Fix stutter on returning to song select when updating large beatmap sets

osu.Game.Tests/Visual/SongSelect/TestSceneBeatmapCarouselUpdateHandling.cs

@@ -430,6 +430,56 @@
             AddAssert("Order didn't change", () => Carousel.PostFilterBeatmaps.Select(b => b.ID), () => Is.EqualTo(originalOrder));
         }
 
+        /// <summary>
+        /// Replicates the #34826 scenario: the matched beatmap is present in the replace snapshot, but has been
+        /// deleted from realm by the time the replace is processed, see https://github.com/ppy/osu/issues/34826.
+        /// </summary>
+        [Test]
+        public void TestBeatmapSetReplacedWithDeletedCurrentBeatmap()
+        {
+            int targetSetIndex = 0;
+
+            AddStep("select first difficulty", () =>
+            {
+                Carousel.CurrentBeatmap = baseTestBeatmap.Beatmaps[0];
+                BeatmapRequestedSelections.Clear();
+            });
+
+            AddStep("delete current beatmap from realm and replace set", () =>
+            {
+                targetSetIndex = BeatmapSets.IndexOf(baseTestBeatmap);
+                var detachedSet = BeatmapSets[targetSetIndex];
+                var selectedBeatmap = detachedSet.Beatmaps[0];
+
+                Realm.Write(r =>
+                {
+                    var toDelete = r.Find<BeatmapInfo>(selectedBeatmap.ID);
+                    if (toDelete != null)
+                        r.Remove(toDelete);
+                });
+
+                // Trigger the Replace action with a beatmap that is not in realm.
+                var staleSet = new BeatmapSetInfo
+                {
+                    ID = detachedSet.ID,
+                    OnlineID = detachedSet.OnlineID,
+                    DateAdded = detachedSet.DateAdded,
+                    DateSubmitted = detachedSet.DateSubmitted,
+                    Status = detachedSet.Status,
+                    Hash = detachedSet.Hash,
+                    Protected = detachedSet.Protected,
+                };
+
+                var staleBeatmap = createBeatmap(staleSet, selectedBeatmap);
+                staleSet.Beatmaps.Add(staleBeatmap);
+                BeatmapSets.ReplaceRange(targetSetIndex, 1, [staleSet]);
+            });
+
+            WaitForFiltering();
+
+            AddAssert("deleted match never requested for selection", () => BeatmapRequestedSelections, () => Is.Empty);
+        }
+
         private void assertDidFilter(int count = 1) => AddAssert("did filter", () => Carousel.FilterCount, () => Is.EqualTo(initial_filter_count + count));
 
         private void assertDidNotFilter() => AddAssert("did not filter", () => Carousel.FilterCount, () => Is.EqualTo(initial_filter_count));

osu.Game/Screens/Select/BeatmapCarousel.cs

@@ -259,20 +259,26 @@
                             newSetBeatmaps.FirstOrDefault(b => b.OnlineID > 0 && b.OnlineID == beatmap.OnlineID) ??
                             newSetBeatmaps.FirstOrDefault(b => b.DifficultyName == beatmap.DifficultyName && b.Ruleset.Equals(beatmap.Ruleset));
 
-                        // The matching beatmap may have been deleted or invalidated in some way since this event was fired.
-                        // Let's make sure we have the most up-to-date realm state.
-                        if (matchingNewBeatmap?.ID is Guid matchingID)
-                            matchingNewBeatmap = realm.Run(r => r.FindWithRefresh<BeatmapInfo>(matchingID)?.Detach());
-
                         if (matchingNewBeatmap != null)
                         {
                             // TODO: should this exist in song select instead of here?
                             // we need to ensure the global beatmap is also updated alongside changes.
                             if (CurrentBeatmap != null && beatmap.Equals(CurrentBeatmap))
-                                // we don't know in which group the matching new beatmap is, but that's fine - we can keep the previous one for now.
-                                // we are about to modify `Items`, which - if required - will trigger a re-filter,
-                                // which will pick a correct group - if one is present - via `HandleFilterCompleted()`.
-                                RequestSelection(new GroupedBeatmap(CurrentGroupedBeatmap?.Group, matchingNewBeatmap));
+                            {
+                                // The matching beatmap may have been deleted or invalidated in some way since this event was fired.
+                                // Let's make sure we have the most up-to-date realm state of the current beatmap.
+                                var refreshedNewBeatmap = realm.Run(r => r.FindWithRefresh<BeatmapInfo>(matchingNewBeatmap.ID)?.Detach());
+
+                                if (refreshedNewBeatmap != null)
+                                {
+                                    matchingNewBeatmap = refreshedNewBeatmap;
+
+                                    // we don't know in which group the matching new beatmap is, but that's fine - we can keep the previous one for now.
+                                    // we are about to modify `Items`, which - if required - will trigger a re-filter,
+                                    // which will pick a correct group - if one is present - via `HandleFilterCompleted()`.
+                                    RequestSelection(new GroupedBeatmap(CurrentGroupedBeatmap?.Group, matchingNewBeatmap));
+                                }
+                            }
 
                             Items.ReplaceRange(previousIndex, 1, [matchingNewBeatmap]);
                             newSetBeatmaps.Remove(matchingNewBeatmap);