[BUG] Cowork: yukonSilver not supported on Intel i7-4770K (Dell OptiPlex 9020, Win 10 Pro)

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 fails to start with "VM service not running". The log shows
yukonSilver not supported (status=unsupported), meaning Cowork is
rejecting the CPU entirely and never attempts to boot the VM.

What Should Happen?

The Cowork VM should start successfully. The Intel i7-4770K supports
all required virtualization features (VT-x, Hyper-V). It should not
be silently rejected as "unsupported" with no clear error to the user.

Error Messages/Logs

[cleanupVMBundleIfUnsupported] yukonSilver not supported (status=unsupported)
HCS operation failed: failed to create compute system: HCS not initialized - call InitHCS() first

Steps to Reproduce

1. Install Claude Desktop on Dell OptiPlex 9020 (i7-4770K, Win 10 Pro 22H2)
2. Enable Hyper-V and confirm VT-x is enabled in BIOS
3. Open Cowork tab
4. Observe: "Failed to start Claude's workspace — VM service not running"
5. Check cowork_vm_node.log: shows "yukonSilver not supported (status=unsupported)"

Claude Model

None

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

1.14328

Platform

Other

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

Hardware: Dell OptiPlex 9020, Intel i7-4770K @ 3.50GHz
Hyper-V fully enabled, VT-x confirmed enabled in BIOS
vmcompute and hns services both running
All VM files downloaded successfully (rootfs.vhdx, vmlinuz, initrd checksums validated)
Issue appears to be CPU blocklist - log shows "yukonSilver not supported (status=unsupported)"
i7-4770K supports all required virtualization features but is being rejected silently