Smooth store source transitions: cancel stale batches and batch grid updates

app/gui.py

@@ -2019,9 +2019,27 @@ class StorePage(QWidget):
         if self._items:
             self._apply_filter()
 
+    def _begin_scan(self):
+        """Clear the stale view and invalidate in-flight cover/date batches."""
+        self._generation += 1
+        self._cover_busy = False
+        self._date_busy = False
+        self._cover_queue = []
+        self._cover_next = 0
+        self._date_queue = []
+        self._date_next = 0
+        self._cover_attempted.clear()
+        for loader in self._loaders:
+            loader.cancel()
+        self._loaders = []
+        self.grid.clear()
+        self.table.setRowCount(0)
+        self.status.setText("Loading…")
+
     def refresh(self, force=False):
         if self._closing:
             return
+        self._begin_scan()
         self._scan_gen += 1
         gen = self._scan_gen
         if self.source_combo.currentIndex() == 0:  # Server
@@ -2082,6 +2100,8 @@ class StorePage(QWidget):
         self._items = []
         self._filtered = []
         self._dirty = False
+        self.grid.clear()
+        self.table.setRowCount(0)
         log.warning("store unavailable: %s", message)
         self.status.setText(f"Store unavailable: {message}")
 
@@ -2193,6 +2213,7 @@ class StorePage(QWidget):
         self._loaders = []
 
         self.grid.clear()
+        self.grid.setUpdatesEnabled(False)
         self.table.setUpdatesEnabled(False)
         self.table.setSortingEnabled(False)
         self.table.setRowCount(show_count)
@@ -2297,6 +2318,7 @@ class StorePage(QWidget):
     def _finish_fill(self):
         if self._fill_timer is not None:
             self._fill_timer.stop()
+        self.grid.setUpdatesEnabled(True)
         self.table.setUpdatesEnabled(True)
         self.table.setSortingEnabled(True)
         total = len(self._filtered)