[Bug] Advisor tool fails with "unavailable" error when using Fable 5 model

Question

**Bug Description**
When I tried to use the Advisor tool, I got the following error:

```
⏺ Advising using Fable 5
Advisor unavailable (unavailable)
```

The model I'm using is Opus 4.8, and I specified Fable 5 for the Advisor.

**Environment Info**
- Platform: darwin
- Terminal: iTerm.app
- Version: 2.1.206
- Feedback ID: da958f47-ca87-467c-a912-4ce762fa9b66

**Errors**
```json
[]
```