[BUG] CoworkVMService crashes when external/USB drive cannot be mounted as Plan9 share (v1.569.0.0)

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?

Starting with v1.569.0.0, the CoworkVMService (Claude VM Service) crashes on startup if any
fixed drive cannot be successfully mounted as a Plan9 share inside the HCS virtual machine.
The service does not gracefully skip inaccessible drives — it terminates entirely with exit
code 1067.

What Should Happen?

Expected Behavior

If a drive cannot be mounted as a Plan9 share (e.g. due to permission issues with an external drive), the service should log a warning and continue starting normally, skipping
that drive.

Error Messages/Logs

Actual Behavior

  The service crashes immediately after failing to mount the drive. From                        C:\ProgramData\Claude\Logs\cowork-service.log:
                                                                                                [VM] Adding Plan9 share via HcsModifyComputeSystem: name=d path=D:\ port=9903 flags=0x10 d…
  hasToken=true                                                                                 [VM] Failed to add Plan9 share 'd': HcsWaitForOperationResult failed with HRESULT
  0x80070005: {"Error":-2147024891,"ErrorMessage":""}                                           [VNet] Virtual network stopped                                                           d…
  [RPC] Server stopped                                                                                                                                                                        Error codes observed:
  - 0x80070005 = ERROR_ACCESS_DENIED (HCS cannot access the external drive)                     - 0x80070003 = ERROR_PATH_NOT_FOUND (after drive was temporarily disconnected)

Steps to Reproduce

1. Have Claude installed as a Windows packaged app (v1.569.0.0)
2. Have an external USB hard drive attached to the system (detected as a fixed drive, e.g.

D:)

1. Start the Claude app or attempt to start CoworkVMService
2. Service fails to start; Claude reports "VM service not running. The service failed to

start."

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude 1.569.0.0 (Windows)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

Root Cause Analysis

v1.569.0.0 introduced a new feature: mounting all local fixed drives (C:, D:, E:, ...) into the VM via Plan9 file sharing. Previous versions only mounted the user home directory (home →
C:\Users\admin).

The HCS (Host Compute Service) API cannot access external USB drives the same way it accesses internal drives, resulting in the Plan9 share failing. The service treats this failure as
fatal.

Workaround

Manually grant permissions to the external drive:

icacls "D:\" /grant "NT SERVICE\CoworkVMService:(OI)(CI)(RX)"
icacls "D:\" /grant "NT VIRTUAL MACHINE\Virtual Machines:(OI)(CI)(RX)"

Then start the service:

Start-Service CoworkVMService

Note: This workaround must be re-applied if the drive letter changes or the drive is re-attached.

Suggested Fix

In the VM startup code, wrap each Plan9 share addition in error handling that logs a warning and continues rather than terminating the service when a drive is inaccessible.