| Assistant message             | An output message Item in `response.output`; pass it back in `input` if you manually manage state      |
| Tool or function call         | A `function_call` output Item                                                                          |
| Tool or function result       | A `function_call_output` input Item linked to the call with `call_id`                                  |
| Multiple generations with `n` | Not available in Responses; make separate requests if you need multiple candidate outputs              |
