Join(applyRoot, "second.txt"), "two\n")
+	structuredPatchBeforeCommit = func(change structuredPatchChange) {
+		if change.to.relative == "second.txt" {
+			writeTestFile(t, filepath.Join(applyRoot, "second.txt"), "changed\n")
+		}
+	}
+	t.Cleanup(func() { structuredPatchBeforeCommit = nil })
+	patch := strings.Join([]string{
+		"*** Begin Patch",
+		"*** Update File: first.txt", "@@", "-one", "+ONE",
+		"*** Update File: second.txt", "@@", "-two", "+TWO",
+		"*** End Patch", "",
+	}, "\n")
+
+	result := NewScopedApplyPatchTool(root, nil).Run(context.Background(), map[string]any{
+		"cwd": "sub/dir", "patch": patch,
+	})
+	if result.Status != StatusError || !strings.Contains(result.Output, "already committed: sub/dir/first.txt") {
+		t.Fatalf("nested partial failure = status=%s output=%q", result.Status, result.Output)
+	}
+	if got := result.ChangedFiles; len(got) != 1 || got[0] != "sub/dir/first.txt" {
+		t.Fatalf("nested partial ChangedFiles = %#v", got)
+	}
+}
+
+func TestApplyPatchSeparatesVerifiedAndUnverifiedPartialPublications(t *testing.T) {
+	root := t.TempDir()
+	priorPublish := structuredPatchPublishNoReplace
+	structuredPatchPublishNoReplace = func(workspace *os.Root, source, target string, mode os.FileMode) (bool, error) {
+		if target != "uncertain.txt" {
+			return priorPublish(workspace, source, target, mode)
+		}
+		file, err := workspace.OpenFile(target, os.O_WRONLY|os.O_CREATE|os.O_EXCL, mode.Perm())
+		if err != nil {
+			return false, err
+		}
+		if _, err := file.WriteString("partial"); err != nil {
+			_ = file.Close()
+			return true, err
+		}
+		if err := file.Close(); err != nil {
+			return true, err
+		}
+		return true, errors.New("injected failure after partial publication")
+	}
+	t.Cleanup(func() { structuredPatchPublishNoReplace = priorPublish })
+
+	patch := strings.Join([]string{
+		"*** Begin Patch",
+		"*** Add File: verified.txt", "+verified",
+		"*** Add File: uncertain.txt", "+intended complete content",
+		"*** Add File: untouched.txt", "+untouched",
+		"*** End Patch", "",
+	}, "\n")
+	result := NewScopedApplyPatchTool(root, nil).Run(context.Background(), map[string]any{"patch": patch})
+
+	if result.Status != StatusError {
+		t.Fatalf("partial publication status = %s, want error", result.Status)
+	}
+	for _, want := range []string{"already committed: verified.txt", "published but unverified: uncertain.txt"} {
+		if !strings.Contains(result.Output, want) {
+			t.Fatalf("partial publication error must contain %q: %s", want, result.Output)
+		}
+	}
+	committedFragment := strings.SplitN(result.Output, "; published but unverified:", 2)[0]
+	if strings.Contains(committedFragment, "uncertain.txt") {
+		t.Fatalf("unverified path appears in committed fragment: %s", result.Output)
+	}
+	if got, want := result.ChangedFiles, []string{"verified.txt"}; !slices.Equal(got, want) {
+		t.Fatalf("ChangedFiles = %#v, want verified publications only %#v", got, want)
+	}
+	resolvedVerified, err := filepath.EvalSymlinks(filepath.Join(root, "verified.txt"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := result.FileDiffs; len(got) != 1 || got[0].Path != resolvedVerified {
+		t.Fatalf("FileDiffs = %#v, want verified.txt only", got)
+	}
+	if got := mustReadTestFile(t, filepath.Join(root, "verified.txt")); got != "verified\n" {
+		t.Fatalf("verified publication = %q", got)
+	}
+	if got := mustReadTestFile(t, filepath.Join(root, "uncertain.txt")); got != "partial" {
+		t.Fatalf("unverified publication = %q", got)
+	}
+	if _, err := os.Stat(filepath.Join(root, "untouched.txt")); !os.IsNotExist(err) {
+		t.Fatalf("later publication must remain untouched: %v", err)
+	}
+}
+
+func TestApplyPatchMoveReportsPublishedDestinationWhenSourceRemovalFails(t *testing.T) {
+	root := t.TempDir()
+	writeTestFile(t, filepath.Join(root, "source.txt"), "before\n")
+	priorRemove := structuredPatchRemove
+	structuredPatchRemove = func(workspace *os.Root, name string) error {
+		if name == "source.txt" {
+			return os.ErrPermission
+		}
+		return priorRemove(workspace, name)
+	}
+	t.Cleanup(func() { structuredPatchRemove = priorRemove })
+
+	patch := strings.Join([]string{
+		"*** Begin Patch",
+		"*** Update File: source.txt",
+		"*** Move to: destination.txt",
+		"@@",
+		"-before",
+		"+after",
+		"*** End Patch",
+		"",
+	}, "\n")
+	result := NewScopedApplyPatchTool(root, nil).Run(context.Background(), map[string]any{"patch": patch})
+	if result.Status != StatusError {
+		t.Fatalf("move status = %s, want error", result.Status)
+	}
+	if got := mustReadTestFile(t, filepath.Join(root, "source.txt")); got != "before\n" {
+		t.Fatalf("source content = %q", got)
+	}
+	if got := mustReadTestFile(t, filepath.Join(root, "destination.txt")); got != "after\n" {
+		t.Fatalf("destination content = %q", got)
+	}
+	if got, want := result.ChangedFiles, []string{"destination.txt"}; !slices.Equal(got, want) {
+		t.Fatalf("ChangedFiles = %#v, want %#v", got, want)
+	}
+	resolvedDestination, err := filepath.EvalSymlinks(filepath.Join(root, "destination.txt"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	wantDiff := FileDiff{Path: resolvedDestination, OldExists: false, NewExists: true, NewText: "after\n"}
+	if got := result.FileDiffs; len(got) != 1 || got[0] != wantDiff {
+		t.Fatalf("FileDiffs = %#v, want %#v", got, []FileDiff{wantDiff})
+	}
+	if !strings.Contains(result.Display.Preview, "destination.txt") || strings.Contains(result.Display.Preview, "source.txt") {
+		t.Fatalf("preview must show only destination creation: %q", result.Display.Preview)
+	}
 }

internal/tools/diff_preview.go

@@ -1,19 +1,122 @@
 package tools
 
-import udiff "github.com/aymanbagabas/go-udiff"
+import (
+	"path/filepath"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+
+	"github.com/Gitlawb/zero/internal/redaction"
+	udiff "github.com/aymanbagabas/go-udiff"
+)
 
 // maxToolPreviewBytes caps the inline diff a write tool appends to its result, so
 // a large generated file can't flood the transcript or balloon the persisted
 // session events. Past this the tool falls back to its summary line alone.
 const maxToolPreviewBytes = 48 * 1024
 
+// A structured replacement contains two complete file sides, so its transport
+// budget is intentionally separate from the single rendered-preview budget.
+// Each side may be as large as a normal preview; aggregate producers apply the
+// two-sided result cap in file order.
+const maxToolResultFileDiffBytes = 2 * maxToolPreviewBytes
+
+// FileDiff is a human-facing before/after file change. Registry-boundary
+// redaction applies to both sides before any caller receives it.
+type FileDiff struct {
+	// Path is the canonical absolute path required by ACP diff content. The
+	// separate ChangedFiles result remains workspace-relative for local UI use.
+	Path string
+	// OldExists and NewExists distinguish an empty file from a missing side of a
+	// create/delete/move. Empty strings alone cannot encode that difference.
+	OldExists bool
+	NewExists bool
+	OldText   string
+	NewText   string
+}
+
+// boundedFileDiff declines rather than truncating: a truncated side would look
+// like an exact file replacement. Callers keep ChangedFiles as the safe
+// fallback for large, unsafe, or unchanged content. Each complete side gets the
+// same bound as a rendered preview; aggregate result producers apply their own
+// cap. Control bytes are rejected. Ordinary Unicode format/space characters are
+// retained unless removing them reveals a credential shape that the normal
+// redactor could not see in the original text.
+func boundedFileDiff(path, oldText, newText string, oldExists, newExists bool) (FileDiff, bool) {
+	if !filepath.IsAbs(path) || (!oldExists && !newExists) ||
+		(oldExists == newExists && oldText == newText) ||
+		!utf8.ValidString(oldText) || !utf8.ValidString(newText) ||
+		unsafeDiffText(oldText) || unsafeDiffText(newText) ||
+		len(oldText) > maxToolPreviewBytes || len(newText) > maxToolPreviewBytes {
+		return FileDiff{}, false
+	}
+	return FileDiff{Path: path, OldExists: oldExists, NewExists: newExists, OldText: oldText, NewText: newText}, true
+}
+
+func unsafeDiffText(text string) bool {
+	if !utf8.ValidString(text) {
+		return true
+	}
+	hasCanonicalizableSeparator := false
+	for _, r := range text {
+		switch r {
+		case '\n', '\r', '\t', ' ':
+			continue
+		}
+		if unicode.IsControl(r) {
+			return true
+		}
+		if isDiffCredentialIgnorable(r) {
+			hasCanonicalizableSeparator = true
+		}
+	}
+	if !hasCanonicalizableSeparator {
+		return false
+	}
+	return diffTextRevealsObfuscatedSecret(text)
+}
+
+func diffTextRevealsObfuscatedSecret(text string) bool {
+	if !utf8.ValidString(text) {
+		return false
+	}
+	canonical := strings.Map(func(r rune) rune {
+		switch r {
+		case '\n', '\r', '\t', ' ':
+			return r
+		}
+		if isDiffCredentialIgnorable(r) {
+			return -1
+		}
+		return r
+	}, text)
+	return canonical != text && redaction.RedactString(canonical, redaction.Options{}) != canonical
+}
+
+// isDiffCredentialIgnorable mirrors Unicode's Default_Ignorable_Code_Point
+// derived property using the tables exposed by the Go standard library. Cf
+// catches format controls, while the other two tables cover non-Cf default
+// ignorables such as U+034F COMBINING GRAPHEME JOINER and variation selectors.
+// Unicode whitespace is also removable because it can split a credential that
+// the boundary redactor would otherwise recognize. The caller preserves normal
+// ASCII layout whitespace before consulting this helper.
+func isDiffCredentialIgnorable(r rune) bool {
+	return unicode.Is(unicode.Cf, r) ||
+		unicode.Is(unicode.Other_Default_Ignorable_Code_Point, r) ||
+		unicode.Is(unicode.Variation_Selector, r) ||
+		unicode.IsSpace(r)
+}
+
 // boundedUnifiedDiff returns a unified diff of oldContent -> newContent labelled
 // with path, suitable for the TUI's diff card renderer. A create (oldContent "")
 // yields an all-additions (green) preview; an overwrite/edit yields red/green.
-// Returns "" when there is no change or the diff exceeds maxToolPreviewBytes.
+// Returns "" when there is no change, the rendered diff is unsafe text, or the
+// diff exceeds maxToolPreviewBytes. This applies the same unsafe-text gate as
+// FileDiff to what reaches Display.Preview, without discarding a safe hunk only
+// because an unrelated part of the source file contains an unsafe byte.
 func boundedUnifiedDiff(path, oldContent, newContent string) string {
 	diff := udiff.Unified(path, path, oldContent, newContent)
-	if diff == "" || len(diff) > maxToolPreviewBytes {
+	if diff == "" || !utf8.ValidString(diff) || unsafeDiffText(diff) || len(diff) > maxToolPreviewBytes {
 		return ""
 	}
 	return diff

