fix: Update session last update time when appending events

The `database_session_service` now updates the `update_time` of a session to the event's timestamp when an event is appended

Close #2721

Co-authored-by: George Weale <gweale@google.com>
PiperOrigin-RevId: 834994070

src/google/adk/sessions/database_session_service.py

@@ -722,6 +722,11 @@ class DatabaseSessionService(BaseSessionService):
         if session_state_delta:
           storage_session.state = storage_session.state | session_state_delta
 
+      if storage_session._dialect_name == "sqlite":
+        update_time = datetime.utcfromtimestamp(event.timestamp)
+      else:
+        update_time = datetime.fromtimestamp(event.timestamp)
+      storage_session.update_time = update_time
       sql_session.add(StorageEvent.from_event(session, event))
 
       await sql_session.commit()

src/google/adk/sessions/sqlite_session_service.py

@@ -323,7 +323,7 @@ class SqliteSessionService(BaseSessionService):
 
     # Trim temp state before persisting
     event = self._trim_temp_delta_state(event)
-    now = time.time()
+    event_timestamp = event.timestamp
 
     async with self._get_db_connection() as db:
       # Check for stale session
@@ -355,11 +355,15 @@ class SqliteSessionService(BaseSessionService):
 
         if app_state_delta:
           await self._upsert_app_state(
-              db, session.app_name, app_state_delta, now
+              db, session.app_name, app_state_delta, event_timestamp
           )
         if user_state_delta:
           await self._upsert_user_state(
-              db, session.app_name, session.user_id, user_state_delta, now
+              db,
+              session.app_name,
+              session.user_id,
+              user_state_delta,
+              event_timestamp,
           )
         if session_state_delta:
           await self._update_session_state_in_db(
@@ -368,7 +372,7 @@ class SqliteSessionService(BaseSessionService):
               session.user_id,
               session.id,
               session_state_delta,
-              now,
+              event_timestamp,
           )
           has_session_state_delta = True
 
@@ -392,12 +396,17 @@ class SqliteSessionService(BaseSessionService):
         await db.execute(
             "UPDATE sessions SET update_time=? WHERE app_name=? AND user_id=?"
             " AND id=?",
-            (now, session.app_name, session.user_id, session.id),
+            (
+                event_timestamp,
+                session.app_name,
+                session.user_id,
+                session.id,
+            ),
         )
       await db.commit()
 
-      # Update timestamp with commit time
-      session.last_update_time = now
+      # Update timestamp based on event time
+      session.last_update_time = event_timestamp
 
     # Also update the in-memory session
     await super().append_event(session=session, event=event)

tests/unittests/sessions/test_session_service.py

@@ -531,6 +531,79 @@ async def test_append_event_complete(service_type, tmp_path):
   )
 
 
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    'service_type',
+    [
+        SessionServiceType.IN_MEMORY,
+        SessionServiceType.DATABASE,
+        SessionServiceType.SQLITE,
+    ],
+)
+async def test_session_last_update_time_updates_on_event(
+    service_type, tmp_path
+):
+  session_service = get_session_service(service_type, tmp_path)
+  app_name = 'my_app'
+  user_id = 'user'
+
+  session = await session_service.create_session(
+      app_name=app_name, user_id=user_id
+  )
+  original_update_time = session.last_update_time
+
+  event_timestamp = original_update_time + 10
+  event = Event(
+      invocation_id='invocation',
+      author='user',
+      timestamp=event_timestamp,
+  )
+  await session_service.append_event(session=session, event=event)
+
+  assert session.last_update_time == pytest.approx(event_timestamp, abs=1e-6)
+
+  refreshed_session = await session_service.get_session(
+      app_name=app_name, user_id=user_id, session_id=session.id
+  )
+  assert refreshed_session is not None
+  assert refreshed_session.last_update_time == pytest.approx(
+      event_timestamp, abs=1e-6
+  )
+  assert refreshed_session.last_update_time > original_update_time
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    'service_type',
+    [
+        SessionServiceType.IN_MEMORY,
+        SessionServiceType.DATABASE,
+        SessionServiceType.SQLITE,
+    ],
+)
+async def test_get_session_with_config(service_type):
+  session_service = get_session_service(service_type)
+  app_name = 'my_app'
+  user_id = 'user'
+
+  session = await session_service.create_session(
+      app_name=app_name, user_id=user_id
+  )
+  original_update_time = session.last_update_time
+
+  event = Event(invocation_id='invocation', author='user')
+  await session_service.append_event(session=session, event=event)
+
+  assert session.last_update_time >= event.timestamp
+
+  refreshed_session = await session_service.get_session(
+      app_name=app_name, user_id=user_id, session_id=session.id
+  )
+  assert refreshed_session is not None
+  assert refreshed_session.last_update_time >= event.timestamp
+  assert refreshed_session.last_update_time > original_update_time
+
+
 @pytest.mark.asyncio
 @pytest.mark.parametrize(
     'service_type',