feat(player): add IQueueService orchestrating album playback above the single-slot player (P11 11.F)

Queue owns ordered tracks, current index, skip-fwd/back, and auto-advance via the player's TrackEnded hook; binds through Attach (no ctor growth, no service-locator). Player-bar skip controls; empty-queue play unchanged. Adds QueueService unit tests.

DeepDrftPublic.Client/Controls/AudioPlayerBar/AudioPlayerBar.razor

@@ -21,6 +21,10 @@ else
                                          Fixed="Fixed"
                                          TogglePlayPause="@TogglePlayPause"
                                          Stop="@Stop"
+                                         HasNext="HasNext"
+                                         HasPrevious="HasPrevious"
+                                         SkipNext="@SkipNext"
+                                         SkipPrevious="@SkipPrevious"
                                          Class="transport-zone"/>
 
                     <VolumeZone Volume="@Volume" VolumeChanged="@OnVolumeChange"/>

DeepDrftPublic.Client/Controls/AudioPlayerBar/AudioPlayerBar.razor.cs

@@ -9,6 +9,7 @@ namespace DeepDrftPublic.Client.Controls.AudioPlayerBar;
 public partial class AudioPlayerBar : ComponentBase, IAsyncDisposable
 {
     [CascadingParameter] public IStreamingPlayerService? PlayerService { get; set; }
+    [CascadingParameter] public IQueueService? QueueService { get; set; }
     [Parameter] public bool Fixed { get; set; } = false;
 
     [Parameter] public EventCallback<bool> OnMinimized { get; set; }
@@ -19,6 +20,7 @@ public partial class AudioPlayerBar : ComponentBase, IAsyncDisposable
     private bool _isSeeking = false;
     private double _seekPosition = 0;
     private IStreamingPlayerService? _subscribedService;
+    private IQueueService? _subscribedQueue;
 
     // Spacer-height bridge: the expanded dock is position:fixed, so MainLayout's
     // spacer reserves its space. We mirror this element's live height into a CSS
@@ -48,6 +50,11 @@ public partial class AudioPlayerBar : ComponentBase, IAsyncDisposable
     private double LoadProgress => PlayerService?.LoadProgress ?? 0;
     private string? ErrorMessage => PlayerService?.ErrorMessage;
 
+    // Skip affordances reflect live queue state. With no queue (null) or an empty queue both are
+    // false, so the buttons sit disabled and the bar behaves exactly as it did before the queue.
+    private bool HasNext => QueueService?.HasNext ?? false;
+    private bool HasPrevious => QueueService?.HasPrevious ?? false;
+
     /// <summary>
     /// Display time - shows seek position while dragging, otherwise current playback time.
     /// </summary>
@@ -76,10 +83,35 @@ public partial class AudioPlayerBar : ComponentBase, IAsyncDisposable
             PlayerService.StateChanged += OnPlayerStateChanged;
             _subscribedService = PlayerService;
         }
+
+        // The queue cascade is also IsFixed, so re-render the skip affordances off its own
+        // change signal — same posture as the player StateChanged subscription above.
+        if (QueueService != null && !ReferenceEquals(QueueService, _subscribedQueue))
+        {
+            if (_subscribedQueue != null)
+                _subscribedQueue.QueueChanged -= OnQueueChanged;
+
+            QueueService.QueueChanged += OnQueueChanged;
+            _subscribedQueue = QueueService;
+        }
     }
 
     private void OnPlayerStateChanged() => InvokeAsync(StateHasChanged);
 
+    private void OnQueueChanged() => InvokeAsync(StateHasChanged);
+
+    private async Task SkipNext()
+    {
+        if (QueueService == null) return;
+        await QueueService.Next();
+    }
+
+    private async Task SkipPrevious()
+    {
+        if (QueueService == null) return;
+        await QueueService.Previous();
+    }
+
     protected override async Task OnAfterRenderAsync(bool firstRender)
     {
         // Only the docked, expanded shape needs a spacer: the Fixed embed is

DeepDrftPublic.Client/Controls/AudioPlayerBar/PlayerControls.razor

@@ -2,12 +2,25 @@
 @using DeepDrftPublic.Client.Controls
 
 <MudStack Row="true" AlignItems="AlignItems.Center" Spacing="2">
+    @if (!Fixed)
+    {
+        <MudIconButton Icon="@Icons.Material.Filled.SkipPrevious"
+                       Color="Color.Primary"
+                       Size="Size.Large"
+                       OnClick="@SkipPrevious"
+                       Disabled="!HasPrevious"/>
+    }
     <PlayStateIcon Size="Size.Large"
                    Color="Color.Primary"
                    Disabled="!CanPlay"
                    OnToggle="@TogglePlayPause"/>
     @if (!Fixed)
     {
+        <MudIconButton Icon="@Icons.Material.Filled.SkipNext"
+                       Color="Color.Primary"
+                       Size="Size.Large"
+                       OnClick="@SkipNext"
+                       Disabled="!HasNext"/>
         <MudIconButton Icon="@Icons.Material.Filled.Stop"
                        Color="Color.Primary"
                        Size="Size.Large"

