Fix scrape crash + cover compose responsiveness

- Cache the UMD/game cover templates AND their transparent-window rects
  (computed once, under a lock). The old code re-ran an O(w*h) Python pixel
  scan on every composited cover, stalling video cover loading and scraping
  for ~1s per cover with GIL contention.
- ScrapeDialog: ignore stale search/scrape results via a generation counter
  and cancel in-flight workers when a new search/scrape starts; clear threads
  on close.
- MetadataWorker (library details): cancel stale metadata fetches and delete
  finished workers/threads instead of leaking one per item selection.

app/covers.py

@@ -773,11 +773,16 @@ def save_cover(release_id, system, data):
 # --------------------------------------------------------------------------- #
 # Game cover compositing (IGDB key art -> full PSP cover)
 # --------------------------------------------------------------------------- #
-_game_template_image = None
+_game_template_cache = None  # (template QImage or None, window (x, y, w, h))
+_game_template_lock = threading.Lock()
 
 
 def _transparent_rect(img):
-    """Bounding box of the fully-transparent pixels in `img`."""
+    """Bounding box of the fully-transparent pixels in `img`.
+
+    Run once per template (the result is cached) — an O(w*h) scan is far too
+    slow to repeat for every composed cover.
+    """
     minx, miny, maxx, maxy = img.width(), img.height(), -1, -1
     for y in range(img.height()):
         for x in range(img.width()):
@@ -790,24 +795,31 @@ def _transparent_rect(img):
 
 
 def _game_template():
-    """Load the PSP game cover template (top header + transparent window)."""
-    global _game_template_image
-    if _game_template_image is None:
-        try:
-            from PySide6.QtGui import QImage
-        except Exception:  # noqa: BLE001 - headless API may lack PySide6
-            return None
-        img = QImage()
-        for path in (
-            config.COVERS_DIR / "UMD_GAME_COVER_TEMPLATE.png",
-            config.DATA_DIR / "covers" / "UMD_GAME_COVER_TEMPLATE.png",
-        ):
-            if path.exists():
-                img.load(str(path))
-                if not img.isNull():
-                    break
-        _game_template_image = img.convertToFormat(QImage.Format_ARGB32) if not img.isNull() else None
-    return _game_template_image
+    """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:
+                try:
+                    from PySide6.QtGui import QImage
+                except Exception:  # noqa: BLE001 - headless API may lack PySide6
+                    _game_template_cache = (None, (0, 0, 0, 0))
+                    return _game_template_cache
+                img = QImage()
+                for path in (
+                    config.COVERS_DIR / "UMD_GAME_COVER_TEMPLATE.png",
+                    config.DATA_DIR / "covers" / "UMD_GAME_COVER_TEMPLATE.png",
+                ):
+                    if path.exists():
+                        img.load(str(path))
+                        if not img.isNull():
+                            break
+                img = img.convertToFormat(QImage.Format_ARGB32) if not img.isNull() else None
+                _game_template_cache = (
+                    img,
+                    _transparent_rect(img) if img is not None and not img.isNull() else (0, 0, 0, 0),
+                )
+    return _game_template_cache
 
 
 def compose_game_cover(key_art_bytes):
@@ -822,14 +834,13 @@ def compose_game_cover(key_art_bytes):
     except Exception:  # noqa: BLE001
         return key_art_bytes
 
-    template = _game_template()
+    template, (x, y, w, h) = _game_template()
     art = QImage.fromData(key_art_bytes)
     if template is None or template.isNull() or art.isNull():
         return key_art_bytes
     art = art.convertToFormat(QImage.Format_ARGB32)
     out = QImage(template.size(), QImage.Format_ARGB32)
     out.fill(Qt.transparent)
-    x, y, w, h = _transparent_rect(template)
 
     painter = QPainter(out)
     if w > 0 and h > 0:

app/gui.py

@@ -165,55 +165,65 @@ class CoverLoader(QObject):
         self.finished.emit()
 
 
-_template_image = None
+_template_cache = None  # (template QImage, transparent window (x, y, w, h))
+_template_lock = threading.Lock()
 
 
 def _umd_template():
-    global _template_image
-    if _template_image is None:
-        img = QImage()
-        for path in (
-            config.COVERS_DIR / "UMD_COVER_TEMPLATE.png",
-            config.DATA_DIR / "covers" / "UMD_COVER_TEMPLATE.png",
-        ):
-            if path.exists():
-                img.load(str(path))
-                if not img.isNull():
-                    break
-        _template_image = img.convertToFormat(QImage.Format_ARGB32)
-    return _template_image
+    """Return ``(template QImage, transparent window rect)`` — loaded once."""
+    global _template_cache
+    if _template_cache is None:
+        with _template_lock:
+            if _template_cache is None:
+                img = QImage()
+                for path in (
+                    config.COVERS_DIR / "UMD_COVER_TEMPLATE.png",
+                    config.DATA_DIR / "covers" / "UMD_COVER_TEMPLATE.png",
+                ):
+                    if path.exists():
+                        img.load(str(path))
+                        if not img.isNull():
+                            break
+                img = img.convertToFormat(QImage.Format_ARGB32)
+                _template_cache = (img, _transparent_window(img))
+    return _template_cache
 
