Execution failed: 421 Misdirected Request listing models

Describe the bug

Hello, sorry for resuming the issue #173 , but today:

GitHub Copilot CLI 1.0.85.
Run 'copilot update' to check for updates.

Free copilot plan, i try to do /model and i get the issue:
Error loading model list: Error: 421 "Misdirected Request\n" (Request ID: ....)

Then i tried /model auto and that worked:
Model changed from claude-sonnet-5 (medium) to Auto for this session

And now i cant go back to my selected model, doing /model claude-sonnet-5 gives:
Unable to load available models list

Is this a bug or something expected related to free plan?

Affected version

GitHub Copilot CLI 1.0.85.

Steps to reproduce the behavior

1. Resumed an old session, using a free plan
2. type /model
3. See the 421 error

Expected behavior

I expect to see the list of models when typing /model and to get a "model changed" confirmation when typing /model claude-sonnet-5

Additional context

No response

使用免费计划恢复会话并运行 /model，重现 GitHub Copilot CLI 1.0.85 中的故障，然后将其与 /model auto 和 /model claude-sonnet-5 进行比较。跟踪 model-list 请求的处理和 421 响应；当模型列表和 claude-sonnet-5 的选择都能在确认后成功时，该 issue 即完成。