Streaming · Anthropic format
/v1/messages 的事件序列
/v1/messages 带 stream: true 时，不论由哪个上游 provider 服务，都会发出以下事件序列:
event: message_start
data: {"type":"message_start","message":{...}}
event: content_block_start
data: {"type":"content_block_start","index":0,"content_block":{"type":"text","text":""}}
# one per delta:
event: content_block_delta
data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":"..."}}
event: content_block_stop
data: {"type":"content_block_stop","index":0}
event: message_delta
data: {"type":"message_delta","delta":{"stop_reason":"end_turn"},"usage":{"output_tokens":N}}
event: message_stop
data: {"type":"message_stop"}stop_reason 依 provider 对应:stop → end_turn，length → max_tokens。