[BUG] /copy command corrupts UTF-8 characters on Windows again (regression from #22346)

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?

The /copy command corrupts all non-ASCII characters (Japanese/CJK) when copying to the Windows clipboard. The response.md file contains correct UTF-8 text, but the clipboard content is garbled (mojibake).

Example clipboard output:
���m�������܂����B
�ł́A���L�̓���猟�������iTRANSFER_CD LIKE ''�j���폜�������܂��B

What Should Happen?

Japanese text should be correctly copied to the clipboard, as it was in v2.1.70–v2.1.75.

Error Messages/Logs

(No error messages — the command reports success but the clipboard content is corrupted)

Steps to Reproduce

1. Run Claude Code on Windows with a non-English locale (e.g., Japanese)
2. Get a response containing Japanese characters
3. Run /copy
4. Paste from clipboard — Japanese characters are garbled
5. Open the response.md file written by /copy — content is correct UTF-8

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Last Working Version: 2.1.75 (confirmed working in #22346 comments)

Claude Code Version

2.1.88

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

This is a regression of #22346, which was fixed in v2.1.70 by switching to PowerShell's Set-Clipboard.

Environment details:

• Windows 11 Pro (10.0.26200)
• Shell: Git Bash
• PowerShell [Console]::OutputEncoding.CodePage: 932 (Shift_JIS)
• $LANG: ja_JP.UTF-8

Workaround:
powershell -Command "Get-Content '$env:TEMP\claude\response.md' -Encoding UTF8 -Raw | Set-Clipboard"