[BUG] [BUG] Cowork fails on Windows 11 Home (AMD): Plan9 share 'c' HRESULT 0x8007273f; persists after full troubleshooting

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's Cowork workspace fails to start every time with:

Failed to start Claude's workspace
failed to add Plan9 share 'c': HcsWaitForOperationResult failed with HRESULT 0x8007273f (result len=39)

The VM boots successfully (vm_boot completes), but fails specifically at the add_plan9_shares step. 0x8007273f corresponds to WSAEAFNOSUPPORT (address family not supported), suggesting a networking-layer failure rather than a permissions issue.

Note: checked #59320, #47556, #47211 - different HRESULT codes and root causes (access denied / missing drive / drive-letter-count theory), so filing as a distinct issue.

What I've Already Tried (all unsuccessful)

• Added user to Hyper-V Administrators group + rebooted
• Granted SYSTEM full permissions (icacls) on the correct MSIX-scoped data path (%LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude)
• Full netsh winsock reset + netsh int ip reset + reboot
• Enabled IPv6 binding on all network adapters (was disabled, now enabled and confirmed via Get-NetAdapterBinding)
• Confirmed VirtualMachinePlatform enabled
• Enabled HypervisorPlatform (was disabled) + reboot
• Confirmed hypervisorlaunchtype = Auto via bcdedit
• Confirmed VT-x/virtualization present via systeminfo ("A hypervisor has been detected")
• Disabled Memory Integrity / Credential Guard via Windows Security Core Isolation + reboot (confirmed SecurityServicesRunning went from {2} to {0})
• Confirmed no WSL2, VirtualBox, or VMware running/installed
• Confirmed Smart App Control is off (VerifiedAndReputablePolicyState = 0)
• Checked Microsoft-Windows-CodeIntegrity/Operational log at failure timestamp — only unrelated Nahimic audio DLL signing warnings, nothing blocking Claude
• Checked System event log for Hyper-V/HNS/VmCompute errors at failure timestamp — vmswitch.sys loaded cleanly, no errors logged
• Full uninstall + reinstall of Claude Desktop (multiple times)
• Multiple full computer restarts

What Should Happen?

Cowork workspace should start successfully, with the Plan9 share mounting correctly and the VM becoming reachable.

Error Messages/Logs

2026-07-01 12:07:18 [info] [VM:steps] vm_boot completed (570ms)
2026-07-01 12:07:19 [info] [VM:steps] add_plan9_shares started
2026-07-01 12:07:19 [error] [VM:start] VM boot failed: failed to add Plan9 share 'c': HcsWaitForOperationResult failed with HRESULT 0x8007273f (result len=39)
2026-07-01 12:07:19 [error] [VM:start] Startup failed: Error: failed to add Plan9 share 'c': HcsWaitForOperationResult failed with HRESULT 0x8007273f (result len=39)
    at o7i (...\app.asar\.vite\build\index.js:964:4864)
    at async Object.startVM (...\app.asar\.vite\build\index.js:3639:9169)

Steps to Reproduce

1. Open Claude Desktop
2. Go to the Cowork tab
3. Attempt to start workspace
4. Failure occurs consistently, every attempt

Claude Model

Sonnet (default)

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.195 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

• OS: Windows 11 Home, 10.0.26200 Build 26200
• Device: Lenovo Legion Pro 5-16ARX8, System SKU 82WM
• CPU: AMD Ryzen 7 7745HX
• Claude Desktop version: 1.17377.1.0 (MSIX, package family Claude_pzs8sxrjxfjjc)
• BIOS: LENOVO LPCN65WW, 3/25/2026, UEFI mode, Secure Boot Off