Harden Library tab thread cleanup (covers + items)

Library covers used the same QThread+worker architecture as the store but
never deleted finished threads/loaders, so every reload leaked one QThread
and one CoverLoader. Library item loading leaked its QThread too.

CoverShowcase now removes + deleteLater's loaders on their finished signal
and deletes their threads on thread.finished; MainWindow.load_library deletes
the finished worker and thread instead of only untracking them.

app/gui.py

@@ -463,7 +463,9 @@ 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 +523,26 @@ 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
@@ -2044,7 +2066,6 @@ class StorePage(QWidget):
         self._cover_attempted.clear()
         for loader in self._loaders:
             loader.cancel()
-        self._loaders = []
         self.grid.clear()
         self.table.setRowCount(0)
         self.status.setText("Loading…")
@@ -2220,10 +2241,12 @@ class StorePage(QWidget):
         self._cover_attempted.clear()
         self._placeholder = QIcon(_placeholder_pixmap(self.ICON_W, self.ICON_H))
 
-        # Cancel any in-flight cover loaders (stale generation).
+        # Cancel any in-flight cover loaders (stale generation). Each loader
+        # removes itself from ``_loaders`` via its own ``finished`` handler once
+        # its thread winds down — dropping the list here would garbage-collect
+        # live QObjects and crash Qt.
         for loader in self._loaders:
             loader.cancel()
-        self._loaders = []
 
         self.grid.clear()
         self.grid.setUpdatesEnabled(False)
@@ -2401,6 +2424,7 @@ class StorePage(QWidget):
         thread.started.connect(loader.run)
         loader.loaded.connect(self._on_date_loaded)
         loader.finished.connect(self._on_date_batch_done)
+        loader.finished.connect(self._on_loader_finished)
         loader.finished.connect(thread.quit)
         thread.finished.connect(self._on_thread_finished)
         self._threads.append(thread)
@@ -2425,6 +2449,21 @@ class StorePage(QWidget):
         if cell is not None:
             cell.setText(date)
 
+    def _on_loader_finished(self):
+        """Drop a finished cover/date loader from tracking.
+
+        Loaders stay in ``_loaders`` until their thread finishes so their
+        QObject wrapper is never garbage-collected while its thread is still
+        winding down (that left a dangling thread affinity and crashed Qt on
+        filter/refresh).
+        """
+        loader = self.sender()
+        if loader is None:
+            return
+        if loader in self._loaders:
+            self._loaders.remove(loader)
+        loader.deleteLater()
+
     def _start_cover_loader(self, gen, tasks):
         if self._closing or not tasks:
             return
@@ -2434,6 +2473,7 @@ class StorePage(QWidget):
         thread.started.connect(loader.run)
         loader.loaded.connect(self._on_cover_loaded)
         loader.finished.connect(self._on_cover_batch_done)
+        loader.finished.connect(self._on_loader_finished)
         loader.finished.connect(thread.quit)
         thread.finished.connect(self._on_thread_finished)
         self._threads.append(thread)
@@ -4772,6 +4812,8 @@ 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)