请求补充 websocket 协议文档

您好！目前，项目内没有 websocket 协议相关的文档。这导致开发第三方客户端时，严重依赖于追踪现有代码。若协议更改，维护者可能不方便进行跟踪。因此请求补充有关 websocket 协议的文档，谢谢！

The issue names no files, tests, or entry points. Start by tracing the existing WebSocket handling referenced in the issue, then identify the protocol behavior a third-party client needs; done means the WebSocket protocol is documented well enough that clients no longer need to track the implementation.

Written by the indexing model from the issue text.