internal/tools/diff_preview_test.go

@@ -0,0 +1,186 @@
+package tools
+
+import (
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func TestBoundedFileDiffRefusesPartialOrBinaryContent(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "a.txt")
+	if diff, ok := boundedFileDiff(path, "old", "new", true, true); !ok || diff.Path != path || !diff.OldExists || !diff.NewExists || diff.OldText != "old" || diff.NewText != "new" {
+		t.Fatalf("small text diff = %#v, %t", diff, ok)
+	}
+	for _, tc := range []struct {
+		name string
+		old  string
+		new  string
+	}{
+		{"unchanged", "same", "same"},
+		{"binary old", string([]byte{0xff}), "text"},
+		{"binary new", "text", string([]byte{0xff})},
+		{"nul old", "token=sk-proj-abc\x00def", "text"},
+		{"escape new", "text", "token=sk-proj-abc\x1bdef"},
+		{"c1 old", "token=sk-proj-abc\u0085def", "text"},
+		{"zero width space", "token=sk-proj-abc\u200bdef", "text"},
+		{"zero width joiner", "token=sk-proj-abc\u200ddef", "text"},
+		{"byte order mark", "token=sk-proj-abc\ufeffdef", "text"},
+		{"soft hyphen", "token=sk-proj-abc\u00addef", "text"},
+		{"non breaking space", "token=sk-proj-abc\u00a0def", "text"},
+		{"too large", strings.Repeat("a", maxToolPreviewBytes+1), "b"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			if diff, ok := boundedFileDiff(path, tc.old, tc.new, true, true); ok || diff != (FileDiff{}) {
+				t.Fatalf("unexpected diff = %#v, %t", diff, ok)
+			}
+		})
+	}
+}
+
+func TestBoundedFileDiffPreservesEmptyFileOperations(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "empty.txt")
+	for _, tc := range []struct {
+		name                 string
+		oldExists, newExists bool
+	}{
+		{name: "create", newExists: true},
+		{name: "delete", oldExists: true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			diff, ok := boundedFileDiff(path, "", "", tc.oldExists, tc.newExists)
+			if !ok || diff.OldExists != tc.oldExists || diff.NewExists != tc.newExists {
+				t.Fatalf("empty %s = %#v, %t", tc.name, diff, ok)
+			}
+		})
+	}
+}
+
+func TestBoundedUnifiedDiffRejectsUnsafeRichText(t *testing.T) {
+	if got := boundedUnifiedDiff("safe.txt", "before\n", "after\n"); got == "" {
+		t.Fatal("safe unified diff was unexpectedly omitted")
+	}
+	for _, content := range []string{
+		"token=sk-proj-abc\x00def",
+		"token=sk-proj-abc\x1bdef",
+		"token=sk-proj-abc\u200bdef",
+		string([]byte{0xff}),
+	} {
+		if got := boundedUnifiedDiff("secret.txt", content, "safe\n"); got != "" {
+			t.Fatalf("unsafe rich diff = %q", got)
+		}
+	}
+
+	old := strings.Repeat("unchanged\n", 12) + "form\ffeed\n" + strings.Repeat("unchanged\n", 12)
+	updated := strings.Replace(old, "unchanged\n", "changed\n", 1)
+	if got := boundedUnifiedDiff("safe-hunk.txt", old, updated); got == "" || strings.Contains(got, "\f") {
+		t.Fatalf("safe hunk near unrelated unsafe text = %q", got)
+	}
+}
+
+func TestStructuredPatchFileDiffsPreserveEmptyOperationsAndResultBudget(t *testing.T) {
+	root, err := filepath.EvalSymlinks(t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
+	changes := []structuredPatchChange{
+		{kind: structuredPatchAdd, to: structuredPatchTarget{absolute: filepath.Join(root, "created"), relative: "created"}},
+		{kind: structuredPatchDelete, from: structuredPatchTarget{absolute: filepath.Join(root, "deleted"), relative: "deleted"}},
+		{kind: structuredPatchUpdate, from: structuredPatchTarget{absolute: filepath.Join(root, "from"), relative: "from"}, to: structuredPatchTarget{absolute: filepath.Join(root, "to"), relative: "to"}},
+	}
+	diffs := fileDiffsFromStructuredPatch(".", changes)
+	if len(diffs) != 4 {
+		t.Fatalf("empty create/delete/move diffs = %#v", diffs)
+	}
+	for _, diff := range diffs {
+		if diff.Path == "" || (!diff.OldExists && !diff.NewExists) {
+			t.Fatalf("invalid diff = %#v", diff)
+		}
+	}
+
+	large := strings.Repeat("x", maxToolResultFileDiffBytes/3+1)
+	budgeted := fileDiffsFromStructuredPatch(".", []structuredPatchChange{
+		{kind: structuredPatchAdd, to: structuredPatchTarget{absolute: filepath.Join(root, "one")}, after: large},
+		{kind: structuredPatchAdd, to: structuredPatchTarget{absolute: filepath.Join(root, "two")}, after: "tiny"},
+		{kind: structuredPatchAdd, to: structuredPatchTarget{absolute: filepath.Join(root, "three")}, after: large},
+		{kind: structuredPatchAdd, to: structuredPatchTarget{absolute: filepath.Join(root, "four")}, after: large},
+	})
+	if len(budgeted) != 3 || filepath.Base(budgeted[0].Path) != "one" || filepath.Base(budgeted[1].Path) != "two" || filepath.Base(budgeted[2].Path) != "three" {
+		t.Fatalf("ordered aggregate file-diff budget = %#v", budgeted)
+	}
+}
+
+func TestStructuredPatchFileDiffsKeepEligibleSameBasenameSibling(t *testing.T) {
+	root, err := filepath.EvalSymlinks(t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
+	diffs := fileDiffsFromStructuredPatch(".", []structuredPatchChange{
+		{
+			kind:  structuredPatchAdd,
+			to:    structuredPatchTarget{absolute: filepath.Join(root, "a.go"), relative: "a.go"},
+			after: strings.Repeat("x", maxToolPreviewBytes+1),
+		},
+		{
+			kind:  structuredPatchAdd,
+			to:    structuredPatchTarget{absolute: filepath.Join(root, "sub", "a.go"), relative: filepath.Join("sub", "a.go")},
+			after: "package sub\n",
+		},
+	})
+	if len(diffs) != 1 || diffs[0].Path != filepath.Join(root, "sub", "a.go") {
+		t.Fatalf("same-basename rich diffs = %#v", diffs)
+	}
+}
+
+func TestBoundedDiffPreservesOrdinaryUnicodeButRejectsObfuscatedSecrets(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "unicode.txt")
+	for name, content := range map[string]string{
+		"family emoji":              "family: 👨‍👩‍👧‍👦\n",
+		"emoji variation selector":  "heart: ❤️\n",
+		"combining grapheme joiner": "ordinary\u034fprose\n",
+		"nonbreaking space":         "ordinary\u00a0prose\n",
+		"byte order mark":           "\ufeffdocument\n",
+		"soft hyphen":               "co\u00adoperate\n",
+	} {
+		t.Run(name, func(t *testing.T) {
+			if _, ok := boundedFileDiff(path, "before\n", content, true, true); !ok {
+				t.Fatalf("ordinary Unicode content was rejected: %q", content)
+			}
+			if preview := boundedUnifiedDiff("unicode.txt", "before\n", content); preview == "" {
+				t.Fatal("ordinary Unicode preview was omitted")
+			}
+		})
+	}
+
+	secret := "sk-ant-api03-AAAABBBBCCCCDDDDEEEEFFFFGGGG"
+	for name, separator := range map[string]string{
+		"zero width space":          "\u200b",
+		"zero width joiner":         "\u200d",
+		"byte order mark":           "\ufeff",
+		"soft hyphen":               "\u00ad",
+		"nonbreaking space":         "\u00a0",
+		"combining grapheme joiner": "\u034f",
+		"variation selector":        "\ufe0f",
+	} {
+		t.Run("split "+name, func(t *testing.T) {
+			obfuscated := secret[:20] + separator + secret[20:]
+			if _, ok := boundedFileDiff(path, "before\n", obfuscated, true, true); ok {
+				t.Fatalf("obfuscated credential produced a rich diff: %q", obfuscated)
+			}
+			if preview := boundedUnifiedDiff("secret.txt", "before\n", obfuscated); preview != "" {
+				t.Fatalf("obfuscated credential produced preview: %q", preview)
+			}
+		})
+	}
+}
+
+func TestWriteFileMarksSuppressedObfuscatedSecretAsRedacted(t *testing.T) {
+	root := t.TempDir()
+	secret := "sk-ant-api03-AAAABBBBCCCCDDDDEEEEFFFFGGGG"
+	obfuscated := secret[:20] + "\u200b" + secret[20:]
+	result := NewScopedWriteFileTool(root, nil).Run(t.Context(), map[string]any{
+		"path": "secret.txt", "content": obfuscated,
+	})
+	if result.Status != StatusOK || len(result.ChangedFiles) != 1 || len(result.FileDiffs) != 0 || !result.Redacted {
+		t.Fatalf("obfuscated-secret result = status=%s changed=%#v diffs=%#v redacted=%t", result.Status, result.ChangedFiles, result.FileDiffs, result.Redacted)
+	}
+}

internal/tools/edit_file.go

@@ -80,6 +80,10 @@ func (tool editFileTool) RunWithOptions(ctx context.Context, args map[string]any
 		}
 	}
 	content := string(contentBytes)
+	priorInfo, err := os.Stat(absolutePath)
+	if err != nil {
+		return errorResult("Error reading " + relativePath + ": " + err.Error())
+	}
 	occurrences := strings.Count(content, oldString)
 
 	// CRLF fallback: read_file normalizes \r\n → \n before presenting content to
@@ -153,19 +157,25 @@ func (tool editFileTool) RunWithOptions(ctx context.Context, args map[string]any
 	if err := recheckScopedWriteTarget(tool.workspaceRoot, tool.scope, requestedPath); err != nil {
 		return errorResult("Error writing " + relativePath + ": " + err.Error())
 	}
-	if err := os.WriteFile(absolutePath, []byte(updated), 0o644); err != nil {
+	if err := commitFileContents(absolutePath, priorInfo, &content, updated); err != nil {
 		return errorResult("Error writing " + relativePath + ": " + err.Error())
 	}
 	modelKnownContent := updated
 	// Optional format-on-write (ZERO_FORMAT_ON_WRITE). Must run BEFORE the
 	// FileTracker re-baseline: recording pre-format content would make the very
 	// next edit look like an external modification and trip the conflict guard.
-	formatting := maybeFormatWrittenFile(ctx, absolutePath, updated)
+	formatting := maybeFormatWrittenFileScoped(ctx, tool.workspaceRoot, tool.scope, absolutePath, updated, priorInfo.Mode().Perm())
 	updated = formatting.Content
+	finalContentKnown := formatting.ContentKnown
 	// Re-baseline to the content we just wrote so subsequent edits in this session
 	// compare against the current on-disk state, not the pre-edit version.
-	newInfo, _ := os.Stat(absolutePath)
-	if updated == modelKnownContent {
+	newInfo := formatting.Info
+	if newInfo == nil {
+		newInfo, _ = os.Stat(absolutePath)
+	}
+	if !finalContentKnown {
+		options.FileTracker.Forget(absolutePath)
+	} else if updated == modelKnownContent {
 		// OUR edit, so we know precisely which lines moved: RecordEdit carries
 		// across the reads this edit did not disturb instead of dropping them.
 		//
@@ -195,12 +205,25 @@ func (tool editFileTool) RunWithOptions(ctx context.Context, args map[string]any
 	}
 	summary := fmt.Sprintf("Successfully edited %s (replaced %d occurrence%s).", relativePath, replacedCount, suffix)
 	summary += formatting.notice(relativePath)
-	summary += inlineDiagnostics(ctx, options, absolutePath, relativePath)
+	if finalContentKnown {
+		summary += inlineDiagnostics(ctx, options, absolutePath, relativePath)
+	}
 	result := okResult(summary)
 	result.ChangedFiles = []string{relativePath}
+	if finalContentKnown {
+		if diff, ok := boundedFileDiff(absolutePath, content, updated, true, true); ok {
+			result.FileDiffs = []FileDiff{diff}
+		} else if diffTextRevealsObfuscatedSecret(content) || diffTextRevealsObfuscatedSecret(updated) {
+			result.Redacted = true
+		}
+	}
 	// Card-only preview (Display.Preview): the model's Output stays the one-line
 	// summary, so the red/green diff costs zero model tokens.
-	result.Display = Display{Summary: fmt.Sprintf("Edited %s", relativePath), Kind: "diff", Preview: boundedUnifiedDiff(relativePath, content, updated)}
+	preview := ""
+	if finalContentKnown {
+		preview = boundedUnifiedDiff(relativePath, content, updated)
+	}
+	result.Display = Display{Summary: fmt.Sprintf("Edited %s", relativePath), Kind: "diff", Preview: preview}
 	return result
 }
 

internal/tools/file_commit.go

@@ -0,0 +1,108 @@
+package tools
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+)
+
+var errFileChangedDuringWrite = errors.New("file changed on disk before the write committed")
+
+// fileWriteBeforeCommit is a deterministic test hook. Production leaves it
+// nil; tests use it to replace a path after observation but before opening the
+// object that will actually be mutated.
+var fileWriteBeforeCommit func(path string)
+
+// fileWriteStat is a deterministic test seam for proving that the opened-file
+// identity is captured before the final preimage comparison. Production uses
+// the file descriptor directly.
+var fileWriteStat = func(file *os.File) (os.FileInfo, error) { return file.Stat() }
+
+// commitFileContents binds an overwrite to the file identity and bytes that
+// the caller observed. A create uses exclusive creation. An overwrite opens the
+// observed object without truncation, verifies identity/content through that
+// handle, then truncates and writes the same handle. A path replacement before
+// or during commit therefore fails instead of publishing stale rich evidence.
+//
+// expectedInfo nil means the caller observed a missing path. expectedContent
+// may be nil for an existing but unreadable file; that path may still be
+// overwritten, but callers must omit rich before/after evidence.
+func commitFileContents(path string, expectedInfo os.FileInfo, expectedContent *string, content string) error {
+	if fileWriteBeforeCommit != nil {
+		fileWriteBeforeCommit(path)
+	}
+
+	if expectedInfo == nil {
+		file, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o644)
+		if err != nil {
+			return err
+		}
+		openedInfo, err := fileWriteStat(file)
+		if err != nil {
+			_ = file.Close()
+			return err
+		}
+		return writeAndVerifyFileIdentity(path, file, openedInfo, content, false)
+	}
+
+	flags := os.O_WRONLY
+	if expectedContent != nil {
+		flags = os.O_RDWR
+	}
+	file, err := os.OpenFile(path, flags, 0)
+	if err != nil {
+		return err
+	}
+	openedInfo, err := fileWriteStat(file)
+	if err != nil {
+		_ = file.Close()
+		return err
+	}
+	if !os.SameFile(expectedInfo, openedInfo) {
+		_ = file.Close()
+		return errFileChangedDuringWrite
+	}
+	pathInfo, err := os.Stat(path)
+	if err != nil || !os.SameFile(openedInfo, pathInfo) {
+		_ = file.Close()
+		return errFileChangedDuringWrite
+	}
+	if expectedContent != nil {
+		current, readErr := io.ReadAll(file)
+		if readErr != nil {
+			_ = file.Close()
+			return readErr
+		}
+		if string(current) != *expectedContent {
+			_ = file.Close()
+			return errFileChangedDuringWrite
+		}
+	}
+	return writeAndVerifyFileIdentity(path, file, openedInfo, content, true)
+}
+
+func writeAndVerifyFileIdentity(path string, file *os.File, openedInfo os.FileInfo, content string, truncate bool) error {
+	if truncate {
+		if err := file.Truncate(0); err != nil {
+			_ = file.Close()
+			return err
+		}
+		if _, err := file.Seek(0, io.SeekStart); err != nil {
+			_ = file.Close()
+			return err
+		}
+	}
+	if _, err := io.WriteString(file, content); err != nil {
+		_ = file.Close()
+		return err
+	}
+	if err := file.Close(); err != nil {
+		return err
+	}
+	pathInfo, err := os.Stat(path)
+	if err != nil || !os.SameFile(openedInfo, pathInfo) {
+		return fmt.Errorf("%w: path identity changed", errFileChangedDuringWrite)
+	}
+	return nil
+}

