Merge remote-tracking branch 'upstream/master' into fix-byname-queries

# Conflicts:
#	src/Jellyfin.Database/Jellyfin.Database.Providers.Sqlite/Migrations/JellyfinDbModelSnapshot.cs

8 files changed, 213 insertions, 248 deletions

diff --git a/Jellyfin.Server.Implementations/Extensions/ExpressionExtensions.cs b/Jellyfin.Server.Implementations/Extensions/ExpressionExtensions.cs
index d70ac672f2..0f166fc6e0 100644
--- a/Jellyfin.Server.Implementations/Extensions/ExpressionExtensions.cs
+++ b/Jellyfin.Server.Implementations/Extensions/ExpressionExtensions.cs
@@ -40,6 +40,19 @@ public static class ExpressionExtensions
     }
 
     /// <summary>
+    /// Negates a predicate.
+    /// </summary>
+    /// <typeparam name="T">The predicate parameter type.</typeparam>
+    /// <param name="predicate">The predicate expression to negate.</param>
+    /// <returns>A new expression representing the negation of the input predicate.</returns>
+    public static Expression<Func<T, bool>> Not<T>(this Expression<Func<T, bool>> predicate)
+    {
+        ArgumentNullException.ThrowIfNull(predicate);
+
+        return Expression.Lambda<Func<T, bool>>(Expression.Not(predicate.Body), predicate.Parameters);
+    }
+
+    /// <summary>
     /// Combines two predicates into a single predicate using a logical AND operation.
     /// </summary>
     /// <typeparam name="T">The predicate parameter type.</typeparam>
diff --git a/Jellyfin.Server.Implementations/Item/BaseItemMapper.cs b/Jellyfin.Server.Implementations/Item/BaseItemMapper.cs
index c64e6ac068..958d11e21e 100644
--- a/Jellyfin.Server.Implementations/Item/BaseItemMapper.cs
+++ b/Jellyfin.Server.Implementations/Item/BaseItemMapper.cs
@@ -183,7 +183,7 @@ public static class BaseItemMapper
         if (dto is Folder folder)
         {
             folder.DateLastMediaAdded = entity.DateLastMediaAdded ?? DateTime.SpecifyKind(DateTime.MinValue, DateTimeKind.Utc);
-            if (entity.LinkedChildEntities is not null && entity.LinkedChildEntities.Count > 0)
+            if (entity.LinkedChildEntities is not null)
             {
                 folder.LinkedChildren = entity.LinkedChildEntities
                     .OrderBy(e => e.SortOrder)
diff --git a/Jellyfin.Server.Implementations/Item/BaseItemRepository.QueryBuilding.cs b/Jellyfin.Server.Implementations/Item/BaseItemRepository.QueryBuilding.cs
index 96a23d2d12..5aa2d7c46b 100644
--- a/Jellyfin.Server.Implementations/Item/BaseItemRepository.QueryBuilding.cs
+++ b/Jellyfin.Server.Implementations/Item/BaseItemRepository.QueryBuilding.cs
@@ -621,62 +621,31 @@ public sealed partial class BaseItemRepository
     }
 
     /// <inheritdoc />
-    public IQueryable<Guid> GetFullyPlayedFolderIdsQuery(JellyfinDbContext context, IQueryable<Guid> folderIds, User user)
+    public IQueryable<BaseItemEntity> GetAccessFilteredLeafItemsQuery(JellyfinDbContext context, User user, bool includeOwnedItems = false)
     {
         ArgumentNullException.ThrowIfNull(context);
-        ArgumentNullException.ThrowIfNull(folderIds);
         ArgumentNullException.ThrowIfNull(user);
 
-        var filter = new InternalItemsQuery(user);
-        var userId = user.Id;
-
         var leafItems = context.BaseItems
             .AsNoTracking()
-            .Where(b => !b.IsFolder && !b.IsVirtualItem);
-        leafItems = ApplyAccessFiltering(context, leafItems, filter);
-
-        var playedLeafItems = leafItems
-            .Select(b => new { b.Id, Played = b.UserData!.Any(ud => ud.UserId == userId && ud.Played) });
-
-        var ancestorLeaves = context.AncestorIds
-            .Where(a => folderIds.Contains(a.ParentItemId))
-            .Join(
-                playedLeafItems,
-                a => a.ItemId,
-                b => b.Id,
-                (a, b) => new { FolderId = a.ParentItemId, b.Id, b.Played });
+            .Where(e => !e.IsFolder && !e.IsVirtualItem);
 
