feat: block issue closure on unproven expected pre-existing failure (#529)

Delivers #529 acceptance criterion 6: controller issue closure must be
blocked when the closure report calls a non-zero test-suite exit an
"expected pre-existing"/baseline failure without pre-merge proof.

- controller_closure_baseline_proof.py: assess_controller_closure_baseline_proof
  reuses the #533 pre-merge baseline verifier; empty report -> skipped/allowed,
  clean pass -> allowed, proven baseline -> allowed, unproven baseline -> block.
- gitea_close_issue: optional closure_report param; fails closed (no state PATCH)
  when the gate blocks.
- final_report_validator: new controller_close task kind (alias close_issue)
  wired to the pre-merge baseline proof rule so a closure can be pre-checked.
- Tests: tests/test_controller_closure_baseline_proof.py plus two
  gitea_close_issue gate tests.

Scope: criteria 2/3 (non-zero exit not a clean pass; baseline claims need
proof) are already enforced on master via premerge_baseline_proof (#533) and
the reviewer schema rules. Criteria 1/4/5 (post-merge moot canonical wording
and validation:* process-state labels) remain follow-up work.

Validation: full suite 2365 passed, 6 skipped; the 9 remaining failures
(tests/test_config.py TestAuthIntegration, tests/test_credentials.py
TestGetCredentials, test_issue_540 reviewer-role) are baseline-proven —
identical failures on clean prgs/master 6913ac9 (keychain/env dependent),
unrelated to this change.

Refs #529

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

tests/test_mcp_server.py

@@ -2672,6 +2672,56 @@ class TestTrackerHygieneCleanup(unittest.TestCase):
         self.assertTrue(res["success"])
         self.assertEqual(res["cleanup_status"].get(1), "not present")
 
+    def test_close_issue_blocks_unproven_expected_preexisting_failure(self):
+        # #529: a closure report calling a non-zero suite exit an "expected
+        # pre-existing failure" without pre-merge proof must fail closed and
+        # never PATCH the issue state.
+        patched = []
+
+        def api_side_effect(method, url, auth, payload=None):
+            if method == "PATCH":
+                patched.append(url)
+            return {}
+        self.mock_api.side_effect = api_side_effect
+
+        res = gitea_close_issue(
+            issue_number=1,
+            closure_report=(
+                "Full suite: 1 failed. Expected pre-existing failure, safe to close."
+            ),
+        )
+        self.assertFalse(res["success"])
+        self.assertTrue(res.get("blocked"))
+        self.assertTrue(res.get("reasons"))
+        self.assertFalse(
+            patched, "must not PATCH issue state when the closure gate blocks"
+        )
+
+    def test_close_issue_allows_proven_baseline_closure(self):
+        def api_side_effect(method, url, auth, payload=None):
+            if method == "PATCH" and "issues/1" in url:
+                return {"state": "closed"}
+            if method == "GET" and "labels" in url and "issues" not in url:
+                return [{"name": "bug", "id": 2}]
+            if method == "GET" and "issues/1" in url:
+                return {"labels": [{"name": "bug"}]}
+            return {}
+        self.mock_api.side_effect = api_side_effect
+
+        res = gitea_close_issue(
+            issue_number=1,
+            closure_report=(
+                "Full suite: 1 failed, expected pre-existing baseline failure "
+                "proven on the PR pre-merge base commit.\n"
+                "Pre-merge base commit: 1a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0b\n"
+                "Tested commit: 1a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0b\n"
+                "Command: venv/bin/python -m pytest -q\n"
+                "Exit status: 1\n"
+                "Failure signature: AssertionError: None is not true\n"
+            ),
+        )
+        self.assertTrue(res["success"])
+
     def test_merge_pr_with_closes_removes_label(self):
         import reviewer_pr_lease