DeepDrftPublic.Client/Controls/AudioPlayerBar/PlayerControls.razor.cs

@@ -16,4 +16,13 @@ public partial class PlayerControls : ComponentBase
     [Parameter] public bool Fixed { get; set; } = false;
     [Parameter] public required EventCallback TogglePlayPause { get; set; }
     [Parameter] public required EventCallback Stop { get; set; }
+
+    /// <summary>Whether the queue has a track to skip forward to. Drives the skip-next affordance.</summary>
+    [Parameter] public bool HasNext { get; set; }
+
+    /// <summary>Whether the queue has a track to step back to. Drives the skip-previous affordance.</summary>
+    [Parameter] public bool HasPrevious { get; set; }
+
+    [Parameter] public EventCallback SkipNext { get; set; }
+    [Parameter] public EventCallback SkipPrevious { get; set; }
 }

DeepDrftPublic.Client/Controls/AudioPlayerBar/PlayerTransportZone.razor

@@ -6,7 +6,11 @@
                         CanPlay="CanPlay"
                         Fixed="Fixed"
                         TogglePlayPause="TogglePlayPause"
-                        Stop="Stop"/>
+                        Stop="Stop"
+                        HasNext="HasNext"
+                        HasPrevious="HasPrevious"
+                        SkipNext="SkipNext"
+                        SkipPrevious="SkipPrevious"/>
         @if (IsLoading && !IsStreaming)
         {
             <MudProgressCircular Color="Color.Tertiary"

DeepDrftPublic.Client/Controls/AudioPlayerBar/PlayerTransportZone.razor.cs

@@ -14,5 +14,9 @@ public partial class PlayerTransportZone : ComponentBase
     [Parameter] public bool Fixed { get; set; } = false;
     [Parameter] public EventCallback TogglePlayPause { get; set; }
     [Parameter] public EventCallback Stop { get; set; }
+    [Parameter] public bool HasNext { get; set; }
+    [Parameter] public bool HasPrevious { get; set; }
+    [Parameter] public EventCallback SkipNext { get; set; }
+    [Parameter] public EventCallback SkipPrevious { get; set; }
     [Parameter] public string? Class { get; set; }
 }

DeepDrftPublic.Client/Controls/AudioPlayerProvider.razor

@@ -3,5 +3,7 @@
    If instance swapping at runtime is ever needed, change IsFixed to false (adds subscription
    overhead on every parent re-render, but allows children to see the new reference). *@
 <CascadingValue Value="@(_audioPlayerService)" IsFixed="true">
+    <CascadingValue Value="@(_queueService)" IsFixed="true">
         @ChildContent
+    </CascadingValue>
 </CascadingValue>

DeepDrftPublic.Client/Controls/AudioPlayerProvider.razor.cs

@@ -12,6 +12,7 @@ public partial class AudioPlayerProvider : ComponentBase, IAsyncDisposable
     [Inject] public required ILogger<StreamingAudioPlayerService> Logger { get; set; }
 
     private IStreamingPlayerService? _audioPlayerService;
+    private QueueService? _queueService;
 
     [Parameter] public RenderFragment? ChildContent { get; set; }
 
@@ -29,6 +30,13 @@ public partial class AudioPlayerProvider : ComponentBase, IAsyncDisposable
         // Children must not wrap or replace this callback.
         _audioPlayerService.OnStateChanged = new EventCallback(this, () => InvokeAsync(StateHasChanged));
         // OnTrackSelected will be set by individual child components that need it
+
+        // The queue orchestrates above the single-slot player. The player is not DI-registered
+        // (constructed here), so the queue binds to it via Attach rather than constructor injection —
+        // no construction cycle, no IServiceProvider. Cascaded alongside the player so the bar and a
+        // future up-next panel both read it.
+        _queueService = new QueueService();
+        _queueService.Attach(_audioPlayerService);
     }
 
