[BUG] Edit tool silently clears file to 0 bytes on Windows

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 Edit tool reported "updated successfully" but actually wrote 0 bytes to the file, completely erasing its content. No error was thrown.

Evidence from file-history (path: ~/.claude/file-history/<session-id>/):

• v3: 1576 bytes (May 1 16:47) — last known good version
• v4: 0 bytes (May 1 23:43) — Edit tool produced an empty file
• v5: 1841 bytes (May 2 14:38) — manually restored via Write tool

The affected file was ~/.claude/CLAUDE.md (global user instructions). The Edit tool was adding 3 new lines to the existing content. It claimed success but the
file became completely empty.

What Should Happen?

The Edit tool should correctly apply the edit and preserve existing file content. If an error occurs, it should report the error instead of silently zeroing
out the file.

Error Messages/Logs

Steps to Reproduce

1. Have a non-empty file (e.g., ~/.claude/CLAUDE.md with ~1576 bytes)
2. Use Claude Code Edit tool to make a small modification (e.g., add a few lines to the end)
3. Edit tool reports success: "updated successfully"
4. Check file content — it is now empty (0 bytes)

Note: This is intermittent. It happened once during a long session on Windows. Possible triggers:

• Long session with /compact triggered
• Windows CRLF/LF encoding edge case
• Concurrent file access during context compaction

Environment: Windows 11 Pro, bash shell in Windows Terminal, Java project with ~50 Maven modules.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.119

Platform

Other

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_