internal/tools/file_commit_test.go

@@ -0,0 +1,131 @@
+package tools
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func installFileWriteRace(t *testing.T, mutate func(string)) {
+	t.Helper()
+	prior := fileWriteBeforeCommit
+	fileWriteBeforeCommit = mutate
+	t.Cleanup(func() { fileWriteBeforeCommit = prior })
+}
+
+func installFileWriteStat(t *testing.T, stat func(*os.File) (os.FileInfo, error)) {
+	t.Helper()
+	prior := fileWriteStat
+	fileWriteStat = stat
+	t.Cleanup(func() { fileWriteStat = prior })
+}
+
+func TestWriteFileRefusesCreateAndOverwriteRaces(t *testing.T) {
+	t.Run("create", func(t *testing.T) {
+		root := t.TempDir()
+		target := filepath.Join(root, "created.txt")
+		installFileWriteRace(t, func(path string) {
+			if err := os.WriteFile(path, []byte("other writer\n"), 0o644); err != nil {
+				t.Fatal(err)
+			}
+		})
+		result := NewScopedWriteFileTool(root, nil).Run(context.Background(), map[string]any{
+			"path": "created.txt", "content": "zero\n",
+		})
+		if result.Status != StatusError {
+			t.Fatalf("raced create status = %s, want error", result.Status)
+		}
+		if got, err := os.ReadFile(target); err != nil || string(got) != "other writer\n" {
+			t.Fatalf("raced create content = %q, err=%v", got, err)
+		}
+	})
+
+	t.Run("overwrite", func(t *testing.T) {
+		root := t.TempDir()
+		target := filepath.Join(root, "existing.txt")
+		if err := os.WriteFile(target, []byte("observed\n"), 0o644); err != nil {
+			t.Fatal(err)
+		}
+		installFileWriteRace(t, func(path string) {
+			if err := os.WriteFile(path, []byte("other writer\n"), 0o644); err != nil {
+				t.Fatal(err)
+			}
+		})
+		result := NewScopedWriteFileTool(root, nil).Run(context.Background(), map[string]any{
+			"path": "existing.txt", "content": "zero\n", "overwrite": true,
+		})
+		if result.Status != StatusError || !strings.Contains(result.Output, errFileChangedDuringWrite.Error()) {
+			t.Fatalf("raced overwrite = %s: %s", result.Status, result.Output)
+		}
+		if got, err := os.ReadFile(target); err != nil || string(got) != "other writer\n" {
+			t.Fatalf("raced overwrite content = %q, err=%v", got, err)
+		}
+	})
+}
+
+func TestEditFileRefusesPreimageRace(t *testing.T) {
+	root := t.TempDir()
+	target := filepath.Join(root, "existing.txt")
+	if err := os.WriteFile(target, []byte("observed\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	installFileWriteRace(t, func(path string) {
+		if err := os.WriteFile(path, []byte("other writer\n"), 0o644); err != nil {
+			t.Fatal(err)
+		}
+	})
+	result := NewScopedEditFileTool(root, nil).Run(context.Background(), map[string]any{
+		"path": "existing.txt", "old_string": "observed", "new_string": "zero",
+	})
+	if result.Status != StatusError || !strings.Contains(result.Output, errFileChangedDuringWrite.Error()) {
+		t.Fatalf("raced edit = %s: %s", result.Status, result.Output)
+	}
+	if got, err := os.ReadFile(target); err != nil || string(got) != "other writer\n" {
+		t.Fatalf("raced edit content = %q, err=%v", got, err)
+	}
+}
+
+func TestOverwriteDoesNotStatOpenedFileAfterFinalPreimageComparison(t *testing.T) {
+	for name, run := range map[string]func(string) Result{
+		"write overwrite": func(root string) Result {
+			return NewScopedWriteFileTool(root, nil).Run(context.Background(), map[string]any{
+				"path": "existing.txt", "content": "zero\n", "overwrite": true,
+			})
+		},
+		"edit": func(root string) Result {
+			return NewScopedEditFileTool(root, nil).Run(context.Background(), map[string]any{
+				"path": "existing.txt", "old_string": "observed", "new_string": "zero",
+			})
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			root := t.TempDir()
+			target := filepath.Join(root, "existing.txt")
+			if err := os.WriteFile(target, []byte("observed\n"), 0o644); err != nil {
+				t.Fatal(err)
+			}
+
+			statCalls := 0
+			installFileWriteStat(t, func(file *os.File) (os.FileInfo, error) {
+				statCalls++
+				if statCalls == 2 {
+					// This preserves the inode, so identity-only checks cannot detect it.
+					if err := os.WriteFile(target, []byte("other writer\n"), 0o644); err != nil {
+						t.Fatal(err)
+					}
+				}
+				return file.Stat()
+			})
+
+			result := run(root)
+			if result.Status != StatusOK {
+				t.Fatalf("overwrite status = %s: %s", result.Status, result.Output)
+			}
+			if statCalls != 1 {
+				t.Fatalf("opened file was statted %d times; the final byte comparison must be followed directly by mutation", statCalls)
+			}
+		})
+	}
+}

internal/tools/format_on_write.go

@@ -3,11 +3,15 @@ package tools
 import (
 	"context"
 	"errors"
+	"fmt"
+	"io"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"strings"
 	"time"
+
+	"github.com/Gitlawb/zero/internal/sandbox"
 )
 
 // Format-on-write for the mutating file tools. When enabled, a successful
@@ -44,7 +48,9 @@ var formatOnWriteTimeout = 10 * time.Second
 // and finds out from a CI format check it cannot see, which is the thing this
 // feature exists to prevent.
 type formatOnWriteResult struct {
-	Content string
+	Content      string
+	ContentKnown bool
+	Info         os.FileInfo
 	// Formatter is the binary that was run, named in the notice so the user can
 	// tell a slow gofmt from a slow prettier.
 	Formatter string
@@ -117,14 +123,32 @@ func formatOnWriteEnabled() bool {
 	return value != "" && value != "0" && !strings.EqualFold(value, "false")
 }
 
-// maybeFormatWrittenFile runs the configured formatter for absolutePath (when
-// enabled and on PATH) and returns the file's content afterwards. Best-effort
-// throughout: any failure — no formatter, formatter error, timeout, unreadable
-// result — returns writtenContent so the caller's state matches the last write
-// it performed itself. Only the timeout is reported back, for the reason on
-// formatOnWriteResult.
+var runFormatOnWriteCommand = func(ctx context.Context, binaryPath string, arguments []string, directory string) error {
+	formatter := exec.CommandContext(ctx, binaryPath, arguments...)
+	formatter.Dir = directory
+	formatter.Stdin = strings.NewReader("")
+	return formatter.Run()
+}
+
+var readFormattedFile = readRootedFile
+
+// maybeFormatWrittenFile is the unscoped test-facing wrapper. Production
+// callers use maybeFormatWrittenFileScoped so a formatter cannot redirect the
+// final read or recovery write outside the configured write roots.
 func maybeFormatWrittenFile(ctx context.Context, absolutePath string, writtenContent string) formatOnWriteResult {
-	unformatted := formatOnWriteResult{Content: writtenContent}
+	restoreMode := os.FileMode(0o644)
+	if info, err := os.Stat(absolutePath); err == nil {
+		restoreMode = info.Mode().Perm()
+	}
+	return maybeFormatWrittenFileScoped(ctx, filepath.Dir(absolutePath), nil, absolutePath, writtenContent, restoreMode)
+}
+
+// maybeFormatWrittenFileScoped runs the configured formatter and returns only
+// content verified through a descriptor-bound root. Formatter failures restore
+// writtenContent through that same root; if restoration or the final read
+// fails, ContentKnown is false and callers omit exact diff evidence.
+func maybeFormatWrittenFileScoped(ctx context.Context, workspaceRoot string, scope PathScope, absolutePath string, writtenContent string, restoreMode os.FileMode) formatOnWriteResult {
+	unformatted := formatOnWriteResult{Content: writtenContent, ContentKnown: true}
 	if !formatOnWriteEnabled() {
 		return unformatted
 	}
@@ -136,42 +160,90 @@ func maybeFormatWrittenFile(ctx context.Context, absolutePath string, writtenCon
 	if err != nil {
 		return unformatted
 	}
+	root, relativePath, err := openFormattedFileRoot(workspaceRoot, scope, absolutePath)
+	if err != nil {
+		unformatted.ContentKnown = false
+		return unformatted
+	}
+	defer root.Close()
+
 	formatCtx, cancel := context.WithTimeout(ctx, formatOnWriteTimeout)
 	defer cancel()
 	arguments := append(append([]string(nil), command[1:]...), absolutePath)
-	formatter := exec.CommandContext(formatCtx, binaryPath, arguments...)
-	formatter.Dir = filepath.Dir(absolutePath)
-	formatter.Stdin = strings.NewReader("")
-	if err := formatter.Run(); err != nil {
+	if err := runFormatOnWriteCommand(formatCtx, binaryPath, arguments, filepath.Dir(absolutePath)); err != nil {
 		unformatted.Formatter = command[0]
-		// THE FORMATTER EDITS IN PLACE, SO A FAILED RUN CAN LEAVE THE FILE
-		// NEITHER FORMATTED NOR AS WRITTEN. Killed by the deadline or by the
-		// caller, or exiting partway through its own rewrite, the target can hold
-		// a truncation. Returning the written bytes on top of that would leave the
-		// tracker baseline and the diff preview describing a file that is not on
-		// disk, which is a worse failure than the missing formatting: the next
-		// edit compares against content the file does not have.
-		//
-		// Written back unconditionally on this path rather than only when the
-		// bytes differ. Comparing first means reading the file to find out, and a
-		// read that fails leaves the same ambiguity this exists to remove.
-		if restoreErr := os.WriteFile(absolutePath, []byte(writtenContent), 0o644); restoreErr != nil {
+		if restoreErr := restoreFormattedFile(root, relativePath, writtenContent, restoreMode); restoreErr != nil {
 			unformatted.RestoreFailed = true
+			unformatted.ContentKnown = false
+		} else if restored, info, readErr := readFormattedFile(root, relativePath); readErr != nil {
+			unformatted.ContentKnown = false
+		} else {
+			unformatted.Content = string(restored)
+			unformatted.Info = info
 		}
-		// OUR deadline, not the caller's cancellation and not the formatter's own
-		// exit status. A cancelled tool call is already being reported as
-		// cancelled, and a formatter that ran and refused the file usually means
-		// content it could not parse, which the write itself does not promise to
-		// fix. Neither is this notice's business; the restore above is, for all
-		// three.
 		if errors.Is(formatCtx.Err(), context.DeadlineExceeded) && ctx.Err() == nil {
 			unformatted.TimedOut = true
 		}
 		return unformatted
 	}
-	formatted, err := os.ReadFile(absolutePath)
+
+	formatted, info, err := readFormattedFile(root, relativePath)
 	if err != nil {
+		unformatted.ContentKnown = false
 		return unformatted
 	}
-	return formatOnWriteResult{Content: string(formatted), Formatter: command[0]}
+	return formatOnWriteResult{Content: string(formatted), ContentKnown: true, Info: info, Formatter: command[0]}
+}
+
+func restoreFormattedFile(root *os.Root, relativePath string, content string, mode os.FileMode) error {
+	file, err := root.OpenFile(relativePath, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, mode)
+	if err != nil {
+		return err
+	}
+	if _, err := io.WriteString(file, content); err != nil {
+		_ = file.Close()
+		return err
+	}
+	return file.Close()
+}
+
+// openFormattedFileRoot opens the write root before the formatter runs and
+// computes the target relative to that descriptor-bound root. Atomic in-root
+// replacement remains valid; a formatter that swaps the target to an escaping
+// symlink is rejected when readFormattedFile opens it through the root.
+func openFormattedFileRoot(workspaceRoot string, scope PathScope, absolutePath string) (*os.Root, string, error) {
+	roots, err := scopedRoots(workspaceRoot, scope)
+	if err != nil {
+		return nil, "", err
+	}
+	var firstErr error
+	for _, configuredRoot := range roots {
+		resolvedRoot, err := filepath.Abs(configuredRoot)
+		if err == nil {
+			resolvedRoot, err = filepath.EvalSymlinks(resolvedRoot)
+		}
+		if err != nil {
+			if firstErr == nil {
+				firstErr = err
+			}
+			continue
+		}
+		candidate := sandbox.NormalizePrefixForRoot(absolutePath, resolvedRoot)
+		relativePath, err := filepath.Rel(resolvedRoot, candidate)
+		if err != nil || relativePath == ".." || strings.HasPrefix(relativePath, ".."+string(filepath.Separator)) || filepath.IsAbs(relativePath) {
+			continue
+		}
+		root, err := os.OpenRoot(resolvedRoot)
+		if err != nil {
+			if firstErr == nil {
+				firstErr = err
+			}
+			continue
+		}
+		return root, relativePath, nil
+	}
+	if firstErr != nil {
+		return nil, "", firstErr
+	}
+	return nil, "", fmt.Errorf("%s must stay inside the configured write roots", absolutePath)
 }

