feat(dock): the TRAX bay — track, play/pause, level, duck badge

Unit 7. The bay shows the track name (left-click toggles playback, right-click opens the picker —
the label stays the control), a play/pause button, the duck badge, and a dB level.

No ladder here, deliberately: nothing measures the music bed, and a decorative ladder would break
the measured-not-painted rule. A test asserts the bay has no SegmentMeter.

The level is real: `ITraxPlayer.UserGain` is a new creator gain multiplied onto the fixed design
volume, separate from `LocalGain` (which follows the desktop mute). The VM's `TraxVolumeDb` is the
same dB scale as the other faders, so unity means the bed's design level.

Controls/AudioDock.xaml

@@ -114,10 +114,60 @@
                     </Grid>
                 </Border>
                 <Border Grid.Column="2" Background="{StaticResource Brush.SurfaceContainerLow}" CornerRadius="{StaticResource Radius.Sm}" Margin="4,0" Padding="10,6">
-                    <StackPanel>
-                        <TextBlock Text="TRAX" FontSize="10" FontWeight="SemiBold" Foreground="{StaticResource Brush.OnSurfaceVariant}"/>
-                        <TextBlock x:Name="TraxBayBody" Text="—" FontSize="11" Foreground="{StaticResource Brush.OnSurfaceDisabled}"/>
-                    </StackPanel>
+                    <Grid>
+                        <Grid.RowDefinitions>
+                            <RowDefinition Height="Auto"/>
+                            <RowDefinition Height="*"/>
+                        </Grid.RowDefinitions>
+
+                        <Grid Grid.Row="0">
+                            <Grid.ColumnDefinitions>
+                                <ColumnDefinition Width="Auto"/>
+                                <ColumnDefinition Width="*"/>
+                                <ColumnDefinition Width="Auto"/>
+                                <ColumnDefinition Width="Auto"/>
+                            </Grid.ColumnDefinitions>
+                            <Border Background="{StaticResource Brush.SurfaceContainerHighest}" CornerRadius="{StaticResource Radius.Sm}" Padding="5,1">
+                                <TextBlock Text="TRAX" FontSize="9" FontWeight="Bold" Foreground="{StaticResource Brush.OnSurfaceVariant}"/>
+                            </Border>
+                            <!-- The name is the control: left-click toggles play, right-click picks (§TRAX). -->
+                            <TextBlock Grid.Column="1" Margin="6,0,0,0" FontSize="11" VerticalAlignment="Center"
+                                       TextTrimming="CharacterEllipsis" Foreground="{StaticResource Brush.OnSurface}"
+                                       Text="{Binding TraxTrackLabel}"
+                                       MouseLeftButtonUp="TraxLabel_MouseLeftButtonUp"
+                                       MouseRightButtonUp="TraxLabel_MouseRightButtonUp" Cursor="Hand"/>
+                            <Button Grid.Column="2" Width="22" Height="18" Style="{StaticResource YtButtonSecondary}" Padding="0"
+                                    Margin="4,0,0,0" Click="TraxPlayPause_Click" ToolTip="{Binding TraxToolTip}">
+                                <TextBlock FontSize="10" Foreground="{StaticResource Brush.OnSurface}">
+                                    <TextBlock.Style>
+                                        <Style TargetType="TextBlock">
+                                            <Setter Property="Text" Value="▶"/>
+                                            <Style.Triggers>
+                                                <DataTrigger Binding="{Binding IsMusicPlaying}" Value="True">
+                                                    <Setter Property="Text" Value="❚❚"/>
+                                                </DataTrigger>
+                                            </Style.Triggers>
+                                        </Style>
+                                    </TextBlock.Style>
+                                </TextBlock>
+                            </Button>
+                            <Border Grid.Column="3" Margin="4,0,0,0" Background="{StaticResource Brush.SurfaceContainerHighest}"
+                                    CornerRadius="{StaticResource Radius.Sm}" Padding="5,1"
+                                    Visibility="{Binding IsTraxDucking, Converter={StaticResource BoolToVis}}">
+                                <TextBlock FontSize="9" FontWeight="Bold" FontFamily="{StaticResource FontFamily.Mono}"
+                                           Foreground="{StaticResource Brush.Secondary}" Text="DUCK"/>
+                            </Border>
+                        </Grid>
+
+                        <DockPanel Grid.Row="1" Margin="0,6,0,0" VerticalAlignment="Bottom">
+                            <TextBlock DockPanel.Dock="Right" Width="56" TextAlignment="Right" FontSize="10"
+                                       FontFamily="{StaticResource FontFamily.Mono}" VerticalAlignment="Center"
+                                       Foreground="{StaticResource Brush.OnSurfaceVariant}"
+                                       Text="{Binding TraxVolumeDbLabel}"/>
+                            <Slider Minimum="-60" Maximum="6" SmallChange="0.5" LargeChange="3"
+                                    Value="{Binding TraxVolumeDb, Mode=TwoWay}" VerticalAlignment="Center"/>
+                        </DockPanel>
+                    </Grid>
                 </Border>
                 <Border Grid.Column="3" Background="{StaticResource Brush.SurfaceContainerLow}" CornerRadius="{StaticResource Radius.Sm}" Margin="4,0,0,0" Padding="10,6">
                     <StackPanel>

