Copilot CLI incorrectly switches back to previous model after switching to BYOK

### Describe the bug

I ran out of AIC while using claude-sonnet-4.6. After exiting GitHub Copilot and resuming my session using BYOK, the Copilot CLI automatically switched back to claude-sonnet-4.6, despite having supposedly switched to the BYOK configuration.

### Affected version

_No response_

### Steps to reproduce the behavior

1. Run out of AIC while using claude-sonnet-4.6.
2. Exit GitHub Copilot.
3. Resume session using BYOK.
4. Observe that Copilot CLI automatically switches back to claude-sonnet-4.6 or showing this:

```
Model 'glm-5.2:cloud' not found on provider at https://ollama.com/v1 (HTTP 404).
Check that the model is available on your provider.
```

### Expected behavior

The CLI should respect the BYOK configuration and not revert to the previously used model after a session restart.

### Additional context

_No response_

Empieza reproduciendo el flujo de reinicio de sesión indicado: agota AIC, sal de Copilot CLI y reanuda con BYOK. Traza cómo se restauran la configuración de BYOK y el modelo seleccionado, incluido el error del proveedor Ollama. Se considera completado cuando una sesión BYOK reanudada conserva su modelo configurado en lugar de volver al modelo anterior.

Escrito por el modelo de indexación a partir del texto del issue.