fix(fastapi): pass state_delta to runner in /run endpoint

[pguerra-ce]

Fixes #2789

Summary

Forward state_delta from the FastAPI /run request to Runner.run_async(...), aligning behavior with the documented
API and the /run_sse endpoint.

Why

The documentation for /run explicitly includes:

state_delta (object, optional): A delta of the state to apply before the run.

However, the non‑SSE /run handler did not pass this value through, so Runner.run_async always received None. The
/run_sse path already forwarded it correctly.

Changes

• src/google/adk/cli/adk_web_server.py
  • Add state_delta=req.state_delta to the "/run" handler’s runner.run_async(...) call.
• tests/unittests/cli/test_fast_api.py
  • Add test_agent_run_passes_state_delta to test the fix.

[gemini-code-assist]

Summary of Changes

Hello @pguerra-ce, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a functional discrepancy in the FastAPI /run endpoint, ensuring that the state_delta parameter is correctly processed and forwarded. This change brings the endpoint's behavior into alignment with its specified API documentation and the existing /run_sse endpoint, improving consistency and reliability.

Highlights

• API Consistency: The /run FastAPI endpoint now correctly passes the state_delta parameter to Runner.run_async, resolving an inconsistency with its documented behavior and the /run_sse endpoint.
• Bug Fix: Addresses a bug where the state_delta value from the /run request was not being forwarded, always resulting in None for Runner.run_async.
• Test Coverage: A new unit test, test_agent_run_passes_state_delta, has been added to ensure the state_delta is properly handled and passed through the /run endpoint.

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[gemini-code-assist]

Code Review

This pull request correctly forwards the state_delta from the /run endpoint to the runner, aligning it with the /run_sse endpoint and the API documentation. The added test test_agent_run_passes_state_delta effectively verifies this fix. However, there is a critical issue that will break existing tests. The mock function dummy_run_async in tests/unittests/cli/test_fast_api.py, used by test_agent_run, is not updated to accept the new state_delta argument. Please update its signature to include state_delta=None to prevent a TypeError during testing.