there is no import TaskCallback

### What happened?

Traceback (most recent call last): File "/Users/ninebot/Desktop/workspace/A2A/a2a-samples/demo/ui/main.py", line 28, in from service.server.server import ConversationServer File "/Users/ninebot/Desktop/workspace/A2A/a2a-samples/demo/ui/service/server/server.py", line 27, in from .adk_host_manager import ADKHostManager, get_message_id File "/Users/ninebot/Desktop/workspace/A2A/a2a-samples/demo/ui/service/server/adk_host_manager.py", line 35, in from hosts.multiagent.remote_agent_connection import ( TaskCallbackArg, ) ImportError: cannot import name 'TaskCallbackArg' from 'hosts.multiagent.remote_agent_connection' (/Users/ninebot/Desktop/workspace/A2A/a2a-samples/samples/python/hosts/multiagent/remote_agent_connection.py) (a2a-

### Relevant log output

```shell

```

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

O erro é um ImportError para 'TaskCallbackArg' de 'hosts.multiagent.remote_agent_connection'. Veja o arquivo /samples/python/hosts/multiagent/remote_agent_connection.py para ver o que é exportado. Verifique se TaskCallbackArg está definido ali ou precisa ser importado de outro módulo. A correção provavelmente envolve adicionar o import ausente ou corrigir a lista de exportação nesse arquivo. Execute o import que falha em demo/ui/main.py para verificar a correção.

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