-        var linkedLeaves = context.LinkedChildren
-            .Where(lc => folderIds.Contains(lc.ParentId))
-            .Join(
-                playedLeafItems,
-                lc => lc.ChildId,
-                b => b.Id,
-                (lc, b) => new { FolderId = lc.ParentId, b.Id, b.Played });
+        return ApplyAccessFiltering(context, leafItems, new InternalItemsQuery(user) { IncludeOwnedItems = includeOwnedItems });
+    }
 
-        var linkedFolderLeaves = context.LinkedChildren
-            .Where(lc => folderIds.Contains(lc.ParentId))
-            .Join(
-                context.BaseItems.Where(b => b.IsFolder),
-                lc => lc.ChildId,
-                b => b.Id,
-                (lc, b) => new { lc.ParentId, FolderChildId = b.Id })
-            .Join(
-                context.AncestorIds,
-                x => x.FolderChildId,
-                a => a.ParentItemId,
-                (x, a) => new { x.ParentId, DescendantId = a.ItemId })
-            .Join(
-                playedLeafItems,
-                x => x.DescendantId,
-                b => b.Id,
-                (x, b) => new { FolderId = x.ParentId, b.Id, b.Played });
-
-        return ancestorLeaves
-            .Union(linkedLeaves)
-            .Union(linkedFolderLeaves)
-            .GroupBy(x => x.FolderId)
-            .Where(g => g.Select(x => x.Id).Distinct().Count() == g.Where(x => x.Played).Select(x => x.Id).Distinct().Count())
-            .Select(g => g.Key);
+    /// <inheritdoc />
+    public Expression<Func<BaseItemEntity, bool>> BuildHasDescendantFilter(JellyfinDbContext context, IQueryable<BaseItemEntity> descendants)
+    {
+        ArgumentNullException.ThrowIfNull(context);
+        ArgumentNullException.ThrowIfNull(descendants);
+
+        // Descendants are reachable through the ancestor chain and - for BoxSets and Playlists - as
+        // linked children, which can themselves be folders contributing their own descendants.
+        // Every step is a correlated index seek, so only the rows the outer query keeps are visited
+        // and a folder is left as soon as its first matching descendant is found.
+        return e => context.AncestorIds.Any(a => a.ParentItemId == e.Id && descendants.Any(d => d.Id == a.ItemId))
+            || context.LinkedChildren.Any(lc => lc.ParentId == e.Id
+                && (descendants.Any(d => d.Id == lc.ChildId)
+                    || context.AncestorIds.Any(a => a.ParentItemId == lc.ChildId && descendants.Any(d => d.Id == a.ItemId))));
     }
 }
diff --git a/Jellyfin.Server.Implementations/Item/BaseItemRepository.TranslateQuery.cs b/Jellyfin.Server.Implementations/Item/BaseItemRepository.TranslateQuery.cs
index fb9bbf0d47..1694e89179 100644
--- a/Jellyfin.Server.Implementations/Item/BaseItemRepository.TranslateQuery.cs
+++ b/Jellyfin.Server.Implementations/Item/BaseItemRepository.TranslateQuery.cs
@@ -31,6 +31,10 @@ public sealed partial class BaseItemRepository
     private static readonly string TmdbProviderName = MetadataProvider.Tmdb.ToString().ToLowerInvariant();
     private static readonly string TvdbProviderName = MetadataProvider.Tvdb.ToString().ToLowerInvariant();
 
+    // A fresh expression per access: EF rejects a query tree that reuses one lambda parameter
+    // instance across several lambdas, and this filter is combined into a tree more than once.
+    private static Expression<Func<BaseItemEntity, bool>> IsFolderFilter => e => e.IsFolder;
+
     /// <inheritdoc />
     public IQueryable<BaseItemEntity> TranslateQuery(
         IQueryable<BaseItemEntity> baseQuery,
@@ -466,97 +470,45 @@ public sealed partial class BaseItemRepository
 
         if (filter.IsPlayed.HasValue)
         {
-            var hasSeries = filter.IncludeItemTypes.Contains(BaseItemKind.Series);
-            var hasBoxSet = filter.IncludeItemTypes.Contains(BaseItemKind.BoxSet);
+            var userId = filter.User!.Id;
 
