Harden worker cleanup + reduce cover-loading churn

- 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.

app/covers.py

@@ -797,9 +797,8 @@ def _transparent_rect(img):
 def _game_template():
     """Load the PSP game cover template; return ``(template, window)``."""
     global _game_template_cache
-    if _game_template_cache is None:
-        with _game_template_lock:
-            if _game_template_cache is None:
+    if _game_template_cache is not None:
+        return _game_template_cache
     try:
         from PySide6.QtGui import QImage
     except Exception:  # noqa: BLE001 - headless API may lack PySide6
@@ -815,10 +814,13 @@ def _game_template():
             if not img.isNull():
                 break
     img = img.convertToFormat(QImage.Format_ARGB32) if not img.isNull() else None
-                _game_template_cache = (
+    entry = (
         img,
         _transparent_rect(img) if img is not None and not img.isNull() else (0, 0, 0, 0),
     )
+    with _game_template_lock:
+        if _game_template_cache is None:
+            _game_template_cache = entry
     return _game_template_cache
 
 

app/gui.py

@@ -172,9 +172,8 @@ _template_lock = threading.Lock()
 def _umd_template():
     """Return ``(template QImage, transparent window rect)`` — loaded once."""
     global _template_cache
-    if _template_cache is None:
-        with _template_lock:
-            if _template_cache is None:
+    if _template_cache is not None:
+        return _template_cache
     img = QImage()
     for path in (
         config.COVERS_DIR / "UMD_COVER_TEMPLATE.png",
@@ -185,7 +184,10 @@ def _umd_template():
             if not img.isNull():
                 break
     img = img.convertToFormat(QImage.Format_ARGB32)
-                _template_cache = (img, _transparent_window(img))
+    entry = (img, _transparent_window(img))
+    with _template_lock:
+        if _template_cache is None:
+            _template_cache = entry
     return _template_cache
 
 
@@ -969,10 +971,11 @@ class ScrapeSearchWorker(QObject):
     results = Signal(list)  # candidates with thumb_bytes added
     finished = Signal()
 
-    def __init__(self, system, query):
+    def __init__(self, system, query, gen):
         super().__init__()
         self.system = system
         self.query = query
+        self.gen = gen
         self._cancel = threading.Event()
 
     def cancel(self):
@@ -1003,11 +1006,12 @@ class ScrapeFetchWorker(QObject):
     result = Signal(dict)  # {"meta": {...}, "cover": bytes|None}
     finished = Signal()
 
-    def __init__(self, system, rid, candidate):
+    def __init__(self, system, rid, candidate, gen):
         super().__init__()
         self.system = system
         self.rid = rid
         self.candidate = candidate
+        self.gen = gen
         self._cancel = threading.Event()
 
     def cancel(self):
@@ -1122,17 +1126,17 @@ class ScrapeDialog(QDialog):
         self.list.clear()
         self.candidates = []
         thread = QThread(self)
-        worker = ScrapeSearchWorker(self.system, query)
+        worker = ScrapeSearchWorker(self.system, query, gen)
         worker.moveToThread(thread)
         thread.started.connect(worker.run)
-        worker.results.connect(lambda r, g=gen: self._on_results(r, g))
+        worker.results.connect(self._on_results)
         worker.finished.connect(thread.quit)
         self._threads.append(thread)
         self._workers.append(worker)
         thread.start()
 
-    def _on_results(self, results, gen):
-        if gen != self._search_gen:
+    def _on_results(self, results):
+        if getattr(self.sender(), "gen", None) != self._search_gen:
             return
         self.search_btn.setEnabled(True)
         self.candidates = results
@@ -1172,17 +1176,17 @@ class ScrapeDialog(QDialog):
         self.search_btn.setEnabled(False)
         self.status.setText("Scraping…")
         thread = QThread(self)
-        worker = ScrapeFetchWorker(self.system, self.rid, candidate)
+        worker = ScrapeFetchWorker(self.system, self.rid, candidate, gen)
         worker.moveToThread(thread)
         thread.started.connect(worker.run)
-        worker.result.connect(lambda p, g=gen: self._on_scraped(p, g))
+        worker.result.connect(self._on_scraped)
         worker.finished.connect(thread.quit)
         self._threads.append(thread)
         self._workers.append(worker)
         thread.start()
 
-    def _on_scraped(self, payload, gen):
-        if gen != self._search_gen:
+    def _on_scraped(self, payload):
+        if getattr(self.sender(), "gen", None) != self._search_gen:
             return
         meta = payload.get("meta") or {}
         cover = payload.get("cover")
@@ -1198,7 +1202,15 @@ class ScrapeDialog(QDialog):
             self.search_btn.setEnabled(True)
             self.status.setText("Could not fetch anything for that selection.")
 
