feat(ui/playlists): drag-and-drop + hover-swap-icon (Tier B2) — Zune 4.8 fan-loved playlist flow

Each playlist card in the left rail is now a drag-drop target. Dragging a
track from the right rail (PointerPressed starts DragDrop.DoDragDropAsync
with a TrackListPayload) over a playlist card highlights it with the
accent color (MultiBinding + PlaylistDropHighlightConverter comparing
each Playlist's Id to the VM's HoveredPlaylist).

After a 300ms dwell (Zune's signature hover pause), the hover-swap popup
appears next to the hovered playlist listing the OTHER playlists; hovering
each one swaps the drop target via SwapHoverTargetCommand (the user's
'hover-swap-icon' affordance from the r/Zune quote). Releasing the drag
on the current hover target fires AddTracksToPlaylistCommand which
calls the existing IMediaLibraryService.AddTrackToPlaylistAsync per
track, sets a status message, and reloads the current tracklist.

Nine new VM-level tests cover: EnterPlaylistDropZone / Leave / Refresh,
ClearPlaylistHover, HoverSwapAlternatives filtering, SwapHoverTargetCommand,
AddTracksToPlaylistCommand payload + status message, and HoverSwapPlaylistName
mirroring.

src/NotZune.UI/Converters/PlaylistDropHighlightConverter.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using Avalonia.Data.Converters;
+using Avalonia.Media;
+using NotZune.Domain.Models;
+
+namespace NotZune.UI.Converters;
+
+/// <summary>
+/// Tier B2 — returns an accent brush when the bound Playlist equals the VM's currently
+/// hovered drop target, transparent otherwise.
+/// </summary>
+public sealed class PlaylistDropHighlightConverter : IMultiValueConverter
+{
+    public static readonly PlaylistDropHighlightConverter Instance = new();
+
+    public object? Convert(IList<object?> values, Type targetType, object? parameter, CultureInfo culture)
+    {
+        if (values.Count < 2) return Avalonia.Media.Brushes.Transparent;
+        var playlist = values[0] as Playlist;
+        var hovered = values[1] as Playlist;
+
+        if (playlist == null || hovered == null) return Avalonia.Media.Brushes.Transparent;
+        return playlist.Id == hovered.Id
+            ? new SolidColorBrush(Color.FromArgb(0x33, 0xF1, 0x0D, 0xA2))
+            : Avalonia.Media.Brushes.Transparent;
+    }
+}

src/NotZune.UI/ViewModels/PlaylistsViewModel.cs

@@ -127,6 +127,49 @@ public class PlaylistsViewModel : ViewModelBase
     public ICommand DeleteSmartPlaylistCommand { get; }
     public ICommand PlaySmartPlaylistCommand { get; }
     public ICommand RefreshSmartPlaylistCommand { get; }
+    public ICommand AddTracksToPlaylistCommand { get; }
+    public ICommand SwapHoverTargetCommand { get; }
+
+    // Tier B2 (Zune 4.8 playlist drag-drop): the playlist currently highlighted as the drop target.
+    // While a track is being dragged, the playlist under the cursor sets this; releasing the
+    // drag on HoveredPlaylistId triggers AddTracksToPlaylistCommand.
+    private Playlist? _hoveredPlaylist;
+    public Playlist? HoveredPlaylist
+    {
+        get => _hoveredPlaylist;
+        private set
+        {
+            if (SetProperty(ref _hoveredPlaylist, value))
+            {
+                OnPropertyChanged(nameof(IsPlaylistHovered));
+                OnPropertyChanged(nameof(HoverSwapPlaylistName));
+            }
+        }
+    }
+
+    public bool IsPlaylistHovered => _hoveredPlaylist != null;
+
+    /// <summary>True after ~300ms dwell on a playlist — shows the hover-swap popup of alternative drop targets.</summary>
+    private bool _isHoverSwapExpanded;
+    public bool IsHoverSwapExpanded
+    {
+        get => _isHoverSwapExpanded;
+        private set
+        {
+            if (SetProperty(ref _isHoverSwapExpanded, value))
+            {
+                OnPropertyChanged(nameof(HoverSwapAlternatives));
+            }
+        }
+    }
+
+    /// <summary>Other playlists the user can land on while still hovering (Tier B2 hover-swap parity).</summary>
+    public System.Collections.Generic.IReadOnlyList<Playlist> HoverSwapAlternatives =>
+        Playlists.Where(p => p.Id != _hoveredPlaylist?.Id).ToList();
+
+    public string HoverSwapPlaylistName => _hoveredPlaylist?.Name ?? string.Empty;
+
+    private readonly System.Collections.Generic.Dictionary<Guid, Avalonia.Threading.DispatcherTimer> _hoverSwapTimers = new();
 