Controls/AudioDock.xaml.cs

@@ -39,6 +39,21 @@ public partial class AudioDock : UserControl
             vm.OpenMicPickerCommand.Execute(null);
     }
 
+    private void TraxPlayPause_Click(object sender, RoutedEventArgs e)
+    {
+        if (DataContext is ViewModels.MainViewModel vm) vm.TraxLeftClick();
+    }
+
+    private void TraxLabel_MouseLeftButtonUp(object sender, System.Windows.Input.MouseButtonEventArgs e)
+    {
+        if (DataContext is ViewModels.MainViewModel vm) vm.TraxLeftClick();
+    }
+
+    private void TraxLabel_MouseRightButtonUp(object sender, System.Windows.Input.MouseButtonEventArgs e)
+    {
+        if (DataContext is ViewModels.MainViewModel vm) vm.ChooseTrack();
+    }
+
     private void OnLoaded(object sender, RoutedEventArgs e)
     {
         _window = Window.GetWindow(this);

Services/Audio/ITraxPlayer.cs

@@ -8,6 +8,10 @@ public interface ITraxPlayer : IDisposable
     string? TrackName { get; }
     bool IsPlaying { get; }
     float LocalGain { get; set; }
+
+    /// <summary>The creator's TRAX level (1 = the bed's fixed design level). Separate from
+    /// <see cref="LocalGain"/>, which follows the desktop mute; the dock's fader moves this.</summary>
+    float UserGain { get; set; }
     void Load(string path);
     void Play();
     void Pause();

Services/Audio/MusicPlayer.cs

@@ -41,6 +41,19 @@ public sealed class MusicPlayer : ITraxPlayer
 
     /// <summary>Local gain multiplier from the desktop/game audio bar (0 = mute,
     /// 1 = full bed). Applied live on top of the fixed <see cref="MusicVolume"/>.</summary>
+    private float _userGain = 1f;
+
+    /// <summary>Creator-set level, multiplied onto the fixed design volume.</summary>
+    public float UserGain
+    {
+        get => _userGain;
+        set
+        {
+            _userGain = Math.Clamp(value, 0f, 2f);
+            if (_output != null) _output.Volume = MusicVolume * _userGain * LocalGain;
+        }
+    }
+
     public float LocalGain
     {
         get => _localGain;
@@ -61,7 +74,7 @@ public sealed class MusicPlayer : ITraxPlayer
         Stop();
         TrackPath = path;
         _reader = new MediaFoundationReader(path);
-        _volume = new VolumeWaveProvider16(_reader) { Volume = MusicVolume * _localGain };
+        _volume = new VolumeWaveProvider16(_reader) { Volume = MusicVolume * _userGain * _localGain };
         _output = new WaveOutEvent();
         _output.PlaybackStopped += OnPlaybackStopped;
         _output.Init(_volume);

ViewModels/MainViewModel.Trax.cs

@@ -63,6 +63,28 @@ public partial class MainViewModel
         ? BarOnBrush
         : TraxError != null ? BarOffBrush : TraxIdleBrush;
 
