[BUG] False positive safeguard trigger on safe coding conversation (reasoning_extraction)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Normal coding session (building pixel art project), no sensitive content. Asked about progress and got flagged. Error spreads to every new conversation window. Both Opus 5 and Fable 5.1 affected.

What Should Happen?

Normal coding conversations should not trigger safeguards.

Error Messages/Logs

API Error: Opus 5's safeguards flagged this message. Details: [reasoning_extraction]

fable5.1

Steps to Reproduce

1. Have custom user preferences set (in Chinese) 2. Work on a normal coding project 3. Ask about progress 4. Get blocked on all subsequent conversations

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

v2.1.277

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_