-            if (hasSeries || hasBoxSet)
-            {
-                var userId = filter.User!.Id;
-                var isPlayed = filter.IsPlayed.Value;
-                var seriesTypeName = _itemTypeLookup.BaseItemKindNames[BaseItemKind.Series];
-                var boxSetTypeName = _itemTypeLookup.BaseItemKindNames[BaseItemKind.BoxSet];
-
-                // Series: played = at least one episode AND all episodes played; unplayed = otherwise.
-                IQueryable<Guid> playedSeriesIds = hasSeries
-                    ? context.BaseItems
-                        .AsNoTracking()
-                        .Where(e => !e.IsFolder && !e.IsVirtualItem && e.SeriesId.HasValue)
-                        .GroupBy(e => e.SeriesId!.Value)
-                        .Where(g => !g.Any(e => !e.UserData!.Any(ud => ud.UserId == userId && ud.Played)))
-                        .Select(g => g.Key)
-                    : Enumerable.Empty<Guid>().AsQueryable();
-
-                // BoxSet: played = all children played.
-                IQueryable<Guid> playedBoxSetIds = hasBoxSet
-                    ? GetFullyPlayedFolderIdsQuery(
-                        context,
-                        baseQuery.Where(e => e.Type == boxSetTypeName).Select(e => e.Id),
-                        filter.User!)
-                    : Enumerable.Empty<Guid>().AsQueryable();
-
-                // Non-folder items: check UserData directly
-                var playedItemIds = context.UserData
-                    .Where(ud => ud.UserId == userId && ud.Played)
-                    .Select(ud => ud.ItemId);
-
-                if (isPlayed)
-                {
-                    baseQuery = baseQuery.Where(e =>
-                        (e.Type == seriesTypeName && playedSeriesIds.Contains(e.Id))
-                        || (e.Type == boxSetTypeName && playedBoxSetIds.Contains(e.Id))
-                        || (e.Type != seriesTypeName && e.Type != boxSetTypeName && playedItemIds.Contains(e.Id)));
-                }
-                else
-                {
-                    baseQuery = baseQuery.Where(e =>
-                        (e.Type == seriesTypeName && !playedSeriesIds.Contains(e.Id))
-                        || (e.Type == boxSetTypeName && !playedBoxSetIds.Contains(e.Id))
-                        || (e.Type != seriesTypeName && e.Type != boxSetTypeName && !playedItemIds.Contains(e.Id)));
-                }
-            }
-            else
-            {
-                var playedItemIds = context.UserData
-                    .Where(ud => ud.UserId == filter.User!.Id && ud.Played)
-                    .Select(ud => ud.ItemId);
-                var isPlayedItem = filter.IsPlayed.Value;
-                baseQuery = baseQuery.Where(e => playedItemIds.Contains(e.Id) == isPlayedItem);
-            }
+            // Leaf items carry their own played state.
+            var playedItemIds = context.UserData
+                .Where(ud => ud.UserId == userId && ud.Played)
+                .Select(ud => ud.ItemId);
+
+            // Folders (Series, Seasons, BoxSets, albums, ...) have none and count as played once no
+            // descendant is left unplayed, matching what the DTO reports for them. This has to key off
+            // the item itself rather than off the requested item types: tag and collection listings mix
+            // folders and leaf items in a single query.
+            var unplayedLeafItems = GetAccessFilteredLeafItemsQuery(context, filter.User!)
+                .Where(e => !e.UserData!.Any(ud => ud.UserId == userId && ud.Played));
+
+            var isPlayedFilter = IsFolderFilter.And(BuildHasDescendantFilter(context, unplayedLeafItems).Not())
+                .Or(IsFolderFilter.Not().And(e => playedItemIds.Contains(e.Id)));
+
+            baseQuery = baseQuery.Where(filter.IsPlayed.Value ? isPlayedFilter : isPlayedFilter.Not());
         }
 
         if (filter.IsResumable.HasValue)
         {
-            var hasSeries = filter.IncludeItemTypes.Contains(BaseItemKind.Series);
             var userId = filter.User!.Id;
             var isResumable = filter.IsResumable.Value;
-            var seriesTypeName = _itemTypeLookup.BaseItemKindNames[BaseItemKind.Series];
 
             // In-progress user data rows; alternate versions track their own progress.
             var inProgress = context.UserData
                 .Where(ud => ud.UserId == userId && ud.PlaybackPositionTicks > 0);
 