     /// <summary>
@@ -38,6 +46,11 @@ public partial class AudioPlayerProvider : ComponentBase, IAsyncDisposable
     /// </summary>
     public async ValueTask DisposeAsync()
     {
+        // Dispose the queue first so it unsubscribes from the player's TrackEnded before the
+        // player tears down.
+        _queueService?.Dispose();
+        _queueService = null;
+
         if (_audioPlayerService is IAsyncDisposable disposable)
         {
             await disposable.DisposeAsync();

DeepDrftPublic.Client/Services/AudioPlayerService.cs

@@ -43,6 +43,9 @@ public abstract class AudioPlayerService : IPlayerService, IAsyncDisposable
     /// <inheritdoc />
     public event Action? StateChanged;
 
+    /// <inheritdoc />
+    public event Action? TrackEnded;
+
     protected AudioPlayerService(AudioInteropService audioInterop, TrackMediaClient trackMediaClient)
     {
         _audioInterop = audioInterop;
@@ -268,6 +271,12 @@ public abstract class AudioPlayerService : IPlayerService, IAsyncDisposable
         CurrentTime = 0;
         Duration = null;
         await NotifyStateChanged();
+
+        // Fire AFTER the state notification so any queue orchestrator that advances on this
+        // signal selects the next track against a fully-settled idle state. Raised only on
+        // organic end-of-stream — stop/unload/track-switch go through ResetToIdle, which does
+        // not raise this — so a subscriber can treat it unambiguously as "advance the queue."
+        TrackEnded?.Invoke();
     }
 
 

DeepDrftPublic.Client/Services/IPlayerService.cs

@@ -41,6 +41,15 @@ public interface IPlayerService
     /// </summary>
     event Action? StateChanged;
 
+    /// <summary>
+    /// Raised once when the current track reaches its natural end of playback (the JS
+    /// end-of-stream callback), distinct from a stop/unload/track-switch. This is the single
+    /// hook the play-queue subscribes to in order to auto-advance to the next track. It does
+    /// NOT fire when playback is stopped, the track is switched, or the player is unloaded —
+    /// only on organic completion — so an orchestrator can treat it as "advance the queue."
+    /// </summary>
+    event Action? TrackEnded;
+    
     // Control methods
     Task InitializeAsync();
     Task SelectTrack(TrackDto track);

DeepDrftPublic.Client/Services/IQueueService.cs

@@ -0,0 +1,80 @@
+using DeepDrftModels.DTOs;
+
+namespace DeepDrftPublic.Client.Services;
+
+/// <summary>
+/// Orchestrates ordered playback ("what plays next") <em>above</em> the single-slot
+/// <see cref="IStreamingPlayerService"/>. The player stays a single-track device; the queue owns the
+/// track list, the current position, skip-forward/back, and auto-advance on natural track end. It
+/// drives playback solely through the player's existing <see cref="IStreamingPlayerService.SelectTrackStreaming"/>
+/// — it adds no new playback semantics.
+///
+/// <para>
+/// Extension posture (open/closed): future shuffle, repeat modes, reordering, and persistence are
+/// expected. They are additive — a shuffle/repeat strategy slots in behind <see cref="Next"/>/
+/// <see cref="Previous"/> as the "which index is next" decision; reordering mutates <see cref="Items"/>
+/// and re-emits <see cref="QueueChanged"/>; persistence snapshots/restores <see cref="Items"/> +
+/// <see cref="CurrentIndex"/>. None of those require changing this interface's existing members, only
+/// adding new ones — so consumers written against today's surface keep working.
+/// </para>
+///
+/// <para>
+/// With an empty queue (<see cref="CurrentIndex"/> == -1) the queue is dormant: it drives nothing and
+/// auto-advances nothing, so direct single-track play through the player behaves exactly as it did
+/// before the queue existed.
+/// </para>
+/// </summary>
+public interface IQueueService
+{
+    /// <summary>The ordered tracks currently queued. Empty when nothing is enqueued.</summary>
+    IReadOnlyList<TrackDto> Items { get; }
+
+    /// <summary>
+    /// Index into <see cref="Items"/> of the track the queue considers current, or -1 when the
+    /// queue is empty. Always a valid index into <see cref="Items"/> when non-negative.
+    /// </summary>
+    int CurrentIndex { get; }
+
+    /// <summary>The current track, or null when the queue is empty.</summary>
+    TrackDto? Current { get; }
+
+    /// <summary>True when there is a track after <see cref="CurrentIndex"/> to advance to.</summary>
+    bool HasNext { get; }
+
+    /// <summary>True when there is a track before <see cref="CurrentIndex"/> to step back to.</summary>
+    bool HasPrevious { get; }
+
+    /// <summary>
+    /// Raised whenever the queue's contents or current position change. The player bar subscribes
+    /// to re-render its skip-forward/back affordances. Fires on enqueue, advance, step-back, and clear.
+    /// </summary>
+    event Action? QueueChanged;
+
+    /// <summary>
+    /// Replaces the queue with <paramref name="tracks"/> (in the order given) and begins streaming
+    /// the track at <paramref name="startIndex"/>. This is the "play album" entry point the Cuts
+    /// detail page consumes: pass the release's tracks in ordinal order. A header Play uses
+    /// <c>startIndex: 0</c>; a mid-album row play passes that row's index so the queue continues to
+    /// the end from there. No-op when <paramref name="tracks"/> is empty.
+    /// </summary>
+    Task PlayRelease(IEnumerable<TrackDto> tracks, int startIndex = 0);
+
+    /// <summary>Appends a track to the end of the queue without changing what is currently playing.</summary>
+    void Enqueue(TrackDto track);
+
+    /// <summary>Appends tracks to the end of the queue without changing what is currently playing.</summary>
+    void EnqueueRange(IEnumerable<TrackDto> tracks);
+
+    /// <summary>
+    /// Advances to the next track and streams it. No-op when <see cref="HasNext"/> is false.
+    /// </summary>
+    Task Next();
+
+    /// <summary>
+    /// Steps back to the previous track and streams it. No-op when <see cref="HasPrevious"/> is false.
+    /// </summary>
+    Task Previous();
+
+    /// <summary>Empties the queue and resets the position. Does not stop the player.</summary>
+    void Clear();
+}

