fix: Return session state in list_session API endpoint

Resolves https://github.com/google/adk-python/issues/2193
Resolves https://github.com/google/adk-python/issues/781

PiperOrigin-RevId: 789143973

src/google/adk/sessions/database_session_service.py

@@ -515,9 +515,22 @@ class DatabaseSessionService(BaseSessionService):
           .filter(StorageSession.user_id == user_id)
           .all()
       )
+
+      # Fetch states from storage
+      storage_app_state = sql_session.get(StorageAppState, (app_name))
+      storage_user_state = sql_session.get(
+          StorageUserState, (app_name, user_id)
+      )
+
+      app_state = storage_app_state.state if storage_app_state else {}
+      user_state = storage_user_state.state if storage_user_state else {}
+
       sessions = []
       for storage_session in results:
-        sessions.append(storage_session.to_session())
+        session_state = storage_session.state
+        merged_state = _merge_state(app_state, user_state, session_state)
+
+        sessions.append(storage_session.to_session(state=merged_state))
       return ListSessionsResponse(sessions=sessions)
 
   @override

src/google/adk/sessions/in_memory_session_service.py

@@ -224,7 +224,7 @@ class InMemorySessionService(BaseSessionService):
     for session in self.sessions[app_name][user_id].values():
       copied_session = copy.deepcopy(session)
       copied_session.events = []
-      copied_session.state = {}
+      copied_session = self._merge_state(app_name, user_id, copied_session)
       sessions_without_events.append(copied_session)
     return ListSessionsResponse(sessions=sessions_without_events)
 

src/google/adk/sessions/vertex_ai_session_service.py

@@ -280,24 +280,28 @@ class VertexAiSessionService(BaseSessionService):
       parsed_user_id = urllib.parse.quote(f'''"{user_id}"''', safe='')
       path = path + f'?filter=user_id={parsed_user_id}'
 
-    api_response = await api_client.async_request(
+    list_sessions_api_response = await api_client.async_request(
         http_method='GET',
         path=path,
         request_dict={},
     )
-    api_response = _convert_api_response(api_response)
+    list_sessions_api_response = _convert_api_response(
+        list_sessions_api_response
+    )
 
     # Handles empty response case
-    if not api_response or api_response.get('httpHeaders', None):
+    if not list_sessions_api_response or list_sessions_api_response.get(
+        'httpHeaders', None
+    ):
       return ListSessionsResponse()
 
     sessions = []
-    for api_session in api_response['sessions']:
+    for api_session in list_sessions_api_response['sessions']:
       session = Session(
           app_name=app_name,
           user_id=user_id,
           id=api_session['name'].split('/')[-1],
-          state={},
+          state=api_session.get('sessionState', {}),
           last_update_time=isoparse(api_session['updateTime']).timestamp(),
       )
       sessions.append(session)

tests/unittests/sessions/test_session_service.py

@@ -106,7 +106,10 @@ async def test_create_and_list_sessions(service_type):
   session_ids = ['session' + str(i) for i in range(5)]
   for session_id in session_ids:
     await session_service.create_session(
-        app_name=app_name, user_id=user_id, session_id=session_id
+        app_name=app_name,
+        user_id=user_id,
+        session_id=session_id,
+        state={'key': 'value' + session_id},
     )
 
   list_sessions_response = await session_service.list_sessions(
@@ -115,6 +118,7 @@ async def test_create_and_list_sessions(service_type):
   sessions = list_sessions_response.sessions
   for i in range(len(sessions)):
     assert sessions[i].id == session_ids[i]
+    assert sessions[i].state == {'key': 'value' + session_ids[i]}
 
 
 @pytest.mark.asyncio