Growing number of active sessions start failing with persistent CAPI errors

After a couple interactions in a session, Github Copilot App starts to generate errors like
Execution failed: CAPIError: 400 The resource you requested was not found. (Request ID: 00000-a81acc34-0aa3-4947-9ac9-5cb965bb84b9)
The errors persist until I switch to a new session or tentatively restart the Github Copilot App.
I am using Github Copilot App using my Microsoft employee account so I have a Copilot license.

首先，在一个会话中进行几次交互后，重现 GitHub Copilot App 中的故障，并记录 CAPI 400 错误和 request ID。比较切换会话或重启应用后的行为；在继续使用期间不再出现持续性错误即表示完成。

由索引模型根据 Issue 内容生成。