GetSessionConfig ignored in A2aAgentExecutor._prepare_session()

[vnykdfd]

Environment

• ADK Version: 2.4.0 (latest main branch)
• Python: 3.10-3.14
• Operating System: All platforms
• Component: [Component] a2a

Bug Description

_prepare_session() in A2aAgentExecutor ignores GetSessionConfig(num_recent_events=N) by not forwarding it to session_service.get_session(), causing the entire event history to be loaded instead of respecting the configured limit.

Reproduction Steps

from google.adk.agents.run_config import RunConfig
from google.adk.sessions.base_session_service import GetSessionConfig
from google.adk.a2a.executor.a2a_agent_executor import A2aAgentExecutor

# Configure to load only 10 recent events
run_config = RunConfig(
    get_session_config=GetSessionConfig(num_recent_events=10)
)

# When A2A request is processed:
# _prepare_session() calls get_session() WITHOUT config parameter
# Result: ALL events loaded (e.g., 291 events instead of 10)

Expected Behavior

Session service should load at most 10 events when num_recent_events=10 is configured.

Observed Behavior

Session service loads ALL events regardless of get_session_config setting, causing:

• 10-100x more database I/O than configured
• 200-300ms added latency per request (observed in production)
• Higher memory usage (~300KB vs ~10KB)
• Higher token costs (sending excessive context to LLM)

Root Cause

File: src/google/adk/a2a/executor/a2a_agent_executor.py
Function: _prepare_session() (lines 310-339)

Line 320 calls session_service.get_session() without passing config=:

# CURRENT (BUG)
session = await runner.session_service.get_session(
    app_name=runner.app_name,
    user_id=user_id,
    session_id=session_id,
    # ← Missing: config=get_session_config
)

Proposed Solution

Extract get_session_config from run_request.run_config and forward it:

# FIX
get_session_config = None
if run_request.run_config:
    get_session_config = run_request.run_config.get_session_config

session = await runner.session_service.get_session(
    app_name=runner.app_name,
    user_id=user_id,
    session_id=session_id,
    config=get_session_config,  # ← ADDED
)

Impact

• Severity: High for production A2A agents with chat mode
• Affected Users: Anyone using A2A protocol with session history and GetSessionConfig
• Workaround: None (config is silently ignored)

Willingness to Contribute

Yes, I have a fix ready with:

• 4-line code change
• 3 new unit tests
• All 372 A2A tests passing
• Pre-commit hooks passing

I will submit a PR shortly.

Additional Context

This only affects the legacy A2aAgentExecutor path. The newer _A2aAgentExecutor implementation doesn't have this issue.

[surajksharma07]

@vnykdfd thanks for the detailed report and the PR — reproduced the bug independently and confirmed your fix (forwarding get_session_config through to get_session()) resolves it cleanly on our end, so no further repro details needed from you.

One thing worth confirming before we move #6412 forward: does the newer _A2aAgentExecutor path actually forward a caller's real get_session_config anywhere in its run flow, or does it only zero it out for the existence check?

Once that's clarified we're good to proceed with review!

[vdoifode-equinix]

Hey @surajksharma07
Got similar comment in the PR I raised.

#6412 (comment)

Please review the comments..