-            IQueryable<Guid>? resumableSeriesIds = null;
-            if (hasSeries)
-            {
-                // Aggregate per series in a single GROUP BY pass, instead of three full scans.
-                var seriesEpisodeStats = context.BaseItems
-                    .AsNoTracking()
-                    .Where(e => !e.IsFolder && !e.IsVirtualItem && e.SeriesId.HasValue)
-                    .GroupBy(e => e.SeriesId!.Value)
-                    .Select(g => new
-                    {
-                        SeriesId = g.Key,
-                        HasInProgress = g.Any(e => e.UserData!.Any(ud => ud.UserId == userId && ud.PlaybackPositionTicks > 0)),
-                        HasPlayed = g.Any(e => e.UserData!.Any(ud => ud.UserId == userId && ud.Played)),
-                        HasUnplayed = g.Any(e => !e.UserData!.Any(ud => ud.UserId == userId && ud.Played))
-                    });
-
-                // A series is resumable if it has an in-progress episode,
-                // or if it has both played and unplayed episodes (partially watched).
-                resumableSeriesIds = seriesEpisodeStats
-                    .Where(s => s.HasInProgress || (s.HasPlayed && s.HasUnplayed))
-                    .Select(s => s.SeriesId);
-            }
+            // Folders are resumable when a descendant is in progress, or when they hold both played and
+            // unplayed descendants (partially watched). Alternate versions keep their own progress, so
+            // they count towards the in-progress check but not towards the played/unplayed one.
+            var leafItems = GetAccessFilteredLeafItemsQuery(context, filter.User!);
+            var inProgressLeafItems = GetAccessFilteredLeafItemsQuery(context, filter.User!, includeOwnedItems: true)
+                .Where(e => e.UserData!.Any(ud => ud.UserId == userId && ud.PlaybackPositionTicks > 0));
+
+            var folderResumableFilter = BuildHasDescendantFilter(context, inProgressLeafItems)
+                .Or(BuildHasDescendantFilter(context, leafItems.Where(e => e.UserData!.Any(ud => ud.UserId == userId && ud.Played)))
+                    .And(BuildHasDescendantFilter(context, leafItems.Where(e => !e.UserData!.Any(ud => ud.UserId == userId && ud.Played)))));
 
             if (isResumable)
             {
@@ -564,18 +516,15 @@ public sealed partial class BaseItemRepository
                 // Match each version on its own progress rather than coalescing onto the primary.
                 var inProgressIds = inProgress.Select(ud => ud.ItemId);
 
-                baseQuery = hasSeries
-                    ? baseQuery.Where(e =>
-                        (e.Type == seriesTypeName && resumableSeriesIds!.Contains(e.Id))
-                        || (e.Type != seriesTypeName && inProgressIds.Contains(e.Id)))
-                    : baseQuery.Where(e => inProgressIds.Contains(e.Id));
+                baseQuery = baseQuery.Where(IsFolderFilter.And(folderResumableFilter)
+                    .Or(IsFolderFilter.Not().And(e => inProgressIds.Contains(e.Id))));
 
                 // When several versions of the same item are in progress, keep only the most recently played one, use id as tiebreaker.
                 // Only in-progress siblings can eliminate a candidate: a version without progress has a NULL max LastPlayedDate,
                 // which is never greater and never ties. Restricting the sibling scan to the in-progress set keeps this bounded by
                 // the user's Continue Watching count instead of forcing a full BaseItems scan (COALESCE keys are non-indexable) per row.
                 // Items in no version group at all have no sibling that could eliminate them, so short-circuit the scan for those.
-                baseQuery = baseQuery.Where(e => e.Type == seriesTypeName
+                baseQuery = baseQuery.Where(e => e.IsFolder
                     || (e.PrimaryVersionId == null && !context.BaseItems.Any(a => a.PrimaryVersionId == e.Id))
                     || !context.BaseItems
                         .Where(s => s.Id != e.Id
@@ -594,11 +543,8 @@ public sealed partial class BaseItemRepository
                 var resumableMovieIds = inProgress
                     .Join(context.BaseItems, ud => ud.ItemId, bi => bi.Id, (ud, bi) => bi.PrimaryVersionId ?? bi.Id);
 
