test: mock assess_infra_stop in route_task_session merge blocker test

route_task_session now calls assess_infra_stop() live instead of
check_mid_merge(). Update TestMCPHealth.test_route_task_session_blocks_during_merge
to mock the infra-stop assessment path and assert infra_stop_assessment
is returned when blocked.

Part of #285 / PR #286 review fix.

tests/test_health.py

@@ -120,7 +120,7 @@ class TestMCPHealth(unittest.TestCase):
             stderr_text,
         )
 
-    @patch("role_session_router.check_mid_merge", return_value=True)
+    @patch("role_session_router.assess_infra_stop")
     @patch(
         "mcp_server.get_profile",
         return_value={
@@ -128,10 +128,21 @@ class TestMCPHealth(unittest.TestCase):
             "allowed_operations": ["gitea.pr.review"],
         },
     )
-    def test_route_task_session_blocks_during_merge(self, mock_profile, mock_check):
+    def test_route_task_session_blocks_during_merge(self, mock_profile, mock_assess):
+        mock_assess.return_value = {
+            "infra_stop": True,
+            "project_root": "/repo",
+            "conflict_file": None,
+            "mid_merge": True,
+            "infra_stop_reasons": [
+                "mid-merge markers detected in /repo/.git/MERGE_HEAD (project_root=/repo)"
+            ],
+        }
         res = gitea_route_task_session("review_pr")
         self.assertEqual(res["route_result"], "infra_stop")
         self.assertIn("infra_stop", res["message"])
+        self.assertTrue(res.get("infra_stop_assessment", {}).get("infra_stop"))
+        mock_assess.assert_called()
 
     @patch("role_session_router.assess_infra_stop")
     @patch(