test: seed session owner before cleanup

Author: mikemikimike

tests/server/test_streamable_http_manager.py

@@ -3,7 +3,7 @@
 import json
 import logging
 from collections.abc import Iterator
-from typing import Any
+from typing import Any, cast
 from unittest.mock import AsyncMock, patch
 
 import anyio
@@ -289,6 +289,10 @@ async def mock_receive():
 
     assert session_id is not None, "Session ID not found in response headers"
 
+    # Seed the owner registry so this assertion verifies that the cleanup path
+    # removes the session owner as well as the server instance.
+    manager._session_owners[session_id] = cast(Any, None)
+
     mock_serve.assert_called_once()
 
     # At this point, mock_serve has completed, and the finally block in