feat(FN-4546): complete Step 5 — document and audit stale active reclaim

Fusion-Task-Id: FN-4546
Fusion-Task-Lineage: f10f8fcb-b26d-4ee8-b83e-b741de01983b

.changeset/fn-4546-stale-active-branch-reclaim.md

@@ -0,0 +1,5 @@
+---
+"@runfusion/fusion": patch
+---
+
+Reclaim zero-unique-commit `fusion/<task-id>` branches owned by active tasks with no live worktree (FN-4546).

AGENTS.md

@@ -196,7 +196,7 @@ Port 4040 is the production dashboard port. A user's live dashboard session is t
 
 ## Architecture
 
-- Merge deadlock self-healing now layers `recoverAlreadyMergedReviewTasks()`, `clearStaleBlockedBy()`, and `reclaimSelfOwnedBranchConflicts()` in `packages/engine/src/self-healing.ts`, plus the paused-aware in-review scope filter in `packages/engine/src/scheduler.ts` (`inReviewWithWorktree` excludes `paused` tasks). `reclaimSelfOwnedBranchConflicts()` now also recovers paused `branch-conflict-unrecoverable` review rows when ownership is self-proven, auto-reclaims `fusion/<task-id>` branches that are still live-mapped but have zero unique commits vs main by force-removing the stale worktree and deleting the branch, and clears `task.worktree`/`task.branch` so retries recreate a fresh checkout. `inspectBranchConflict()` backs this with a patch-id fallback for degraded/empty `git cherry` output before declaring zero-unique-commit subsumption, treats ghost live-worktree admin entries (mapping path missing on disk) as `stale-resolved`, and classifies tips already reachable from the integration target as `tip-already-merged` so stale cached `baseCommitSha` values are invalidated instead of enumerating main's forward progress as stranded commits. Orphan `fusion/*` branches are still resolved by prune-or-rescue logic (subsumed branches pruned; unique-commit branches rescued into triage tasks instead of force delete). Completion fan-out now runs synchronously on `in-review → done` via `SelfHealingManager.reconcileCompletedTask()`, so downstream stale `blockedBy` links and residual `fusion/<task-id>` branch/worktree artifacts are reconciled immediately instead of waiting for periodic sweeps.
+- Merge deadlock self-healing now layers `recoverAlreadyMergedReviewTasks()`, `clearStaleBlockedBy()`, and `reclaimSelfOwnedBranchConflicts()` in `packages/engine/src/self-healing.ts`, plus the paused-aware in-review scope filter in `packages/engine/src/scheduler.ts` (`inReviewWithWorktree` excludes `paused` tasks). `reclaimSelfOwnedBranchConflicts()` now also recovers paused `branch-conflict-unrecoverable` review rows when ownership is self-proven, auto-reclaims `fusion/<task-id>` branches that are still live-mapped but have zero unique commits vs main by force-removing the stale worktree and deleting the branch, and clears `task.worktree`/`task.branch` so retries recreate a fresh checkout. `inspectBranchConflict()` backs this with a patch-id fallback for degraded/empty `git cherry` output before declaring zero-unique-commit subsumption, treats ghost live-worktree admin entries (mapping path missing on disk) as `stale-resolved`, and classifies tips already reachable from the integration target as `tip-already-merged` so stale cached `baseCommitSha` values are invalidated instead of enumerating main's forward progress as stranded commits. FN-4546 adds a separate `reclaim-stale-active-branches` stage in startup and maintenance sweeps to close the gap where an active task owns a `fusion/<task-id>` branch with zero unique commits but has no usable worktree mapping; that stage now prunes the stale branch, clears task branch/worktree/base metadata, and emits `branch:stale-active-reclaim` audit telemetry. Orphan `fusion/*` branches are still resolved by prune-or-rescue logic (subsumed branches pruned; unique-commit branches rescued into triage tasks instead of force delete). Completion fan-out now runs synchronously on `in-review → done` via `SelfHealingManager.reconcileCompletedTask()`, so downstream stale `blockedBy` links and residual `fusion/<task-id>` branch/worktree artifacts are reconciled immediately instead of waiting for periodic sweeps.
 - Restart recovery is coordinated through `RestartRecoveryCoordinator` (`packages/engine/src/restart-recovery-coordinator.ts`), which classifies interrupted `in-progress` runs at runtime startup: no-progress `fn_task_done` failures are safely requeued to `todo`, then remaining orphaned work is resumed via the executor.
 
 ## Engine Process Rules

packages/engine/src/run-audit.ts

@@ -77,6 +77,7 @@ export type GitMutationType =
   | "merge:file-scope-violation"
   | "merge:audit-failure"
   | "branch:auto-reclaim"
+  | "branch:stale-active-reclaim"
   | "branch:orphan-prune"
   | "branch:orphan-rescued"
   | "branch:reanchor"