Bug: broadcast step is failed

### Describe Bug

发现在 #5 中有提到失效的问题，目前我似乎也遇到这个问题。我目前定位到的有可能是 broadcast 的问题。

GitHub 成功发送了信息，并且在 ctx.broadcast 前似乎都是正常的，但在 ctx.broadcast 后却什么都没有返回，信息也没有发出去。

中间发生了什么错误我没去继续查

### Addition Context

Bot 的发言没有受到 QQ 限制

Reproduce the reported GitHub message flow and compare what happens before and after ctx.broadcast. Inspect the broadcast failure and its error output; the issue is resolved when the message is successfully sent through broadcast and the failure cause is understood.

Written by the indexing model from the issue text.