     public PlaylistsViewModel(
         IMediaLibraryService libraryService,
@@ -149,6 +192,13 @@ public class PlaylistsViewModel : ViewModelBase
         PlaySmartPlaylistCommand = new AsyncRelayCommand(OnPlaySmartPlaylistAsync);
         RefreshSmartPlaylistCommand = new AsyncRelayCommand(OnRefreshSmartPlaylistAsync);
 
+        // Tier B2: drag-drop + hover-swap commands. The parameters are tuples of
+        // (Playlist playlist, IReadOnlyList<Track> tracks) — Avalonia's drag-drop payload
+        // is deserialized on the drop site.
+        AddTracksToPlaylistCommand = new AsyncRelayCommand<(Playlist Playlist, IReadOnlyList<Track> Tracks)>(
+            async payload => await OnAddTracksAsync(payload.Playlist, payload.Tracks));
+        SwapHoverTargetCommand = new RelayCommand<Playlist>(p => HoveredPlaylist = p);
+
         _ = LoadPlaylistsAsync();
     }
 
@@ -362,4 +412,85 @@ public class PlaylistsViewModel : ViewModelBase
         var tracks = SelectedSmartPlaylistTracks.ToList();
         await _playerCoordinator.PlayTrackAsync(tracks[0], tracks);
     }
+
+    // ----------------------------------------------------------------------
+    // Tier B2: drag-drop + hover-swap for playlists (Zune 4.8 parity)
+    // ----------------------------------------------------------------------
+
+    /// <summary>Called when a track enters a playlist's drop zone. Sets hover state and arms the swap timer.</summary>
+    public void EnterPlaylistDropZone(Playlist playlist)
+    {
+        HoveredPlaylist = playlist;
+        ArmHoverSwapTimer(playlist);
+    }
+
+    /// <summary>Called when the cursor moves between drop targets inside the same playlist (re-arms the timer).</summary>
+    public void RefreshPlaylistDropZone(Playlist playlist)
+    {
+        if (_hoveredPlaylist?.Id != playlist.Id)
+        {
+            HoveredPlaylist = playlist;
+        }
+        ArmHoverSwapTimer(playlist);
+    }
+
+    /// <summary>Called when the cursor leaves a playlist's drop zone — collapses the swap popup and clears highlight.</summary>
+    public void LeavePlaylistDropZone(Playlist playlist)
+    {
+        if (_hoveredPlaylist?.Id == playlist.Id)
+        {
+            HoveredPlaylist = null;
+            IsHoverSwapExpanded = false;
+        }
+        CancelHoverSwapTimer(playlist);
+    }
+
+    /// <summary>Called when the drop is released over a playlist — clears transient state.</summary>
+    public void ClearPlaylistHover()
+    {
+        HoveredPlaylist = null;
+        IsHoverSwapExpanded = false;
+    }
+
+    private void ArmHoverSwapTimer(Playlist playlist)
+    {
+        CancelHoverSwapTimer(playlist);
+        var timer = new Avalonia.Threading.DispatcherTimer
+        {
+            Interval = TimeSpan.FromMilliseconds(300)
+        };
+        timer.Tick += (_, _) =>
+        {
+            timer.Stop();
+            if (_hoveredPlaylist?.Id == playlist.Id)
+            {
+                IsHoverSwapExpanded = true;
+            }
+        };
+        _hoverSwapTimers[playlist.Id] = timer;
+        timer.Start();
+    }
+
+    private void CancelHoverSwapTimer(Playlist playlist)
+    {
+        if (_hoverSwapTimers.TryGetValue(playlist.Id, out var timer))
+        {
+            timer.Stop();
+            _hoverSwapTimers.Remove(playlist.Id);
+        }
+    }
+
+    private async Task OnAddTracksAsync(Playlist playlist, IReadOnlyList<Track> tracks)
+    {
+        foreach (var t in tracks)
+        {
+            await _libraryService.AddTrackToPlaylistAsync(playlist.Id, t.Id);
+        }
+
+        StatusMessage = $"Added {tracks.Count} track{(tracks.Count == 1 ? string.Empty : "s")} to {playlist.Name}.";
+        if (SelectedPlaylist?.Id == playlist.Id)
+        {
+            await LoadSelectedPlaylistTracksAsync(playlist);
+        }
+    }
 }

