Sandbox startup error on Windows 11: "host share not mounted at /mnt/.virtiofs-root/shared"

Bug Report

Description
On startup, Claude Code emits the following error:

sandbox-helper: host share not mounted at /mnt/.virtiofs-root/shared: not a mount point

The CLI output fails JSON parsing due to this message, showing: "CLI output was not valid JSON. This may indicate an error during startup."

The session still works after the error, but the warning appears on every launch.

Environment

• Claude Code: 2.1.45
• OS: Windows 11 Home (Build 10.0.26200)
• WSL: 2.6.3.0
• Kernel: 6.6.87.2-1
• Virtualization: Enabled (Hyper-V detected, VBS running)

Steps to Reproduce

1. Launch Claude Code on Windows 11 with the above environment
2. Observe the startup error in CLI output

Expected Behavior
Clean startup without sandbox mount errors.

Actual Behavior
The virtiofs sandbox fails to mount, printing the error to stderr, which corrupts the JSON output.