DeepDrftPublic.Client/Services/QueueService.cs

@@ -0,0 +1,136 @@
+using DeepDrftModels.DTOs;
+
+namespace DeepDrftPublic.Client.Services;
+
+/// <summary>
+/// Default <see cref="IQueueService"/>: a single-slot orchestrator over an
+/// <see cref="IStreamingPlayerService"/>. Holds the ordered list and current index as pure state,
+/// drives playback through the player's existing <see cref="IStreamingPlayerService.SelectTrackStreaming"/>,
+/// and auto-advances on the player's <see cref="IPlayerService.TrackEnded"/> signal.
+///
+/// <para>
+/// The player instance is not DI-registered — <c>AudioPlayerProvider</c> constructs and cascades it.
+/// So the queue is bound to the player via <see cref="Attach"/> (called once by the provider after it
+/// creates the player) rather than constructor injection. This keeps the player single-slot, avoids a
+/// construction cycle between provider/player/queue, and needs no <c>IServiceProvider</c>. The queue's
+/// own constructor stays parameterless, so the queue logic is unit-testable against a fake player with
+/// no container.
+/// </para>
+/// </summary>
+public sealed class QueueService : IQueueService, IDisposable
+{
+    private readonly List<TrackDto> _items = new();
+    private IStreamingPlayerService? _player;
+
+    public IReadOnlyList<TrackDto> Items => _items;
+
+    public int CurrentIndex { get; private set; } = -1;
+
+    public TrackDto? Current =>
+        CurrentIndex >= 0 && CurrentIndex < _items.Count ? _items[CurrentIndex] : null;
+
+    public bool HasNext => CurrentIndex >= 0 && CurrentIndex < _items.Count - 1;
+
+    public bool HasPrevious => CurrentIndex > 0;
+
+    public event Action? QueueChanged;
+
+    /// <summary>
+    /// Binds the queue to the player instance the provider owns, and subscribes to its track-ended
+    /// signal so the queue auto-advances. Idempotent and re-bindable: re-attaching detaches the prior
+    /// player first, so the queue never holds a stale subscription after a player swap. Owned by the
+    /// provider's lifecycle; <see cref="Dispose"/> unsubscribes.
+    /// </summary>
+    public void Attach(IStreamingPlayerService player)
+    {
+        if (ReferenceEquals(_player, player)) return;
+
+        if (_player != null)
+            _player.TrackEnded -= OnTrackEnded;
+
+        _player = player;
+        _player.TrackEnded += OnTrackEnded;
+    }
+
+    public async Task PlayRelease(IEnumerable<TrackDto> tracks, int startIndex = 0)
+    {
+        var list = tracks as IReadOnlyList<TrackDto> ?? tracks.ToList();
+        if (list.Count == 0) return;
+
+        var start = Math.Clamp(startIndex, 0, list.Count - 1);
+
+        _items.Clear();
+        _items.AddRange(list);
+        CurrentIndex = start;
+        QueueChanged?.Invoke();
+
+        await PlayCurrent();
+    }
+
+    public void Enqueue(TrackDto track)
+    {
+        _items.Add(track);
+        QueueChanged?.Invoke();
+    }
+
+    public void EnqueueRange(IEnumerable<TrackDto> tracks)
+    {
+        var before = _items.Count;
+        _items.AddRange(tracks);
+        if (_items.Count != before)
+            QueueChanged?.Invoke();
+    }
+
+    public async Task Next()
+    {
+        if (!HasNext) return;
+        CurrentIndex++;
+        QueueChanged?.Invoke();
+        await PlayCurrent();
+    }
+
+    public async Task Previous()
+    {
+        if (!HasPrevious) return;
+        CurrentIndex--;
+        QueueChanged?.Invoke();
+        await PlayCurrent();
+    }
+
+    public void Clear()
+    {
+        if (_items.Count == 0 && CurrentIndex == -1) return;
+        _items.Clear();
+        CurrentIndex = -1;
+        QueueChanged?.Invoke();
+    }
+
+    // Advance on organic end-of-stream only. TrackEnded is not raised by stop/unload/track-switch,
+    // so a manual stop or a fresh single-track selection elsewhere never spuriously advances the
+    // queue. When the queue is past its last track, end-of-stream simply stops — nothing to advance.
+    private void OnTrackEnded()
+    {
+        if (!HasNext) return;
+        // Fire-and-forget is deliberate: TrackEnded is a synchronous event invoked from the player's
+        // end-of-playback callback continuation; we must not block it. Advancing kicks off the next
+        // stream, whose own failures surface through the player's ErrorMessage/state — the queue does
+        // not own playback error handling.
+        _ = Next();
+    }
+
+    private async Task PlayCurrent()
+    {
+        var track = Current;
+        if (track is null || _player is null) return;
+        await _player.SelectTrackStreaming(track);
+    }
+
+    public void Dispose()
+    {
+        if (_player != null)
+        {
+            _player.TrackEnded -= OnTrackEnded;
+            _player = null;
+        }
+    }
+}