src/NotZune.UI/Views/PlaylistsView.axaml

@@ -4,6 +4,7 @@
              xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
              xmlns:vm="clr-namespace:NotZune.UI.ViewModels;assembly=NotZune.UI"
              xmlns:models="clr-namespace:NotZune.Domain.Models;assembly=NotZune.Domain"
+             xmlns:conv="clr-namespace:NotZune.UI.Converters;assembly=NotZune.UI"
              mc:Ignorable="d" d:DesignWidth="1000" d:DesignHeight="600"
              x:Class="NotZune.UI.Views.PlaylistsView"
              x:DataType="vm:PlaylistsViewModel">
@@ -40,12 +41,60 @@
                  CornerRadius="0">
           <ListBox.ItemTemplate>
             <DataTemplate DataType="models:Playlist">
-              <Border Padding="6,8" CornerRadius="0">
-                <StackPanel Spacing="2">
-                  <TextBlock Text="{Binding Name}" Classes="body" FontWeight="SemiBold" TextTrimming="CharacterEllipsis" />
-                  <TextBlock Text="{Binding UpdatedAtUtc, StringFormat='{}Updated {0:d}'}" Classes="caption" FontSize="9" Foreground="{DynamicResource ZuneTextDimmedBrush}" />
-                </StackPanel>
-              </Border>
+              <!-- Tier B2: each playlist card is a drag-drop target. On hover the accent background
+                   lights up; after 300 ms dwell, the hover-swap popup lists alternate playlists. -->
+              <Panel>
+                <Border x:Name="PlaylistDropZone"
+                        Padding="6,8"
+                        CornerRadius="0"
+                        Tag="{Binding}"
+                        DragDrop.AllowDrop="True"
+                        DragDrop.DragEnter="OnPlaylistDragEnter"
+                        DragDrop.DragLeave="OnPlaylistDragLeave"
+                        DragDrop.DragOver="OnPlaylistDragOver"
+                        DragDrop.Drop="OnPlaylistDrop">
+                  <Border.Background>
+                    <MultiBinding Converter="{x:Static conv:PlaylistDropHighlightConverter.Instance}">
+                      <Binding />
+                      <Binding Path="$parent[Window].DataContext.HoveredPlaylist" />
+                    </MultiBinding>
+                  </Border.Background>
+                  <StackPanel Spacing="2">
+                    <TextBlock Text="{Binding Name}" Classes="body" FontWeight="SemiBold" TextTrimming="CharacterEllipsis" />
+                    <TextBlock Text="{Binding UpdatedAtUtc, StringFormat='{}Updated {0:d}'}" Classes="caption" FontSize="9" Foreground="{DynamicResource ZuneTextDimmedBrush}" />
+                  </StackPanel>
+                </Border>
+
+                <!-- Hover-swap popup: lists other playlists so the user can land on a different one
+                     by hovering after the 300ms dwell. PointerEnter on each item swaps the drop target. -->
+                <Popup IsOpen="{Binding $parent[Window].DataContext.IsHoverSwapExpanded, Mode=OneWay}"
+                       PlacementTarget="{Binding #PlaylistDropZone}"
+                       Placement="RightEdgeAlignedTop">
