Fix: add systemd unit to make /mnt/wsl recursive slave before umount

[chemwolf6922]

Summary of the Pull Request

Systemd globally unmounts shared mounts under /mnt/wsl during graceful shutdown.

This PR adds a systemd unit to set /mnt/wsl as recursive slave during shutdown before unmounting to avoid the unmount from propagating to other namespaces.

PR Checklist

• Closes: Graceful shutdown of any systemd distro unmounts shared /mnt/wsl mounts in ALL distros (breaks Docker Desktop WSL integration VM-wide) #41084
• Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• Tests: Added/updated if needed and all pass
• Localization: All end user facing strings can be localized
• Dev docs: Added/updated if needed
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

Add regression test:
UnitTests::UnitTests::SharedMountSurvivesDistroTermination

[Copilot]

Pull request overview

This PR addresses a WSL2 systemd shutdown regression where unmounts under /mnt/wsl in one systemd-enabled distro can propagate across shared mount peer groups and break other running distros (notably Docker Desktop’s WSL integration). It does so by generating/enabling a systemd unit that switches /mnt/wsl to rslave propagation during shutdown, preventing unmount propagation to other namespaces.

Changes:

• Generate and enable a wsl-mnt-guard.service unit to run mount --make-rslave /mnt/wsl on shutdown (ExecStop) before unmount propagation can escape the terminating distro.
• Add a Windows UnitTests regression test that creates a shared mount under /mnt/wsl, terminates a peer systemd distro, and verifies the mount remains available.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/linux/init/init.cpp	Generates and enables a new systemd unit (wsl-mnt-guard) to prevent shutdown unmount propagation from escaping the distro.
test/windows/UnitTests.cpp	Adds a regression test to ensure a /mnt/wsl shared mount survives termination of a peer systemd-enabled distro.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.