+    /// <summary>The dock's TRAX fader, in dB. Unity means the bed's design level, not the raw file.</summary>
+    public double TraxVolumeDb
+    {
+        get => Helpers.GainDb.ToDb(_musicPlayer.UserGain);
+        set
+        {
+            var gain = Helpers.GainDb.FromDb(value);
+            if (Math.Abs(gain - _musicPlayer.UserGain) < 1e-6) return;
+            _musicPlayer.UserGain = (float)gain;
+            OnPropertyChanged(nameof(TraxVolumeDb));
+            OnPropertyChanged(nameof(TraxVolumeDbLabel));
+        }
+    }
+
+    public string TraxVolumeDbLabel => Helpers.GainDb.Label(TraxVolumeDb) + " dB";
+
+    /// <summary>Track name, or an honest "No track".</summary>
+    public string TraxTrackLabel => _musicPlayer.TrackName ?? "No track";
+
+    /// <summary>Same ducker signal as the game bay — the bed ducks with it.</summary>
+    public bool IsTraxDucking => IsGameDucking;
+
     public string TraxToolTip => _musicPlayer.TrackName != null
         ? $"TRAX: {_musicPlayer.TrackName} — left-click {(IsMusicPlaying ? "pauses" : "plays")}, right-click chooses a track"
         : "No track — left-click or right-click to choose background music";
@@ -81,6 +103,9 @@ public partial class MainViewModel
     /// <summary>Right-click on TRAX: always open the track picker (never the OS viewer).</summary>
     public void TraxRightClick() => PickTraxTrack();
 
+    /// <summary>Open the track picker (the dock's right-click on the TRAX name).</summary>
+    internal void ChooseTrack() => PickTraxTrack();
+
     private void PickTraxTrack()
     {
         var dialog = new OpenFileDialog

ytLive.Tests/TraxBayTests.cs

@@ -0,0 +1,41 @@
+using Xunit;
+using ytLive.Helpers;
+using ytLive.Services.Audio;
+using ytLive.ViewModels;
+
+namespace ytLive.Tests;
+
+/// <summary>The TRAX bay shows the track, plays/pauses it, and carries a level — but no meter:
+/// nothing measures the bed, and a decorative ladder would be a lie. Its fader moves a gain the
+/// player actually applies, separate from the desktop-mute follow.
+/// </summary>
+public class TraxBayTests
+{
+    [Fact]
+    public void The_trax_bay_binds_the_track_level_and_play_state_without_inventing_a_meter()
+    {
+        var dock = SourceAssert.Text("Controls", "AudioDock.xaml");
+        Assert.Contains("Text=\"{Binding TraxTrackLabel}\"", dock);
+        Assert.Contains("Value=\"{Binding TraxVolumeDb, Mode=TwoWay}\"", dock);
+        Assert.Contains("Text=\"{Binding TraxVolumeDbLabel}\"", dock);
+        Assert.Contains("Binding=\"{Binding IsMusicPlaying}\" Value=\"True\"", dock);
+        Assert.Contains("Click=\"TraxPlayPause_Click\"", dock);
+
+        // No ladder in the TRAX bay: nothing measures the bed, so there is nothing honest to show.
+        var traxBay = dock[dock.IndexOf("Text=\"TRAX\"", System.StringComparison.Ordinal)
+                           ..dock.IndexOf("Text=\"LIP-SYNC\"", System.StringComparison.Ordinal)];
+        Assert.Contains("TraxTrackLabel", traxBay);
+        Assert.DoesNotContain("SegmentMeter", traxBay);
+
+        foreach (var name in new[] { "TraxVolumeDb", "TraxVolumeDbLabel", "TraxTrackLabel", "IsTraxDucking" })
+            Assert.NotNull(typeof(MainViewModel).GetProperty(name));
+
+        // The player gained a real user level, separate from the mute-follow LocalGain.
+        Assert.NotNull(typeof(ITraxPlayer).GetProperty("UserGain"));
+        Assert.NotNull(typeof(MusicPlayer).GetProperty("UserGain"));
+
+        // Unity means the bed's design level, and the fader's scale is the same one as the others.
+        Assert.Equal(0, GainDb.ToDb(1f), 6);
+        Assert.Contains("∞", GainDb.Label(GainDb.FloorDb));   // true silence, not "-60.0"
+    }
+}

ytLive.Tests/TraxToggleTests.cs

@@ -21,6 +21,7 @@ public sealed class TraxToggleTests
         public string? TrackName { get; private set; }
         public bool IsPlaying { get; private set; }
         public float LocalGain { get; set; } = 1f;
+        public float UserGain { get; set; } = 1f;
         public void Load(string path) => TrackName = Path.GetFileNameWithoutExtension(path);
         public void Play() => IsPlaying = Starts;
         public void Pause() => IsPlaying = false;