feat(sessions): add get_user_state(app_name, user_id) to BaseSessionService

Closes: #5592

Problem:
BaseSessionService has no public method to read user-scoped state without an active session_id. Callers that need to bootstrap user context before a new session exists are forced to call the expensive list_sessions or maintain a separate process-level cache as a workaround.

Solution:
Add get_user_state(app_name, user_id) -> dict[str, Any] to BaseSessionService. Implemented in InMemorySessionService, DatabaseSessionService, and SqliteSessionService. VertexAiSessionService raises NotImplementedError because the Vertex AI Agent Engine API does not expose user state independently of a session. The default in BaseSessionService also raises NotImplementedError to preserve backward compatibility for existing custom subclasses.

Keys are returned without the user: prefix, consistent with how user state is stored internally (the prefix is applied by the state-merging layer).

Merge #5596

Change-Id: Id1015034c62810aafd2b2411a0376742bb80e8c8

Author: nicolasmota

src/google/adk/cli/utils/local_storage.py

@@ -18,6 +18,7 @@
 import asyncio
 import logging
 from pathlib import Path
+from typing import Any
 from typing import Mapping
 from typing import Optional
 
@@ -205,6 +206,13 @@ async def delete_session(
         app_name=app_name, user_id=user_id, session_id=session_id
     )
 
+  @override
+  async def get_user_state(
+      self, *, app_name: str, user_id: str
+  ) -> dict[str, Any]:
+    service = await self._get_service(app_name)
+    return await service.get_user_state(app_name=app_name, user_id=user_id)
+
   @override
   async def append_event(self, session: Session, event: Event) -> Event:
     service = await self._get_service(session.app_name)

src/google/adk/sessions/base_session_service.py

@@ -111,6 +111,46 @@ async def delete_session(
   ) -> None:
     """Deletes a session."""
 
+  async def get_user_state(
+      self, *, app_name: str, user_id: str
+  ) -> dict[str, Any]:
+    """Returns the user-scoped state for the given app and user.
+
+    User state is keyed by ``(app_name, user_id)`` and shared across all
+    sessions of the same user within the same app.  The returned dictionary
+    uses raw keys **without** the ``user:`` prefix (e.g. ``"my_key"`` rather
+    than ``"user:my_key"``).
+
+    This method exists so that callers can read user state without holding an
+    active ``session_id``.  A common use case is bootstrapping context at the
+    start of a new session before calling ``create_session``, which would
+    otherwise require an expensive ``list_sessions`` call just to access
+    user-scoped data.
+
+    Returns an empty dict when no user state has been stored for this
+    ``(app_name, user_id)`` combination.
+
+    Args:
+      app_name: The name of the app.
+      user_id: The ID of the user.
+
+    Returns:
+      A dictionary of raw (un-prefixed) user-scoped key/value pairs, or an
+      empty dict when no user state exists.
+
+    Raises:
+      NotImplementedError: When the concrete ``BaseSessionService``
+        implementation does not support reading user state independently of a
+        session.  Callers should catch this, then enumerate sessions via
+        ``list_sessions`` and call ``get_session`` on each result to access
+        the merged state, or accept that user state is unavailable.
+    """
+    raise NotImplementedError(
+        f'{type(self).__name__} does not support get_user_state. '
+        'To read user state, enumerate sessions via list_sessions and '
+        'call get_session on each result to access the merged state.'
+    )
+
   async def append_event(self, session: Session, event: Event) -> Event:
     """Appends an event to a session object."""
     if event.partial:

src/google/adk/sessions/database_session_service.py

@@ -329,7 +329,7 @@ async def _with_session_lock(
         else:
           self._session_lock_ref_count[lock_key] = remaining
 
-  async def _prepare_tables(self):
+  async def _prepare_tables(self) -> None:
     """Ensure database tables are ready for use.
 
