ResponseStreamEvent
SSE stream event. Discriminate by the `type` field: - `response.created`: Initial response object - `response.in_progress`: Response processing started - `response.completed`: Final response with output - `response.failed`: Error occurred - `response.output_item.added`: New output item started - `response.output_item.done`: Output item completed - `response.output_text.delta`: Streaming text delta - `response.output_text.done`: Final text content - `response.reasoning.started`: Reasoning phase started - `response.reasoning.search_queries`: Search queries issued - `response.reasoning.search_results`: Search results received - `response.reasoning.fetch_url_queries`: URL fetch queries issued - `response.reasoning.fetch_url_results`: URL fetch results received - `response.reasoning.stopped`: Reasoning phase complete