[BUG] Japanese IME text moves to the right edge only when Claude Code is active in the VSCode integrated terminal

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?

When using the Claude Code extension inside the VSCode integrated terminal,
the text width of Japanese full-width characters becomes incorrect only while Claude Code is active.

The issue appears after launching claude (via the integrated terminal).
Japanese characters overflow to the right.

<img width="1920" height="1080" alt="Image" src="https://github.com/user-attachments/assets/14f3ed39-ad1e-489c-b040-e19f1ab6fbbf" />

This issue does not occur:

• in Windows Terminal (outside VSCode)
• in VSCode terminal when Claude Code is not running
• when typing in English

What Should Happen?

Japanese IME input should appear directly next to the > prompt without shifting.

Error Messages/Logs

Steps to Reproduce

1. Open VSCode on Windows
2. Open integrated terminal (PowerShell)
3. Run claude
4. Type Japanese text using IME
5. Observe misaligned characters

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.53 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

_No response_