[BUG] Cowork installation fails with HRESULT 0x80073CFF on Windows 11 Pro - installer cannot remove orphaned package/service

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?

Claude Desktop Cowork is completely broken on Windows 11 Pro. The installer fails repeatedly with HRESULT 0x80073CFF on every reinstall attempt. The stale Claude_1.1.3189.0 package cannot be removed (HRESULT 0x80073CFA), and the orphaned CoworkVMService cannot be removed even with elevation (Access denied). This creates an unrecoverable installation loop. Claude.ai web and Claude Code work fine - only Cowork is broken.

Even when the service is running, cowork-service.log shows the client never issues a "Start VM" command, hcsdiag list returns empty, and Get-HnsNetwork shows no Cowork network is created.

Logs attached: ClaudeSetup.log and cowork-service.log

ClaudeSetup.log
cowork-service.log

What Should Happen?

Installer should successfully remove the old package and conflicting service, then install the new version. Cowork workspace should boot.

Error Messages/Logs

Steps to Reproduce

1. Download Claude Setup from claude.ai/download
2. Run as administrator
3. Installer fails with HRESULT 0x80073CFF
4. Error dialog: "Administrator access is required to install Claude with full features"
5. Repeats on every attempt

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

n/a

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

• OS: Windows 11 Professional, 10.0.26200, x64
• Plan: Max
• Hyper-V: Enabled, hypervisor loaded
• HypervisorPlatform: Enabled
• VirtualMachinePlatform: Enabled
• hypervisorlaunchtype: Auto
• vmcompute, vmms: Running
• BIOS virtualization: Enabled
• Sideloading: Enabled
• No VMware/VirtualBox
• Possibly related: #25663, #37312, #54011, #56566