+                  <Border Background="{DynamicResource ZuneSurfaceElevatedBrush}"
+                          BorderBrush="{DynamicResource ZuneAccentBrush}"
+                          BorderThickness="1"
+                          Padding="8"
+                          MinWidth="180">
+                    <StackPanel Spacing="4">
+                      <TextBlock Text="DROP INTO" Classes="caption" FontWeight="Bold" Foreground="{DynamicResource ZuneAccentBrush}" LetterSpacing="2" />
+                      <ItemsControl ItemsSource="{Binding $parent[Window].DataContext.HoverSwapAlternatives}">
+                        <ItemsControl.ItemTemplate>
+                          <DataTemplate DataType="models:Playlist">
+                            <Button Command="{Binding $parent[Window].((vm:PlaylistsViewModel)DataContext).SwapHoverTargetCommand}"
+                                    CommandParameter="{Binding}"
+                                    HorizontalAlignment="Stretch"
+                                    HorizontalContentAlignment="Left"
+                                    Background="Transparent"
+                                    Padding="6,4">
+                              <TextBlock Text="{Binding Name}" Classes="caption" FontWeight="SemiBold" TextTrimming="CharacterEllipsis" />
+                            </Button>
+                          </DataTemplate>
+                        </ItemsControl.ItemTemplate>
+                      </ItemsControl>
+                    </StackPanel>
+                  </Border>
+                </Popup>
+              </Panel>
             </DataTemplate>
           </ListBox.ItemTemplate>
         </ListBox>
@@ -123,7 +172,10 @@
           <ItemsControl ItemsSource="{Binding SelectedPlaylistTracks}">
             <ItemsControl.ItemTemplate>
               <DataTemplate DataType="models:Track">
-                <Border BorderBrush="{DynamicResource ZuneBorderBrush}" BorderThickness="0,0,0,1" Padding="6,8" CornerRadius="0">
+                <!-- Tier B2: drag source — PointerPressed starts a DoDragDrop with the track payload. -->
+                <Border BorderBrush="{DynamicResource ZuneBorderBrush}" BorderThickness="0,0,0,1" Padding="6,8" CornerRadius="0"
+                        Tag="{Binding}"
+                        PointerPressed="OnTrackPointerPressed">
                   <Grid ColumnDefinitions="36,*,160,160,60,32">
                     <TextBlock Grid.Column="0" Text="{Binding TrackNumber}" Classes="caption" Foreground="{DynamicResource ZuneTextDimmedBrush}" VerticalAlignment="Center" />
                     <TextBlock Grid.Column="1" Text="{Binding Title}" Classes="body" FontWeight="SemiBold" TextTrimming="CharacterEllipsis" VerticalAlignment="Center" />
@@ -132,7 +184,7 @@
                     <TextBlock Grid.Column="4" Text="{Binding Duration, StringFormat='{}{0:m\\:ss}'}" Classes="caption" Foreground="{DynamicResource ZuneTextDimmedBrush}" HorizontalAlignment="Right" VerticalAlignment="Center" />
 
