[BUG] Cowork regression -- working at 15:32, broke at 20:19 after auto-update to v1.6608.2 (yukonSilver unsupported)

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 was fully functional today and broke after an auto-update. At 20:19 the update triggered the yukonSilver platform check, which deleted the VM boot files (rootfs.vhdx, vmlinuz, initrd) from the bundle. Every subsequent launch detects "unsupported," deletes the now-empty bundle, and exits without attempting to re-download or start the VM.

What Should Happen?

Cowork should continue working after an auto-update on a machine where it was running successfully. The VM bundle should be preserved or correctly re-downloaded, and yukonSilver should be recognized as supported on a system where it was actively running hours earlier.

Error Messages/Logs

2026-05-08 20:19:49 [info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...
2026-05-08 20:19:49 [info] [deleteVMBundle] Deleted rootfs.vhdx
2026-05-08 20:19:49 [info] [deleteVMBundle] Deleted .rootfs.vhdx.origin
2026-05-08 20:19:49 [info] [deleteVMBundle] Deleted vmlinuz
2026-05-08 20:19:49 [info] [deleteVMBundle] Deleted .vmlinuz.origin
2026-05-08 20:19:49 [info] [deleteVMBundle] Deleted initrd
2026-05-08 20:19:49 [info] [deleteVMBundle] Deleted .initrd.origin
2026-05-08 20:19:49 [info] [deleteVMBundle] Reinstall files deleted (sessiondata.img and compressed cache preserved)
2026-05-08 20:19:49 [info] [cleanupVMBundleIfUnsupported] Deleted stale VM bundle
2026-05-08 20:28:40 [info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...
2026-05-08 20:32:38 [info] [cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported), checking for stale bundle...

Steps to Reproduce

Run Claude Desktop on Windows 11 Pro with Cowork working (VM connected)
Allow auto-update to v1.6608.2 to apply
Relaunch Claude Desktop
Observe: Cowork shows "Virtual Machine Platform not available" error
Check log: yukonSilver marked unsupported on every launch, VM boot files deleted and never re-downloaded

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Unknown -- auto-update did not display the previous version number. Last confirmed working: 2026-05-08 at approximately 15:32 local time (CST).

Claude Code Version

Claude Desktop 1.6608.2 (ebf1a1), 2026-05-08T23:17:27.000Z

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Both CoworkVMService and vmms are Running / Automatic. Virtual Machine Platform is enabled in Windows Features. This is not a fresh-install detection failure -- the system was running Cowork successfully on the same day. The update deleted VM boot files and the platform check now permanently blocks re-initialization. No rollback path is available since previous installers are not publicly hosted.