feat: canonical cleanup for stale #332 review decision locks (#594)

Durable review-decision locks (#559) can outlive the PR they protect.
When the last terminal mutation references a PR that is already
merged/closed, expose gitea_cleanup_stale_review_decision_lock so a
reviewer can clear the lock with identity/profile gates and a durable
audit trail — without weakening #332 for open PRs or deleting
session-state files by hand.

Also auto-clear same-profile locks after a successful merge of the
approved PR, and document allowed vs forbidden cleanup.

Closes #594

docs/llm-workflow-runbooks.md

@@ -1049,6 +1049,72 @@ Special states:
 Final reports must not claim a comment was posted when
 `canonical_comment_validation.allowed` is false (#496 AC14).
 
+## Stale #332 review-decision lock cleanup (#594)
+
+#332 hard-stops a reviewer session after a terminal live review mutation
+(`approve` / `request_changes`). After #559 those locks are **durable** under
+`~/.cache/gitea-tools/session-state/review_decision_lock-<profile>.json`, so they
+can outlive the PR they protected.
+
+### When cleanup is **allowed**
+
+Use `gitea_cleanup_stale_review_decision_lock` from a **reviewer** profile when:
+
+1. A durable review-decision lock has a terminal live mutation, **and**
+2. Live Gitea state shows that terminal PR is already **merged** or **closed**
+   (so no same-PR merge sequence remains), **and**
+3. The active profile identity matches the lock, **and**
+4. Authenticated identity can be verified.
+
+Workflow:
+
+```text
+# 1) Assess only (default)
+gitea_cleanup_stale_review_decision_lock(apply=false, remote=prgs, ...)
+
+# 2) Apply after is_moot=true and cleanup_allowed=true
+gitea_cleanup_stale_review_decision_lock(
+  apply=true,
+  expected_terminal_pr=<merged-or-closed-pr>,
+  remote=prgs,
+  ...
+)
+```
+
+Successful apply:
+
+* clears in-memory + durable decision lock for that profile
+* returns a structured `audit` payload
+* posts an audit comment on the mooted PR when `gitea.pr.comment` is allowed
+  (`post_audit_comment=true` default)
+
+Same-profile auto-expire: if `gitea_merge_pr` succeeds on a PR that this same
+profile just approved, the decision lock is cleared after merge. Cross-profile
+locks (reviewer vs merger) still require the cleanup tool.
+
+### When cleanup is **forbidden**
+
+Do **not** clear when:
+
+* the last terminal PR is still **open** (active #332 hard-stop — continue merge
+  for that approve, or stop after request_changes)
+* live PR state cannot be fetched (fail closed)
+* profile identity does not match the lock
+* identity cannot be verified
+* `expected_terminal_pr` does not match the last terminal PR
+
+**Never** use manual deletion of session-state files as the normal workflow.
+**Never** use cleanup to skip review of an open PR or to bypass eligibility /
+mark-ready / submit gates on active work.
+
+### Related tools
+
+| Tool | Purpose |
+|------|---------|
+| `gitea_cleanup_stale_review_decision_lock` | Moot decision-lock cleanup (#594) |
+| `gitea_authorize_review_correction` | Operator-approved correction after a **mistaken** live review on still-active work (#211) |
+| `gitea_cleanup_post_merge_moot_lease` | Moot **lease** cleanup after merge (#515) — different object |
+
 ## Fail-closed behavior
 
 Before any mutating action the workflow verifies identity, active profile,