From 24342e95f868ab6511fa4472bffcb1356b3d952c Mon Sep 17 00:00:00 2001
From: "Wei Sun (Jack)" <weisun@google.com>
Date: Wed, 8 Oct 2025 16:13:08 -0700
Subject: [PATCH] chore: Remove temp state deltas before appending an event

PiperOrigin-RevId: 816902208
---
 .../adk/sessions/base_session_service.py      | 19 ++++++++--
 .../adk/sessions/database_session_service.py  |  3 ++
 .../sessions/test_session_service.py          | 36 +++++++++++++++++++
 3 files changed, 56 insertions(+), 2 deletions(-)

diff --git a/src/google/adk/sessions/base_session_service.py b/src/google/adk/sessions/base_session_service.py
index 25e46ba1..a76a6b9d 100644
--- a/src/google/adk/sessions/base_session_service.py
+++ b/src/google/adk/sessions/base_session_service.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from __future__ import annotations
+
 import abc
 from typing import Any
 from typing import Optional
@@ -95,11 +97,24 @@ class BaseSessionService(abc.ABC):
     """Appends an event to a session object."""
     if event.partial:
       return event
-    self.__update_session_state(session, event)
+    event = self._trim_temp_delta_state(event)
+    self._update_session_state(session, event)
     session.events.append(event)
     return event
 
-  def __update_session_state(self, session: Session, event: Event) -> None:
+  def _trim_temp_delta_state(self, event: Event) -> Event:
+    """Removes temporary state delta keys from the event."""
+    if not event.actions or not event.actions.state_delta:
+      return event
+
+    event.actions.state_delta = {
+        key: value
+        for key, value in event.actions.state_delta.items()
+        if not key.startswith(State.TEMP_PREFIX)
+    }
+    return event
+
+  def _update_session_state(self, session: Session, event: Event) -> None:
     """Updates the session state based on the event."""
     if not event.actions or not event.actions.state_delta:
       return
diff --git a/src/google/adk/sessions/database_session_service.py b/src/google/adk/sessions/database_session_service.py
index 959524c6..3ed87847 100644
--- a/src/google/adk/sessions/database_session_service.py
+++ b/src/google/adk/sessions/database_session_service.py
@@ -599,6 +599,9 @@ class DatabaseSessionService(BaseSessionService):
     if event.partial:
       return event
 
+    # Trim temp state before persisting
+    event = self._trim_temp_delta_state(event)
+
     # 1. Check if timestamp is stale
     # 2. Update session attributes based on event config
     # 3. Store event to table
diff --git a/tests/unittests/sessions/test_session_service.py b/tests/unittests/sessions/test_session_service.py
index c2a3a1d9..2ca265cb 100644
--- a/tests/unittests/sessions/test_session_service.py
+++ b/tests/unittests/sessions/test_session_service.py
@@ -441,3 +441,39 @@ async def test_append_event_with_fields(service_type):
   retrieved_event = retrieved_session.events[0]
 
   assert retrieved_event == event
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    'service_type', [SessionServiceType.IN_MEMORY, SessionServiceType.DATABASE]
+)
+async def test_append_event_should_trim_temp_delta_state(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
+  )
+
+  event = Event(
+      invocation_id='invocation',
+      author='user',
+      content=types.Content(role='user', parts=[types.Part(text='text')]),
+      actions=EventActions(
+          state_delta={
+              'app:key': 'app_value',
+              'temp:key': 'temp_value',
+          }
+      ),
+  )
+
+  await session_service.append_event(session, event)
+
+  updated_session = await session_service.get_session(
+      app_name=app_name, user_id=user_id, session_id=session.id
+  )
+
+  last_event = updated_session.events[-1]
+  assert 'temp:key' not in last_event.actions.state_delta
+  assert last_event.actions.state_delta['app:key'] == 'app_value'