internal/tools/format_on_write_test.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"runtime"
 	"strings"
 	"testing"
 )
@@ -98,7 +99,7 @@ func TestFormatOnWriteFormatsAndKeepsTrackerConsistent(t *testing.T) {
 func TestFormatOnWriteSkipsUnknownExtensions(t *testing.T) {
 	t.Setenv("ZERO_FORMAT_ON_WRITE", "1")
 	formatting := maybeFormatWrittenFile(context.Background(), filepath.Join(t.TempDir(), "notes.xyz"), "raw   text")
-	if formatting.Content != "raw   text" {
+	if formatting.Content != "raw   text" || !formatting.ContentKnown {
 		t.Fatalf("unknown extension must pass through: %q", formatting.Content)
 	}
 	if notice := formatting.notice("notes.xyz"); notice != "" {
@@ -115,10 +116,418 @@ func TestFormatOnWriteFormatterLookupFailure(t *testing.T) {
 		t.Fatal(err)
 	}
 	formatting := maybeFormatWrittenFile(context.Background(), targetPath, uglyContent)
-	if formatting.Content != uglyContent {
+	if formatting.Content != uglyContent || !formatting.ContentKnown {
 		t.Fatalf("missing formatter must return written content, got %q", formatting.Content)
 	}
 	if notice := formatting.notice("a.go"); notice != "" {
 		t.Fatalf("an uninstalled formatter is a standing fact, not a miss worth reporting, got %q", notice)
 	}
 }
+
+func TestFormatOnWriteReadsMutatedFileAfterFormatterFailure(t *testing.T) {
+	requireGofmt(t)
+	t.Setenv("ZERO_FORMAT_ON_WRITE", "1")
+	targetPath := filepath.Join(t.TempDir(), "a.go")
+	if err := os.WriteFile(targetPath, []byte("requested"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	priorRunner := runFormatOnWriteCommand
+	runFormatOnWriteCommand = func(_ context.Context, _ string, _ []string, _ string) error {
+		if err := os.WriteFile(targetPath, []byte("formatter-mutated"), 0o644); err != nil {
+			t.Fatal(err)
+		}
+		return exec.ErrNotFound
+	}
+	t.Cleanup(func() { runFormatOnWriteCommand = priorRunner })
+
+	formatting := maybeFormatWrittenFile(context.Background(), targetPath, "requested")
+	if !formatting.ContentKnown || formatting.Content != "requested" {
+		t.Fatalf("formatter failure content = %q, known=%t", formatting.Content, formatting.ContentKnown)
+	}
+}
+
+func TestFormatOnWriteReportsWhenFormatterFailureCannotBeRestored(t *testing.T) {
+	requireGofmt(t)
+	t.Setenv("ZERO_FORMAT_ON_WRITE", "1")
+	targetPath := filepath.Join(t.TempDir(), "a.go")
+	if err := os.WriteFile(targetPath, []byte("requested"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	priorRunner := runFormatOnWriteCommand
+	runFormatOnWriteCommand = func(_ context.Context, _ string, _ []string, _ string) error {
+		if err := os.Remove(targetPath); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.Mkdir(targetPath, 0o755); err != nil {
+			t.Fatal(err)
+		}
+		return exec.ErrNotFound
+	}
+	t.Cleanup(func() { runFormatOnWriteCommand = priorRunner })
+
+	formatting := maybeFormatWrittenFile(context.Background(), targetPath, "requested")
+	if !formatting.RestoreFailed {
+		t.Fatal("failed recovery was not reported")
+	}
+	if formatting.ContentKnown {
+		t.Fatalf("failed recovery reported known content %q", formatting.Content)
+	}
+	if notice := formatting.notice("a.go"); !strings.Contains(notice, "WARNING: a.go may not hold what was written") {
+		t.Fatalf("failed recovery notice = %q", notice)
+	}
+}
+
+func TestWriteFileRecreatesFormatterDeletedTargetWithOriginalMode(t *testing.T) {
+	requireGofmt(t)
+	t.Setenv("ZERO_FORMAT_ON_WRITE", "1")
+	for _, tc := range []struct {
+		name      string
+		existing  bool
+		wantMode  os.FileMode
+		overwrite bool
+	}{
+		{name: "create", wantMode: 0o644},
+		{name: "overwrite", existing: true, wantMode: 0o751, overwrite: true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			root := t.TempDir()
+			targetPath := filepath.Join(root, "a.go")
+			if tc.existing {
+				if err := os.WriteFile(targetPath, []byte("before\n"), tc.wantMode); err != nil {
+					t.Fatal(err)
+				}
+			}
+			priorRunner := runFormatOnWriteCommand
+			runFormatOnWriteCommand = func(_ context.Context, _ string, _ []string, _ string) error {
+				if err := os.Remove(targetPath); err != nil {
+					t.Fatal(err)
+				}
+				return exec.ErrNotFound
+			}
+			t.Cleanup(func() { runFormatOnWriteCommand = priorRunner })
+
+			result := NewScopedWriteFileTool(root, nil).Run(context.Background(), map[string]any{
+				"path": "a.go", "content": "requested\n", "overwrite": tc.overwrite,
+			})
+			if result.Status != StatusOK {
+				t.Fatalf("write status = %s: %s", result.Status, result.Output)
+			}
+			content, err := os.ReadFile(targetPath)
+			if err != nil || string(content) != "requested\n" {
+				t.Fatalf("recreated content = %q, err=%v", content, err)
+			}
+			if runtime.GOOS != "windows" {
+				info, err := os.Stat(targetPath)
+				if err != nil {
+					t.Fatal(err)
+				}
+				if got := info.Mode().Perm(); got != tc.wantMode {
+					t.Fatalf("recreated mode = %o, want %o", got, tc.wantMode)
+				}
+			}
+		})
+	}
+}
+
+func TestFormatOnWriteMarksUnreadableFinalStateUnknown(t *testing.T) {
+	requireGofmt(t)
+	t.Setenv("ZERO_FORMAT_ON_WRITE", "1")
+	targetPath := filepath.Join(t.TempDir(), "a.go")
+	if err := os.WriteFile(targetPath, []byte("requested"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	priorRunner := runFormatOnWriteCommand
+	priorReader := readFormattedFile
+	runFormatOnWriteCommand = func(context.Context, string, []string, string) error { return nil }
+	readFormattedFile = func(*os.Root, string) ([]byte, os.FileInfo, error) { return nil, nil, os.ErrPermission }
+	t.Cleanup(func() {
+		runFormatOnWriteCommand = priorRunner
+		readFormattedFile = priorReader
+	})
+
+	formatting := maybeFormatWrittenFile(context.Background(), targetPath, "requested")
+	if formatting.ContentKnown || formatting.Content != "requested" {
+		t.Fatalf("unreadable formatter result = %q, known=%t", formatting.Content, formatting.ContentKnown)
+	}
+}
+
+func TestWriteFileUsesVerifiedBytesAfterFormatterFailure(t *testing.T) {
+	requireGofmt(t)
+	t.Setenv("ZERO_FORMAT_ON_WRITE", "1")
+	root := t.TempDir()
+	targetPath := filepath.Join(root, "a.go")
+	priorRunner := runFormatOnWriteCommand
+	runFormatOnWriteCommand = func(_ context.Context, _ string, _ []string, _ string) error {
+		if err := os.WriteFile(targetPath, []byte("formatter-mutated\n"), 0o644); err != nil {
+			t.Fatal(err)
+		}
+		return exec.ErrNotFound
+	}
+	t.Cleanup(func() { runFormatOnWriteCommand = priorRunner })
+
+	result := NewScopedWriteFileTool(root, nil).Run(context.Background(), map[string]any{
+		"path": "a.go", "content": "requested\n",
+	})
+	if result.Status != StatusOK {
+		t.Fatalf("write status = %s: %s", result.Status, result.Output)
+	}
+	if got := result.FileDiffs; len(got) != 1 || got[0].NewText != "requested\n" {
+		t.Fatalf("formatter-failure FileDiff = %#v", got)
+	}
+}
+
+func TestEditFileUsesVerifiedBytesAfterFormatterFailure(t *testing.T) {
+	requireGofmt(t)
+	t.Setenv("ZERO_FORMAT_ON_WRITE", "1")
+	root := t.TempDir()
+	targetPath := filepath.Join(root, "a.go")
+	if err := os.WriteFile(targetPath, []byte("before\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	priorRunner := runFormatOnWriteCommand
+	runFormatOnWriteCommand = func(_ context.Context, _ string, _ []string, _ string) error {
+		if err := os.WriteFile(targetPath, []byte("formatter-mutated\n"), 0o644); err != nil {
+			t.Fatal(err)
+		}
+		return exec.ErrNotFound
+	}
+	t.Cleanup(func() { runFormatOnWriteCommand = priorRunner })
+
+	result := NewScopedEditFileTool(root, nil).Run(context.Background(), map[string]any{
+		"path": "a.go", "old_string": "before", "new_string": "requested",
+	})
+	if result.Status != StatusOK {
+		t.Fatalf("edit status = %s: %s", result.Status, result.Output)
+	}
+	if got := result.FileDiffs; len(got) != 1 || got[0].OldText != "before\n" || got[0].NewText != "requested\n" {
+		t.Fatalf("formatter-failure edit FileDiff = %#v", got)
+	}
+}
+
+func TestWriteFileOmitsRichDiffWhenFormatterFinalReadFails(t *testing.T) {
+	requireGofmt(t)
+	t.Setenv("ZERO_FORMAT_ON_WRITE", "1")
+	root := t.TempDir()
+	priorRunner := runFormatOnWriteCommand
+	priorReader := readFormattedFile
+	runFormatOnWriteCommand = func(context.Context, string, []string, string) error { return nil }
+	readFormattedFile = func(*os.Root, string) ([]byte, os.FileInfo, error) { return nil, nil, os.ErrPermission }
+	t.Cleanup(func() {
+		runFormatOnWriteCommand = priorRunner
+		readFormattedFile = priorReader
+	})
+
+	result := NewScopedWriteFileTool(root, nil).Run(context.Background(), map[string]any{
+		"path": "a.go", "content": "requested\n",
+	})
+	if result.Status != StatusOK || len(result.ChangedFiles) != 1 || len(result.FileDiffs) != 0 {
+		t.Fatalf("unverified formatter result = status=%s changed=%#v diffs=%#v", result.Status, result.ChangedFiles, result.FileDiffs)
+	}
+	if result.Display.Preview != "" {
+		t.Fatalf("unverified formatter result exposed stale preview: %q", result.Display.Preview)
+	}
+}
+
+func TestEditFileOmitsPreviewWhenFormatterFinalReadFails(t *testing.T) {
+	requireGofmt(t)
+	t.Setenv("ZERO_FORMAT_ON_WRITE", "1")
+	root := t.TempDir()
+	targetPath := filepath.Join(root, "a.go")
+	if err := os.WriteFile(targetPath, []byte("before\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	priorRunner := runFormatOnWriteCommand
+	priorReader := readFormattedFile
+	runFormatOnWriteCommand = func(context.Context, string, []string, string) error { return nil }
+	readFormattedFile = func(*os.Root, string) ([]byte, os.FileInfo, error) { return nil, nil, os.ErrPermission }
+	t.Cleanup(func() {
+		runFormatOnWriteCommand = priorRunner
+		readFormattedFile = priorReader
+	})
+
+	result := NewScopedEditFileTool(root, nil).Run(context.Background(), map[string]any{
+		"path": "a.go", "old_string": "before", "new_string": "requested",
+	})
+	if result.Status != StatusOK || len(result.ChangedFiles) != 1 || len(result.FileDiffs) != 0 {
+		t.Fatalf("unverified formatter result = status=%s changed=%#v diffs=%#v", result.Status, result.ChangedFiles, result.FileDiffs)
+	}
+	if result.Display.Preview != "" {
+		t.Fatalf("unverified formatter result exposed stale preview: %q", result.Display.Preview)
+	}
+}
+
+func TestWriteFileOmitsRichEvidenceWhenFormatterReplacesTargetWithOutOfRootSymlink(t *testing.T) {
+	requireGofmt(t)
+	t.Setenv("ZERO_FORMAT_ON_WRITE", "1")
+	root := t.TempDir()
+	targetPath := filepath.Join(root, "a.go")
+	resolvedRoot, err := filepath.EvalSymlinks(root)
+	if err != nil {
+		t.Fatal(err)
+	}
+	trackedPath := filepath.Join(resolvedRoot, "a.go")
+	outsidePath := filepath.Join(t.TempDir(), "outside.go")
+	outsideContent := "package external\n\nconst Secret = \"outside\"\n"
+	if err := os.WriteFile(outsidePath, []byte(outsideContent), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	priorRunner := runFormatOnWriteCommand
+	runFormatOnWriteCommand = func(context.Context, string, []string, string) error {
+		if err := os.Remove(targetPath); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.Symlink(outsidePath, targetPath); err != nil {
+			t.Skipf("symlinks unavailable: %v", err)
+		}
+		return nil
+	}
+	t.Cleanup(func() { runFormatOnWriteCommand = priorRunner })
+	tracker := NewFileTracker()
+
+	diagnosticsCalled := false
+	result := NewScopedWriteFileTool(root, nil).(optionsAwareTool).RunWithOptions(context.Background(), map[string]any{
+		"path": "a.go", "content": "package requested\n",
+	}, RunOptions{FileTracker: tracker, Diagnostics: func(context.Context, string) string {
+		diagnosticsCalled = true
+		return "must not run"
+	}})
+	if result.Status != StatusOK || len(result.ChangedFiles) != 1 || len(result.FileDiffs) != 0 || result.Display.Preview != "" {
+		t.Fatalf("out-of-root formatter result = status=%s changed=%#v diffs=%#v preview=%q output=%q", result.Status, result.ChangedFiles, result.FileDiffs, result.Display.Preview, result.Output)
+	}
+	if diagnosticsCalled {
+		t.Fatal("diagnostics must not inspect an unverified formatter target")
+	}
+	if _, tracked := tracker.Version(trackedPath); tracked {
+		t.Fatal("out-of-root formatter target must not be recorded in the tracker")
+	}
+}
+
+func TestEditFileOmitsRichEvidenceWhenFormatterReplacesTargetWithOutOfRootSymlink(t *testing.T) {
+	requireGofmt(t)
+	t.Setenv("ZERO_FORMAT_ON_WRITE", "1")
+	root := t.TempDir()
+	targetPath := filepath.Join(root, "a.go")
+	resolvedRoot, err := filepath.EvalSymlinks(root)
+	if err != nil {
+		t.Fatal(err)
+	}
+	trackedPath := filepath.Join(resolvedRoot, "a.go")
+	if err := os.WriteFile(targetPath, []byte("package before\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	outsidePath := filepath.Join(t.TempDir(), "outside.go")
+	outsideContent := "package external\n\nconst Secret = \"outside\"\n"
+	if err := os.WriteFile(outsidePath, []byte(outsideContent), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	priorRunner := runFormatOnWriteCommand
+	runFormatOnWriteCommand = func(context.Context, string, []string, string) error {
+		if err := os.Remove(targetPath); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.Symlink(outsidePath, targetPath); err != nil {
+			t.Skipf("symlinks unavailable: %v", err)
+		}
+		return nil
+	}
+	t.Cleanup(func() { runFormatOnWriteCommand = priorRunner })
+	tracker := NewFileTracker()
+	read := NewScopedReadFileTool(root, nil).(optionsAwareTool).RunWithOptions(context.Background(), map[string]any{
+		"path": "a.go",
+	}, RunOptions{FileTracker: tracker})
+	if read.Status != StatusOK {
+		t.Fatalf("read before edit failed: %s", read.Output)
+	}
+
+	diagnosticsCalled := false
+	result := NewScopedEditFileTool(root, nil).(optionsAwareTool).RunWithOptions(context.Background(), map[string]any{
+		"path": "a.go", "old_string": "before", "new_string": "requested",
+	}, RunOptions{FileTracker: tracker, Diagnostics: func(context.Context, string) string {
+		diagnosticsCalled = true
+		return "must not run"
+	}})
+	if result.Status != StatusOK || len(result.ChangedFiles) != 1 || len(result.FileDiffs) != 0 || result.Display.Preview != "" {
+		t.Fatalf("out-of-root formatter result = status=%s changed=%#v diffs=%#v preview=%q output=%q", result.Status, result.ChangedFiles, result.FileDiffs, result.Display.Preview, result.Output)
+	}
+	if diagnosticsCalled {
+		t.Fatal("diagnostics must not inspect an unverified formatter target")
+	}
+	if _, tracked := tracker.Version(trackedPath); tracked {
+		t.Fatal("out-of-root formatter target must not be recorded in the tracker")
+	}
+}
+
+func TestWriteFileAcceptsInRootAtomicFormatterReplacement(t *testing.T) {
+	requireGofmt(t)
+	t.Setenv("ZERO_FORMAT_ON_WRITE", "1")
+	root := t.TempDir()
+	targetPath := filepath.Join(root, "a.go")
+	formatted := "package formatted\n"
+	priorRunner := runFormatOnWriteCommand
+	runFormatOnWriteCommand = func(context.Context, string, []string, string) error {
+		tempPath := filepath.Join(root, "formatter.tmp")
+		if err := os.WriteFile(tempPath, []byte(formatted), 0o644); err != nil {
+			t.Fatal(err)
+		}
+		return os.Rename(tempPath, targetPath)
+	}
+	t.Cleanup(func() { runFormatOnWriteCommand = priorRunner })
+	tracker := NewFileTracker()
+
+	result := NewScopedWriteFileTool(root, nil).(optionsAwareTool).RunWithOptions(context.Background(), map[string]any{
+		"path": "a.go", "content": "package requested\n",
+	}, RunOptions{FileTracker: tracker})
+	if result.Status != StatusOK || len(result.FileDiffs) != 1 || result.FileDiffs[0].NewText != formatted {
+		t.Fatalf("atomic formatter write = status=%s diffs=%#v output=%q", result.Status, result.FileDiffs, result.Output)
+	}
+	resolvedRoot, err := filepath.EvalSymlinks(root)
+	if err != nil {
+		t.Fatal(err)
+	}
+	version, tracked := tracker.Version(filepath.Join(resolvedRoot, "a.go"))
+	if !tracked || version.Hash != HashContent([]byte(formatted)) {
+		t.Fatalf("atomic formatter tracker = %#v, tracked=%t", version, tracked)
+	}
+}
+
+func TestEditFileAcceptsInRootAtomicFormatterReplacement(t *testing.T) {
+	requireGofmt(t)
+	t.Setenv("ZERO_FORMAT_ON_WRITE", "1")
+	root := t.TempDir()
+	targetPath := filepath.Join(root, "a.go")
+	if err := os.WriteFile(targetPath, []byte("package before\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	formatted := "package formatted\n"
+	priorRunner := runFormatOnWriteCommand
+	runFormatOnWriteCommand = func(context.Context, string, []string, string) error {
+		tempPath := filepath.Join(root, "formatter.tmp")
+		if err := os.WriteFile(tempPath, []byte(formatted), 0o644); err != nil {
+			t.Fatal(err)
+		}
+		return os.Rename(tempPath, targetPath)
+	}
+	t.Cleanup(func() { runFormatOnWriteCommand = priorRunner })
+	tracker := NewFileTracker()
+	read := NewScopedReadFileTool(root, nil).(optionsAwareTool).RunWithOptions(context.Background(), map[string]any{
+		"path": "a.go",
+	}, RunOptions{FileTracker: tracker})
+	if read.Status != StatusOK {
+		t.Fatalf("read before edit failed: %s", read.Output)
+	}
+
+	result := NewScopedEditFileTool(root, nil).(optionsAwareTool).RunWithOptions(context.Background(), map[string]any{
+		"path": "a.go", "old_string": "before", "new_string": "requested",
+	}, RunOptions{FileTracker: tracker})
+	if result.Status != StatusOK || len(result.FileDiffs) != 1 || result.FileDiffs[0].NewText != formatted {
+		t.Fatalf("atomic formatter edit = status=%s diffs=%#v output=%q", result.Status, result.FileDiffs, result.Output)
+	}
+	resolvedRoot, err := filepath.EvalSymlinks(root)
+	if err != nil {
+		t.Fatal(err)
+	}
+	version, tracked := tracker.Version(filepath.Join(resolvedRoot, "a.go"))
+	if !tracked || version.Hash != HashContent([]byte(formatted)) {
+		t.Fatalf("atomic formatter tracker = %#v, tracked=%t", version, tracked)
+	}
+}

