[BUG] Cowork fails with Plan9 share 'd': HRESULT 0x800703ed — no D: drive exists, Windows 11 Pro 25H2

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?

Cowork workspace fails to start. The VM attempts to mount a Plan9 share for drive D: but no D: drive exists on this machine. Error persists after all troubleshooting steps.

What Should Happen?

Cowork workspace should start successfully without trying to mount a non-existent D: drive.

Error Messages/Logs

Failed to start Claude's workspace
failed to add Plan9 share 'd': HcsWaitForOperationResult failed with HRESULT 0x800703ed: {"Error":-2147023891,"ErrorMessage":""}

Steps to Reproduce

1. Open Claude Desktop
2. Click Cowork tab
3. Error appears immediately

Claude Model

None

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

Not applicable - this is Claude Desktop / Cowork

Platform

Other

Operating System

Windows

Terminal/Shell

Non-interactive/CI environment

Additional Information

• Claude Desktop version: 1.1617.0.0 (MSIX/Microsoft Store)
• Machine has only a C: drive — no D: drive exists
• Hyper-V is enabled, hypervisor detected and running
• Steps tried: restarted Claude and PC, reinstalled workspace, granted SYSTEM permissions to AppData\Claude, removed phantom D: mount point via mountvol D: /D, deleted vm_bundles folder, manually started CoworkVMService via PowerShell
• Related issue: #43482