Git Bash fails inside Windows sandbox with "couldn't create signal pipe, Win32 error 5"

Summary

On Windows, exec_command fails when shell is set to bash and Windows sandbox is enabled.

In my local testing, the same workflow worked on 0.114.0 and started failing on 0.115.0.

This reproduces with both:

• sandbox = "unelevated"
• sandbox = "elevated"

Setting sandbox_private_desktop = false does not change the behavior.

Reproduction

1. Enable Windows sandbox in config.toml, for example:

[windows]
sandbox = "unelevated"
sandbox_private_desktop = false

1. Run an exec_command call with shell: "bash", for example:

{"cmd":"sed -n '1,100p' CHANGELOG_CN.md","shell":"bash"}

1. Observe this error:

[main] bash (4572) C:\Program Files\Git\usr\bin\bash.exe: *** fatal error - couldn't create signal pipe, Win32 error 5

Expected

Git Bash commands should run normally when invoked through exec_command.

Actual

bash.exe immediately fails with:

fatal error - couldn't create signal pipe, Win32 error 5

whenever Windows sandbox is enabled.

Notes

• Removing [windows].sandbox makes everything work again.
• sandbox_private_desktop = false does not help, so this does not appear to be specific to private desktop mode.
• PowerShell works as a workaround.