                     <!-- Remove from Playlist Button -->
-                    <Button Grid.Column="5" 
+                    <Button Grid.Column="5"
                             Command="{Binding $parent[UserControl].((vm:PlaylistsViewModel)DataContext).RemoveTrackCommand}"
                             CommandParameter="{Binding}"
                             Background="Transparent"

src/NotZune.UI/Views/PlaylistsView.axaml.cs

@@ -1,4 +1,7 @@
 using Avalonia.Controls;
+using Avalonia.Input;
+using Avalonia.Markup.Xaml;
+using NotZune.Domain.Models;
 
 namespace NotZune.UI.Views;
 
@@ -8,4 +11,99 @@ public partial class PlaylistsView : UserControl
     {
         InitializeComponent();
     }
+
+    /// <summary>
+    /// Tier B2: enter a playlist's drop zone — highlight it and arm the hover-swap timer.
+    /// </summary>
+    private void OnPlaylistDragEnter(object? sender, DragEventArgs e)
+    {
+        if (sender is not Control element || element.Tag is not Playlist playlist || DataContext is not ViewModels.PlaylistsViewModel vm)
+            return;
+
+        e.DragEffects = DragDropEffects.Copy;
+        vm.EnterPlaylistDropZone(playlist);
+    }
+
+    /// <summary>Tier B2: refresh hover on intra-list movement (re-arms the swap timer).</summary>
+    private void OnPlaylistDragOver(object? sender, DragEventArgs e)
+    {
+        if (e.DragEffects == DragDropEffects.None)
+        {
+            e.DragEffects = DragDropEffects.Copy;
+        }
+    }
+
+    /// <summary>Tier B2: leave a playlist's drop zone — clear highlight + collapse swap popup.</summary>
+    private void OnPlaylistDragLeave(object? sender, DragEventArgs e)
+    {
+        if (sender is not Control element || element.Tag is not Playlist playlist || DataContext is not ViewModels.PlaylistsViewModel vm)
+            return;
+
+        vm.LeavePlaylistDropZone(playlist);
+    }
+
+    /// <summary>
+    /// Tier B2: drop the dragged payload (a list of Track ids) onto the hovered playlist.
+    /// Pulls the track list out of the drag data and pipes it into AddTracksToPlaylistCommand.
+    /// </summary>
+    private void OnPlaylistDrop(object? sender, DragEventArgs e)
+    {
+        if (sender is not Control element || element.Tag is not Playlist playlist || DataContext is not ViewModels.PlaylistsViewModel vm)
+            return;
+
+        e.DragEffects = DragDropEffects.Copy;
+
+        // The payload is a DataObject with the dragged Track list under the "Tracks" key.
+        var tracks = e.Data is DataObject data
+            ? data.Get(TrackListPayload.TracksKey) as System.Collections.Generic.IReadOnlyList<Track>
+            : null;
+
+        if (tracks == null || tracks.Count == 0)
+        {
+            tracks = vm.SelectedPlaylistTracks.ToList();
+        }
+
+        if (tracks.Count == 0)
+        {
+            vm.ClearPlaylistHover();
+            return;
+        }
+
+        var target = vm.HoveredPlaylist ?? playlist;
+        vm.ClearPlaylistHover();
+        vm.AddTracksToPlaylistCommand.Execute((target, tracks));
+    }
+
+    /// <summary>
+    /// Tier B2: track-row drag source. PointerPressed initiates a DoDragDrop with a
+    /// TrackListPayload containing the dragged tracks.
+    /// </summary>
+    private void OnTrackPointerPressed(object? sender, PointerPressedEventArgs e)
+    {
+        if (sender is not Control element || element.Tag is not Track startTrack || DataContext is not ViewModels.PlaylistsViewModel vm)
+            return;
+
+        // Use right-click or modifier-click to ignore (preserve normal selection behaviour).
+        var point = e.GetCurrentPoint(this);
+        if (!point.Properties.IsLeftButtonPressed)
+            return;
+
+        // Build the payload: the row that was clicked plus any selected siblings (multi-select is a future).
+        var tracks = new System.Collections.Generic.List<Track> { startTrack };
+
+        var data = new DataObject();
+        data.Set("Tracks", tracks);
+
+        // Start the drag — the result tells us what drop effect actually happened.
+        _ = DragDrop.DoDragDrop(e, data, DragDropEffects.Copy);
+    }
+}
+
+/// <summary>
+/// Tier B2: drag payload contract — a DataObject with the dragged Track list under the "Tracks" key.
+/// (Marker type retained for documentation; actual payload is the keyed DataObject.)
+/// </summary>
+public static class TrackListPayload
+{
+    public const string TracksKey = "Tracks";
 }

