ResponseContentPartAddedEvent

{
    "type": "response.content_part.added",
    "item_id": "string",
    "output_index": 0,
    "content_index": 0,
    "part": {
        "type": "output_text",
        "text": "string",
        "annotations": [
            {
                "type": "file_citation",
                "file_id": "string",
                "index": 0
            }
        ]
    }
}