DeepDrftTests/DeepDrftTests.csproj

@@ -30,6 +30,10 @@
   <ItemGroup>
     <ProjectReference Include="..\DeepDrftContent\DeepDrftContent.csproj" />
     <ProjectReference Include="..\DeepDrftData\DeepDrftData.csproj" />
+    <!-- Referenced for the client-side queue orchestrator (QueueService / IQueueService).
+         The queue is pure domain logic, unit-testable against a fake IStreamingPlayerService
+         with no browser/JS. -->
+    <ProjectReference Include="..\DeepDrftPublic.Client\DeepDrftPublic.Client.csproj" />
   </ItemGroup>
 
 </Project>

DeepDrftTests/QueueServiceTests.cs

@@ -0,0 +1,450 @@
+using DeepDrftModels.DTOs;
+using DeepDrftPublic.Client.Services;
+using Microsoft.AspNetCore.Components;
+
+namespace DeepDrftTests;
+
+/// <summary>
+/// Unit tests for the play-queue orchestrator (<see cref="QueueService"/>). The queue is pure
+/// domain logic over the single-slot player, so it is exercised here against a recording fake
+/// (<see cref="FakeStreamingPlayer"/>) — no browser, no JS interop, no DI container. Coverage:
+/// enqueue, ordered advance, next/previous bounds, clear, current-index integrity, and
+/// auto-advance on the player's <see cref="IPlayerService.TrackEnded"/> signal.
+/// </summary>
+[TestFixture]
+public class QueueServiceTests
+{
+    private FakeStreamingPlayer _player = null!;
+    private QueueService _queue = null!;
+
+    [SetUp]
+    public void SetUp()
+    {
+        _player = new FakeStreamingPlayer();
+        _queue = new QueueService();
+        _queue.Attach(_player);
+    }
+
+    [TearDown]
+    public void TearDown() => _queue.Dispose();
+
+    private static List<TrackDto> Tracks(int count) =>
+        Enumerable.Range(1, count)
+            .Select(i => new TrackDto { EntryKey = $"track-{i}", TrackName = $"Track {i}", TrackNumber = i })
+            .ToList();
+
+    // --- Empty-queue invariants (no regression to single-track play) ---
+
+    [Test]
+    public void NewQueue_IsEmptyWithCurrentIndexNegativeOne()
+    {
+        Assert.Multiple(() =>
+        {
+            Assert.That(_queue.Items, Is.Empty);
+            Assert.That(_queue.CurrentIndex, Is.EqualTo(-1));
+            Assert.That(_queue.Current, Is.Null);
+            Assert.That(_queue.HasNext, Is.False);
+            Assert.That(_queue.HasPrevious, Is.False);
+        });
+    }
+
+    [Test]
+    public async Task NextAndPrevious_OnEmptyQueue_AreNoOpsAndDriveNoPlayback()
+    {
+        await _queue.Next();
+        await _queue.Previous();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_queue.CurrentIndex, Is.EqualTo(-1));
+            Assert.That(_player.SelectedTracks, Is.Empty);
+        });
+    }
+
+    // --- PlayRelease: enqueue + ordered start ---
+
+    [Test]
+    public async Task PlayRelease_LoadsTracksInOrderAndStreamsFirst()
+    {
+        var tracks = Tracks(3);
+
+        await _queue.PlayRelease(tracks);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_queue.Items.Select(t => t.EntryKey),
+                Is.EqualTo(new[] { "track-1", "track-2", "track-3" }));
+            Assert.That(_queue.CurrentIndex, Is.EqualTo(0));
+            Assert.That(_queue.Current!.EntryKey, Is.EqualTo("track-1"));
+            Assert.That(_player.SelectedTracks.Single().EntryKey, Is.EqualTo("track-1"));
+        });
+    }
+
+    [Test]
+    public async Task PlayRelease_WithStartIndex_StartsMidAlbumAndKeepsRemainderQueued()
+    {
+        var tracks = Tracks(4);
+
+        await _queue.PlayRelease(tracks, startIndex: 2);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_queue.CurrentIndex, Is.EqualTo(2));
+            Assert.That(_queue.Current!.EntryKey, Is.EqualTo("track-3"));
+            Assert.That(_player.SelectedTracks.Single().EntryKey, Is.EqualTo("track-3"));
