## Why
Desktop uninstall cleanup needs an installation owner even when the user has not signed in or configured the Windows sandbox. Recording ownership only during provisioning leaves those installations unregistered.
## What changed
- Add an authenticated installation registration request and attempt it during Windows desktop stdio initialization, with a five-second timeout before the initialization response.
- Persist ownership independently of provisioning, preserve existing desktop ownership, and prevent another user or home from replacing the registered owner.
- Validate write authority and retain directory handles and guards to protect the registered home against junction conversion through privileged cleanup.
- Preserve existing CLI homes during desktop uninstall while removing their `CodexSandboxUsers` ACL entries. Report ACL revocation errors and avoid propagating unchanged ACLs.
- Grant the owner `WRITE_DAC` on `.sandbox-bin` and allow elevated-helper fallback when older permissions need repair or the service cannot establish an uninstall watcher.
## Testing
Add tests for installation registration without sandbox settings and for preserving a child's null DACL when revoking an absent SID from its parent.
GitOrigin-RevId: fb48923e9d76758d1bf5b50c7305aa60f91629db
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