Cannot switch models in sessions using the 1.1M context window #4802

What happened?

In GitHub Copilot App v1.1.29, after starting or using a session with GPT-5.6 Sol using the 1.1M context window, trying to switch to another model (for example, GPT-6.1 Sol) does not take effect. The model selection switches back to GPT-5.6 Sol.

Steps to reproduce

1. Start or use a session with GPT-5.6 Sol and the 1.1M context window.
2. Try to switch the session to GPT-6.1 Sol.
3. Observe that the selection reverts to GPT-5.6 Sol.

Expected behavior

The session should switch to the selected model, or the app should explain why that model cannot be used with the session’s current context-window setting and provide a way to resolve it.

Additional context

One possible cause is that the target model uses a lower default context window than the current 1.1M setting, but this is only a hypothesis.

Affected version: v1.1.29.