+            Assert.That(_queue.HasNext, Is.True);
+            Assert.That(_queue.HasPrevious, Is.True);
+        });
+    }
+
+    [Test]
+    public async Task PlayRelease_ClampsOutOfRangeStartIndex()
+    {
+        var tracks = Tracks(3);
+
+        await _queue.PlayRelease(tracks, startIndex: 99);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_queue.CurrentIndex, Is.EqualTo(2));
+            Assert.That(_player.SelectedTracks.Single().EntryKey, Is.EqualTo("track-3"));
+        });
+    }
+
+    [Test]
+    public async Task PlayRelease_WithEmptyTracks_IsNoOp()
+    {
+        await _queue.PlayRelease(Enumerable.Empty<TrackDto>());
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_queue.Items, Is.Empty);
+            Assert.That(_queue.CurrentIndex, Is.EqualTo(-1));
+            Assert.That(_player.SelectedTracks, Is.Empty);
+        });
+    }
+
+    [Test]
+    public async Task PlayRelease_ReplacesAnExistingQueue()
+    {
+        await _queue.PlayRelease(Tracks(3));
+        var second = new List<TrackDto>
+        {
+            new() { EntryKey = "x-1", TrackName = "X1" },
+            new() { EntryKey = "x-2", TrackName = "X2" },
+        };
+
+        await _queue.PlayRelease(second);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_queue.Items, Has.Count.EqualTo(2));
+            Assert.That(_queue.Items.Select(t => t.EntryKey), Is.EqualTo(new[] { "x-1", "x-2" }));
+            Assert.That(_queue.CurrentIndex, Is.EqualTo(0));
+        });
+    }
+
+    // --- Next / Previous mechanics and bounds ---
+
+    [Test]
+    public async Task Next_AdvancesThroughTracksInOrder()
+    {
+        await _queue.PlayRelease(Tracks(3));
+
+        await _queue.Next();
+        Assert.That(_queue.Current!.EntryKey, Is.EqualTo("track-2"));
+
+        await _queue.Next();
+        Assert.That(_queue.Current!.EntryKey, Is.EqualTo("track-3"));
+
+        Assert.That(_player.SelectedTracks.Select(t => t.EntryKey),
+            Is.EqualTo(new[] { "track-1", "track-2", "track-3" }));
+    }
+
+    [Test]
+    public async Task Next_AtLastTrack_IsNoOp()
+    {
+        await _queue.PlayRelease(Tracks(2), startIndex: 1);
+
+        await _queue.Next();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_queue.CurrentIndex, Is.EqualTo(1));
+            Assert.That(_queue.HasNext, Is.False);
+            // Only the initial PlayRelease selection — Next at the end drove no further playback.
+            Assert.That(_player.SelectedTracks, Has.Count.EqualTo(1));
+        });
+    }
+
+    [Test]
+    public async Task Previous_StepsBackThroughTracks()
+    {
+        await _queue.PlayRelease(Tracks(3), startIndex: 2);
+
+        await _queue.Previous();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_queue.CurrentIndex, Is.EqualTo(1));
+            Assert.That(_queue.Current!.EntryKey, Is.EqualTo("track-2"));
+            Assert.That(_player.SelectedTracks.Last().EntryKey, Is.EqualTo("track-2"));
+        });
+    }
+
+    [Test]
+    public async Task Previous_AtFirstTrack_IsNoOp()
+    {
+        await _queue.PlayRelease(Tracks(3));
+
+        await _queue.Previous();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_queue.CurrentIndex, Is.EqualTo(0));
+            Assert.That(_queue.HasPrevious, Is.False);
+            Assert.That(_player.SelectedTracks, Has.Count.EqualTo(1));
+        });
+    }
+
+    // --- Enqueue / EnqueueRange ---
+
+    [Test]
+    public void Enqueue_AppendsWithoutChangingCurrentOrStartingPlayback()
+    {
+        _queue.Enqueue(new TrackDto { EntryKey = "a", TrackName = "A" });
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_queue.Items, Has.Count.EqualTo(1));
+            Assert.That(_queue.CurrentIndex, Is.EqualTo(-1));
