[BUG] Spurious syntax highlighting colors random words/characters in plain text output

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?

<img width="1492" height="435" alt="Image" src="https://github.com/user-attachments/assets/693887b5-73cf-45a2-aeed-4e2857331466" />

Plain text output from Claude has random words and individual characters colored/highlighted, making the output look broken. This appears to
be the markdown renderer's syntax highlighting misinterpreting German prose and technical terms as code syntax.

Expected Behavior:

Plain prose text should render in a uniform color without syntax highlighting.

Actual Behavior:

Random fragments are colored differently:

• Partial words highlighted (e.g. "todomaschine", "Doppelpunkt", "Highlighting")
• Single words highlighted mid-sentence ("ist", "auf")
• CamelCase terms partially colored ("TaskCreate")
• Words after line-wrap colored ("verpackt", "konsistent")

Environment:

• Claude Code CLI (latest)
• Windows 11
• Terminal: Windows Terminal

Notes:

The issue is especially noticeable with non-English text (German) mixed with technical English terms. It seems like the CommonMark renderer
applies syntax highlighting heuristics to prose, matching patterns like /path/, key:, CamelCase identifiers, and line-wrap boundaries.

What Should Happen?

no rendering bugs

Error Messages/Logs

Steps to Reproduce

Steps to Reproduce:

1. Ask Claude Code a question that produces a mixed German/English response with technical terms
2. Observe the rendered output in the terminal

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.20.27

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

_No response_