-                baseQuery = hasSeries
-                    ? baseQuery.Where(e =>
-                        (e.Type == seriesTypeName && !resumableSeriesIds!.Contains(e.Id))
-                        || (e.Type != seriesTypeName && !resumableMovieIds.Contains(e.Id)))
-                    : baseQuery.Where(e => !resumableMovieIds.Contains(e.Id));
+                baseQuery = baseQuery.Where(IsFolderFilter.And(folderResumableFilter.Not())
+                    .Or(IsFolderFilter.Not().And(e => !resumableMovieIds.Contains(e.Id))));
             }
         }
 
diff --git a/Jellyfin.Server.Implementations/Item/ItemCountService.cs b/Jellyfin.Server.Implementations/Item/ItemCountService.cs
index 604db9f839..4aa65769fd 100644
--- a/Jellyfin.Server.Implementations/Item/ItemCountService.cs
+++ b/Jellyfin.Server.Implementations/Item/ItemCountService.cs
@@ -141,32 +141,32 @@ public class ItemCountService : IItemCountService
         switch (kind)
         {
             case BaseItemKind.Person:
-                baseQuery = context.PeopleBaseItemMap
+                baseQuery = ItemsById(context, context.PeopleBaseItemMap
                     .AsNoTracking()
                     .Where(m => m.People.Name == item.Name)
-                    .Select(m => m.Item);
+                    .Select(m => m.ItemId));
                 break;
             case BaseItemKind.MusicArtist:
-                baseQuery = context.ItemValuesMap
+                baseQuery = ItemsById(context, context.ItemValuesMap
                     .AsNoTracking()
                     .Where(ivm => ivm.ItemValue.CleanValue == item.CleanName
                         && (ivm.ItemValue.Type == ItemValueType.Artist || ivm.ItemValue.Type == ItemValueType.AlbumArtist))
-                    .Select(ivm => ivm.Item);
+                    .Select(ivm => ivm.ItemId));
                 break;
             case BaseItemKind.Genre:
             case BaseItemKind.MusicGenre:
-                baseQuery = context.ItemValuesMap
+                baseQuery = ItemsById(context, context.ItemValuesMap
                     .AsNoTracking()
                     .Where(ivm => ivm.ItemValue.CleanValue == item.CleanName
                         && ivm.ItemValue.Type == ItemValueType.Genre)
-                    .Select(ivm => ivm.Item);
+                    .Select(ivm => ivm.ItemId));
                 break;
             case BaseItemKind.Studio:
-                baseQuery = context.ItemValuesMap
+                baseQuery = ItemsById(context, context.ItemValuesMap
                     .AsNoTracking()
                     .Where(ivm => ivm.ItemValue.CleanValue == item.CleanName
                         && ivm.ItemValue.Type == ItemValueType.Studios)
-                    .Select(ivm => ivm.Item);
+                    .Select(ivm => ivm.ItemId));
                 break;
             case BaseItemKind.Year:
                 if (int.TryParse(item.Name, NumberStyles.Integer, CultureInfo.InvariantCulture, out var year))
@@ -254,6 +254,9 @@ public class ItemCountService : IItemCountService
         return result;
     }
 
+    private static IQueryable<BaseItemEntity> ItemsById(JellyfinDbContext context, IQueryable<Guid> itemIds)
+        => context.BaseItems.AsNoTracking().Where(e => itemIds.Contains(e.Id));
+
     /// <inheritdoc/>
     public int GetPlayedCount(InternalItemsQuery filter, Guid ancestorId)
     {
diff --git a/Jellyfin.Server.Implementations/Item/ItemPersistenceService.cs b/Jellyfin.Server.Implementations/Item/ItemPersistenceService.cs
index b10f7c527e..827c766449 100644
--- a/Jellyfin.Server.Implementations/Item/ItemPersistenceService.cs
+++ b/Jellyfin.Server.Implementations/Item/ItemPersistenceService.cs
@@ -428,106 +428,144 @@ public class ItemPersistenceService : IItemPersistenceService
 