 
 def _transparent_window(img):
-    minx, miny, maxx, maxy = img.width(), img.height(), -1, -1
-    for y in range(img.height()):
-        for x in range(img.width()):
+    """Bounding box of fully-transparent pixels as ``(x, y, w, h)``.
+
+    Run once per template (the result is cached), since this is an O(w*h)
+    scan that is far too slow to repeat per cover.
+    """
+    w, h = img.width(), img.height()
+    minx, miny, maxx, maxy = w, h, -1, -1
+    for y in range(h):
+        for x in range(w):
             if ((img.pixel(x, y) >> 24) & 0xFF) == 0:
                 minx, miny = min(minx, x), min(miny, y)
                 maxx, maxy = max(maxx, x), max(maxy, y)
     if maxx < minx or maxy < miny:
-        return QRect()
-    return QRect(minx, miny, maxx - minx + 1, maxy - miny + 1)
+        return (0, 0, 0, 0)
+    return (minx, miny, maxx - minx + 1, maxy - miny + 1)
 
 
 def compose_umd_cover(poster_bytes):
     """Paste a movie poster into the UMD template's transparent window (PNG bytes)."""
-    template = _umd_template()
+    template, (wx, wy, ww, wh) = _umd_template()
     poster = QImage.fromData(poster_bytes)
     if template.isNull() or poster.isNull():
         return None
     poster = poster.convertToFormat(QImage.Format_ARGB32)
     out = QImage(template.size(), QImage.Format_ARGB32)
     out.fill(Qt.transparent)
-    window = _transparent_window(template)
 
     painter = QPainter(out)
-    if window.width() > 0 and window.height() > 0:
-        scaled = poster.scaled(window.size(), Qt.KeepAspectRatioByExpanding, Qt.SmoothTransformation)
-        ox = window.x() + (window.width() - scaled.width()) // 2
-        oy = window.y() + (window.height() - scaled.height()) // 2
+    if ww > 0 and wh > 0:
+        scaled = poster.scaled(QSize(ww, wh), Qt.KeepAspectRatioByExpanding, Qt.SmoothTransformation)
+        ox = wx + (ww - scaled.width()) // 2
+        oy = wy + (wh - scaled.height()) // 2
         painter.save()
-        painter.setClipRect(window)
+        painter.setClipRect(wx, wy, ww, wh)
         painter.drawImage(ox, oy, scaled)
         painter.restore()
     painter.drawImage(0, 0, template)
@@ -463,7 +473,9 @@ class CoverShowcase(QWidget):
         self.loader.loaded.connect(self._on_loaded)
         self.loader.failed.connect(self._on_failed)
         self.loader.finished.connect(self._on_loading_done)
+        self.loader.finished.connect(self._on_loader_finished)
         self.loader.finished.connect(self.thread.quit)
+        self.thread.finished.connect(self._on_thread_finished)
         self._threads.append(self.thread)
         self._loaders.append(self.loader)
         self.thread.start()
@@ -521,6 +533,26 @@ class CoverShowcase(QWidget):
         self._loading = False
         self._update_status()
 
+    def _on_loader_finished(self):
+        """Drop a finished cover loader from tracking and schedule its deletion."""
+        loader = self.sender()
+        if loader is None:
+            return
+        if loader in self._loaders:
+            self._loaders.remove(loader)
+        if self.loader is loader:
+            self.loader = None
+        loader.deleteLater()
+
+    def _on_thread_finished(self):
+        """Delete a finished cover-loader thread."""
+        thread = self.sender()
+        if thread in self._threads:
+            self._threads.remove(thread)
+        if self.thread is thread:
+            self.thread = None
+        thread.deleteLater()
+
     def _update_status(self):
         if self._closing:
             return
@@ -632,9 +664,16 @@ class MetadataWorker(QObject):
         self.gen = gen
         self.system = system
         self.release_id = release_id
+        self._cancel = threading.Event()
+
+    def cancel(self):
+        self._cancel.set()
 
     def run(self):
         meta = info.get_or_fetch(self.release_id, self.system, self.title)
+        if self._cancel.is_set():
+            self.finished.emit()
+            return
         self.result.emit(self.gen, meta or {})
         self.finished.emit()
 
@@ -934,10 +973,16 @@ class ScrapeSearchWorker(QObject):
         super().__init__()
         self.system = system
         self.query = query
+        self._cancel = threading.Event()
+
+    def cancel(self):
+        self._cancel.set()
 
     def run(self):
         found = covers.search_metadata_candidates(self.system, self.query, limit=20, timeout=10)
         for r in found:
+            if self._cancel.is_set():
+                break
             src = r.get("source")
             if src == "openvgdb":
                 r["thumb_bytes"] = covers.fetch_openvgdb_local(r.get("title") or "")
@@ -949,7 +994,8 @@ class ScrapeSearchWorker(QObject):
             else:
                 url = r.get("thumb_url")
                 r["thumb_bytes"] = covers.download_image(url, timeout=8) if url else None
-        self.results.emit(found)
+        if not self._cancel.is_set():
+            self.results.emit(found)
         self.finished.emit()
 
