Claude Desktop v1.1.5749: cowork VM fails on Windows — duplicate Plan9 share in HCS config #32828

Environment

• OS: Windows 11 Home 10.0.26200
• Claude Desktop: v1.1.5749.0 (MSIX)
• Previous working version: v1.1.3647.0
• Virtualization: VirtualMachinePlatform + HypervisorPlatform (no Hyper-V — Home edition)

Bug Summary

cowork-svc.exe in v1.1.5749 creates duplicate Plan9 filesystem shares in the HCS (Host Compute Service) JSON configuration when starting the cowork VM. HCS rejects the config with hr=0x800707de (ERROR_INVALID_PARAMETER), preventing the VM from booting.

User-Visible Error

Failed to start Claude's workspace
VM service not running. The service failed to start.

Root Cause

The service constructs an HCS JSON config with the home directory Plan9 share added twice:

v5749 (broken):

"Plan9": {
  "Shares": [
    {"AccessName":"home","Name":"home","Path":"C:\Users\konst","Port":9999},
    {"AccessName":"home","Name":"home","Path":"C:\Users\konst","Port":9999}
  ]
}

v3647 (working):

"Plan9": {
  "Shares": [
    {"AccessName":"home","Name":"home","Path":"C:\Users\konst","Port":9999}
  ]
}

HCS rejects duplicate share names, so HcsCreateComputeSystem fails.

Evidence from cowork-service.log

The Electron app sends this config to the service via the named pipe:

HomeDir: "C:\Users\konst"
AdditionalPlan9Mounts: []

AdditionalPlan9Mounts is empty — the duplicate originates inside cowork-svc.exe, not from the Electron app.

The service log at C:\ProgramData\Claude\Logs\cowork-service.log shows:

[HCS] HcsCreateComputeSystem failed: hr=0x800707de

The full HCS JSON config (logged in the same file) contains the duplicate Plan9 shares shown above.

Attempted Workaround

Swapping the service binary back to v3647 via registry (HKLM:\SYSTEM\CurrentControlSet\Services\CoworkVMService\ImagePath) allows the VM to boot with a single Plan9 share. However, the VM cannot reach the Claude API from inside — the v3647 service creates an HCN ICS network that doesn't properly NAT traffic when paired with v5749's Electron app. The networking stack was significantly rewritten between versions (3.3MB → 11MB binary).

Additional Issues

1. Dual startVM race condition: The v5749 Electron app calls startVM from two code paths simultaneously (ensureReady via addMarketplace and startVM directly), creating duplicate HNS endpoints for the same VM.

2. Plan9 mount instability: Inside the VM, Plan9 mounts frequently drop and remount: [coworkd] Plan9 mount lost, remounting /mnt/.virtiofs-root/shared

Reproduction

1. Install Claude Desktop v1.1.5749 on Windows 11 Home (no Hyper-V, VirtualMachinePlatform enabled)
2. Open Claude Desktop → start a workspace/task
3. CoworkVMService crashes; "VM service not running" error appears

Suggested Fix

Deduplicate Plan9 shares before passing the config to HcsCreateComputeSystem, or ensure the home directory share is only added once during config construction in cowork-svc.exe.

Relevant Log Files