Align event filtering and ordering logic

Copybara import of the project:

--
d01a8fd5f079bc4fca9e4b71796dbe65312ce9ff by Leo Yongsul Kim <ystory84@gmail.com>:

fix(DatabaseSessionService): Align event filtering and ordering logic

This commit addresses inconsistencies in how DatabaseSessionService
handles config.after_timestamp and config.num_recent_events
parameters, aligning its behavior with InMemorySessionService and
VertexAiSessionService.

Key changes:
- Made after_timestamp filtering inclusive
- Corrected num_recent_events behavior to fetch the N most recent events
- Refined timezone handling for after_timestamp
- Updated the unit test test_get_session_with_config to includeSessionServiceType.DATABASE, allowing verification of these fixes.

Fixes #911

COPYBARA_INTEGRATE_REVIEW=https://github.com/google/adk-python/pull/915 from ystory:fix/database-session-timestamp-recency 5cc8cf5f5a5c0cb3e87f6ab178a5725d3f696c88
PiperOrigin-RevId: 763874840

src/google/adk/sessions/database_session_service.py

@@ -13,7 +13,6 @@
 # limitations under the License.
 import copy
 from datetime import datetime
-from datetime import timezone
 import json
 import logging
 from typing import Any
@@ -371,10 +370,8 @@ class DatabaseSessionService(BaseSessionService):
         return None
 
       if config and config.after_timestamp:
-        after_dt = datetime.fromtimestamp(
-            config.after_timestamp, tz=timezone.utc
-        )
-        timestamp_filter = StorageEvent.timestamp > after_dt
+        after_dt = datetime.fromtimestamp(config.after_timestamp)
+        timestamp_filter = StorageEvent.timestamp >= after_dt
       else:
         timestamp_filter = True
 
@@ -382,7 +379,7 @@ class DatabaseSessionService(BaseSessionService):
           session_factory.query(StorageEvent)
           .filter(StorageEvent.session_id == storage_session.id)
           .filter(timestamp_filter)
-          .order_by(StorageEvent.timestamp.asc())
+          .order_by(StorageEvent.timestamp.desc())
           .limit(
               config.num_recent_events
               if config and config.num_recent_events
@@ -429,7 +426,7 @@ class DatabaseSessionService(BaseSessionService):
               error_message=e.error_message,
               interrupted=e.interrupted,
           )
-          for e in storage_events
+          for e in reversed(storage_events)
       ]
     return session
 

tests/unittests/sessions/test_session_service.py

@@ -315,7 +315,7 @@ async def test_append_event_complete(service_type):
 
 
 @pytest.mark.asyncio
-@pytest.mark.parametrize('service_type', [SessionServiceType.IN_MEMORY])
+@pytest.mark.parametrize('service_type', [SessionServiceType.IN_MEMORY, SessionServiceType.DATABASE])
 async def test_get_session_with_config(service_type):
   session_service = get_session_service(service_type)
   app_name = 'my_app'