[Bug] Claude Opus model selection ignored, running Opus 4.8 instead of specified claude-opus-5

**Bug Description**
in 50% of runs - Runs Opus 4.8 despite '--model claude-opus-5'

**Environment Info**
- Platform: darwin
- Terminal: Orca
- Version: 2.1.275
- Feedback ID: 713ff897-6c94-4f7a-9600-160817cbba7d

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

Start by reproducing model selection with --model claude-opus-5 on darwin using Orca and version 2.1.275, checking which model is selected across multiple runs. Trace the model-selection entry point and verify that every run honors the requested model; add coverage for the intermittent behavior if the relevant test area is found.

Written by the indexing model from the issue text.