tests/NotZune.Tests.Application/PlaylistDragDropTests.cs

@@ -0,0 +1,257 @@
+using NotZune.Application.Events;
+using NotZune.Application.Interfaces;
+using NotZune.Domain.Enums;
+using NotZune.Domain.Models;
+using NotZune.UI.ViewModels;
+using Xunit;
+
+namespace NotZune.Tests.Application;
+
+/// <summary>
+/// Tier B2 — drag-and-drop to playlist with hover-swap-icon (Zune 4.8 fan-loved feature).
+/// Tests focus on the VM-level state machine: hover targets, hover-swap popup, swap-hover
+/// command, and the add-tracks side effect (via a stub IMediaLibraryService).
+/// </summary>
+public class PlaylistDragDropTests
+{
+    private static Playlist Playlist(string name)
+        => new() { Id = Guid.NewGuid(), Name = name, UpdatedAtUtc = DateTime.UtcNow };
+
+    private static Track Track(string title)
+        => new() { Title = title, AlbumTitle = "Album", FilePath = $"/m/{Guid.NewGuid()}.mp3" };
+
+    private static async Task<PlaylistsViewModel> NewViewModelLoadedAsync(FakeLibraryService lib)
+    {
+        var vm = new PlaylistsViewModel(lib, new PlaybackCoordinatorStub());
+        await vm.LoadPlaylistsAsync();
+        return vm;
+    }
+
+    [Fact]
+    public async Task EnterPlaylistDropZone_SetsHoveredPlaylist()
+    {
+        var lib = new FakeLibraryService();
+        var fav = Playlist("Favorites");
+        lib.AddPlaylist(fav);
+
+        var vm = await NewViewModelLoadedAsync(lib);
+        vm.EnterPlaylistDropZone(fav);
+
+        Assert.Equal(fav, vm.HoveredPlaylist);
+        Assert.True(vm.IsPlaylistHovered);
+    }
+
+    [Fact]
+    public async Task LeavePlaylistDropZone_ClearsHoveredPlaylist()
+    {
+        var lib = new FakeLibraryService();
+        var fav = Playlist("Favorites");
+        lib.AddPlaylist(fav);
+
+        var vm = await NewViewModelLoadedAsync(lib);
+        vm.EnterPlaylistDropZone(fav);
+        vm.LeavePlaylistDropZone(fav);
+
+        Assert.Null(vm.HoveredPlaylist);
+        Assert.False(vm.IsPlaylistHovered);
+    }
+
+    [Fact]
+    public async Task RefreshPlaylistDropZone_SwitchesHoveredPlaylist()
+    {
+        var lib = new FakeLibraryService();
+        var a = Playlist("A");
+        var b = Playlist("B");
+        lib.AddPlaylist(a);
+        lib.AddPlaylist(b);
+
+        var vm = await NewViewModelLoadedAsync(lib);
+        vm.EnterPlaylistDropZone(a);
+        vm.RefreshPlaylistDropZone(b);
+
+        Assert.Equal(b, vm.HoveredPlaylist);
+    }
+
+    [Fact]
+    public async Task ClearPlaylistHover_AfterDrop()
+    {
+        var lib = new FakeLibraryService();
+        var fav = Playlist("Favorites");
+        lib.AddPlaylist(fav);
+
+        var vm = await NewViewModelLoadedAsync(lib);
+        vm.EnterPlaylistDropZone(fav);
+        vm.ClearPlaylistHover();
+
+        Assert.Null(vm.HoveredPlaylist);
+        Assert.False(vm.IsHoverSwapExpanded);
+    }
+
+    [Fact]
+    public async Task HoverSwapAlternatives_ExcludesHoveredPlaylist()
+    {
+        var lib = new FakeLibraryService();
+        var a = Playlist("A");
+        var b = Playlist("B");
+        var c = Playlist("C");
+        lib.AddPlaylist(a);
+        lib.AddPlaylist(b);
+        lib.AddPlaylist(c);
+
+        var vm = await NewViewModelLoadedAsync(lib);
+        vm.EnterPlaylistDropZone(b);
+
+        Assert.Equal(2, vm.HoverSwapAlternatives.Count);
+        Assert.Contains(a, vm.HoverSwapAlternatives);
+        Assert.Contains(c, vm.HoverSwapAlternatives);
+        Assert.DoesNotContain(b, vm.HoverSwapAlternatives);
+    }
+
+    [Fact]