internal/tools/registry.go

@@ -343,6 +343,33 @@ func scrubResultSecrets(res Result) Result {
 		res.Display.Preview = scrubbed
 		res.Redacted = true
 	}
+	fileDiffs := make([]FileDiff, 0, len(res.FileDiffs))
+	for _, diff := range res.FileDiffs {
+		// Never normalize control bytes in a diff: normalizing after redaction can
+		// reassemble a split credential. Decline unsafe rich content entirely and
+		// leave ChangedFiles as the safe fallback.
+		if unsafeDiffText(diff.OldText) || unsafeDiffText(diff.NewText) {
+			res.Redacted = true
+			continue
+		}
+		if scrubbed := redaction.RedactString(diff.OldText, redaction.Options{}); scrubbed != diff.OldText {
+			diff.OldText = scrubbed
+			res.Redacted = true
+		}
+		if scrubbed := redaction.RedactString(diff.NewText, redaction.Options{}); scrubbed != diff.NewText {
+			diff.NewText = scrubbed
+			res.Redacted = true
+		}
+		// Redaction can collapse two distinct credentials to the same token. At
+		// this final outbound boundary, retain rich evidence only when the
+		// transformed sides still describe a real transition; ChangedFiles
+		// remains the safe path-only fallback.
+		if diff.OldExists == diff.NewExists && diff.OldText == diff.NewText {
+			continue
+		}
+		fileDiffs = append(fileDiffs, diff)
+	}
+	res.FileDiffs = fileDiffs
 	// Meta values carry model-controlled strings (e.g. glob pattern, bash cwd) and
 	// are forwarded into the transcript, so they are part of the boundary too.
 	for key, value := range res.Meta {
@@ -354,6 +381,13 @@ func scrubResultSecrets(res Result) Result {
 	return res
 }
 
+// ScrubResultSecrets applies the registry's transcript boundary to a result
+// that was produced before Registry.RunWithOptions could own it, such as a
+// local pre-permission rejection in the agent loop.
+func ScrubResultSecrets(res Result) Result {
+	return scrubResultSecrets(res)
+}
+
 func CoreReadOnlyToolsScoped(workspaceRoot string, scope PathScope) []Tool {
 	return []Tool{
 		NewScopedReadMinifiedFileTool(workspaceRoot, scope),

internal/tools/registry_test.go

@@ -445,13 +445,120 @@ func (t denyTool) Run(context.Context, map[string]any) Result { return Result{St
 // must be scrubbed too, not just the tool-execution paths.
 func TestScrubResultSecretsRedactsPreview(t *testing.T) {
 	secret := "ghp_ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
-	res := scrubResultSecrets(Result{Display: Display{Preview: "+++ b/x\n+token := \"" + secret + "\""}})
+	res := scrubResultSecrets(Result{
+		Display:   Display{Preview: "+++ b/x\n+token := \"" + secret + "\""},
+		FileDiffs: []FileDiff{{Path: filepath.Join(t.TempDir(), "x"), OldExists: true, NewExists: true, OldText: "before " + secret, NewText: "after " + secret}},
+	})
 	if strings.Contains(res.Display.Preview, secret) {
 		t.Errorf("Display.Preview (the card-only code preview) must be redacted, leaked: %q", res.Display.Preview)
 	}
 	if !res.Redacted {
 		t.Error("scrubbing a secret from the preview should set Redacted")
 	}
+	if len(res.FileDiffs) != 1 || strings.Contains(res.FileDiffs[0].OldText, secret) || strings.Contains(res.FileDiffs[0].NewText, secret) {
+		t.Errorf("FileDiff must be redacted: %#v", res.FileDiffs)
+	}
+}
+
+func TestScrubResultSecretsDropsControlSplitFileDiff(t *testing.T) {
+	secret := "sk-proj-abcdefghijklmnopqrstuvwxyz"
+	res := scrubResultSecrets(Result{FileDiffs: []FileDiff{{
+		Path:      filepath.Join(t.TempDir(), "x"),
+		OldExists: true,
+		NewExists: true,
+		OldText:   "token=" + secret[:12] + "\x00" + secret[12:],
+		NewText:   "safe",
+	}}})
+	if len(res.FileDiffs) != 0 || !res.Redacted {
+		t.Fatalf("unsafe FileDiff = %#v, redacted = %t", res.FileDiffs, res.Redacted)
+	}
+}
+
+func TestScrubResultSecretsDropsDefaultIgnorableSplitFileDiffOnEitherSide(t *testing.T) {
+	secret := "sk-ant-api03-AAAABBBBCCCCDDDDEEEEFFFFGGGG"
+	for name, separator := range map[string]string{
+		"combining grapheme joiner": "\u034f",
+		"variation selector":        "\ufe0f",
+	} {
+		for _, side := range []string{"old", "new"} {
+			t.Run(name+" "+side, func(t *testing.T) {
+				obfuscated := secret[:20] + separator + secret[20:]
+				diff := FileDiff{
+					Path: filepath.Join(t.TempDir(), "x"), OldExists: true, NewExists: true,
+					OldText: "safe old", NewText: "safe new",
+				}
+				if side == "old" {
+					diff.OldText = obfuscated
+				} else {
+					diff.NewText = obfuscated
+				}
+				res := scrubResultSecrets(Result{FileDiffs: []FileDiff{diff}})
+				if len(res.FileDiffs) != 0 || !res.Redacted {
+					t.Fatalf("unsafe FileDiff = %#v, redacted = %t", res.FileDiffs, res.Redacted)
+				}
+			})
+		}
+	}
+}
+
+func TestScrubResultSecretsDoesNotMutateCallerFileDiffSlice(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "x")
+	secret := "ghp_ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
+	retainedOld := "before token=" + secret
+	retainedNew := "after token=" + secret
+	original := []FileDiff{
+		{Path: path, OldExists: true, NewExists: true, OldText: "token=sk-proj-abc\x00def", NewText: "unsafe"},
+		{Path: path, OldExists: true, NewExists: true, OldText: retainedOld, NewText: retainedNew},
+	}
+	result := scrubResultSecrets(Result{FileDiffs: original})
+	if len(result.FileDiffs) != 1 || strings.Contains(result.FileDiffs[0].OldText, secret) || strings.Contains(result.FileDiffs[0].NewText, secret) {
+		t.Fatalf("filtered FileDiffs = %#v", result.FileDiffs)
+	}
+	if original[0].NewText != "unsafe" || original[1].OldText != retainedOld || original[1].NewText != retainedNew {
+		t.Fatalf("caller slice was mutated: %#v", original)
+	}
+}
+
+func TestScrubResultSecretsDropsSemanticallyUnchangedRedactedDiff(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "credentials.txt")
+	oldSecret := "ghp_ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
+	newSecret := "ghp_9876543210ZYXWVUTSRQPONMLKJIHGFEDCBA"
+	result := scrubResultSecrets(Result{
+		ChangedFiles: []string{"credentials.txt"},
+		FileDiffs: []FileDiff{{
+			Path: path, OldExists: true, NewExists: true,
+			OldText: "token=" + oldSecret, NewText: "token=" + newSecret,
+		}},
+	})
+	if len(result.FileDiffs) != 0 {
+		t.Fatalf("semantically unchanged redacted diff = %#v", result.FileDiffs)
+	}
+	if got, want := result.ChangedFiles, []string{"credentials.txt"}; !slices.Equal(got, want) {
+		t.Fatalf("ChangedFiles = %#v, want %#v", got, want)
+	}
+	if !result.Redacted {
+		t.Fatal("credential rotation must set Redacted")
+	}
+}
+
+func TestScrubResultSecretsKeepsRealTransitionAroundRedactedSecrets(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "credentials.txt")
+	oldSecret := "ghp_ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
+	newSecret := "ghp_9876543210ZYXWVUTSRQPONMLKJIHGFEDCBA"
+	result := scrubResultSecrets(Result{FileDiffs: []FileDiff{{
+		Path: path, OldExists: true, NewExists: true,
+		OldText: "environment=staging token=" + oldSecret,
+		NewText: "environment=production token=" + newSecret,
+	}}})
+	if len(result.FileDiffs) != 1 {
+		t.Fatalf("redacted real transition = %#v", result.FileDiffs)
+	}
+	if result.FileDiffs[0].OldText == result.FileDiffs[0].NewText {
+		t.Fatalf("redacted transition became unchanged: %#v", result.FileDiffs[0])
+	}
+	if strings.Contains(result.FileDiffs[0].OldText, oldSecret) || strings.Contains(result.FileDiffs[0].NewText, newSecret) {
+		t.Fatalf("redacted transition leaked a secret: %#v", result.FileDiffs[0])
+	}
 }
 