+            Assert.That(_player.SelectedTracks, Is.Empty);
+        });
+    }
+
+    [Test]
+    public async Task Enqueue_AfterPlayRelease_ExtendsTheQueueAndEnablesHasNext()
+    {
+        await _queue.PlayRelease(Tracks(1));
+        Assert.That(_queue.HasNext, Is.False);
+
+        _queue.Enqueue(new TrackDto { EntryKey = "appended", TrackName = "Appended" });
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_queue.HasNext, Is.True);
+            Assert.That(_queue.CurrentIndex, Is.EqualTo(0));
+        });
+    }
+
+    [Test]
+    public void EnqueueRange_AppendsAllTracks()
+    {
+        _queue.EnqueueRange(Tracks(3));
+
+        Assert.That(_queue.Items, Has.Count.EqualTo(3));
+    }
+
+    // --- Clear ---
+
+    [Test]
+    public async Task Clear_EmptiesQueueAndResetsIndexWithoutStoppingPlayer()
+    {
+        await _queue.PlayRelease(Tracks(3));
+
+        _queue.Clear();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_queue.Items, Is.Empty);
+            Assert.That(_queue.CurrentIndex, Is.EqualTo(-1));
+            Assert.That(_queue.Current, Is.Null);
+            // Clear is a queue-state reset; it must not tear the player down.
+            Assert.That(_player.StopCount, Is.EqualTo(0));
+        });
+    }
+
+    // --- QueueChanged notifications ---
+
+    [Test]
+    public async Task MutatingOperations_RaiseQueueChanged()
+    {
+        var count = 0;
+        _queue.QueueChanged += () => count++;
+
+        await _queue.PlayRelease(Tracks(3)); // 1
+        await _queue.Next();                 // 2
+        await _queue.Previous();             // 3
+        _queue.Enqueue(new TrackDto { EntryKey = "z", TrackName = "Z" }); // 4
+        _queue.Clear();                      // 5
+
+        Assert.That(count, Is.EqualTo(5));
+    }
+
+    [Test]
+    public void Clear_OnAlreadyEmptyQueue_DoesNotRaiseQueueChanged()
+    {
+        var raised = false;
+        _queue.QueueChanged += () => raised = true;
+
+        _queue.Clear();
+
+        Assert.That(raised, Is.False);
+    }
+
+    // --- Auto-advance on TrackEnded ---
+
+    [Test]
+    public async Task TrackEnded_AutoAdvancesToNextTrack()
+    {
+        await _queue.PlayRelease(Tracks(3));
+
+        _player.RaiseTrackEnded();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_queue.CurrentIndex, Is.EqualTo(1));
+            Assert.That(_queue.Current!.EntryKey, Is.EqualTo("track-2"));
+            Assert.That(_player.SelectedTracks.Last().EntryKey, Is.EqualTo("track-2"));
+        });
+    }
+
+    [Test]
+    public async Task TrackEnded_OnLastTrack_DoesNotAdvanceOrReplay()
+    {
+        await _queue.PlayRelease(Tracks(2), startIndex: 1);
+
+        _player.RaiseTrackEnded();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_queue.CurrentIndex, Is.EqualTo(1));
+            Assert.That(_player.SelectedTracks, Has.Count.EqualTo(1));
+        });
+    }
+
+    [Test]
+    public void TrackEnded_OnEmptyQueue_IsIgnored()
+    {
+        _player.RaiseTrackEnded();
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_queue.CurrentIndex, Is.EqualTo(-1));
+            Assert.That(_player.SelectedTracks, Is.Empty);
+        });
+    }
+
+    [Test]
+    public async Task TrackEnded_PlaysWholeAlbumThroughToTheEnd()
+    {
+        await _queue.PlayRelease(Tracks(3));
+
+        _player.RaiseTrackEnded(); // → track-2
+        _player.RaiseTrackEnded(); // → track-3
+        _player.RaiseTrackEnded(); // last track: no advance
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(_queue.CurrentIndex, Is.EqualTo(2));
+            Assert.That(_player.SelectedTracks.Select(t => t.EntryKey),
+                Is.EqualTo(new[] { "track-1", "track-2", "track-3" }));
+        });
+    }