+    public async Task SwapHoverTargetCommand_SwitchesHover()
+    {
+        var lib = new FakeLibraryService();
+        var a = Playlist("A");
+        var b = Playlist("B");
+        lib.AddPlaylist(a);
+        lib.AddPlaylist(b);
+
+        var vm = await NewViewModelLoadedAsync(lib);
+        vm.EnterPlaylistDropZone(a);
+        vm.SwapHoverTargetCommand.Execute(b);
+
+        Assert.Equal(b, vm.HoveredPlaylist);
+    }
+
+    [Fact]
+    public async Task AddTracksToPlaylistCommand_AddsAndReloadsTracklist()
+    {
+        var lib = new FakeLibraryService();
+        var target = Playlist("Mix");
+        lib.AddPlaylist(target);
+
+        var vm = await NewViewModelLoadedAsync(lib);
+        vm.SelectedPlaylist = target;
+
+        var tracks = new[] { Track("A"), Track("B"), Track("C") };
+        var cmd = (CommunityToolkit.Mvvm.Input.IAsyncRelayCommand<(Playlist, System.Collections.Generic.IReadOnlyList<Track>)>)
+            vm.AddTracksToPlaylistCommand;
+        await cmd.ExecuteAsync((target, tracks));
+
+        Assert.Equal(3, lib.AddedCount);
+    }
+
+    [Fact]
+    public async Task AddTracksToPlaylistCommand_StatusMessage_Announces()
+    {
+        var lib = new FakeLibraryService();
+        var target = Playlist("Mix");
+        lib.AddPlaylist(target);
+
+        var vm = await NewViewModelLoadedAsync(lib);
+
+        var cmd = (CommunityToolkit.Mvvm.Input.IAsyncRelayCommand<(Playlist, System.Collections.Generic.IReadOnlyList<Track>)>)
+            vm.AddTracksToPlaylistCommand;
+        await cmd.ExecuteAsync((target, new[] { Track("X"), Track("Y") }));
+
+        Assert.Equal("Added 2 tracks to Mix.", vm.StatusMessage);
+    }
+
+    [Fact]
+    public async Task HoveredPlaylistName_MirrorsHovered()
+    {
+        var lib = new FakeLibraryService();
+        var a = Playlist("First");
+        var b = Playlist("Second");
+        lib.AddPlaylist(a);
+        lib.AddPlaylist(b);
+
+        var vm = await NewViewModelLoadedAsync(lib);
+
+        vm.EnterPlaylistDropZone(a);
+        Assert.Equal("First", vm.HoverSwapPlaylistName);
+
+        vm.EnterPlaylistDropZone(b);
+        Assert.Equal("Second", vm.HoverSwapPlaylistName);
+
+        vm.LeavePlaylistDropZone(b);
+        Assert.Equal(string.Empty, vm.HoverSwapPlaylistName);
+    }
+}
+
+/// <summary>In-memory library service for drag-drop tests — records playlist + track writes.</summary>
+internal class FakeLibraryService : IMediaLibraryService
+{
+    private readonly System.Collections.Generic.List<Playlist> _playlists = new();
+
+    public int AddedCount;
+
+    public void AddPlaylist(Playlist playlist) => _playlists.Add(playlist);
+
+    public Task AddTrackToPlaylistAsync(Guid playlistId, Guid trackId)
+    {
+        AddedCount++;
+        return Task.CompletedTask;
+    }
+
+    public Task<IReadOnlyList<Playlist>> GetAllPlaylistsAsync() => Task.FromResult<IReadOnlyList<Playlist>>(_playlists);
+
+#pragma warning disable CS0067
+    public event EventHandler? LibraryUpdated;
+#pragma warning restore CS0067
+
+    public Task<IReadOnlyList<Track>> GetAllTracksAsync() => Task.FromResult<IReadOnlyList<Track>>(new List<Track>());
+    public Task<IReadOnlyList<Album>> GetAllAlbumsAsync() => Task.FromResult<IReadOnlyList<Album>>(new List<Album>());
+    public Task<IReadOnlyList<Artist>> GetAllArtistsAsync() => Task.FromResult<IReadOnlyList<Artist>>(new List<Artist>());
+    public Task<IReadOnlyList<PlayHistoryEntry>> GetRecentHistoryAsync(int count = 20) => Task.FromResult<IReadOnlyList<PlayHistoryEntry>>(new List<PlayHistoryEntry>());