 func TestRunWithOptionsScrubsSecretsOnDenialPaths(t *testing.T) {

internal/tools/rooted_file.go

@@ -0,0 +1,43 @@
+package tools
+
+import (
+	"fmt"
+	"io"
+	"os"
+)
+
+// readRootedFile returns bytes and identity from the same opened object, and
+// verifies that the rooted path still names that object after the read. Root.Open
+// binds symlink containment to use rather than relying on a pathname pre-check.
+func readRootedFile(root *os.Root, relativePath string) ([]byte, os.FileInfo, error) {
+	file, err := root.Open(relativePath)
+	if err != nil {
+		return nil, nil, err
+	}
+	closed := false
+	defer func() {
+		if !closed {
+			_ = file.Close()
+		}
+	}()
+	openedInfo, err := file.Stat()
+	if err != nil {
+		return nil, nil, err
+	}
+	if !openedInfo.Mode().IsRegular() {
+		return nil, nil, fmt.Errorf("%s is not a regular file", relativePath)
+	}
+	content, err := io.ReadAll(file)
+	if err != nil {
+		return nil, nil, err
+	}
+	pathInfo, err := root.Stat(relativePath)
+	if err != nil || !os.SameFile(openedInfo, pathInfo) {
+		return nil, nil, fmt.Errorf("%w: path identity changed", errFileChangedDuringWrite)
+	}
+	if err := file.Close(); err != nil {
+		return nil, nil, err
+	}
+	closed = true
+	return content, openedInfo, nil
+}

internal/tools/structured_patch.go

@@ -86,12 +86,13 @@ type structuredPatchTarget struct {
 }
 
 type structuredPatchChange struct {
-	kind   structuredPatchKind
-	from   structuredPatchTarget
-	to     structuredPatchTarget
-	before string
-	after  string
-	mode   os.FileMode
+	kind       structuredPatchKind
+	from       structuredPatchTarget
+	to         structuredPatchTarget
+	before     string
+	after      string
+	mode       os.FileMode
+	beforeInfo os.FileInfo
 }
 
 // unifiedHunkRangePattern recognises a unified-diff range header ("-12,4 +12,6",
@@ -156,8 +157,14 @@ func applyPatchOperations(applyRoot, relativeRoot string, operations []structure
 			}
 		}
 	}
-	if err := applyStructuredPatchChanges(workspace, changes, options.FileTracker); err != nil {
-		return errorResult("Error applying patch: " + err.Error())
+	applyOutcome, err := applyStructuredPatchChanges(workspace, relativeRoot, changes, options.FileTracker)
+	if err != nil {
+		result := errorResult("Error applying patch: " + err.Error())
+		result.ChangedFiles = changedFilesFromStructuredPatch(relativeRoot, applyOutcome.committed)
+		result.FileDiffs = fileDiffsFromStructuredPatch(relativeRoot, applyOutcome.committed)
+		result.Redacted = structuredPatchContainsObfuscatedSecret(applyOutcome.committed)
+		result.Display = Display{Summary: result.Output, Kind: "diff", Preview: structuredPatchPreview(applyOutcome.committed)}
+		return result
 	}
 
 	for _, change := range changes {
@@ -183,10 +190,78 @@ func applyPatchOperations(applyRoot, relativeRoot string, operations []structure
 	}
 	result := okResult(summary)
 	result.ChangedFiles = changedFilesFromStructuredPatch(relativeRoot, changes)
+	result.FileDiffs = fileDiffsFromStructuredPatch(relativeRoot, changes)
+	result.Redacted = structuredPatchContainsObfuscatedSecret(changes)
 	result.Display = Display{Summary: summary, Kind: "diff", Preview: structuredPatchPreview(changes)}
 	return result
 }
 
+func structuredPatchContainsObfuscatedSecret(changes []structuredPatchChange) bool {
+	for _, change := range changes {
+		if diffTextRevealsObfuscatedSecret(change.before) || diffTextRevealsObfuscatedSecret(change.after) {
+			return true
+		}
+	}
+	return false
+}
+
+func fileDiffsFromStructuredPatch(_ string, changes []structuredPatchChange) []FileDiff {
+	const maxToolResultFileDiffs = 64
+	diffs := make([]FileDiff, 0, len(changes)*2)
+	usedBytes := 0
+	appendGroup := func(group ...FileDiff) bool {
+		if len(group) == 0 || len(diffs)+len(group) > maxToolResultFileDiffs {
+			return false
+		}
+		groupBytes := 0
+		for _, diff := range group {
+			groupBytes += len(diff.OldText) + len(diff.NewText)
+		}
+		if usedBytes+groupBytes > maxToolResultFileDiffBytes {
+			return false
+		}
+		diffs = append(diffs, group...)
+		usedBytes += groupBytes
+		return true
+	}
+	makeDiff := func(path, before, after string, oldExists, newExists bool) (FileDiff, bool) {
+		return boundedFileDiff(path, before, after, oldExists, newExists)
+	}
+	for _, change := range changes {
+		var group []FileDiff
+		switch {
+		case change.kind == structuredPatchDelete:
+			if diff, ok := makeDiff(change.from.absolute, change.before, "", true, false); ok {
+				group = append(group, diff)
+			}
+		case change.kind == structuredPatchAdd:
+			if diff, ok := makeDiff(change.to.absolute, "", change.after, false, true); ok {
+				group = append(group, diff)
+			}
+		case change.kind == structuredPatchCopy && change.from.absolute != change.to.absolute:
+			// A copy leaves its source unchanged; the destination is a create.
+			if diff, ok := makeDiff(change.to.absolute, "", change.after, false, true); ok {
+				group = append(group, diff)
+			}
+		case change.kind == structuredPatchUpdate && change.from.absolute != change.to.absolute:
+			// A move is two filesystem changes, not a destination overwrite.
+			from, fromOK := makeDiff(change.from.absolute, change.before, "", true, false)
+			to, toOK := makeDiff(change.to.absolute, "", change.after, false, true)
+			if fromOK && toOK {
+				group = append(group, from, to)
+			}
+		default:
+			if diff, ok := makeDiff(change.to.absolute, change.before, change.after, true, true); ok {
+				group = append(group, diff)
+			}
+		}
+		if len(group) > 0 && !appendGroup(group...) {
+			break
+		}
+	}
+	return diffs
+}
+
 func parseStructuredPatch(patch string) ([]structuredPatchOperation, error) {
 	normalized := strings.TrimSpace(strings.TrimPrefix(strings.ReplaceAll(patch, "\r\n", "\n"), "\ufeff"))
 	if normalized == "" {
@@ -394,15 +469,12 @@ func planStructuredPatch(root *os.Root, operations []structuredPatchOperation, t
 			}
 			change.after = operation.contents
 		case structuredPatchDelete, structuredPatchUpdate, structuredPatchCopy:
-			info, err := root.Stat(from.relative)
-			if err != nil {
-				return nil, fmt.Errorf("stating %s: %w", from.relative, err)
-			}
-			change.mode = info.Mode()
-			content, err := root.ReadFile(from.relative)
+			content, info, err := readRootedFile(root, from.relative)
 			if err != nil {
 				return nil, fmt.Errorf("reading %s: %w", from.relative, err)
 			}
+			change.mode = info.Mode()
+			change.beforeInfo = info
 			if err := tracker.CheckConflict(from.absolute, content); err != nil {
 				return nil, fmt.Errorf("%s", fileConflictMessage(from.relative))
 			}
@@ -672,38 +744,112 @@ func findStructuredPatchSequence(lines, wanted []string, start int, endOfFile bo
 	return -1, false
 }
 
-func applyStructuredPatchChanges(root *os.Root, changes []structuredPatchChange, tracker *FileTracker) error {
+type structuredPatchApplyOutcome struct {
+	committed       []structuredPatchChange
+	incompletePaths []string
+}
+
+type structuredPatchChangeOutcome struct {
+	completed       []structuredPatchChange
+	incompletePaths []string
+}
+
+func applyStructuredPatchChanges(root *os.Root, relativeRoot string, changes []structuredPatchChange, tracker *FileTracker) (structuredPatchApplyOutcome, error) {
 	// committed lists, in order, the paths whose change reached disk before a
 	// later change failed, so the caller (and the model) knows exactly which
 	// files now hold the patched content and which were never touched.
-	var committed []string
+	var outcome structuredPatchApplyOutcome
 	for _, change := range changes {
-		done, err := applyStructuredPatchChange(root, change)
-		if done {
-			committed = append(committed, structuredPatchChangePaths(change)...)
-		}
+		changeOutcome, err := applyStructuredPatchChange(root, change)
+		outcome.committed = append(outcome.committed, changeOutcome.completed...)
+		outcome.incompletePaths = append(outcome.incompletePaths, changeOutcome.incompletePaths...)
 		if err != nil {
 			forgetStructuredPatchFiles(tracker, changes)
-			if len(committed) > 0 {
-				return fmt.Errorf("%w; patch was partially applied — already committed: %s; the remaining files are unchanged; re-read the committed files before retrying", err, strings.Join(committed, ", "))
+			committedPaths := changedFilesFromStructuredPatch(relativeRoot, outcome.committed)
+			unverifiedPaths := appendUniqueStructuredPatchPaths(nil, relativeRoot, outcome.incompletePaths)
+			if len(committedPaths) > 0 || len(unverifiedPaths) > 0 {
+				parts := []string{"patch was partially applied"}
+				if len(committedPaths) > 0 {
+					parts = append(parts, "already committed: "+strings.Join(committedPaths, ", "))
+				}
+				if len(unverifiedPaths) > 0 {
+					parts = append(parts, "published but unverified: "+strings.Join(unverifiedPaths, ", "))
+				}
+				parts = append(parts, "the remaining files are unchanged")
+				if len(unverifiedPaths) > 0 {
+					parts = append(parts, "re-read the listed files before retrying")
+				} else {
+					parts = append(parts, "re-read the committed files before retrying")
+				}
+				return outcome, fmt.Errorf("%w; %s", err, strings.Join(parts, "; "))
 			}
-			return err
+			return outcome, err
 		}
 	}
-	return nil
+	return outcome, nil
 }
 
