fix: double append bug

PiperOrigin-RevId: 910258324

Author: google-genai-bot

src/google/adk/sessions/in_memory_session_service.py

@@ -342,8 +342,9 @@ def _warning(message: str) -> None:
 
     # Update the storage session
     storage_session = self.sessions[app_name][user_id].get(session_id)
-    storage_session.events.append(event)
-    storage_session.last_update_time = event.timestamp
+    if storage_session is not session:
+      storage_session.events.append(event)
+      storage_session.last_update_time = event.timestamp
 
     if event.actions and event.actions.state_delta:
       state_deltas = _session_util.extract_state_delta(

tests/unittests/sessions/test_session_service.py

@@ -1013,6 +1013,30 @@ async def test_append_event_allows_markerless_current_session():
     await service.close()
 
 
+@pytest.mark.asyncio
+async def test_append_event_when_session_is_same_ref_as_storage_session():
+  """Tests that appending an event to a session only appends it once if the user-passed session and the underlying storage session are the same object."""
+  service = InMemorySessionService()
+  app_name = 'my_app'
+  user_id = 'test_user'
+
+  # Create a session
+  session = await service.create_session(app_name=app_name, user_id=user_id)
+
+  # Get the actual storage event object from the underlying storage
+  storage_session = service.sessions[app_name][user_id][session.id]
+
+  # Append the event to the storage session directly
+  event = Event(invocation_id='inv1', author='user')
+  await service.append_event(session=storage_session, event=event)
+
+  # Verify that the storage session has only one event
+  final_session = await service.get_session(
+      app_name=app_name, user_id=user_id, session_id=session.id
+  )
+  assert len(final_session.events) == 1
+
+
 @pytest.mark.asyncio
 async def test_get_session_with_config(session_service):
   app_name = 'my_app'