Fix TypeError when deck list or overview refreshes during optimal retention

Caused by legacy code blocking the main thread.

https://forums.ankiweb.net/t/anki-23-10-beta/34912/79

pylib/anki/scheduler/dummy.py

@@ -29,5 +29,5 @@ class DummyScheduler(SchedulerBaseWithLegacy):
     def active_decks(self) -> list[DeckId]:
         return []
 
-    def counts(self) -> list[int]:
-        return [0, 0, 0]
+    def counts(self) -> tuple[int, int, int]:
+        return (0, 0, 0)

qt/aqt/deckbrowser.py

@@ -146,12 +146,21 @@ class DeckBrowser:
 
     def _renderPage(self, reuse: bool = False) -> None:
         if not reuse:
-            self._dueTree = self.mw.col.sched.deck_due_tree()
+
+            def success(tree: DeckTreeNode) -> None:
+                self._dueTree = tree
                 self.__renderPage(None)
                 return
+
+            QueryOp(
+                parent=self.mw,
+                op=lambda col: col.sched.deck_due_tree(),
+                success=success,
+            ).run_in_background()
+        else:
             self.web.evalWithCallback("window.pageYOffset", self.__renderPage)
 
-    def __renderPage(self, offset: int) -> None:
+    def __renderPage(self, offset: int | None) -> None:
         content = DeckBrowserContent(
             tree=self._renderDeckTree(self._dueTree),
             stats=self._renderStats(),

qt/aqt/overview.py

@@ -12,6 +12,7 @@ from anki.scheduler import UnburyDeck
 from aqt import gui_hooks
 from aqt.deckdescription import DeckDescriptionDialog
 from aqt.deckoptions import display_options_for_deck
+from aqt.operations import QueryOp
 from aqt.operations.scheduling import (
     empty_filtered_deck,
     rebuild_filtered_deck,
@@ -61,6 +62,7 @@ class Overview:
         self.refresh()
 
     def refresh(self) -> None:
+        def success(_counts: tuple) -> None:
             self._refresh_needed = False
             self.mw.col.reset()
             self._renderPage()
@@ -68,6 +70,10 @@ class Overview:
             self.mw.web.setFocus()
             gui_hooks.overview_did_refresh(self)
 
+        QueryOp(
+            parent=self.mw, op=lambda col: col.sched.counts(), success=success
+        ).run_in_background()
+
     def refresh_if_needed(self) -> None:
         if self._refresh_needed:
             self.refresh()