[BUG] Windows MSIX: opening the sandboxed Browser pane bricks a working install when CoworkVMService is half-registered after auto-update (0x80073D28)

## Summary

A **working** Claude Desktop MSIX installation gets bricked at runtime — *"There's a problem with Claude. Reinstall the application from its original install location or contact your administrator."* — seconds after opening the in-app sandboxed **Browser pane**, when a prior auto-update has left the packaged service `CoworkVMService` half-registered. The pane triggers a **non-elevated** re-registration of the packaged service, which fails with `0x80073D28` and invalidates the package activation state.

Related (all closed, same error family, none document this runtime trigger): #51132, #47877, #35366, #48437, #25162, #55465.

## Environment

- Windows 10 Pro 19045
- Claude Desktop MSIX `Claude_1.34493.0.0` → `1.34493.1.0` (`x64__pzs8sxrjxfjjc`), SignatureKind: Developer
- Machine previously ran the Squirrel build (migration context of #25162)

## Timeline (reconstructed from Event Viewer)

1. **02:33–02:38** — overnight auto-update to `1.34493.0.0`. SCM log (Id 7045/7040) shows `CoworkVMService` installed **4 times in 5 minutes**, StartType flipping auto→disabled→auto. The update leaves the service half-registered.
2. App then runs normally for hours — **plain chat works fine** (no VM needed).
3. User opens the sandboxed **Browser pane** → app attempts to (re)register the packaged service **without elevation** → `AppXDeploymentServer` logs Id 404/401/9621:
> `error 0x80073D28: Cannot register the Claude_..._pzs8sxrjxfjjc package. Administrator privileges required to install packaged service`
4. Package activation state is now invalid → blue "There's a problem with Claude" dialog on every launch. Restarting Windows does not help.
5. **Reproduced twice in one day**: reinstalled, opened the Browser pane again → bricked again within seconds.
6. Recovery reinstall also fights the stale state before eventually succeeding:
> `0x80073D05: An error occurred while deleting the package's previously existing state` / `0x800703FA: Illegal operation attempted on a registry key that has been marked for deletion` (windows.stateExtension), plus `0x80073CFA` (PreserveApplicationData) and `0x80073D02` (apps need to be closed) along the way.

**No WER crash dumps at any point** — this is a registration/elevation failure, not a process crash.

## Expected

Opening the Browser pane should either (a) trigger an **elevated** repair of the packaged service, (b) fail gracefully with the pane unavailable, or (c) the updater should never leave `CoworkVMService` half-registered in the first place. A UI feature toggle should never be able to invalidate the whole package.

## Workaround (verified)

- Prevention: don't open the Browser pane.
- Recovery **with data intact** (what Settings→Apps→Claude→Repair does): elevated
`Add-AppxPackage -Register -DisableDevelopmentMode "\AppxManifest.xml"`

Full event-log timeline available on request.

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*Disclosure: this diagnosis (Event Viewer forensics, root-cause analysis) and this report were produced by Claude — model **Fable 5** (`claude-fable-5`), running in Claude Code on the affected machine — at the machine owner's direction, and posted from the owner's account with their approval.*

No repository file or test is named; begin by reproducing the Browser-pane trigger on Windows and reviewing the supplied Event Viewer timeline for CoworkVMService and MSIX registration. Done means opening the Browser pane no longer invalidates the package, or the feature fails without bricking the installation.

Written by the indexing model from the issue text.