[BUG] CoWork for 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?

Downloaded and installed updated software that enables CoWork on Windows. Every time I try to start a chat, it goes to "Starting up" and then returns this error:

CLI output was not valid JSON. This may indicate an error during startup. Output: sandbox-helper: failed to unmount host share (tried both virtiofs and Plan9): invalid argument

<img width="583" height="109" alt="Image" src="https://github.com/user-attachments/assets/eac6d7f2-359d-4b2e-bd49-7d633df19cbe" />

Windows 11
Claude Desktop app (Claude 1.1.2685 (f39a62) 2026-02-10T19:42:56.000Z)
Claude Code CLI app (2.1.39)

What Should Happen?

Claude should analyze the uploaded document and wait for further instructions.

Error Messages/Logs

CLI output was not valid JSON. This may indicate an error during startup. Output: sandbox-helper: failed to unmount host share (tried both virtiofs and Plan9): invalid argument

<img width="583" height="109" alt="Image" src="https://github.com/user-attachments/assets/eac6d7f2-359d-4b2e-bd49-7d633df19cbe" />

Steps to Reproduce

Log out, close desktop app, reopen and same error every time.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Claude Code CLI app (2.1.39) Claude Desktop app (Claude 1.1.2685 (f39a62) 2026-02-10T19:42:56.000Z) Claude Code CLI app (2.1.39)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

CLI app is working fine. Just this new update to enable CoWork support for Windows.