ADKのA2Aサーバとなったget_fast_api_app()
get_fast_api_app(a2a=True)
https://github.com/google/adk-python/blob/v1.25.0/src/google/adk/cli/fast_api.py#L525-L591
A2AStarletteApplication
a2a.server.request_handlers.DefaultRequestHandler
google.adk.a2a.executor.a2a_agent_executor.A2aAgentExecutor
Python Quickstart Tutorial: Building an A2A Agent