"Restart to Update" answered the renderer with null before the install was
attempted, so a rejected install only reached main.log and the button looked
dead. The apply-update path now keeps the IPC call open until the app quits or
autoUpdater reports the failure, rolls the quit/install flags back when the app
stays up, and the update dialog shows the real reason with a translated hint for
a rejected code signature.
Also settle the download promise on downloadUpdate() itself: an already cached
payload emits no 'update-downloaded', which left that promise pending with its
listeners attached on every retry.
Iuliia Ivashko
52d79cb368