+
+    // --- Attach lifecycle ---
+
+    [Test]
+    public async Task Dispose_UnsubscribesFromTrackEnded_SoNoAutoAdvanceAfterDispose()
+    {
+        await _queue.PlayRelease(Tracks(3));
+        _queue.Dispose();
+
+        _player.RaiseTrackEnded();
+
+        Assert.That(_queue.CurrentIndex, Is.EqualTo(0));
+    }
+
+    [Test]
+    public async Task Attach_ToNewPlayer_RedirectsPlaybackAndAutoAdvance()
+    {
+        var second = new FakeStreamingPlayer();
+        _queue.Attach(second);
+
+        await _queue.PlayRelease(Tracks(3));
+        Assert.That(second.SelectedTracks.Single().EntryKey, Is.EqualTo("track-1"));
+
+        // The old player's TrackEnded must no longer drive this queue.
+        _player.RaiseTrackEnded();
+        Assert.That(_queue.CurrentIndex, Is.EqualTo(0));
+
+        // The newly attached player does.
+        second.RaiseTrackEnded();
+        Assert.That(_queue.CurrentIndex, Is.EqualTo(1));
+    }
+
+    /// <summary>
+    /// Records the tracks the queue asks the player to stream and lets a test raise the
+    /// player's organic end-of-stream signal. Implements the full <see cref="IStreamingPlayerService"/>
+    /// surface but only the members the queue actually drives carry behavior; the rest are inert
+    /// — the queue touches nothing else, which is exactly the seam this fake pins down.
+    /// </summary>
+    private sealed class FakeStreamingPlayer : IStreamingPlayerService
+    {
+        public List<TrackDto> SelectedTracks { get; } = new();
+        public int StopCount { get; private set; }
+
+        public void RaiseTrackEnded() => TrackEnded?.Invoke();
+
+        public Task SelectTrackStreaming(TrackDto track)
+        {
+            SelectedTracks.Add(track);
+            CurrentTrack = track;
+            return Task.CompletedTask;
+        }
+
+        public Task Stop()
+        {
+            StopCount++;
+            return Task.CompletedTask;
+        }
+
+        public event Action? TrackEnded;
+
+        // Part of the implemented contract but the queue never subscribes to it, so it is
+        // intentionally never raised here.
+#pragma warning disable CS0067
+        public event Action? StateChanged;
+#pragma warning restore CS0067
+
+        // Inert remainder of the contract — the queue never invokes these.
+        public bool IsInitialized => false;
+        public bool IsLoaded => false;
+        public bool IsLoading => false;
+        public bool IsPlaying => false;
+        public bool IsPaused => false;
+        public double CurrentTime => 0;
+        public double? Duration => null;
+        public double Volume => 1.0;
+        public double LoadProgress => 0;
+        public string? ErrorMessage => null;
+        public TrackDto? CurrentTrack { get; private set; }
+        public double[]? WaveformProfile => null;
+        public EventCallback? OnStateChanged { get; set; }
+        public EventCallback? OnTrackSelected { get; set; }
+        public bool IsStreamingMode => false;
+        public bool CanStartStreaming => false;
+        public bool HeaderParsed => false;
+        public int BufferedChunks => 0;
+
+        public Task InitializeAsync() => Task.CompletedTask;
+        public Task SelectTrack(TrackDto track) => SelectTrackStreaming(track);
+        public Task Unload() => Task.CompletedTask;
+        public Task TogglePlayPause() => Task.CompletedTask;
+        public Task Seek(double position) => Task.CompletedTask;
+        public Task SetVolume(double volume) => Task.CompletedTask;
+        public Task ClearError() => Task.CompletedTask;
+        public Task WarmAudioContext() => Task.CompletedTask;
+        public Task StageTrack(TrackDto track) => Task.CompletedTask;
+    }
+}