[BUG] Cowork "Missing HCS services: vfpext" — root cause was Windows "Containers" optional feature not enabled (undocumented dependency)

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?

Environment:

OS: Windows 11 Pro, x64
Network adapter: Intel(R) Ethernet Controller I226-V (wired)
Claude Desktop: latest version at time of testing

What Should Happen?

What's Wrong?

Cowork tab was disabled with tooltip "Missing HCS services: vfpext" even after HNS and vmcompute were confirmed Running. The root cause was that the Windows "Containers" optional feature was not enabled — this is a separate feature from Hyper-V / VirtualMachinePlatform, and none of the current documentation or in-app error messaging mentions it as a required dependency.

Error Messages/Logs

Diagnostic steps taken, in order (none resolved the issue until the last one):

Confirmed VirtualMachinePlatform optional feature enabled, restarted with Restart (not Shutdown)
Get-Service vmcompute, hns → both Running
Test-Path C:\Windows\System32\drivers\vfpext.sys → False
sc.exe query vfpext → error 1060, service not installed
DISM /Online /Cleanup-Image /RestoreHealth (elevated) → completed successfully
sfc /scannow (elevated) → no unresolved integrity violations
Full disable/enable cycle of Microsoft-Hyper-V-All with real restarts between each step (not -NoRestart chained) → no effect on vfpext
Created a Hyper-V External virtual switch bound to the physical Ethernet adapter (New-VMSwitch -NetAdapterName "Ethernet" -AllowManagementOS $true) → no effect on vfpext
Hyper-V Manager opened and functioned normally throughout all of the above — misleadingly suggesting the virtualization stack was fully healthy
Enabled the separate "Containers" optional Windows feature (Enable-WindowsOptionalFeature -Online -FeatureName Containers -All), restarted → vfpext.sys was generated, Cowork tab became clickable and functional

Steps to Reproduce

Suggested fix:

Add a check for the "Containers" optional feature in Cowork's readiness/diagnostic checks on Windows, since it's a separate feature from Hyper-V/VirtualMachinePlatform and can be missing even when Hyper-V reports fully enabled and functional.
Update Windows setup documentation to explicitly list "Containers" alongside Hyper-V and Virtual Machine Platform as required features.
Consider making the "Missing HCS services: vfpext" error message mention "Containers" as a possible cause, since Hyper-V being enabled and working does not guarantee vfpext is present.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude 1.24012.9 (03c61d) 2026-07-24T04:59:17.000Z

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_