docs(FN-3882): document clearStaleBlockedBy() in architecture.md SelfHealingManager section

docs/architecture.md

@@ -567,6 +567,7 @@ Runtime action-gate flow (v1):
 - `SelfHealingManager` (`self-healing.ts`) — auto-unpause/maintenance recovery actions
   - `recoverGhostReviewTasks()` is a fallback only for idle, non-terminal `in-review` states. Terminal/actionable states (notably `status: "failed"`) are preserved and **not** auto-kicked back to `todo`.
   - `recoverMergeableReviewTasks()` only re-enqueues truly eligible tasks; retry-exhausted review tasks are skipped to avoid re-enqueue/no-op loops that keep refreshing `updatedAt`.
+  - `clearStaleBlockedBy()` clears `blockedBy` (and transient `status`) on todo tasks when their blocker is missing, done, archived, paused in-review, or failed in-review with merge retries exhausted. This lets the scheduler re-evaluate those tasks cleanly on subsequent ticks instead of leaving them permanently queued behind stale blockers.
   - Merge commit attribution is ownership-aware: a `mergeDetails.commitSha` is trusted only when reachable from `HEAD` **and** attributable to the task via `Fusion-Task-Id` trailer or task-ID-bearing subject. Reachable-but-unowned SHAs are rejected to prevent sibling done tasks from sharing misleading merge metadata.
 - `ProjectEngine` settings lifecycle handlers (`project-engine.ts`) treat `enginePaused` as a soft pause: clearing it dispatches runtime resume and, when `autoMerge` is enabled, performs an `in-review` eligibility sweep to requeue mergeable review tasks.
 - `UsageLimitPauser` (`usage-limit-detector.ts`) and `withRateLimitRetry` (`rate-limit-retry.ts`)