feat(channels): Implement named-session worktree reset (Part 4B)

docs/developers/daemon/00-index.md

@@ -126,7 +126,7 @@ Use these anchors when moving from the docs into the latest `main` code:
 | ------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------- |
 | HTTP routes   | The route catalog lives in `qwen-serve-protocol.md`; this daemon set only references it and explains implementation ownership.                                                                          | [`../qwen-serve-protocol.md`](../qwen-serve-protocol.md), [`20`](./20-quickstart-operations.md)               |
 | Event schema  | `EVENT_SCHEMA_VERSION = 1`; 53 known event types; id-less subscriber synthetic frames; `_meta.serverTimestamp` stamped by `EventBus.publish()` (with `formatSseFrame()` fallback for synthetic frames). | [`09`](./09-event-schema.md), [`10`](./10-event-bus.md)                                                       |
-| Capabilities  | `SERVE_PROTOCOL_VERSION = 'v1'`; 157 registered tags; 45 conditional tags.                                                                                                                              | [`11`](./11-capabilities-versioning.md)                                                                       |
+| Capabilities  | `SERVE_PROTOCOL_VERSION = 'v1'`; 158 registered tags; 45 conditional tags.                                                                                                                              | [`11`](./11-capabilities-versioning.md)                                                                       |
 | Session shell | `POST /session/:id/shell` exists behind `--enable-session-shell`, bearer or trusted-loopback authority, and session-bound `X-Qwen-Client-Id`; capability tag is conditional.                            | [`11`](./11-capabilities-versioning.md), [`17`](./17-configuration.md), [`20`](./20-quickstart-operations.md) |
 | Rate limiting | Optional per-tier HTTP rate limit is exposed by CLI flags/env and conditional capability tag.                                                                                                           | [`11`](./11-capabilities-versioning.md), [`17`](./17-configuration.md)                                        |
 

docs/developers/daemon/08-session-lifecycle.md

@@ -110,7 +110,9 @@ Both:
 1. Use a per-session `pendingRestoreIds` set on the channel so concurrent restore calls coalesce (`RestoreInProgressError`).
 2. Cache `restoreState` on the entry so a late attacher gets the same payload the original restorer did.
 
-For a persisted Part 4A worktree session, restore is an integrity-gated extension of this lifecycle. The sidecar identifies the requested workspace root explicitly, the checkout must be canonically contained below the corresponding `.qwen/worktrees/` directory, and its marker must be a single-link regular file containing the exact restored session ID. The daemon relocates an idle restored child only after those checks; an active child is accepted only when its reported cwd already equals the worktree. Those responses return canonical worktree metadata with `worktreeState: "persisted-v1"`. A cold restore that reports an active prompt without a current cwd returns unverified worktree metadata without that attestation, so isolation-aware clients reject it and may retry after the prompt settles. Invalid Part 4A state detaches an existing attachment or kills a cold restore with `requireZeroAttaches`; a missing sidecar likewise yields no attestation. Whenever the effective restore source is Channel-owned, the route suppresses the ACP agent's best-effort cleanup for Part 4A or unclassifiable sidecar state, so validation failure preserves the uncertain checkout evidence. Persisted source metadata takes precedence; when it is absent, the load/resume request supplies the effective source. A structurally valid legacy sidecar without `workspaceCwd` instead retains the existing best-effort agent restore: it must identify either the requested workspace root or its Git repository top-level, is containment-checked without marker attestation, may be cleaned up by the agent, and may return `worktree` without `worktreeState`. Apart from that explicit legacy compatibility case, only sessions whose effective restore source is not Channel-owned retain the existing best-effort cleanup before route validation.
+For a persisted Part 4A worktree session, restore is an integrity-gated extension of this lifecycle. The sidecar identifies the requested workspace root explicitly, the checkout must be canonically contained below the corresponding `.qwen/worktrees/` directory, and its marker must be a single-link regular file containing the exact restored session ID. The daemon relocates an idle restored child only after those checks; an active child is accepted only when its reported cwd already equals the worktree, and an active child whose reported cwd is absent or elsewhere fails closed instead of being relocated under its prompt — except for a cold restore that could not defer its restore-prompt (`suppressWorktreeContextRestore` off, so the bridge fired the re-hung question instead of parking it): that shape keeps the pre-4B outcome, returning canonical worktree metadata without `worktreeState`, unrelocated, with the session surviving. The relocated and accepted responses return canonical worktree metadata with `worktreeState: "persisted-v1"`. A sidecar carrying `supersededBy` never restores: the route returns `409 worktree_session_superseded` with the replacement session id, a classification decided from that link alone before any marker read, so callers redirect and heal their bookkeeping only once a load of that id has succeeded — a pre-commit interrupted transfer names a replacement that is not the marker owner, cannot itself be restored, and is reaped by the retried reset; a restored replacement whose `supersedes` link agrees with the old sidecar while the marker never moved — or is absent — returns `409 worktree_reset_interrupted`, whose repair is retrying the reset against the superseded session; and a missing marker without that agreeing link pair returns `409 worktree_marker_missing`, whose repair is resetting the task rather than retrying the restore, because no restore path recreates a marker. The interrupted classification is checked first. Invalid Part 4A state detaches an existing attachment or kills a cold restore with `requireZeroAttaches`; a missing sidecar likewise yields no attestation. Whenever the effective restore source is Channel-owned, the route suppresses the ACP agent's best-effort cleanup for Part 4A or unclassifiable sidecar state, so validation failure preserves the uncertain checkout evidence. Persisted source metadata takes precedence; when it is absent, the load/resume request supplies the effective source. A structurally valid legacy sidecar without `workspaceCwd` instead retains the existing best-effort agent restore: it must identify either the requested workspace root or its Git repository top-level, is containment-checked without marker attestation, may be cleaned up by the agent, and may return `worktree` without `worktreeState`. Apart from that explicit legacy compatibility case, only sessions whose effective restore source is not Channel-owned retain the existing best-effort cleanup before route validation.
+
+Worktree ownership transfer (`POST /session/:id/worktree-reset`, advertised by `session_worktree_reset_v1`) extends this lifecycle for Channel task resets: the daemon spawns a fresh thread-scoped replacement in the root workspace, relocates it into the verified checkout, links the sidecar pair (`supersededBy` on the old session first, then `supersedes` on the replacement), flips the marker to the replacement under a per-checkout route lock and an admission barrier that fences prompt admission plus the seven other writers that start work in the checkout or move the session cwd (rewind, cwd change, branch, fork, shell, goal control, workflow-task action), while the release and stop paths stay unfenced by design, and then severs the superseded session's client registrations and in-memory worktree association. The sever reports whether the superseded session is actually gone: a survivor whose child still holds background work keeps the barrier armed, is logged, and is reported to the caller as `supersededSessionLive: true` rather than being papered over by the success response. A fenced writer admitted on the superseded session mid-transfer is refused with `409 worktree_reset_active`; the full failure taxonomy, including which crash windows a retry rolls back and which fail closed for operator repair, is documented with the route in `qwen-serve-protocol.md`.
 
 ### Heartbeat