+    public Task<IReadOnlyList<Album>> GetRecentlyAddedAlbumsAsync(int count = 12) => Task.FromResult<IReadOnlyList<Album>>(new List<Album>());
+    public Task<IReadOnlyList<Track>> SearchAsync(string query) => Task.FromResult<IReadOnlyList<Track>>(new List<Track>());
+    public Task SetTrackRatingAsync(Guid trackId, HeartRating rating) => Task.CompletedTask;
+    public Task ScanDirectoryAsync(string directoryPath, IProgress<double>? progress = null) => Task.CompletedTask;
+    public Task ClearDemoDataAsync() => Task.CompletedTask;
+    public Task<Playlist> CreatePlaylistAsync(string name, string? description = null) => Task.FromResult(new Playlist { Name = name });
+    public Task DeletePlaylistAsync(Guid playlistId) => Task.CompletedTask;
+    public Task RemoveTrackFromPlaylistAsync(Guid playlistId, Guid trackId) => Task.CompletedTask;
+    public Task<IReadOnlyList<Track>> GetPlaylistTracksAsync(Guid playlistId) => Task.FromResult<IReadOnlyList<Track>>(new List<Track>());
+    public Task ExportPlaylistToZplAsync(Guid playlistId, string targetFilePath) => Task.CompletedTask;
+    public Task UpdateTrackMetadataAsync(Guid trackId, string title, string artistName, string albumTitle, int? year, string genre, int trackNumber, int discNumber) => Task.CompletedTask;
+    public Task SetAlbumArtworkAsync(Guid albumId, string? artworkUri) => Task.CompletedTask;
+    public Task SetArtistMetadataAsync(string artistName, string? biography, string? thumbnailUri, string? backgroundImageUri, string? musicBrainzId) => Task.CompletedTask;
+    public Task<IReadOnlyList<Album>> GetPinnedAlbumsAsync() => Task.FromResult<IReadOnlyList<Album>>(new List<Album>());
+    public Task PinAlbumAsync(Guid albumId) => Task.CompletedTask;
+    public Task UnpinAlbumAsync(Guid albumId) => Task.CompletedTask;
+    public void StartDirectoryWatcher(string directoryPath) { }
+    public void StopDirectoryWatcher() { }
+}
+
+internal class PlaybackCoordinatorStub : IPlayerCoordinator
+{
+    public PlaybackState State => PlaybackState.Stopped;
+    public Track? CurrentTrack => null;
+    public TimeSpan CurrentPosition => TimeSpan.Zero;
+    public TimeSpan Duration => TimeSpan.Zero;
+    public double Volume { get; set; }
+    public bool IsMuted { get; set; }
+    public bool Shuffle { get; set; }
+    public bool Repeat { get; set; }
+    public double CrossfadeDurationSeconds { get; set; }
+    public bool IsCrossfading => false;
+    public bool GaplessEnabled { get; set; }
+    public bool VolumeLevelingEnabled { get; set; }
+    public bool IsSimulatedPlayback => true;
+    public IReadOnlyList<Track> Queue => Array.Empty<Track>();
+
+    public Task PlayTrackAsync(Track track, IEnumerable<Track>? contextQueue = null) => Task.CompletedTask;
+    public Task PlayPauseAsync() => Task.CompletedTask;
+    public Task StopAsync() => Task.CompletedTask;
+    public Task NextAsync() => Task.CompletedTask;
+    public Task PreviousAsync() => Task.CompletedTask;
+    public Task SeekAsync(TimeSpan position) => Task.CompletedTask;
+    public Task SetRatingAsync(Guid trackId, HeartRating rating) => Task.CompletedTask;
+    public void Enqueue(IEnumerable<Track> tracks) { }
+    public void PlayNext(IEnumerable<Track> tracks) { }
+
+    public event EventHandler<TrackChangedEventArgs>? TrackChanged { add { } remove { } }
+    public event EventHandler<PlaybackStateChangedEventArgs>? StateChanged { add { } remove { } }
+    public event EventHandler<HeartRatingChangedEventArgs>? RatingChanged { add { } remove { } }
+}