fix: Refactor session retrieval fallback in _streaming_agent_run_with_events.

PiperOrigin-RevId: 869447429

Author: Tongzhou-Jiang

vertexai/agent_engines/templates/adk.py

@@ -1183,13 +1183,16 @@ async def streaming_agent_run_with_events(self, request_json: str):
             session_service = self._tmpl_attrs.get("session_service")
             artifact_service = self._tmpl_attrs.get("artifact_service")
             runner = self._tmpl_attrs.get("runner")
+            session = None
             try:
                 session = await session_service.get_session(
                     app_name=app.name if app else self._tmpl_attrs.get("app_name"),
                     user_id=request.user_id,
                     session_id=request.session_id,
                 )
             except ClientError:
+                pass
+            if not session:
                 #  Fall back to create session if the session is not found.
                 #  Specifying session_id on creation is not supported,
                 #  so session id will be regenerated.

vertexai/preview/reasoning_engines/templates/adk.py

@@ -1017,14 +1017,19 @@ async def _invoke_agent_async():
                 session_service = self._tmpl_attrs.get("session_service")
                 artifact_service = self._tmpl_attrs.get("artifact_service")
                 runner = self._tmpl_attrs.get("runner")
+                session = None
                 try:
                     session = await session_service.get_session(
                         app_name=self._tmpl_attrs.get("app_name"),
                         user_id=request.user_id,
                         session_id=request.session_id,
                     )
                 except ClientError:
+                    pass
+                if not session:
                     #  Fall back to create session if the session is not found.
+                    #  Specifying session_id on creation is not supported,
+                    #  so session id will be regenerated.
                     session = await self._init_session(
                         session_service=session_service,
                         artifact_service=artifact_service,