fix(client): do not mutate SendMessageRequest in BaseClient.send_message (#949)

Updating passed parameter by reference is not great.

Author: ishymko

src/a2a/client/base_client.py

@@ -66,7 +66,7 @@ async def send_message(
         Yields:
             An async iterator of `StreamResponse`
         """
-        self._apply_client_config(request)
+        request = self._apply_client_config(request)
         if not self._config.streaming or not self._card.capabilities.streaming:
             response = await self._execute_with_interceptors(
                 input_data=request,
@@ -100,22 +100,29 @@ async def send_message(
         ):
             yield event
 
-    def _apply_client_config(self, request: SendMessageRequest) -> None:
-        request.configuration.return_immediately |= self._config.polling
-        if (
-            not request.configuration.HasField('task_push_notification_config')
-            and self._config.push_notification_configs
+    def _apply_client_config(
+        self, request: SendMessageRequest
+    ) -> SendMessageRequest:
+        modified_request = SendMessageRequest()
+        modified_request.CopyFrom(request)
+        if self._config.polling:
+            modified_request.configuration.return_immediately = True
+        if self._config.push_notification_configs and (
+            not modified_request.configuration.HasField(
+                'task_push_notification_config'
+            )
         ):
-            request.configuration.task_push_notification_config.CopyFrom(
+            modified_request.configuration.task_push_notification_config.CopyFrom(
                 self._config.push_notification_configs[0]
             )
         if (
-            not request.configuration.accepted_output_modes
-            and self._config.accepted_output_modes
+            self._config.accepted_output_modes
+            and not modified_request.configuration.accepted_output_modes
         ):
-            request.configuration.accepted_output_modes.extend(
+            modified_request.configuration.accepted_output_modes.extend(
                 self._config.accepted_output_modes
             )
+        return modified_request
 
     async def _process_stream(
         self,

tests/client/test_base_client.py

@@ -208,6 +208,41 @@ async def test_send_message_non_streaming_agent_capability_false(
         response = events[0]
         assert response.task.id == 'task-789'
 
+    @pytest.mark.asyncio
+    async def test_send_message_does_not_mutate_request(
+        self,
+        base_client: BaseClient,
+        mock_transport: MagicMock,
+        sample_message: Message,
+    ):
+        base_client._config.streaming = False
+        base_client._config.polling = True
+        base_client._config.accepted_output_modes = ['application/json']
+        base_client._config.push_notification_configs = [
+            TaskPushNotificationConfig(
+                task_id='task-1',
+            )
+        ]
+
+        task = Task(
+            id='task-no-mutate',
+            context_id='ctx-no-mutate',
+            status=TaskStatus(state=TaskState.TASK_STATE_COMPLETED),
+        )
+        response = SendMessageResponse()
+        response.task.CopyFrom(task)
+        mock_transport.send_message.return_value = response
+
+        request = SendMessageRequest(message=sample_message)
+
+        original = SendMessageRequest()
+        original.CopyFrom(request)
+
+        events = [event async for event in base_client.send_message(request)]
+        assert len(events) == 1
+
+        assert request == original
+
     @pytest.mark.asyncio
     async def test_send_message_callsite_config_overrides_non_streaming(
         self,