         foreach (var item in tuples)
         {
-            if (item.Item is Folder folder)
+            // A container that was never hydrated cannot be used to rewrite its links: its empty
+            // array means "unknown", so clearing the stored rows would silently empty the item.
+            if (item.Item is Folder { LinkedChildrenLoaded: false })
             {
-                var existingLinkedChildren = allLinkedChildrenByParent.GetValueOrDefault(item.Item.Id)?.ToList() ?? new List<LinkedChildEntity>();
-                if (folder.LinkedChildren.Length > 0)
+                continue;
+            }
+
+            if (item.Item is Folder or Video
+                && allLinkedChildrenByParent.TryGetValue(item.Item.Id, out var existingLinks)
+                && existingLinks.Count > 0)
+            {
+                // A video only owns its alternate version links; any other link on that parent is
+                // written by the folder branch below and must survive.
+                var staleLinks = item.Item is Folder
+                    ? existingLinks
+                    : existingLinks
+                        .Where(e => e.ChildType is DbLinkedChildType.LocalAlternateVersion or DbLinkedChildType.LinkedAlternateVersion)
+                        .ToList();
+
+                if (staleLinks.Count > 0)
                 {
+                    context.LinkedChildren.RemoveRange(staleLinks);
+                }
+            }
+        }
+
+        context.SaveChanges();
+
+        // A LinkedChild's ItemId is only a cache.
+        var cachedChildIds = tuples
+            .Select(t => t.Item)
+            .OfType<Folder>()
+            .Where(f => f.LinkedChildrenLoaded)
+            .SelectMany(f => f.LinkedChildren)
+            .Where(lc => lc.ItemId.HasValue && !lc.ItemId.Value.IsEmpty())
+            .Select(lc => lc.ItemId!.Value)
+            .Distinct()
+            .ToList();
+
+        var knownChildIds = cachedChildIds.Count > 0
+            ? context.BaseItems
+                .WhereOneOrMany(cachedChildIds, e => e.Id)
+                .Select(e => e.Id)
+                .ToHashSet()
+            : [];
+
+        foreach (var item in tuples)
+        {
+            if (item.Item is Folder { LinkedChildrenLoaded: true } folder && folder.LinkedChildren.Length > 0)
+            {
 #pragma warning disable CS0618 // Type or member is obsolete - legacy path resolution for old data
-                    var pathsToResolve = folder.LinkedChildren
-                        .Where(lc => (!lc.ItemId.HasValue || lc.ItemId.Value.IsEmpty()) && !string.IsNullOrEmpty(lc.Path))
-                        .Select(lc => lc.Path)
-                        .Distinct()
-                        .ToList();
+                var pathsToResolve = folder.LinkedChildren
+                    .Where(lc => !string.IsNullOrEmpty(lc.Path)
+                        && (!lc.ItemId.HasValue || lc.ItemId.Value.IsEmpty() || !knownChildIds.Contains(lc.ItemId.Value)))
+                    .Select(lc => lc.Path)
+                    .Distinct()
+                    .ToList();
 
-                    var pathToIdMap = pathsToResolve.Count > 0
-                        ? context.BaseItems
-                            .Where(e => e.Path != null && pathsToResolve.Contains(e.Path))
-                            .Select(e => new { e.Path, e.Id })
-                            .GroupBy(e => e.Path!)
-                            .ToDictionary(g => g.Key, g => g.First().Id)
-                        : [];
+                var pathToIdMap = pathsToResolve.Count > 0
+                    ? context.BaseItems
+                        .Where(e => e.Path != null && pathsToResolve.Contains(e.Path))
+                        .Select(e => new { e.Path, e.Id })
+                        .GroupBy(e => e.Path!)
+                        .ToDictionary(g => g.Key, g => g.First().Id)
+                    : [];
 
-                    var resolvedChildren = new List<(LinkedChild Child, Guid ChildId)>();
-                    foreach (var linkedChild in folder.LinkedChildren)
+                var resolvedChildren = new List<(LinkedChild Child, Guid ChildId)>();
+                foreach (var linkedChild in folder.LinkedChildren)
+                {
+                    var childItemId = linkedChild.ItemId;
+                    if (!childItemId.HasValue || childItemId.Value.IsEmpty() || !knownChildIds.Contains(childItemId.Value))
                     {
-                        var childItemId = linkedChild.ItemId;
-                        if (!childItemId.HasValue || childItemId.Value.IsEmpty())
+                        if (!string.IsNullOrEmpty(linkedChild.Path) && pathToIdMap.TryGetValue(linkedChild.Path, out var resolvedId))
                         {
-                            if (!string.IsNullOrEmpty(linkedChild.Path) && pathToIdMap.TryGetValue(linkedChild.Path, out var resolvedId))
-                            {
-                                childItemId = resolvedId;
-                            }
+                            childItemId = resolvedId;
                         }
-#pragma warning restore CS0618
-
-                        if (childItemId.HasValue && !childItemId.Value.IsEmpty())
+                        else if (Guid.TryParse(linkedChild.LibraryItemId, out var libraryItemId) && !libraryItemId.IsEmpty())
                         {
-                            resolvedChildren.Add((linkedChild, childItemId.Value));
+                            childItemId = libraryItemId;
                         }
                     }
+#pragma warning restore CS0618
 
