feat(dock): TRAX gets its own ladder — measured at the player's output

Creator: "why is there no meter for when trax is playing?"

Routing answer: TRAX rides the desktop loopback, so it already moved the GAME ladder — there was no
separate TRAX signal in the mix. But that ladder cannot answer the question a deaf creator actually
has: "is the music producing sound at all?" The play glyph cannot either — an open file with a dead
decoder still reports Playing.

So the player now measures its own output: \`MusicPlayer\` wraps the volume stage in an NAudio
\`MeteringSampleProvider\` and exposes \`Level\`; \`ITraxPlayer.Level\` keeps the fake honest. The VM maps
it through the same display scale (\`TraxMeterFraction\`), zeroed when not playing, and the TRAX bay
carries a 24-segment ladder above its fader.

This reverses my earlier "no ladder, nothing honest to show" — the honest thing arrived with a real
measurement. TraxBayTests flipped accordingly (it now asserts the ladder AND its source).

Controls/AudioDock.xaml

@@ -159,7 +159,10 @@
                             </Border>
                         </Grid>
 
-                        <DockPanel Grid.Row="1" Margin="0,6,0,0" VerticalAlignment="Bottom">
+                        <controls:SegmentMeter Grid.Row="1" Height="10" Margin="0,6,0,6" Orientation="Horizontal"
+                                               Level="{Binding TraxMeterFraction}" Segments="24"/>
+
+                        <DockPanel Grid.Row="1" Margin="0,22,0,0" VerticalAlignment="Bottom">
                             <TextBlock DockPanel.Dock="Right" Width="56" TextAlignment="Right" FontSize="10"
                                        FontFamily="{StaticResource FontFamily.Mono}" VerticalAlignment="Center"
                                        Foreground="{StaticResource Brush.OnSurfaceVariant}"

Services/Audio/ITraxPlayer.cs

@@ -7,6 +7,10 @@ public interface ITraxPlayer : IDisposable
     event Action<Exception?>? PlaybackEnded;
     string? TrackName { get; }
     bool IsPlaying { get; }
+
+    /// <summary>The player's OWN measured output level (0…1). A play glyph can lie — an open file
+    /// with a dead decoder still says "playing" — so the dock's TRAX ladder shows sound, not state.</summary>
+    float Level { get; }
     float LocalGain { get; set; }
 
     /// <summary>The creator's TRAX level (1 = the bed's fixed design level). Separate from

Services/Audio/MusicPlayer.cs

@@ -1,5 +1,7 @@
 using System.IO;
+using System.Linq;
 using NAudio.Wave;
+using NAudio.Wave.SampleProviders;
 
 namespace ytLive.Services.Audio;
 
@@ -39,6 +41,11 @@ public sealed class MusicPlayer : ITraxPlayer
 
     public bool IsPlaying => _output?.PlaybackState == PlaybackState.Playing;
 
+    /// <summary>Measured peak of what the player is actually sending to the device.</summary>
+    public float Level { get; private set; }
+
+    private MeteringSampleProvider? _metering;
+
     /// <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;
@@ -75,9 +82,12 @@ public sealed class MusicPlayer : ITraxPlayer
         TrackPath = path;
         _reader = new MediaFoundationReader(path);
         _volume = new VolumeWaveProvider16(_reader) { Volume = MusicVolume * _userGain * _localGain };
+        _metering = new MeteringSampleProvider(_volume.ToSampleProvider());
+        _metering.StreamVolume += (_, e) =>
+            Level = e.MaxSampleValues.Length == 0 ? 0f : e.MaxSampleValues.Max();
         _output = new WaveOutEvent();
         _output.PlaybackStopped += OnPlaybackStopped;
-        _output.Init(_volume);
+        _output.Init(_metering);
     }
 
     public void Play()

ViewModels/MainViewModel.Audio.cs

@@ -56,6 +56,7 @@ public partial class MainViewModel
                 OnPropertyChanged(nameof(MicMeterFraction));
                 UpdateDuckState();
                 RaiseMasterReadouts();
+                OnPropertyChanged(nameof(TraxMeterFraction));
                 OnPropertyChanged(nameof(MicMeterFraction));
                 OnPropertyChanged(nameof(MicVolumeDb));
                 OnPropertyChanged(nameof(MicVolumeDbLabel));

ViewModels/MainViewModel.Trax.cs

@@ -79,6 +79,11 @@ public partial class MainViewModel
 
     public string TraxVolumeDbLabel => Helpers.GainDb.Label(TraxVolumeDb) + " dB";
 
+    /// <summary>The TRAX ladder: the player's own measured output, so "is music actually making
+    /// sound" is answerable without hearing it.</summary>
+    public double TraxMeterFraction =>
+        IsMusicPlaying ? Services.Audio.AudioLevelMeter.ToDisplay(_musicPlayer.Level) : 0;
+
     /// <summary>Track name, or an honest "No track".</summary>
     public string TraxTrackLabel => _musicPlayer.TrackName ?? "No track";
 

ytLive.Tests/TraxBayTests.cs

@@ -21,17 +21,20 @@ public class TraxBayTests
         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.
+        // The bay DOES carry a ladder now — the player measures its own output, so "is music making
+        // sound" is answerable without hearing it (a play glyph cannot answer that).
         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);
+        Assert.Contains("SegmentMeter", traxBay);
+        Assert.Contains("TraxMeterFraction", traxBay);
 
-        foreach (var name in new[] { "TraxVolumeDb", "TraxVolumeDbLabel", "TraxTrackLabel", "IsTraxDucking" })
+        foreach (var name in new[] { "TraxVolumeDb", "TraxVolumeDbLabel", "TraxTrackLabel", "IsTraxDucking", "TraxMeterFraction" })
             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(ITraxPlayer).GetProperty("Level"));
         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.

ytLive.Tests/TraxToggleTests.cs

@@ -22,6 +22,7 @@ public sealed class TraxToggleTests
         public bool IsPlaying { get; private set; }
         public float LocalGain { get; set; } = 1f;
         public float UserGain { get; set; } = 1f;
+        public float Level { get; set; }
         public void Load(string path) => TrackName = Path.GetFileNameWithoutExtension(path);
         public void Play() => IsPlaying = Starts;
         public void Pause() => IsPlaying = false;