[BUG] Diff line numbers appearing as boxes instead in Claude for VS Code

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="628" height="164" alt="Image" src="https://github.com/user-attachments/assets/b8c4784b-177e-485f-91b9-f14e7b505907" />

I see boxes instead of line numbers. I've tried:

1. Restarting VS Code and my PC
2. Updating and restarting Claude Code for VS Code
3. Trying a different computer with a different OS (macOS)
4. Reinstalling Claude for VS Code extension

What Should Happen?

should show line numbers instead of squares

Error Messages/Logs

Steps to Reproduce

install Claude Code for VS Code on either Windows 11 or macOS (26.6.1) and let Claude edit a file

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.227

Platform

Other

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

<img width="588" height="159" alt="Image" src="https://github.com/user-attachments/assets/af364168-22ac-416c-864b-5c21b88c5eac" />