+                    if (childItemId.HasValue && !childItemId.Value.IsEmpty())
+                    {
+                        resolvedChildren.Add((linkedChild, childItemId.Value));
+                    }
+                }
+
+                // Playlists may legitimately contain the same item multiple times (e.g. a song repeated
+                // in an .m3u file). Every other container type keeps a single entry per child.
+                var isPlaylist = folder is Playlist;
+                if (!isPlaylist)
+                {
                     resolvedChildren = resolvedChildren
                         .GroupBy(c => c.ChildId)
                         .Select(g => g.Last())
                         .ToList();
+                }
 
-                    var childIdsToCheck = resolvedChildren.Select(c => c.ChildId).ToList();
-                    var existingChildIds = childIdsToCheck.Count > 0
-                        ? context.BaseItems
-                            .Where(e => childIdsToCheck.Contains(e.Id))
-                            .Select(e => e.Id)
-                            .ToHashSet()
-                        : [];
-
-                    var isPlaylist = folder is Playlist;
-                    var sortOrder = 0;
-                    foreach (var (linkedChild, childId) in resolvedChildren)
-                    {
-                        if (!existingChildIds.Contains(childId))
-                        {
-                            _logger.LogWarning(
-                                "Skipping LinkedChild for parent {ParentName} ({ParentId}): child item {ChildId} does not exist in database",
-                                item.Item.Name,
-                                item.Item.Id,
-                                childId);
-                            continue;
-                        }
-
-                        var existingLink = existingLinkedChildren.FirstOrDefault(e => e.ChildId == childId);
-                        if (existingLink is null)
-                        {
-                            context.LinkedChildren.Add(new LinkedChildEntity()
-                            {
-                                ParentId = item.Item.Id,
-                                ChildId = childId,
-                                ChildType = (DbLinkedChildType)linkedChild.Type,
-                                SortOrder = isPlaylist ? sortOrder : null
-                            });
-                        }
-                        else
-                        {
-                            existingLink.SortOrder = isPlaylist ? sortOrder : null;
-                            existingLink.ChildType = (DbLinkedChildType)linkedChild.Type;
-                            existingLinkedChildren.Remove(existingLink);
-                        }
+                var childIdsToCheck = resolvedChildren.Select(c => c.ChildId).Distinct().ToList();
+                var existingChildIds = childIdsToCheck.Count > 0
+                    ? context.BaseItems
+                        .Where(e => childIdsToCheck.Contains(e.Id))
+                        .Select(e => e.Id)
+                        .ToHashSet()
+                    : [];
 
-                        sortOrder++;
+                var sortOrder = 0;
+                foreach (var (linkedChild, childId) in resolvedChildren)
+                {
+                    if (!existingChildIds.Contains(childId))
+                    {
+#pragma warning disable CS0618 // Type or member is obsolete - legacy path is logged for diagnostics
+                        _logger.LogWarning(
+                            "Skipping LinkedChild for parent {ParentName} ({ParentId}): child item {ChildId} (path {ChildPath}) does not exist in database",
+                            item.Item.Name,
+                            item.Item.Id,
+                            childId,
+                            linkedChild.Path ?? "unknown");
+#pragma warning restore CS0618
+                        continue;
                     }
-                }
 
-                if (existingLinkedChildren.Count > 0)
-                {
-                    context.LinkedChildren.RemoveRange(existingLinkedChildren);
+                    context.LinkedChildren.Add(new LinkedChildEntity()
+                    {
+                        ParentId = item.Item.Id,
+                        ChildId = childId,
+                        ChildType = (DbLinkedChildType)linkedChild.Type,
+                        SortOrder = sortOrder
+                    });
+
+                    sortOrder++;
                 }
             }
 
             if (item.Item is Video video)
             {
-                var existingLinkedChildren = (allLinkedChildrenByParent.GetValueOrDefault(video.Id) ?? new List<LinkedChildEntity>())
-                    .Where(e => (int)e.ChildType == 2 || (int)e.ChildType == 3)
-                    .ToList();
-
                 var newLinkedChildren = new List<(Guid ChildId, LinkedChildType Type)>();
 
                 if (video.LocalAlternateVersions.Length > 0)
@@ -577,7 +615,7 @@ public class ItemPersistenceService : IItemPersistenceService
                         .ToHashSet()
                     : [];
 