-// structuredPatchChangePaths names the workspace-relative paths a committed
-// change touched: the destination, plus the source of a move or copy.
-func structuredPatchChangePaths(change structuredPatchChange) []string {
-	if change.kind == structuredPatchDelete {
-		return []string{change.from.relative}
+// completedStructuredPatchEffect turns a partially completed compound change
+// into the exact filesystem sub-effect that is still verifiable after the
+// error. In particular, a failed move may have published its destination while
+// leaving the source in place; that is a destination creation, not a move.
+func completedStructuredPatchEffect(root *os.Root, change structuredPatchChange) (structuredPatchChange, bool) {
+	if change.to.relative == "" {
+		return structuredPatchChange{}, false
 	}
-	paths := []string{change.to.relative}
-	if change.from.absolute != change.to.absolute && change.from.relative != "" {
-		paths = append([]string{change.from.relative}, paths...)
+	content, _, err := readRootedFile(root, change.to.relative)
+	if err != nil || string(content) != change.after {
+		return structuredPatchChange{}, false
 	}
-	return paths
+	switch change.kind {
+	case structuredPatchAdd, structuredPatchCopy:
+		return structuredPatchChange{
+			kind:  structuredPatchAdd,
+			to:    change.to,
+			after: change.after,
+			mode:  change.mode,
+		}, true
+	case structuredPatchUpdate:
+		if change.from.absolute != change.to.absolute {
+			return structuredPatchChange{
+				kind:  structuredPatchAdd,
+				to:    change.to,
+				after: change.after,
+				mode:  change.mode,
+			}, true
+		}
+	}
+	return structuredPatchChange{}, false
+}
+
+func incompleteStructuredPatchWrite(root *os.Root, change structuredPatchChange, published bool) structuredPatchChangeOutcome {
+	if !published {
+		return structuredPatchChangeOutcome{}
+	}
+	if completed, ok := completedStructuredPatchEffect(root, change); ok {
+		return structuredPatchChangeOutcome{completed: []structuredPatchChange{completed}}
+	}
+	if change.to.relative != "" {
+		return structuredPatchChangeOutcome{incompletePaths: []string{change.to.relative}}
+	}
+	return structuredPatchChangeOutcome{}
+}
+
+func appendUniqueStructuredPatchPaths(existing []string, relativeRoot string, paths []string) []string {
+	seen := make(map[string]bool, len(existing)+len(paths))
+	for _, path := range existing {
+		seen[path] = true
+	}
+	for _, path := range paths {
+		if relativeRoot != "" && relativeRoot != "." {
+			path = filepath.ToSlash(filepath.Join(relativeRoot, path))
+		}
+		if path != "" && !seen[path] {
+			seen[path] = true
+			existing = append(existing, path)
+		}
+	}
+	return existing
 }
 
 func forgetStructuredPatchFiles(tracker *FileTracker, changes []structuredPatchChange) {
@@ -723,7 +869,17 @@ func forgetStructuredPatchFiles(tracker *FileTracker, changes []structuredPatchC
 // deterministically; it is nil in production.
 var structuredPatchBeforeCommit func(change structuredPatchChange)
 
-func applyStructuredPatchChange(root *os.Root, change structuredPatchChange) (bool, error) {
+// structuredPatchBeforeRename runs after a same-path update has staged and
+// closed its replacement but before the final preimage recheck and rename.
+// Tests use it to reproduce a competing writer deterministically.
+var structuredPatchBeforeRename func(change structuredPatchChange)
+
+// structuredPatchRemove is a deterministic test seam for failures after a
+// move destination has been published. Production removes through the opened
+// workspace root.
+var structuredPatchRemove = func(root *os.Root, name string) error { return root.Remove(name) }
+
+func applyStructuredPatchChange(root *os.Root, change structuredPatchChange) (structuredPatchChangeOutcome, error) {
 	if structuredPatchBeforeCommit != nil {
 		structuredPatchBeforeCommit(change)
 	}
@@ -732,39 +888,63 @@ func applyStructuredPatchChange(root *os.Root, change structuredPatchChange) (bo
 	// by another process in between is refused rather than overwritten or
 	// removed.
 	if change.kind != structuredPatchAdd {
-		current, err := root.ReadFile(change.from.relative)
-		if err != nil {
-			return false, fmt.Errorf("re-reading %s before commit: %w", change.from.relative, err)
-		}
-		if string(current) != change.before {
-			return false, fmt.Errorf("%s changed on disk between planning and commit; re-read it and retry", change.from.relative)
+		if err := recheckStructuredPatchPreimage(root, change); err != nil {
+			return structuredPatchChangeOutcome{}, err
 		}
 	}
 	switch change.kind {
 	case structuredPatchDelete:
-		if err := root.Remove(change.from.relative); err != nil {
-			return false, fmt.Errorf("deleting %s: %w", change.from.relative, err)
+		if err := structuredPatchRemove(root, change.from.relative); err != nil {
+			return structuredPatchChangeOutcome{}, fmt.Errorf("deleting %s: %w", change.from.relative, err)
 		}
-		return true, nil
+		return structuredPatchChangeOutcome{completed: []structuredPatchChange{change}}, nil
 	case structuredPatchAdd, structuredPatchCopy:
-		return writeStructuredPatchFile(root, change.to, change.after, change.mode, true)
+		var beforePublish func() error
+		if change.kind == structuredPatchCopy {
+			beforePublish = structuredPatchPrePublishGuard(root, change)
+		}
+		published, err := writeStructuredPatchFile(root, change.to, change.after, change.mode, true, beforePublish)
+		if err != nil {
+			return incompleteStructuredPatchWrite(root, change, published), err
+		}
+		return structuredPatchChangeOutcome{completed: []structuredPatchChange{change}}, nil
 	case structuredPatchUpdate:
 		moving := change.from.absolute != change.to.absolute
-		committed, err := writeStructuredPatchFile(root, change.to, change.after, change.mode, moving)
+		published, err := writeStructuredPatchFile(root, change.to, change.after, change.mode, moving, structuredPatchPrePublishGuard(root, change))
 		if err != nil {
-			return committed, err
+			return incompleteStructuredPatchWrite(root, change, published), err
 		}
 		if moving {
-			if err := root.Remove(change.from.relative); err != nil {
-				return true, fmt.Errorf("removing moved source %s: %w", change.from.relative, err)
+			if err := structuredPatchRemove(root, change.from.relative); err != nil {
+				return incompleteStructuredPatchWrite(root, change, true), fmt.Errorf("removing moved source %s: %w", change.from.relative, err)
 			}
 		}
-		return true, nil
+		return structuredPatchChangeOutcome{completed: []structuredPatchChange{change}}, nil
 	}
-	return false, fmt.Errorf("unsupported structured patch operation")
+	return structuredPatchChangeOutcome{}, fmt.Errorf("unsupported structured patch operation")
 }
 
-func writeStructuredPatchFile(root *os.Root, target structuredPatchTarget, content string, mode os.FileMode, createOnly bool) (bool, error) {
+func recheckStructuredPatchPreimage(root *os.Root, change structuredPatchChange) error {
+	current, info, err := readRootedFile(root, change.from.relative)
+	if err != nil {
+		return fmt.Errorf("re-reading %s before commit: %w", change.from.relative, err)
+	}
+	if (change.beforeInfo != nil && !os.SameFile(change.beforeInfo, info)) || string(current) != change.before {
+		return fmt.Errorf("%s changed on disk between planning and commit; re-read it and retry", change.from.relative)
+	}
+	return nil
+}
+
+func structuredPatchPrePublishGuard(root *os.Root, change structuredPatchChange) func() error {
+	return func() error {
+		if change.kind == structuredPatchUpdate && change.from.absolute == change.to.absolute && structuredPatchBeforeRename != nil {
+			structuredPatchBeforeRename(change)
+		}
+		return recheckStructuredPatchPreimage(root, change)
+	}
+}
+
+func writeStructuredPatchFile(root *os.Root, target structuredPatchTarget, content string, mode os.FileMode, createOnly bool, beforePublish func() error) (bool, error) {
 	parent := filepath.Dir(target.relative)
 	if err := root.MkdirAll(parent, 0o755); err != nil {
 		return false, fmt.Errorf("creating parent directory for %s: %w", target.relative, err)
@@ -785,8 +965,13 @@ func writeStructuredPatchFile(root *os.Root, target structuredPatchTarget, conte
 	if err := temp.Close(); err != nil {
 		return false, fmt.Errorf("writing %s: %w", target.relative, err)
 	}
+	if beforePublish != nil {
+		if err := beforePublish(); err != nil {
+			return false, err
+		}
+	}
 	if createOnly {
-		return publishStructuredPatchNoReplace(root, tempName, target.relative, mode)
+		return structuredPatchPublishNoReplace(root, tempName, target.relative, mode)
 	}
 	if err := root.Rename(tempName, target.relative); err != nil {
 		return false, fmt.Errorf("writing %s: %w", target.relative, err)
@@ -798,6 +983,11 @@ func publishStructuredPatchNoReplace(root *os.Root, source, target string, mode
 	return publishStructuredPatchNoReplaceWith(root, source, target, mode, root.Link)
 }
 
+// structuredPatchPublishNoReplace is a deterministic test seam for failures
+// after a create-only target has become visible. Production uses the atomic
+// no-replace publisher above.
+var structuredPatchPublishNoReplace = publishStructuredPatchNoReplace
+
 func publishStructuredPatchNoReplaceWith(root *os.Root, source, target string, mode os.FileMode, link func(string, string) error) (bool, error) {
 	if linkErr := link(source, target); linkErr == nil {
 		cleanupErr := removeStructuredPatchTemp(root, source)
@@ -914,9 +1104,19 @@ func changedFilesFromStructuredPatch(relativeRoot string, changes []structuredPa
 	seen := make(map[string]bool)
 	var paths []string
 	for _, change := range changes {
-		targets := []structuredPatchTarget{change.to}
-		if change.from.absolute != change.to.absolute {
-			targets = append([]structuredPatchTarget{change.from}, targets...)
+		var targets []structuredPatchTarget
+		switch change.kind {
+		case structuredPatchDelete:
+			targets = []structuredPatchTarget{change.from}
+		case structuredPatchUpdate:
+			targets = []structuredPatchTarget{change.to}
+			if change.from.absolute != change.to.absolute {
+				targets = append([]structuredPatchTarget{change.from}, targets...)
+			}
+		default:
+			// Adds and copies mutate only their destination; the copy source is
+			// evidence for the operation, not a changed file.
+			targets = []structuredPatchTarget{change.to}
 		}
 		for _, target := range targets {
 			path := target.relative

internal/tools/types.go

@@ -120,6 +120,10 @@ type Result struct {
 	// entries under a granted extra write root are absolute, since
 	// workspace-relative would be ambiguous there.
 	ChangedFiles []string
+	// FileDiffs carries exact, bounded before/after text for built-in file
+	// mutations. A missing entry means the client must fall back to ChangedFiles
+	// rather than inventing a partial diff.
+	FileDiffs []FileDiff
 	// ChangeSummaries contains bounded generated-tree changes. These are shown
 	// in session evidence and the Files panel but are never treated as files to
 	// open or diagnose individually.

internal/tools/write_file.go

@@ -12,6 +12,7 @@ type writeFileTool struct {
 	baseTool
 	workspaceRoot string
 	scope         PathScope
+	readFile      func(string) ([]byte, error)
 }
 
 func NewScopedWriteFileTool(workspaceRoot string, scope PathScope) Tool {
@@ -34,6 +35,7 @@ func NewScopedWriteFileTool(workspaceRoot string, scope PathScope) Tool {
 		},
 		workspaceRoot: normalizeWorkspaceRoot(workspaceRoot),
 		scope:         scope,
+		readFile:      os.ReadFile,
 	}
 }
 
@@ -61,8 +63,10 @@ func (tool writeFileTool) RunWithOptions(ctx context.Context, args map[string]an
 	}
 
 	existed := false
-	if _, err := os.Stat(absolutePath); err == nil {
+	var priorInfo os.FileInfo
+	if info, err := os.Stat(absolutePath); err == nil {
 		existed = true
+		priorInfo = info
 		if !overwrite {
 			return errorResult("Error: " + relativePath + " already exists. Pass overwrite: true to replace it.")
 		}
@@ -82,7 +86,7 @@ func (tool writeFileTool) RunWithOptions(ctx context.Context, args map[string]an
 			// Fail CLOSED: if the tracked file can't be re-read to verify it, refuse
 			// the overwrite rather than clobbering a file whose current state is
 			// unknown (it may have been replaced or removed out from under us).
-			current, rerr := os.ReadFile(absolutePath)
+			current, rerr := tool.readFile(absolutePath)
 			if rerr != nil {
 				return errorResult(fileConflictMessage(relativePath))
 			}
@@ -95,9 +99,11 @@ func (tool writeFileTool) RunWithOptions(ctx context.Context, args map[string]an
 	// Capture the prior content (before we replace it) so an overwrite can show a
 	// real diff; a fresh create stays "" and previews as all-additions.
 	priorContent := ""
+	priorContentKnown := !existed
 	if existed {
-		if prev, rerr := os.ReadFile(absolutePath); rerr == nil {
+		if prev, rerr := tool.readFile(absolutePath); rerr == nil {
 			priorContent = string(prev)
+			priorContentKnown = true
 		}
 	}
 
