Squirrel-to-MSIX migration silently breaks Cowork on Windows 11 (yukonSilver unsupported)

Summary

Claude Desktop on Windows fails to enable Cowork with the message "Cowork requires a newer installation — Reinstall the desktop app." The "Reinstall" button does nothing. The root cause is a broken Squirrel-to-MSIX migration path that silently leaves the MSIX package in a non-virtualized state.

Plans affected: Claude Max Plan + Codex Enterprise
OS: Windows 11 Home 10.0.26200 Build 26200
Package: Claude_1.1.9134.0_x64__pzs8sxrjxfjjc (SignatureKind: Developer)

Root Cause (fully diagnosed with log evidence)

The app checks for MSIX filesystem virtualization at:

C:\Users\<user>\AppData\Local\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude

When this path doesn't exist, the app logs:

[MSIX] Filesystem not virtualized — path absent (likely Squirrel upgrade)
[warm] Skipping VM warm download - YukonSilver not supported (Cowork requires Claude Desktop be installed with our modern installer)

The yukonSilver feature is marked status=unsupported, which triggers TWO destructive behaviors:

1. The "Cowork requires a newer installation" banner is shown
2. The app actively deletes VM bundle files via cleanupVMBundleIfUnsupported

The irony: Cowork VM works perfectly

The service log proves the VM runs fine on this machine:

• [HCS] HcsCreateComputeSystem returned: hr=0x0 (VM created successfully)
• [VM] VM started successfully
• [RPC] sdk-daemon is ready
• [RPC] API reachability: REACHABLE
• Dozens of Cowork processes ran successfully (10:29 AM - 3:30 PM on 2026-03-27)

The VM ran, processes completed, API was reachable — then on restart, the app checked the MSIX path, found it missing, declared Cowork unsupported, and deleted reinstall files.

Self-destructive deletion loop

The app repeatedly deletes VM bundle reinstall files every time it starts:

2026-03-26 19:14:19 [info] [deleteVMBundle] Deleting reinstall files
2026-03-26 21:18:43 [info] [deleteVMBundle] Deleting reinstall files
2026-03-26 21:55:45 [info] [deleteVMBundle] Deleting reinstall files
2026-03-26 22:02:59 [info] [deleteVMBundle] Deleting reinstall files
2026-03-26 22:05:50 [info] [deleteVMBundle] Deleting reinstall files
2026-03-26 22:52:28 [info] [deleteVMBundle] Deleting reinstall files
2026-03-26 22:58:49 [info] [deleteVMBundle] Deleting reinstall files
2026-03-26 23:18:23 [info] [deleteVMBundle] Deleting reinstall files
2026-03-27 16:33:28 [info] [deleteVMBundle] Deleting reinstall files
2026-03-27 17:35:07 [info] [deleteVMBundle] Deleting reinstall files

Environment

• CoworkVMService: Installed, starts/stops correctly (Automatic start type)
• HCS/vmcompute: Available and functional (Running)
• HvHost: Running
• WSL2: Installed with Docker Desktop
• MSIX LocalCache\Roaming directory exists but has no Claude subfolder
• Hypervisor detected per systeminfo
• Virtualization-based security: Running

What needs to be fixed

1. The Squirrel-to-MSIX migration must create the virtualized filesystem path. This is the root cause.
2. Stop deleting VM bundle files when yukonSilver is "unsupported." The VM works — destroying the user's 10GB download based on a path check is hostile.
3. Make the Reinstall button work. Or remove it and provide clear instructions.
4. Provide a migration tool that preserves MCP configs, extensions, plugins, and the VM bundle.
5. Test upgrade paths on Windows 11 Home — the most common consumer edition.

Impact

Real monetary loss across Claude Max Plan and Codex Enterprise. Hours of productive time lost diagnosing what turned out to be a missing directory in a broken migration path. 8 daily scheduled tasks for a consulting business were disrupted.

Log files

Available on request:

• C:\ProgramData\Claude\Logs\cowork-service.log (22M lines showing successful VM operation)
• %APPDATA%\Claude\logs\main.log (MSIX virtualization check failures)
• %APPDATA%\Claude\logs\cowork_vm_node.log (yukonSilver unsupported + deleteVMBundle loop)