IMO, for the paranoid, app should use a flag. E.g., a file on disk, created on start, deleted on end, or, better, locked when app starts.

Daemon doesn't updte if file isn't locked, so start and stop daemon is only a matter of resources, not security. So even if it doesn't stop right, it simply sits there.

ETA: App closing could check daemon has stopped. Exiting could issue a kill and inform user it's done or not via a ps | grep