-    def closeEvent(self, event):
+    def _shutdown_threads(self):
+        """Cancel workers and wait for their threads to fully finish.
+
+        Must run before the dialog is destroyed — QThread children abort the
+        process with "QThread: Destroyed while thread is still running" if they
+        are deleted while their worker thread is alive. ``done()`` covers
+        accept()/reject() (including the accept() in ``_on_scraped``); the
+        close event covers the window-manager close path.
+        """
         for w in self._workers:
             w.cancel()
         for t in self._threads:
@@ -1207,8 +1219,15 @@ class ScrapeDialog(QDialog):
                 t.wait()
         self._workers = []
         self._threads = []
+
+    def closeEvent(self, event):
+        self._shutdown_threads()
         event.accept()
 
+    def done(self, result):
+        self._shutdown_threads()
+        super().done(result)
+
 
 class SettingsPage(QWidget):
     saved = Signal()
@@ -2268,11 +2287,11 @@ class StorePage(QWidget):
             return (0, -date_int, -mtime)
         return (1, 0, -mtime)
 
-    CHUNK = 150          # items filled per timer tick
-    COVER_BATCH = 200    # covers fetched for the initially-visible area
-    COVER_SCROLL_BATCH = 100
+    CHUNK = 200          # items filled per timer tick
+    COVER_BATCH = 500    # covers fetched for the initially-visible area
+    COVER_SCROLL_BATCH = 400
     RECENT_LIMIT = 300   # default: show only the newest N store items
-    DATE_BATCH = 150     # release-date metadata fetched per batch
+    DATE_BATCH = 300     # release-date metadata fetched per batch
 
     def _populate(self, items, show_count):
         self._generation += 1
@@ -4856,12 +4875,13 @@ class MainWindow(QMainWindow):
         thread = QThread(self)
         worker = LibraryWorker(self._ps1_dir, self._ps1_output_dir, self._nps_dir)
         worker.moveToThread(thread)
+        thread._worker = worker
         thread.started.connect(worker.run)
         worker.result.connect(self._on_library_loaded)
-        worker.finished.connect(thread.quit)
         worker.finished.connect(worker.deleteLater)
+        worker.finished.connect(thread.quit)
         thread.finished.connect(thread.deleteLater)
-        thread.finished.connect(lambda t=thread, w=worker: self._forget_library_thread(t, w))
+        thread.finished.connect(self._forget_library_thread)
         self._library_threads.append(thread)
         self._library_workers.append(worker)
         thread.start()
@@ -4875,10 +4895,12 @@ class MainWindow(QMainWindow):
             self.store_page.set_library_items(self._library_cache)
         self.statusBar().showMessage("")
 
-    def _forget_library_thread(self, thread, worker):
+    def _forget_library_thread(self):
+        thread = self.sender()
+        worker = getattr(thread, "_worker", None)
         if thread in self._library_threads:
             self._library_threads.remove(thread)
-        if worker in self._library_workers:
+        if worker is not None and worker in self._library_workers:
             self._library_workers.remove(worker)
 
     def _apply_library_filter(self):
@@ -5012,20 +5034,23 @@ class MainWindow(QMainWindow):
         thread = QThread(self)
         worker = MetadataWorker(title, gen, system, rid)
         worker.moveToThread(thread)
+        thread._worker = worker
         thread.started.connect(worker.run)
         worker.result.connect(self._on_metadata)
         worker.finished.connect(worker.deleteLater)
         worker.finished.connect(thread.quit)
         thread.finished.connect(thread.deleteLater)
-        thread.finished.connect(lambda t=thread, w=worker: self._forget_meta_thread(t, w))
+        thread.finished.connect(self._forget_meta_thread)
         self._meta_threads.append(thread)
         self._meta_workers.append(worker)
         thread.start()
 
-    def _forget_meta_thread(self, thread, worker):
+    def _forget_meta_thread(self):
+        thread = self.sender()
+        worker = getattr(thread, "_worker", None)
         if thread in self._meta_threads:
             self._meta_threads.remove(thread)
-        if worker in self._meta_workers:
+        if worker is not None and worker in self._meta_workers:
             self._meta_workers.remove(worker)
 
     def _on_metadata(self, gen, meta):