 
@@ -962,10 +1008,17 @@ class ScrapeFetchWorker(QObject):
         self.system = system
         self.rid = rid
         self.candidate = candidate
+        self._cancel = threading.Event()
+
+    def cancel(self):
+        self._cancel.set()
 
     def run(self):
         meta = covers.link_metadata(self.system, self.candidate, timeout=10) or {}
         cover = _scrape_cover(self.system, self.candidate, self.rid, timeout=20)
+        if self._cancel.is_set():
+            self.finished.emit()
+            return
         self.result.emit({"meta": meta, "cover": cover})
         self.finished.emit()
 
@@ -1013,6 +1066,7 @@ class ScrapeDialog(QDialog):
         self.resize(600, 580)
         self.candidates = []
         self.selected_meta = None
+        self._search_gen = 0
 
         layout = QVBoxLayout(self)
         top = QHBoxLayout()
@@ -1058,6 +1112,10 @@ class ScrapeDialog(QDialog):
         query = self.query_edit.text().strip()
         if not query:
             return
+        self._search_gen += 1
+        gen = self._search_gen
+        for w in self._workers:
+            w.cancel()
         self.status.setText("Searching…")
         self.search_btn.setEnabled(False)
         self.ok_btn.setEnabled(False)
@@ -1067,13 +1125,15 @@ class ScrapeDialog(QDialog):
         worker = ScrapeSearchWorker(self.system, query)
         worker.moveToThread(thread)
         thread.started.connect(worker.run)
-        worker.results.connect(self._on_results)
+        worker.results.connect(lambda r, g=gen: self._on_results(r, g))
         worker.finished.connect(thread.quit)
         self._threads.append(thread)
         self._workers.append(worker)
         thread.start()
 
-    def _on_results(self, results):
+    def _on_results(self, results, gen):
+        if gen != self._search_gen:
+            return
         self.search_btn.setEnabled(True)
         self.candidates = results
         self.list.clear()
@@ -1104,6 +1164,10 @@ class ScrapeDialog(QDialog):
         if item is None:
             return
         candidate = item.data(Qt.UserRole)
+        self._search_gen += 1
+        gen = self._search_gen
+        for w in self._workers:
+            w.cancel()
         self.ok_btn.setEnabled(False)
         self.search_btn.setEnabled(False)
         self.status.setText("Scraping…")
@@ -1111,13 +1175,15 @@ class ScrapeDialog(QDialog):
         worker = ScrapeFetchWorker(self.system, self.rid, candidate)
         worker.moveToThread(thread)
         thread.started.connect(worker.run)
-        worker.result.connect(self._on_scraped)
+        worker.result.connect(lambda p, g=gen: self._on_scraped(p, g))
         worker.finished.connect(thread.quit)
         self._threads.append(thread)
         self._workers.append(worker)
         thread.start()
 
-    def _on_scraped(self, payload):
+    def _on_scraped(self, payload, gen):
+        if gen != self._search_gen:
+            return
         meta = payload.get("meta") or {}
         cover = payload.get("cover")
         if cover:
@@ -1133,11 +1199,14 @@ class ScrapeDialog(QDialog):
             self.status.setText("Could not fetch anything for that selection.")
 
     def closeEvent(self, event):
+        for w in self._workers:
+            w.cancel()
         for t in self._threads:
             if _thread_running(t):
                 t.quit()
                 t.wait()
         self._workers = []
+        self._threads = []
         event.accept()
 
 
@@ -4790,6 +4859,8 @@ class MainWindow(QMainWindow):
         thread.started.connect(worker.run)
         worker.result.connect(self._on_library_loaded)
         worker.finished.connect(thread.quit)
+        worker.finished.connect(worker.deleteLater)
+        thread.finished.connect(thread.deleteLater)
         thread.finished.connect(lambda t=thread, w=worker: self._forget_library_thread(t, w))
         self._library_threads.append(thread)
         self._library_workers.append(worker)
@@ -4930,6 +5001,8 @@ class MainWindow(QMainWindow):
             return
         self._meta_gen += 1
         gen = self._meta_gen
+        for w in self._meta_workers:
+            w.cancel()
         if item.get("title_override"):
             title = item["title_override"]
         elif system == "videos":
@@ -4941,11 +5014,20 @@ class MainWindow(QMainWindow):
         worker.moveToThread(thread)
         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))
         self._meta_threads.append(thread)
         self._meta_workers.append(worker)
         thread.start()
 
+    def _forget_meta_thread(self, thread, worker):
+        if thread in self._meta_threads:
+            self._meta_threads.remove(thread)
+        if worker in self._meta_workers:
+            self._meta_workers.remove(worker)
+
     def _on_metadata(self, gen, meta):
         if gen != self._meta_gen:
             return