     This method is called lazily before each database operation. It checks the
@@ -627,6 +627,22 @@ async def delete_session(
       await sql_session.execute(stmt)
       await sql_session.commit()
 
+  @override
+  async def get_user_state(
+      self, *, app_name: str, user_id: str
+  ) -> dict[str, Any]:
+    await self._prepare_tables()
+    schema = self._get_schema_classes()
+    async with self._rollback_on_exception_session(
+        read_only=True
+    ) as sql_session:
+      storage_user_state = await sql_session.get(
+          schema.StorageUserState, (app_name, user_id)
+      )
+      if storage_user_state is None:
+        return {}
+      return dict(storage_user_state.state or {})
+
   @override
   async def append_event(self, session: Session, event: Event) -> Event:
     await self._prepare_tables()

src/google/adk/sessions/in_memory_session_service.py

@@ -312,6 +312,12 @@ def _delete_session_impl(
 
     self.sessions[app_name][user_id].pop(session_id)
 
+  @override
+  async def get_user_state(
+      self, *, app_name: str, user_id: str
+  ) -> dict[str, Any]:
+    return dict(self.user_state.get(app_name, {}).get(user_id, {}))
+
   @override
   async def append_event(self, session: Session, event: Event) -> Event:
     if event.partial:

src/google/adk/sessions/sqlite_session_service.py

@@ -359,6 +359,13 @@ async def delete_session(
       )
       await db.commit()
 
+  @override
+  async def get_user_state(
+      self, *, app_name: str, user_id: str
+  ) -> dict[str, Any]:
+    async with self._get_db_connection() as db:
+      return await self._get_user_state(db, app_name, user_id)
+
   @override
   async def append_event(self, session: Session, event: Event) -> Event:
     if event.partial:

src/google/adk/sessions/vertex_ai_session_service.py

@@ -276,6 +276,27 @@ async def delete_session(
         logger.error('Error deleting session %s: %s', session_id, e)
         raise
 
+  @override
+  async def get_user_state(
+      self, *, app_name: str, user_id: str
+  ) -> dict[str, Any]:
+    """Not supported by the Vertex AI Agent Engine backend.
+
+    The Vertex AI Agent Engine API does not expose user state independently of
+    a session.  To read user state, enumerate sessions via ``list_sessions``
+    and call ``get_session`` on each result to access the merged state.
+
+    Raises:
+      NotImplementedError: Always, because the Vertex AI Agent Engine API does
+        not provide a way to query user state without a session.
+    """
+    raise NotImplementedError(
+        'VertexAiSessionService does not support get_user_state. '
+        'The Vertex AI Agent Engine API does not expose user state '
+        'independently of a session. To read user state, enumerate sessions '
+        'via list_sessions and call get_session on each result.'
+    )
+
   @override
   async def append_event(self, session: Session, event: Event) -> Event:
     # Update the in-memory session.

tests/unittests/cli/utils/test_local_storage.py

@@ -19,6 +19,8 @@
 from google.adk.cli.utils.local_storage import create_local_database_session_service
 from google.adk.cli.utils.local_storage import create_local_session_service
 from google.adk.cli.utils.local_storage import PerAgentDatabaseSessionService
+from google.adk.events.event import Event
+from google.adk.events.event_actions import EventActions
 from google.adk.sessions.sqlite_session_service import SqliteSessionService
 import pytest
 
@@ -90,3 +92,28 @@ def test_create_local_database_session_service_returns_sqlite(
   service = create_local_database_session_service(base_dir=tmp_path)
 
   assert isinstance(service, SqliteSessionService)
+
+
+@pytest.mark.asyncio
+async def test_per_agent_session_service_get_user_state(tmp_path: Path) -> None:
+  agent_a = tmp_path / "agent_a"
+  agent_b = tmp_path / "agent_b"
+  agent_a.mkdir()
+  agent_b.mkdir()
+
+  service = PerAgentDatabaseSessionService(agents_root=tmp_path)
+
+  session_a = await service.create_session(app_name="agent_a", user_id="user_a")
+  await service.append_event(
+      session_a,
+      Event(
+          author="system",
+          actions=EventActions(state_delta={"user:profile": {"name": "Alice"}}),
+      ),
+  )
+
+  state_a = await service.get_user_state(app_name="agent_a", user_id="user_a")
+  state_b = await service.get_user_state(app_name="agent_b", user_id="user_b")
+
+  assert state_a == {"profile": {"name": "Alice"}}
+  assert state_b == {}

