Cowork VM: 'Virtualization is not enabled' after update to 1.1.3918 - yukonSilver unsupported regression

Description

After updating Claude Desktop from 1.1.3363 to 1.1.3918 on Windows 11, Cowork shows "Virtualization is not enabled" and refuses to start the VM. This is a regression - Cowork was working on 1.1.3363 (Feb 20).

Environment

• OS: Windows 11 Pro 10.0.26200 (x64)
• CPU: Intel Core Ultra 9 275HX
• RAM: 32 GB
• Claude Desktop version: 1.1.3918.0 (Microsoft Store / MSIX)
• Previous working version: 1.1.3363.0

What happened

1. Cowork was working on version 1.1.3363 (Hyper-V event log confirms cowork-vm started successfully on Feb 20)
2. Got an EBUSY error on the VHDX copy (separate issue, likely file lock from prior session)
3. Reinstalled Claude Desktop, which updated to 1.1.3918
4. Cowork now shows "Virtualization is not enabled" permanently
5. Rebooting, reinstalling, and adding user to Hyper-V Administrators group did not help

Root cause from logs

The cowork_vm_node.log shows the new version is not even attempting to start the VM:

[cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...
[startVM] VM not supported (win32/x64), skipping

This repeats on every startup attempt. The old version (1.1.3363) did NOT have this behavior - it attempted VM startup normally.

Hyper-V is fully functional

Confirmed via PowerShell:

• HypervisorPresent: True
• Services running: vmms, vmcompute, CoworkVMService
• Get-VM: works (user is in Hyper-V Administrators group)
• Hyper-V features installed: Microsoft-Hyper-V, Microsoft-Hyper-V-Hypervisor, Microsoft-Hyper-V-Services, VirtualMachinePlatform, HypervisorPlatform

Expected behavior

Cowork should start the VM on win32/x64 with Hyper-V enabled, as it did on version 1.1.3363.

Relevant log excerpts

Old version (1.1.3363) - attempted VM start:

[VM:start] Beginning startup, bundlePath=...
[VM:start] Copying smol-bin.x64.vhdx to bundle...
[VM:start] Startup failed: Error: EBUSY: resource busy or locked, copyfile...

New version (1.1.3918) - skips entirely:

[cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...
[deleteVMBundle] Deleting reinstall files from ...\claudevm.bundle
[startVM] VM not supported (win32/x64), skipping
[Callbacks] Initializing VM event callbacks...
[VM] Loading vmClient (TypeScript) module...
[VM] Module loaded successfully
[Callbacks] VM event callbacks initialized
[startVM] VM not supported (win32/x64), skipping

Steps to reproduce

1. Install Claude Desktop 1.1.3918 on Windows 11 with Hyper-V enabled
2. Open Claude Desktop and click the Cowork tab
3. Observe "Virtualization is not enabled" error
4. Check %APPDATA%\Claude\logs\cowork_vm_node.log for yukonSilver not supported