[Bug]: Declining Windows update UAC leaves OpenScreen closed #1461

Declining UAC during a silent per-machine Windows update leaves OpenScreen closed.

Reproduction

• Windows 11 Home x64, build 26300; official NSIS v2.2.0-rc.3 in C:\Program Files\Openscreen.
• HKLM install key found; HKCU key absent. The Microsoft Store copy is present but not running.
• Real GitHub feed offers v2.2.0-rc.4; downloaded installer SHA-512 matches published latest.yml.
• Click the blue update arrow, then choose No in UAC. The maintainer performed both clicks and explicitly confirmed the refusal.

Actual

Installer command: Openscreen.Setup.2.2.0-rc.4-x64.exe --updated /S --force-run.
The app exits before the elevation decision. After No, the installer exits without restoring the app: 58 process snapshots over 108.8 seconds showed no OpenScreen process. Installed version stays rc.3.

Expected

Declining elevation should leave or restore the current app and allow retrying the downloaded update.

Diagnosis

installSelfUpdate() calls electron-updater.quitAndInstall(true, true). BaseUpdater quits after starting NSIS, without waiting for UAC. In electron-builder's silent per-machine path, UAC result 1223 exits the installer without relaunching the old app.

Confirmed locally on 2026-11-01 after the earlier timeout observation on SARAE. Process timeline and checksums are preserved locally. Related: #1437, #1439. The accepted-update retry is being checked separately.