AdkApp.async_get_session does not support GetSessionConfig, making event filtering impossible for deployed agents

[davkutalek]

Description

There are two issues that prevent external callers from being able to filter the events fetched when calling async_get_session on a deployed Agent Engine agent:

1. AdkApp.async_get_session doesn't deserialize config from kwargs (ADK bug)
   AdkApp.async_get_session accepts **kwargs and forwards them to session_service.get_session():

vertexai/agent_engines/templates/adk.py L1282-1314
async def async_get_session(self, *, user_id: str, session_id: str, **kwargs):

    session = await self._tmpl_attrs.get("session_service").get_session(
        app_name=...,
        user_id=user_id,
        session_id=session_id,
        **kwargs,
    )

BaseSessionService.get_session expects config: Optional[GetSessionConfig], which is a Pydantic BaseModel. If a caller passes config={"num_recent_events": 10} (a dict, as would arrive from JSON deserialization), it will fail because the dict is not automatically coerced into a GetSessionConfig instance.

The fix would be to deserialize the dict in async_get_session:

from google.adk.sessions.base_session_service import GetSessionConfig
async def async_get_session(self, *, user_id: str, session_id: str, **kwargs):
    if "config" in kwargs and isinstance(kwargs["config"], dict):
        kwargs["config"] = GetSessionConfig(**kwargs["config"])
    ...

2. Agent Engine platform does not forward extra params (platform issue)
   Even after the above fix, the Agent Engine platform proxy — the closed-source layer that receives external API requests and invokes methods on the deployed agent — only forwards user_id and session_id to async_get_session. There is no mechanism for an external caller to include config, num_recent_events, after_timestamp, or any other parameter in the request.

Steps to reproduce

Deploy an ADK agent to Agent Engine
Create a session and run a query (generates events)
Call async_get_session through the Agent Engine API with user_id and session_id
Observe there is no way to pass GetSessionConfig params num_recent_events or after_timestamp through the API
Even if you could, the **kwargs would pass a raw dict to session_service.get_session() which expects a GetSessionConfig instance — this would raise an error

Expected behavior

AdkApp.async_get_session should accept and deserialize GetSessionConfig-compatible parameters from kwargs
The Agent Engine platform should forward these parameters from the external API request to the deployed agent method

Related issues

#3562 — Runner.run_async also doesn't pass GetSessionConfig to get_session (same gap, internal code path)
#3039 — VertexAiSessionService.get_session becomes slow with many events (consequence of never filtering)

Environment

google-adk 1.x (latest)
google-cloud-aiplatform (latest)
Deployed to Vertex AI Agent Engine

[klateefa]

@davkutalek Thanks for reporting.Yes, get_session expects a GetSessionConfig, but sometimes it receives a dict (from JSON), which causes an error.Instead of fixing this in async_get_session, Try to handle it inside get_session by converting the dict to GetSessionConfig. Can you please try this and let me know if the issue persists?
Thank you.