tests/unittests/sessions/test_session_service.py

@@ -30,6 +30,7 @@
 from google.adk.sessions.database_session_service import DatabaseSessionService
 from google.adk.sessions.in_memory_session_service import InMemorySessionService
 from google.adk.sessions.sqlite_session_service import SqliteSessionService
+from google.adk.sessions.vertex_ai_session_service import VertexAiSessionService
 from google.genai import types
 import pytest
 from sqlalchemy import delete
@@ -1650,3 +1651,122 @@ async def tracking_fn(**kwargs):
   finally:
     database_session_service._select_required_state = original_fn
     await service.close()
+
+
+@pytest.mark.asyncio
+async def test_get_user_state_returns_empty_dict_when_no_state_exists(
+    session_service,
+):
+  state = await session_service.get_user_state(app_name='my_app', user_id='u1')
+  assert state == {}
+
+
+@pytest.mark.asyncio
+async def test_get_user_state_returns_state_written_via_append_event(
+    session_service,
+):
+  session = await session_service.create_session(
+      app_name='my_app', user_id='u1'
+  )
+  await session_service.append_event(
+      session,
+      Event(
+          author='system',
+          actions=EventActions(
+              state_delta={'user:profile': {'name': 'Alice'}, 'session_key': 1}
+          ),
+      ),
+  )
+
+  state = await session_service.get_user_state(app_name='my_app', user_id='u1')
+
+  assert state == {'profile': {'name': 'Alice'}}
+  assert 'session_key' not in state
+
+
+@pytest.mark.asyncio
+async def test_get_user_state_is_not_visible_across_users(session_service):
+  session = await session_service.create_session(
+      app_name='my_app', user_id='u1'
+  )
+  await session_service.append_event(
+      session,
+      Event(
+          author='system',
+          actions=EventActions(state_delta={'user:secret': 'only-for-u1'}),
+      ),
+  )
+
+  other_state = await session_service.get_user_state(
+      app_name='my_app', user_id='u2'
+  )
+  assert other_state == {}
+
+
+@pytest.mark.asyncio
+async def test_get_user_state_is_not_visible_across_apps(session_service):
+  session = await session_service.create_session(
+      app_name='my_app', user_id='u1'
+  )
+  await session_service.append_event(
+      session,
+      Event(
+          author='system',
+          actions=EventActions(state_delta={'user:data': 'only-app-a'}),
+      ),
+  )
+
+  other_state = await session_service.get_user_state(
+      app_name='other_app', user_id='u1'
+  )
+  assert other_state == {}
+
+
+@pytest.mark.asyncio
+async def test_get_user_state_available_before_session_is_created(
+    session_service,
+):
+  first_session = await session_service.create_session(
+      app_name='my_app', user_id='u1'
+  )
+  await session_service.append_event(
+      first_session,
+      Event(
+          author='system',
+          actions=EventActions(state_delta={'user:ctx': {'v': 1}}),
+      ),
+  )
+
+  state = await session_service.get_user_state(app_name='my_app', user_id='u1')
+  assert state == {'ctx': {'v': 1}}
+
+
+@pytest.mark.asyncio
+async def test_get_user_state_reflects_latest_write(session_service):
+  session = await session_service.create_session(
+      app_name='my_app', user_id='u1'
+  )
+  await session_service.append_event(
+      session,
+      Event(
+          author='system',
+          actions=EventActions(state_delta={'user:counter': 1}),
+      ),
+  )
+  await session_service.append_event(
+      session,
+      Event(
+          author='system',
+          actions=EventActions(state_delta={'user:counter': 2}),
+      ),
+  )
+
+  state = await session_service.get_user_state(app_name='my_app', user_id='u1')
+  assert state['counter'] == 2
+
+
+@pytest.mark.asyncio
+async def test_vertex_ai_session_service_raises_not_implemented_for_get_user_state():
+  service = VertexAiSessionService(project='proj', location='us-central1')
+  with pytest.raises(NotImplementedError):
+    await service.get_user_state(app_name='my_app', user_id='u1')