[Bug] Model fallback to Opus triggered incorrectly by "cyber" keyword in reasoning

**Bug Description**
the model was switched from fable to opus because the word "cyber" appeared in the chain of thought? this whole session has nothing really at all to do with computer security.

**Environment Info**
- Platform: darwin
- Terminal: Apple_Terminal
- Version: 2.1.237
- Feedback ID: 848dd89f-e871-4038-b1fe-9326811e1c83

**Errors**
```json
[{"error":"Error: 500 {\"type\":\"error\",\"error\":{\"type\":\"api_error\",\"message\":\"Internal server error\"},\"request_id\":\"req_011CegaWUCKE7219Qpxc5zDt\"}\n at generate (/$bunfs/root/cli:39:39595)\n at makeRequest (/$bunfs/root/cli:90:8063)\n at processTicksAndRejections (native:7:39)","timestamp":"2026-09-03T13:23:34.321Z"},{"error":"Error: 500 {\"type\":\"error\",\"error\":{\"type\":\"api_error\",\"message\":\"Internal server error\"},\"request_id\":\"req_011Cegajxodi7Zov92XMo287\"}\n at generate (/$bunfs/root/cli:39:39595)\n at makeRequest (/$bunfs/root/cli:90:8063)\n at processTicksAndRejections (native:7:39)","timestamp":"2026-09-03T13:26:36.961Z"}]
```

Begin at the bundled CLI entry point (`/$bunfs/root/cli`) and inspect the `generate` and `makeRequest` path associated with the reported fallback. Use Feedback ID 848dd89f-e871-4038-b1fe-9326811e1c83 and the two error timestamps to correlate the failures; done means an unrelated “cyber” mention no longer triggers the model fallback or these 500 errors.

索引モデルが issue の本文から書いたものです。