[BUG] Cowork sandbox cannot mount any connected folder 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?

[BUG] Cowork sandbox cannot mount any connected folder on Windows
(no Plan9 drive shares) — persists after clean reinstall

Environment

• Claude Desktop 1.49585.0 / Electron 44.2.0 / Node 24.20.0
• Windows 10 Pro x64
• Services all Running: vmcompute, hns, vmms, vfpext, CoworkVMService

Symptom
device_bash returns:
sandbox-helper: no Plan9 drive shares mounted under /mnt/.virtiofs-root/shared
[Note: mnt/<folder> failed to mount and cannot be reached from this shell]

The Linux VM itself boots (sandbox-helper responds), but zero drive shares
are attached, so no shell command can run against any connected folder.

Also: after every reconnect the VM needs ~60s warm-up, during which all
calls return "Workspace unavailable. The isolated Linux environment on this
device failed to start." This is misleading — it recovers on its own.

Ruled out (each tested)

• Multiple / overlapping connected folders — fails with exactly ONE folder
• Drive type — C: system, G: internal SATA, I: USB external all fail
• App restart
• Full OS reboot
• Complete uninstall + reinstall (connectedFolders reset to empty; still fails)
• Missing HCS services / Windows Home Hyper-V gap — all services Running, Pro edition

Still working normally
device_list_dir, device_stage_files, device_commit_files — all fine throughout.
So folder permissions and the bridge itself are healthy; only the VM mount fails.

Impact
No local command execution at all. A 120 GB file-reorganisation task is blocked
mid-way; workaround requires round-tripping every file through the cloud at ~8 MB/s.

What Should Happen?

as above

Error Messages/Logs

as above

Steps to Reproduce

as above

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Claude Desktop 1.49585.0 / Electron 44.2.0 / Node 24.20.0

Claude Code Version

Claude Desktop 1.49585.0 / Electron 44.2.0 / Node 24.20.0

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

WSL (Windows Subsystem for Linux)

Additional Information

actually, the OS is Win11 25H2 (266200.9445)