wsl --update --pre-release fails with Error 1603 (WSLService could not be stopped) and wsl --shutdown hangs

### Windows Version

Windows 10.0.22631.6199

### WSL Version

2.7.10.0

### Are you using WSL 1 or WSL 2?

- [x] WSL 2
- [ ] WSL 1

### Kernel Version

6.18.33.2-2

### Distro Version

Ubuntu 20.04 (WSL2)

### Other Software

Docker Desktop (with WSL2 backend integration)

### Repro Steps

Run an active WSL2 background engine context using Docker Desktop integration.

Attempt to trigger a core subsystem preview update by executing:
PowerShell

wsl --update --pre-release

The installer detects preview version 2.9.3, but terminates abruptly with an explicit service-stop failure.

Try to clean up the environment manually by initiating a subsystem halt:
PowerShell

wsl --shutdown

The terminal hangs indefinitely on the execution of the shutdown command.

### Expected Behavior

The updater should safely trigger an inner component intercept, signal active distributions to store runtime cache, stop WSLService gracefully, apply the version update payload (2.9.3.0), and wsl --shutdown should close all background VM endpoints within a few seconds without locking up the terminal.

### Actual Behavior

The installer fails with an immediate execution denial:

```
Service 'WSL Service' (WSLService) could not be stopped. Verify that you have sufficient privileges to stop system services.
Update failed (exit code: 1603).
Error code: Wsl/UpdatePackage/ERROR_INSTALL_FAILURE
```

Subsequent calls to wsl --shutdown hang indefinitely, indicating that an internal deadlock is maintaining persistent handles on the virtualization layers and preventing WSLService from unmounting.

### Diagnostic Logs

According to the verbose installer trace from wsl-install-logs.txt:

```
=== Verbose logging started: 4/7/2026 14:49:55
Product: C:\Users\gabtz\AppData\Local\Temp\wsl.2.9.3.0.x64.msi
Installation success or error status: 1603.
MainEngineThread is returning 1603
```
The installer engine trips during the transaction context sequence when background host workers or Docker desktop handles fail to safely detach from the operational stack, throwing a hard 1603 block.

Reproduce the reported environment with Windows 10.0.22631.6199, WSL 2.7.10.0, Ubuntu 20.04, and Docker Desktop's WSL2 backend. Run `wsl --update --pre-release` and `wsl --shutdown`, then inspect `wsl-install-logs.txt`; done means the preview update completes and shutdown returns within a few seconds.

Written by the indexing model from the issue text.