fix(worktree-audit): make cleanup audit merged-PR aware for issue worktrees (Closes #858)

gitea_audit_worktree_cleanup had no PR linkage. Issue worktrees therefore
reported pr_number=null and classified as active_issue_work with
removable=false permanently, even once their PR was merged and the head was
already contained in master. Observed on live master 9301739910: 42
issue_work worktrees, 0 removable, 0 with pr_number populated, while
gitea_reconcile_merged_cleanups reported the same worktree safe to remove.

Two independent gaps caused it:

* build_worktree_metadata was never given a pr_number, and only open PRs were
  fetched, so no owning-PR evidence existed at all.
* clean_stale_removable was unreachable for issue_work: it required
  ttl_expired, derived from a last_used_at that nothing populates, and
  is_ttl_expired fail-safes to False when the timestamp is unknown.

This adds deterministic merged-PR linkage and gates removal on the complete
cleanup policy:

* build_pr_index / resolve_owning_pr link a worktree branch to exactly one
  owning PR. Competing PRs on one branch, a still-open owner, a head-branch
  mismatch, or missing PR state all fail closed while still reporting the
  resolved pr_number.
* assess_merged_pr_worktree_cleanup requires all of: conclusive merged
  ownership, branch agreement, containment of the head in authoritative
  master, no open/competing PR, no active lease, no issue lock, no live
  session, a clean tree, and a non-protected checkout. Unknown state blocks.
* Containment reuses merged_cleanup_reconcile.is_head_ancestor_of_ref so the
  audit and the PR-scoped reconciler agree on what "already landed" means.

Lease evidence is now supplied. audit_branches_directory already accepted
leased_branches but the MCP tool never passed it, so has_active_lease was
false for every worktree in a live run. That was inert only while issue
worktrees could never become removable; it is wired to authoritative
control-plane leases here, scoped so a lease on issue N protects that issue's
work worktree and not a baseline or review tree merely named after it.

Issue work no longer becomes removable on TTL age alone, since age is not
proof that a branch landed and would otherwise reclaim a worktree holding
unmerged commits. conflict_fix keeps its existing TTL behaviour, and review,
baseline, merge-simulation, detached, dirty, open-PR, and protected
classifications are unchanged.

The assessor still performs no deletion and gains no cleanup mutation. This
is assessor-side only and does not implement the PR-scoped executor or the
expired-lease reclaim policy tracked separately by #855.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

tests/test_worktree_cleanup_audit.py

@@ -134,13 +134,35 @@ class TestClassification(unittest.TestCase):
         self.assertEqual(cls, wca.CLASS_ACTIVE_OPEN_PR)
         self.assertFalse(wca.is_removable(cls))
 
-    def test_stale_clean_issue_worktree_removable(self):
-        # Scenario 5: clean issue worktree, TTL expired, no lock -> removable.
+    def test_stale_clean_issue_worktree_needs_merged_pr_proof(self):
+        # Scenario 5 (#858): age is not proof that the branch landed, so a
+        # TTL-expired issue worktree stays active work. Only authoritative
+        # merged-PR evidence makes it removable, which is what keeps a
+        # worktree holding unmerged commits from being reclaimed by age.
         cls = wca.classify_worktree(
             workflow_type=wca.WORKFLOW_ISSUE_WORK,
             is_dirty=False,
             ttl_expired=True,
         )
+        self.assertEqual(cls, wca.CLASS_ACTIVE_ISSUE_WORK)
+        self.assertFalse(wca.is_removable(cls))
+
+        cls = wca.classify_worktree(
+            workflow_type=wca.WORKFLOW_ISSUE_WORK,
+            is_dirty=False,
+            ttl_expired=True,
+            merged_pr_cleanup={"proven": True},
+        )
+        self.assertEqual(cls, wca.CLASS_CLEAN_STALE_REMOVABLE)
+        self.assertTrue(wca.is_removable(cls))
+
+    def test_stale_clean_conflict_fix_worktree_removable(self):
+        # conflict_fix keeps the original TTL rule; #858 changed issue work only.
+        cls = wca.classify_worktree(
+            workflow_type=wca.WORKFLOW_CONFLICT_FIX,
+            is_dirty=False,
+            ttl_expired=True,
+        )
         self.assertEqual(cls, wca.CLASS_CLEAN_STALE_REMOVABLE)
         self.assertTrue(wca.is_removable(cls))