test: fix reviewer lease gate regressions in MCP integration tests (#407)

Align merge/review/audit mocks with the per-PR reviewer lease gate introduced
in #407: install owned session leases after init_review_decision_lock, stub
_fetch_pr_comments and _authenticated_username to preserve mock ordering, and
update head-SHA mismatch expectations for lease-first fail-closed paths.

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

tests/test_audit.py

@@ -286,6 +286,21 @@ class TestSimpleToolAudit(_AuditWiringBase):
 
 class TestGatedToolAudit(_AuditWiringBase):
 
+    def setUp(self):
+        super().setUp()
+        from tests.test_mcp_server import _install_owned_reviewer_lease
+        import reviewer_pr_lease
+
+        self._lease_patch = _install_owned_reviewer_lease(8)
+        self._lease_patch.start()
+        self._auth_identity_patch = patch(
+            "mcp_server._authenticated_username", return_value="reviewer-bot"
+        )
+        self._auth_identity_patch.start()
+        self.addCleanup(self._auth_identity_patch.stop)
+        self.addCleanup(self._lease_patch.stop)
+        self.addCleanup(reviewer_pr_lease.clear_session_lease)
+
     def _pr(self, author, state="open", sha="abc123", mergeable=True):
         return {"user": {"login": author}, "state": state,
                 "head": {"sha": sha}, "mergeable": mergeable}
@@ -344,11 +359,22 @@ class TestGatedToolAudit(_AuditWiringBase):
                         GITEA_ALLOWED_OPERATIONS="read,review,approve")
         with patch.dict(os.environ, env, clear=True):
             from mcp_server import init_review_decision_lock, gitea_mark_final_review_decision
+            from tests.test_mcp_server import _install_owned_reviewer_lease
+            import reviewer_pr_lease
+
             init_review_decision_lock("prgs", "review_pr")
             gitea_mark_final_review_decision(8, "approve", remote="prgs")
-            r = gitea_submit_pr_review(pr_number=8, action="approve",
-                                       body="LGTM", remote="prgs",
-                                       final_review_decision_ready=True)
+            lease_patch = _install_owned_reviewer_lease(8)
+            lease_patch.start()
+            try:
+                r = gitea_submit_pr_review(
+                    pr_number=8, action="approve",
+                    body="LGTM", remote="prgs",
+                    final_review_decision_ready=True,
+                )
+            finally:
+                lease_patch.stop()
+                reviewer_pr_lease.clear_session_lease()
         self.assertTrue(r["performed"])
         recs = self._records()
         self.assertEqual(len(recs), 1)