- Library/metadata workers: delete the worker on its own thread via worker.finished -> worker.deleteLater (bound) instead of letting Python GC delete it on the GUI thread after untracking. - Cover templates: compute the transparent-window scan outside the lock so a slow first scan never holds the lock and stalls other cover threads. - Store: larger cover/date batches (500/400/300) so the store loads 3449 archives with far fewer QThread + ThreadPoolExecutor creations.