-                int sortOrder = 0;
+                var sortOrder = 0;
                 foreach (var (childId, childType) in newLinkedChildren)
                 {
                     if (!existingChildIds.Contains(childId))
@@ -590,36 +628,27 @@ public class ItemPersistenceService : IItemPersistenceService
                         continue;
                     }
 
-                    var existingLink = existingLinkedChildren.FirstOrDefault(e => e.ChildId == childId);
-                    if (existingLink is null)
+                    context.LinkedChildren.Add(new LinkedChildEntity
                     {
-                        context.LinkedChildren.Add(new LinkedChildEntity
-                        {
-                            ParentId = video.Id,
-                            ChildId = childId,
-                            ChildType = (DbLinkedChildType)childType,
-                            SortOrder = sortOrder
-                        });
-                    }
-                    else
-                    {
-                        existingLink.ChildType = (DbLinkedChildType)childType;
-                        existingLink.SortOrder = sortOrder;
-                        existingLinkedChildren.Remove(existingLink);
-                    }
+                        ParentId = video.Id,
+                        ChildId = childId,
+                        ChildType = (DbLinkedChildType)childType,
+                        SortOrder = sortOrder
+                    });
 
                     sortOrder++;
                 }
 
-                if (existingLinkedChildren.Count > 0)
+                // A previously-linked LocalAlternateVersion that is no longer present becomes orphaned;
+                var previousLinkedChildren = allLinkedChildrenByParent.GetValueOrDefault(video.Id);
+                if (previousLinkedChildren is { Count: > 0 })
                 {
-                    var orphanedLocalVersionIds = existingLinkedChildren
-                        .Where(e => e.ChildType == DbLinkedChildType.LocalAlternateVersion)
+                    var newChildIds = newLinkedChildren.Select(c => c.ChildId).ToHashSet();
+                    var orphanedLocalVersionIds = previousLinkedChildren
+                        .Where(e => e.ChildType == DbLinkedChildType.LocalAlternateVersion && !newChildIds.Contains(e.ChildId))
                         .Select(e => e.ChildId)
                         .ToList();
 
-                    context.LinkedChildren.RemoveRange(existingLinkedChildren);
-
                     if (orphanedLocalVersionIds.Count > 0)
                     {
                         var orphanedItems = context.BaseItems
diff --git a/Jellyfin.Server.Implementations/Item/LinkedChildrenService.cs b/Jellyfin.Server.Implementations/Item/LinkedChildrenService.cs
index 5e5ce320a5..5f1d9bf87a 100644
--- a/Jellyfin.Server.Implementations/Item/LinkedChildrenService.cs
+++ b/Jellyfin.Server.Implementations/Item/LinkedChildrenService.cs
@@ -159,12 +159,16 @@ public class LinkedChildrenService : ILinkedChildrenService
 
         if (existingLink is null)
         {
+            var nextSortOrder = (context.LinkedChildren
+                .Where(lc => lc.ParentId == parentId)
+                .Max(lc => (int?)lc.SortOrder) ?? -1) + 1;
+
             context.LinkedChildren.Add(new Jellyfin.Database.Implementations.Entities.LinkedChildEntity
             {
                 ParentId = parentId,
                 ChildId = childId,
                 ChildType = dbChildType,
-                SortOrder = null
+                SortOrder = nextSortOrder
             });
         }
         else
diff --git a/Jellyfin.Server.Implementations/StorageHelpers/StorageHelper.cs b/Jellyfin.Server.Implementations/StorageHelpers/StorageHelper.cs
index 13c7895f83..0989ce84ba 100644
--- a/Jellyfin.Server.Implementations/StorageHelpers/StorageHelper.cs
+++ b/Jellyfin.Server.Implementations/StorageHelpers/StorageHelper.cs
@@ -87,8 +87,9 @@ public static class StorageHelper
     /// </summary>
     private static string ResolvePath(string path)
     {
-        var parts = path.Split(Path.DirectorySeparatorChar, StringSplitOptions.RemoveEmptyEntries);
-        var current = Path.DirectorySeparatorChar.ToString();
+        var root = Path.GetPathRoot(path) ?? Path.DirectorySeparatorChar.ToString();
+        var parts = path.Substring(root.Length).Split(Path.DirectorySeparatorChar, StringSplitOptions.RemoveEmptyEntries);
+        var current = root;
         foreach (var part in parts)
         {
             current = Path.Combine(current, part);