Files being truncated by edit in cowork with no warning and way below the 32kb limit

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?

Bug report — Cowork file Write/Edit tool silently truncates files on Windows mount

When using the Write or Edit tool in Cowork mode with a folder mounted from Windows, file writes succeed without any error but the resulting file is silently truncated. The tool reports success, no exception is raised, and the file appears to have been written — but the content is cut off partway through.

Observed behavior:

• Write/Edit tool returns success
• File is truncated (e.g. a function body cut off mid-line, or an if __name__ == "__main__" block missing entirely)
• No warning, no error, no indication anything went wrong
• Python syntax errors or missing logic only discovered at runtime

Why this is serious:

• Silent data loss. If the truncated content had been API keys, credentials, or unique configuration, it would have been gone without any indication.
• The tool says it succeeded, so there is no reason to double-check.
• Files affected were well under 32KB — this is not a large-file edge case.

Environment:

• Cowork mode, Claude desktop app
• Workspace folder mounted from Windows (NTFS)
• Files: Python scripts (~5–8KB), modified via Edit and Write tools

What Should Happen?

Expected behavior:
The tool should either write the file completely or raise an error. Silent partial writes are not acceptable.

Error Messages/Logs

no errors, files just get corrupted

Steps to Reproduce

just use cowork and start doing things with file read/write actions and things get corrupted... claude reports that the 32kb limit caused it but the file is 8kb or 12kb for example

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Claude 1.9659.2 (390d6c) 2026-05-28T21:50:01.000Z

Platform

Other

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_