tests: assert post-run session state from refetched snapshot

tests/unittests/test_runners.py

@@ -676,6 +676,36 @@ async def test_run_config_custom_metadata_propagates_to_events():
   assert user_event.custom_metadata == {"request_id": "req-1"}
 
 
+@pytest.mark.asyncio
+async def test_run_async_assertions_use_refetched_session_snapshot():
+  session_service = InMemorySessionService()
+  runner = Runner(
+      app_name=TEST_APP_ID,
+      agent=MockAgent("snapshot_agent"),
+      session_service=session_service,
+      artifact_service=InMemoryArtifactService(),
+  )
+  created_session = await session_service.create_session(
+      app_name=TEST_APP_ID, user_id=TEST_USER_ID, session_id=TEST_SESSION_ID
+  )
+
+  async for _ in runner.run_async(
+      user_id=TEST_USER_ID,
+      session_id=TEST_SESSION_ID,
+      new_message=types.Content(role="user", parts=[types.Part(text="hi")]),
+  ):
+    pass
+
+  # InMemorySessionService returns copies; the original handle is stale after run_async.
+  assert len(created_session.events) == 0
+
+  refreshed_session = await session_service.get_session(
+      app_name=TEST_APP_ID, user_id=TEST_USER_ID, session_id=TEST_SESSION_ID
+  )
+  assert refreshed_session is not None
+  assert len(refreshed_session.events) > 0
+
+
 class TestRunnerWithPlugins:
   """Tests for Runner with plugins."""