feat(a2a): support passing additional keyword arguments to FastAPI and Starlette constructors

[snooyen]

Description

• feat(a2a): update to_fastapi_app() to allow passing additional keyword arguments to fastapi constructor
• feat(a2a): update to_starlette_app() to allow passing additional keyword arguments to starlette constructor

Use case

• Allowing users to pass additional keyword arguments to fastapi and starlette constructors supports further advanced
  customization of A2A servers.
• For FastAPI specifically, this PR enables users to customize:
  • Startup / Shutdown events by passing a lifespan function
    to the FastAPI constructor. This is preferable to using the now
    deprecated startup/shutdown event
    handlers.
  • enabling/disabling documentation endpoints
  • enabling/disabling debug tracebacks

Example code:

from contextlib import asynccontextmanager
from fastapi import FastAPI
from strands import Agent
from strands.multiagent.a2a import A2AServer

def initialize_app() -> FastAPI:
    """Initialize and configure FastAPI application."""


    @asynccontextmanager
    async def lifespan(app: FastAPI):
        """Manage application lifespan with proper error handling."""
        # Startup tasks
        yield  # Application runs here
        # Shutdown tasks

    # Create your agent and A2A server
    agent = Agent(name="My Agent", description="A customizable agent", callback_handler=None)
    a2a_server = A2AServer(agent=agent)

    serve_docs_enabled = False

    app = a2a_server.to_fastapi_app(
        title=config.app_name,
        docs_url="/docs" if serve_docs_enabled else None,
        redoc_url="/redoc" if serve_docs_enabled else None,
        openapi_url="/openapi.json" if serve_docs_enabled else None,
        debug=config.debug,
        lifespan=lifespan,
    )


    return app

Related Issues

• [FEATURE] Add support for passing keyword arguments to A2A FastAPI and Starlette constructors #1249

Documentation PR

• feat(a2a): updates advanced server customization example code to demonstrate passing additional keyword arguments to FastAPI and Starlette constructors docs#342

Type of Change

New feature

Testing

How have you tested the change? Verify that the changes do not break functionality or introduce warnings in consuming
repositories: agents-docs, agents-tools, agents-cli

• I ran hatch run prepare

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[afarntrog]

This is an older PR so the lint is failing due to a fix we put into main ~last week. Would pass in the merge queue.