feat: add JSON-RPC method to ServerCallContext.state (#463)

# Improvement SDK users sometimes need to know which JSON-RPC method is being processed to adjust their implementation, e.g.: * If the method is `message/send`, they may want to use `invoke()`/`run()` when calling their LLM API, and `stream()`/`run_streamed()` for `message/stream`. # Implementation Added a `method` field to `ServerCallContext.state`, similar to `headers`. # Tests Added a small test to ensure that method parsing is correct. Fixes #451

Author: ovidiutaralesca

src/a2a/server/apps/jsonrpc/jsonrpc_app.py

@@ -337,6 +337,7 @@ async def _handle_requests(self, request: Request) -> Response: # noqa: PLR0911
 
  # 3) Build call context and wrap the request for downstream handling
  call_context = self._context_builder.build(request)
+ call_context.state['method'] = method
 
  request_id = specific_request.id
  a2a_request = A2ARequest(root=specific_request)

tests/server/apps/jsonrpc/test_jsonrpc_app.py

@@ -289,6 +289,26 @@ def test_request_with_comma_separated_extensions_no_space(
  call_context = mock_handler.on_message_send.call_args[0][1]
  assert call_context.requested_extensions == {'foo', 'bar', 'baz'}
 
+ def test_method_added_to_call_context_state(self, client, mock_handler):
+ response = client.post(
+ '/',
+ json=SendMessageRequest(
+ id='1',
+ params=MessageSendParams(
+ message=Message(
+ message_id='1',
+ role=Role.user,
+ parts=[Part(TextPart(text='hi'))],
+ )
+ ),
+ ).model_dump(),
+ )
+ response.raise_for_status()
+
+ mock_handler.on_message_send.assert_called_once()
+ call_context = mock_handler.on_message_send.call_args[0][1]
+ assert call_context.state['method'] == 'message/send'
+
  def test_request_with_multiple_extension_headers(
  self, client, mock_handler
  ):