fix(mcp): enforce role capability invariants (Closes #723)

tests/test_resolve_task_capability.py

@@ -242,6 +242,32 @@ class TestResolveTaskCapability(unittest.TestCase):
             self.assertTrue(res.get("stop_required"))
             self.assertIs(res.get("mutation_performed"), False)
 
+    @patch("mcp_server.api_request", return_value={"login": "author-user"})
+    @patch("mcp_server.get_auth_header", return_value="token author-pass")
+    def test_denied_role_exclusive_resolution_does_not_stamp_role(
+        self, _auth, _api
+    ):
+        with patch.dict(os.environ, self._env("author-profile")):
+            with patch.object(
+                mcp_server,
+                "record_preflight_check",
+                wraps=mcp_server.record_preflight_check,
+            ) as record:
+                result = mcp_server.gitea_resolve_task_capability(
+                    task="review_pr", remote="prgs"
+                )
+
+        self.assertFalse(result["allowed_in_current_session"], result)
+        self.assertFalse(
+            any(
+                len(call.args) > 1 and call.args[1] == "reviewer"
+                for call in record.call_args_list
+            ),
+            "denied reviewer resolution must never record a reviewer stamp",
+        )
+        self.assertIsNone(mcp_server._preflight_resolved_role)
+        self.assertIsNone(mcp_server._preflight_resolved_task)
+
     # Additional regression tests per #145 for permission boundaries and structured guidance
     def test_issue_comment_does_not_imply_close(self):
         # Author profile has issue.comment but not issue.close