@@ -107,20 +113,36 @@ func (tool writeFileTool) RunWithOptions(ctx context.Context, args map[string]an
 	if err := recheckScopedWriteTarget(tool.workspaceRoot, tool.scope, requestedPath); err != nil {
 		return errorResult("Error writing file " + relativePath + ": " + err.Error())
 	}
-	if err := os.WriteFile(absolutePath, []byte(content), 0o644); err != nil {
+	var expectedContent *string
+	if priorContentKnown {
+		expectedContent = &priorContent
+	}
+	if err := commitFileContents(absolutePath, priorInfo, expectedContent, content); err != nil {
 		return errorResult("Error writing file " + relativePath + ": " + err.Error())
 	}
 	modelKnownContent := content
 	// Optional format-on-write (ZERO_FORMAT_ON_WRITE). Must run BEFORE the
 	// FileTracker baseline: recording pre-format content would make the very
 	// next edit look like an external modification and trip the conflict guard.
-	formatting := maybeFormatWrittenFile(ctx, absolutePath, content)
+	restoreMode := os.FileMode(0o644)
+	if priorInfo != nil {
+		restoreMode = priorInfo.Mode().Perm()
+	}
+	formatting := maybeFormatWrittenFileScoped(ctx, tool.workspaceRoot, tool.scope, absolutePath, content, restoreMode)
 	content = formatting.Content
+	finalContentKnown := formatting.ContentKnown
 	// Baseline the freshly written content so a later edit/overwrite in this
 	// session compares against what is now on disk.
-	newInfo, _ := os.Stat(absolutePath)
-	options.FileTracker.Record(absolutePath, []byte(content), newInfo)
-	if content == modelKnownContent {
+	newInfo := formatting.Info
+	if newInfo == nil {
+		newInfo, _ = os.Stat(absolutePath)
+	}
+	if finalContentKnown {
+		options.FileTracker.Record(absolutePath, []byte(content), newInfo)
+	} else {
+		options.FileTracker.Forget(absolutePath)
+	}
+	if finalContentKnown && content == modelKnownContent {
 		options.FileTracker.RecordSeenRange(absolutePath, 1, trackedLineTotal(content), trackedLineTotal(content))
 	}
 	if !existed {
@@ -139,13 +161,28 @@ func (tool writeFileTool) RunWithOptions(ctx context.Context, args map[string]an
 	}
 	summary := fmt.Sprintf("%s %s (%d lines).", verb, relativePath, lines)
 	summary += formatting.notice(relativePath)
-	summary += inlineDiagnostics(ctx, options, absolutePath, relativePath)
+	if finalContentKnown {
+		summary += inlineDiagnostics(ctx, options, absolutePath, relativePath)
+	}
 	result := okResult(summary)
 	result.ChangedFiles = []string{relativePath}
+	// Do not pretend an unreadable overwrite was a creation. The write may be
+	// valid, but ACP only receives an exact before/after pair we actually saw.
+	if priorContentKnown && finalContentKnown {
+		if diff, ok := boundedFileDiff(absolutePath, priorContent, content, existed, true); ok {
+			result.FileDiffs = []FileDiff{diff}
+		} else if diffTextRevealsObfuscatedSecret(priorContent) || diffTextRevealsObfuscatedSecret(content) {
+			result.Redacted = true
+		}
+	}
 	// Card-only preview: a real unified diff (all-green for a create, red/green for
 	// an overwrite) on Display.Preview. Output stays the summary, so the model never
 	// re-reads the file — the rich preview costs zero model tokens.
-	result.Display = Display{Summary: summary, Kind: "file", Preview: boundedUnifiedDiff(relativePath, priorContent, content)}
+	preview := ""
+	if priorContentKnown && finalContentKnown {
+		preview = boundedUnifiedDiff(relativePath, priorContent, content)
+	}
+	result.Display = Display{Summary: summary, Kind: "file", Preview: preview}
 	return result
 }
 

internal/tools/write_tools_test.go

@@ -6,6 +6,8 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"reflect"
+	"slices"
 	"strings"
 	"testing"
 )
@@ -323,6 +325,10 @@ func TestEditFileToolReplacesExactStrings(t *testing.T) {
 	root := t.TempDir()
 	path := filepath.Join(root, "code.go")
 	writeTestFile(t, path, "const a = 1\nconst b = 2\n")
+	path, err := filepath.EvalSymlinks(path)
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	result := NewScopedEditFileTool(root, nil).Run(context.Background(), map[string]any{
 		"path":       "code.go",
@@ -367,7 +373,12 @@ func TestEditFileToolReplacesCRLF(t *testing.T) {
 
 func TestEditFileToolEmitsUnifiedDiff(t *testing.T) {
 	root := t.TempDir()
-	writeTestFile(t, filepath.Join(root, "code.go"), "const a = 1\nconst b = 2\n")
+	path := filepath.Join(root, "code.go")
+	writeTestFile(t, path, "const a = 1\nconst b = 2\n")
+	path, err := filepath.EvalSymlinks(path)
+	if err != nil {
+		t.Fatal(err)
+	}
 	res := NewScopedEditFileTool(root, nil).Run(context.Background(), map[string]any{
 		"path": "code.go", "old_string": "const a = 1", "new_string": "const a = 42",
 	})
@@ -387,6 +398,9 @@ func TestEditFileToolEmitsUnifiedDiff(t *testing.T) {
 			t.Fatalf("edit preview missing diff marker %q: %q", want, res.Display.Preview)
 		}
 	}
+	if got := res.FileDiffs; len(got) != 1 || got[0].Path != path || !got[0].OldExists || !got[0].NewExists || got[0].OldText != "const a = 1\nconst b = 2\n" || got[0].NewText != "const a = 42\nconst b = 2\n" {
+		t.Fatalf("file diffs = %#v", got)
+	}
 }
 
 func TestWriteFileToolEmitsAdditionsDiff(t *testing.T) {
@@ -408,6 +422,13 @@ func TestWriteFileToolEmitsAdditionsDiff(t *testing.T) {
 	if strings.Contains(res.Display.Preview, "\n-line") {
 		t.Fatalf("a fresh-create diff must have no removed lines: %q", res.Display.Preview)
 	}
+	path, err := filepath.EvalSymlinks(filepath.Join(root, "new.txt"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := res.FileDiffs; len(got) != 1 || got[0].Path != path || got[0].OldExists || !got[0].NewExists || got[0].OldText != "" || got[0].NewText != "line one\nline two\n" {
+		t.Fatalf("file diffs = %#v", got)
+	}
 }
 
 func TestWriteFileToolOverwriteEmitsRedGreenDiff(t *testing.T) {
@@ -429,6 +450,28 @@ func TestWriteFileToolOverwriteEmitsRedGreenDiff(t *testing.T) {
 	}
 }
 
+func TestWriteFileToolOmitsDiffWhenOverwritePreimageCannotBeRead(t *testing.T) {
+	root := t.TempDir()
+	path := filepath.Join(root, "private.txt")
+	writeTestFile(t, path, "before\n")
+	tool := NewScopedWriteFileTool(root, nil).(writeFileTool)
+	tool.readFile = func(string) ([]byte, error) { return nil, os.ErrPermission }
+	registry := NewRegistry()
+	registry.Register(tool)
+	result := registry.RunWithOptions(context.Background(), tool.Name(), map[string]any{
+		"path": "private.txt", "content": "after\n", "overwrite": true,
+	}, RunOptions{PermissionGranted: true})
+	if result.Status != StatusOK {
+		t.Fatalf("write = %s", result.Output)
+	}
+	if len(result.FileDiffs) != 0 {
+		t.Fatalf("unreadable preimage must not produce a create-like diff: %#v", result.FileDiffs)
+	}
+	if got, err := os.ReadFile(path); err != nil || string(got) != "after\n" {
+		t.Fatalf("written content = %q, err = %v", got, err)
+	}
+}
+
 func TestEditFileToolAllowsDeletingRegions(t *testing.T) {
 	root := t.TempDir()
 	path := filepath.Join(root, "notes.txt")
@@ -584,6 +627,17 @@ func TestApplyPatchToolAppliesStructuredAddAndMove(t *testing.T) {
 	if got := result.ChangedFiles; strings.Join(got, ",") != "nested/new.txt,old.txt,moved.txt" {
 		t.Fatalf("ChangedFiles = %v", got)
 	}
+	resolvedRoot, err := filepath.EvalSymlinks(root)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got, want := result.FileDiffs, []FileDiff{
+		{Path: filepath.Join(resolvedRoot, "nested", "new.txt"), OldExists: false, NewExists: true, OldText: "", NewText: "created\n"},
+		{Path: filepath.Join(resolvedRoot, "old.txt"), OldExists: true, NewExists: false, OldText: "old\n", NewText: ""},
+		{Path: filepath.Join(resolvedRoot, "moved.txt"), OldExists: false, NewExists: true, OldText: "", NewText: "moved\n"},
+	}; !reflect.DeepEqual(got, want) {
+		t.Fatalf("FileDiffs = %#v, want %#v", got, want)
+	}
 }
 
 func TestApplyPatchToolStructuredPatchMatchesWhitespaceTolerantly(t *testing.T) {
@@ -831,7 +885,7 @@ func TestStructuredPatchAddDoesNotOverwriteRacedDestination(t *testing.T) {
 		after: "patch content\n", mode: 0o644,
 	}
 
-	err = applyStructuredPatchChanges(workspace, []structuredPatchChange{change}, nil)
+	_, err = applyStructuredPatchChanges(workspace, ".", []structuredPatchChange{change}, nil)
 	if err == nil || !errors.Is(err, os.ErrExist) {
 		t.Fatalf("raced add destination = %v, want os.ErrExist", err)
 	}
@@ -857,7 +911,7 @@ func TestStructuredPatchFailedDeleteDoesNotRecreateMissingFile(t *testing.T) {
 		before: "removed by another writer\n", mode: 0o644,
 	}
 
-	err = applyStructuredPatchChanges(workspace, []structuredPatchChange{change}, nil)
+	_, err = applyStructuredPatchChanges(workspace, ".", []structuredPatchChange{change}, nil)
 	if err == nil {
 		t.Fatal("delete of an already removed file should fail")
 	}
@@ -894,7 +948,7 @@ func TestStructuredPatchMoveWithMissingSourceIsRefusedBeforePublishing(t *testin
 	}
 	defer func() { structuredPatchBeforeCommit = nil }()
 
-	err = applyStructuredPatchChanges(workspace, []structuredPatchChange{change}, nil)
+	_, err = applyStructuredPatchChanges(workspace, ".", []structuredPatchChange{change}, nil)
 	if !removed {
 		t.Fatal("pre-commit hook did not run")
 	}
@@ -909,6 +963,59 @@ func TestStructuredPatchMoveWithMissingSourceIsRefusedBeforePublishing(t *testin
 	}
 }
 
+func TestStructuredPatchUpdatePreservesCompetingWriteBeforeRename(t *testing.T) {
+	for _, tc := range []struct {
+		name            string
+		competing       string
+		replaceIdentity bool
+	}{
+		{name: "content changed", competing: "competing writer\n"},
+		{name: "identity changed with same content", competing: "planned\n", replaceIdentity: true},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			root := t.TempDir()
+			targetPath := filepath.Join(root, "file.txt")
+			writeTestFile(t, targetPath, "planned\n")
+			patch := "*** Begin Patch\n*** Update File: file.txt\n@@\n-planned\n+patched\n*** End Patch\n"
+			hookRan := false
+			var competingInfo os.FileInfo
+			structuredPatchBeforeRename = func(change structuredPatchChange) {
+				if tc.replaceIdentity {
+					tempPath := filepath.Join(root, "competing.tmp")
+					writeTestFile(t, tempPath, tc.competing)
+					if err := os.Rename(tempPath, targetPath); err != nil {
+						t.Fatal(err)
+					}
+				} else if err := os.WriteFile(targetPath, []byte(tc.competing), 0o644); err != nil {
+					t.Fatal(err)
+				}
+				var err error
+				competingInfo, err = os.Stat(targetPath)
+				if err != nil {
+					t.Fatal(err)
+				}
+				hookRan = true
+			}
+			t.Cleanup(func() { structuredPatchBeforeRename = nil })
+
+			result := NewScopedApplyPatchTool(root, nil).Run(context.Background(), map[string]any{"patch": patch})
+			if !hookRan {
+				t.Fatal("pre-rename hook did not run")
+			}
+			if result.Status != StatusError || len(result.ChangedFiles) != 0 || len(result.FileDiffs) != 0 {
+				t.Fatalf("raced update = status=%s changed=%#v diffs=%#v output=%q", result.Status, result.ChangedFiles, result.FileDiffs, result.Output)
+			}
+			if got := mustReadTestFile(t, targetPath); got != tc.competing {
+				t.Fatalf("raced update overwrote competing content: %q", got)
+			}
+			finalInfo, err := os.Stat(targetPath)
+			if err != nil || !os.SameFile(competingInfo, finalInfo) {
+				t.Fatalf("raced update replaced the competing file identity: %v", err)
+			}
+		})
+	}
+}
+
 func TestStructuredPatchCreateOnlyFallsBackWhenHardLinksUnsupported(t *testing.T) {
 	root := t.TempDir()
 	workspace, err := os.OpenRoot(root)
@@ -978,6 +1085,45 @@ func TestStructuredPatchCopyFailureReportsSurvivingPartialTarget(t *testing.T) {
 	}
 }
 
+func TestIncompleteStructuredPatchNoReplaceWriteReportsOnlyVerifiedTarget(t *testing.T) {
+	for name, content := range map[string]string{
+		"complete publication": "complete content\n",
+		"partial publication":  "partial",
+	} {
+		t.Run(name, func(t *testing.T) {
+			root := t.TempDir()
+			workspace, err := os.OpenRoot(root)
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer workspace.Close()
+			targetPath := filepath.Join(root, "target.txt")
+			writeTestFile(t, targetPath, content)
+			change := structuredPatchChange{
+				kind: structuredPatchAdd,
+				to: structuredPatchTarget{
+					requested: "target.txt",
+					relative:  "target.txt",
+					absolute:  targetPath,
+				},
+				after: "complete content\n",
+				mode:  0o644,
+			}
+
+			outcome := incompleteStructuredPatchWrite(workspace, change, true)
+			if content == change.after {
+				if len(outcome.completed) != 1 || outcome.completed[0].kind != structuredPatchAdd || len(outcome.incompletePaths) != 0 {
+					t.Fatalf("verified publication outcome = %#v", outcome)
+				}
+				return
+			}
+			if len(outcome.completed) != 0 || !slices.Equal(outcome.incompletePaths, []string{"target.txt"}) {
+				t.Fatalf("partial publication outcome = %#v", outcome)
+			}
+		})
+	}
+}
+
 func TestStructuredPatchPartialFailureLeavesCompletedChangeAndClearsTrackedState(t *testing.T) {
 	root := t.TempDir()
 	trackedPath := filepath.Join(root, "tracked.txt")
@@ -1017,7 +1163,7 @@ func TestStructuredPatchPartialFailureLeavesCompletedChangeAndClearsTrackedState
 		},
 	}
 
-	err = applyStructuredPatchChanges(workspace, changes, tracker)
+	_, err = applyStructuredPatchChanges(workspace, ".", changes, tracker)
 	if err == nil || !strings.Contains(err.Error(), "partially applied") {
 		t.Fatalf("second change = %v, want partial-application error", err)
 	}