[Bug] Model downgraded from Sonnet 5.1 to Opus 5.0 on legitimate scientific research content

**Bug Description**
I am writing a science-fiction novel in which two characters develop resistance to venom of snakes. I showed an article about that to Claude as scientific backing, and Fable 5.1 flagged it and changed my model to Opus 5.0. I was using this as background material to make scientifically valid rationale in my sci-fi writing only. I showed Claude a web capture of this article only: https://www.science.org/content/article/he-injected-himself-venom-decades-can-his-antibodies-help-snakebite-victims?utm_source=sfmc&utm_medium=email&utm_campaign=ScienceAdviser&utm_content=distillation&et_cid=6067930

**Environment Info**
- Platform: darwin
- Terminal: Apple_Terminal
- Version: 2.1.270
- Feedback ID: ea7dffb6-635e-4135-b7d9-cd5d4ec862ea

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

No source file, test, or entry point is identified. Start by reviewing feedback ID ea7dffb6-635e-4135-b7d9-cd5d4ec862ea and reproducing the model downgrade with the linked Science article on the reported platform and version; done means legitimate scientific-research content no longer triggers the unintended change, with regression coverage identified.

Written by the indexing model from the issue text.