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_pr_queue_inventory.py

@@ -156,9 +156,22 @@ class TestPRQueueInventory(unittest.TestCase):
         ]
 
         from mcp_server import init_review_decision_lock, gitea_mark_final_review_decision
-        init_review_decision_lock("prgs", "review_pr")
-        gitea_mark_final_review_decision(1, "approve", remote="prgs")
-        result = gitea_review_pr(pr_number=1, event="APPROVE", remote="prgs", final_review_decision_ready=True)
+        from tests.test_mcp_server import _install_owned_reviewer_lease
+        import reviewer_pr_lease
+
+        with patch("mcp_server._authenticated_username", return_value="reviewer1"):
+            init_review_decision_lock("prgs", "review_pr")
+            gitea_mark_final_review_decision(1, "approve", remote="prgs")
+            lease_patch = _install_owned_reviewer_lease(
+                1, head_sha="abc1", session_id="inventory-review-lease",
+            )
+            lease_patch.start()
+            self.addCleanup(lease_patch.stop)
+            self.addCleanup(reviewer_pr_lease.clear_session_lease)
+            result = gitea_review_pr(
+                pr_number=1, event="APPROVE", remote="prgs",
+                final_review_decision_ready=True,
+            )
         self.assertTrue(result["success"])
         self.assertIn("=== PR Queue Inventory ===", result["message"])
         self.assertIn("Repository:", result["message"])