refactor(server)!: migrate from Application wrappers to Starlette route-based endpoints for jsonrpc (#873)

# Description

This PR refactors the jsonrpc server implementation to expose Starlette
Route components directly (via AgentCardRoutes, JsonRpcRoutes) instead
of requiring full FastAPI or Starlette application wrappers.

Ref #797  🦕

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: guglielmo-san

samples/hello_world_agent.py

@@ -11,12 +11,13 @@
 from a2a.compat.v0_3.grpc_handler import CompatGrpcHandler
 from a2a.server.agent_execution.agent_executor import AgentExecutor
 from a2a.server.agent_execution.context import RequestContext
-from a2a.server.apps import A2AFastAPIApplication, A2ARESTFastAPIApplication
+from a2a.server.apps import A2ARESTFastAPIApplication
 from a2a.server.events.event_queue import EventQueue
 from a2a.server.request_handlers import GrpcHandler
 from a2a.server.request_handlers.default_request_handler import (
     DefaultRequestHandler,
 )
+from a2a.server.routes import create_agent_card_routes, create_jsonrpc_routes
 from a2a.server.tasks.inmemory_task_store import InMemoryTaskStore
 from a2a.server.tasks.task_updater import TaskUpdater
 from a2a.types import (
@@ -197,14 +198,17 @@ async def serve(
     )
     rest_app = rest_app_builder.build()
 
-    jsonrpc_app_builder = A2AFastAPIApplication(
+    jsonrpc_routes = create_jsonrpc_routes(
+        agent_card=agent_card,
+        request_handler=request_handler,
+        rpc_url='/a2a/jsonrpc/',
+    )
+    agent_card_routes = create_agent_card_routes(
         agent_card=agent_card,
-        http_handler=request_handler,
-        enable_v0_3_compat=True,
     )
-
     app = FastAPI()
-    jsonrpc_app_builder.add_routes_to_app(app, rpc_url='/a2a/jsonrpc/')
+    app.routes.extend(jsonrpc_routes)
+    app.routes.extend(agent_card_routes)
     app.mount('/a2a/rest', rest_app)
 
     grpc_server = grpc.aio.server()

src/a2a/compat/v0_3/jsonrpc_adapter.py

@@ -10,8 +10,8 @@
 if TYPE_CHECKING:
     from starlette.requests import Request
 
-    from a2a.server.apps.jsonrpc.jsonrpc_app import CallContextBuilder
     from a2a.server.request_handlers.request_handler import RequestHandler
+    from a2a.server.routes import CallContextBuilder
     from a2a.types.a2a_pb2 import AgentCard
 
     _package_starlette_installed = True

src/a2a/compat/v0_3/rest_adapter.py

@@ -33,12 +33,9 @@
 
 from a2a.compat.v0_3 import conversions
 from a2a.compat.v0_3.rest_handler import REST03Handler
-from a2a.server.apps.jsonrpc.jsonrpc_app import (
-    CallContextBuilder,
-    DefaultCallContextBuilder,
-)
 from a2a.server.apps.rest.rest_adapter import RESTAdapterInterface
 from a2a.server.context import ServerCallContext
+from a2a.server.routes import CallContextBuilder, DefaultCallContextBuilder
 from a2a.utils.error_handlers import (
     rest_error_handler,
     rest_stream_error_handler,

src/a2a/server/apps/__init__.py

@@ -1,18 +1,8 @@
 """HTTP application components for the A2A server."""
 
-from a2a.server.apps.jsonrpc import (
-    A2AFastAPIApplication,
-    A2AStarletteApplication,
-    CallContextBuilder,
-    JSONRPCApplication,
-)
 from a2a.server.apps.rest import A2ARESTFastAPIApplication
 
 
 __all__ = [
-    'A2AFastAPIApplication',
     'A2ARESTFastAPIApplication',
-    'A2AStarletteApplication',
-    'CallContextBuilder',
-    'JSONRPCApplication',
 ]