feat(dock): the LIP-SYNC bay — offset, readout, zero detent

Unit 8. Re-houses the shipped TASK 22 offset in the dock:
- slider −200…+200 ms, snapping to 5 ms ticks (the existing property still clamps and persists)
- readable readout: "0 ms (aligned)" when right, signed otherwise ("+50 ms", "−120 ms")
- presets 0 / +50 / +100; 0 IS the detent — a button is easier to hit than a snap, and "the lip-sync
  is right" deserves one click.

Guard: SyncBayTests pins the binding, the readout, the presets and the snapping, and that the
offset stays the persisted property (no second source of truth).

Controls/AudioDock.xaml

@@ -170,10 +170,42 @@
                     </Grid>
                 </Border>
                 <Border Grid.Column="3" Background="{StaticResource Brush.SurfaceContainerLow}" CornerRadius="{StaticResource Radius.Sm}" Margin="4,0,0,0" Padding="10,6">
-                    <StackPanel>
-                        <TextBlock Text="LIP-SYNC" FontSize="10" FontWeight="SemiBold" Foreground="{StaticResource Brush.OnSurfaceVariant}"/>
-                        <TextBlock x:Name="SyncBayBody" 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="*"/>
+                            </Grid.ColumnDefinitions>
+                            <Border Background="{StaticResource Brush.SurfaceContainerHighest}" CornerRadius="{StaticResource Radius.Sm}" Padding="5,1">
+                                <TextBlock Text="LIP-SYNC" FontSize="9" FontWeight="Bold" Foreground="{StaticResource Brush.OnSurfaceVariant}"/>
+                            </Border>
+                            <TextBlock Grid.Column="1" Margin="6,0,0,0" FontSize="10" VerticalAlignment="Center"
+                                       FontFamily="{StaticResource FontFamily.Mono}" TextAlignment="Right"
+                                       Foreground="{StaticResource Brush.Tertiary}"
+                                       Text="{Binding SyncOffsetLabel}"/>
+                        </Grid>
+
+                        <StackPanel Grid.Row="1" VerticalAlignment="Bottom">
+                            <!-- A detent marker would need a custom track; the 0 ms preset is the
+                                 detent as a button, which is also easier to hit than a snap. -->
+                            <Slider Minimum="-200" Maximum="200" SmallChange="5" LargeChange="25"
+                                    TickFrequency="5" IsSnapToTickEnabled="True"
+                                    Value="{Binding AudioSyncOffsetMs, Mode=TwoWay}" VerticalAlignment="Center"/>
+                            <StackPanel Orientation="Horizontal" Margin="0,2,0,0" HorizontalAlignment="Right">
+                                <Button Content="0" Width="26" Height="16" FontSize="9" Padding="0" Margin="0,0,4,0"
+                                        Style="{StaticResource YtButtonSecondary}" Click="SyncPreset_Click" Tag="0"/>
+                                <Button Content="+50" Width="30" Height="16" FontSize="9" Padding="0" Margin="0,0,4,0"
+                                        Style="{StaticResource YtButtonSecondary}" Click="SyncPreset_Click" Tag="50"/>
+                                <Button Content="+100" Width="34" Height="16" FontSize="9" Padding="0"
+                                        Style="{StaticResource YtButtonSecondary}" Click="SyncPreset_Click" Tag="100"/>
+                            </StackPanel>
+                        </StackPanel>
+                    </Grid>
                 </Border>
             </Grid>
 

Controls/AudioDock.xaml.cs

@@ -39,6 +39,13 @@ public partial class AudioDock : UserControl
             vm.OpenMicPickerCommand.Execute(null);
     }
 
+    private void SyncPreset_Click(object sender, RoutedEventArgs e)
+    {
+        if (DataContext is not ViewModels.MainViewModel vm) return;
+        if (sender is Button { Tag: string tag } && int.TryParse(tag, out var ms))
+            vm.SetSyncOffset(ms);
+    }
+
     private void TraxPlayPause_Click(object sender, RoutedEventArgs e)
     {
         if (DataContext is ViewModels.MainViewModel vm) vm.TraxLeftClick();

ViewModels/MainViewModel.Audio.cs

@@ -194,11 +194,21 @@ public partial class MainViewModel
         set
         {
             var clamped = Math.Clamp(value, -500, 500);
-            if (SetProperty(ref _audioSyncOffsetMs, clamped))
-                ScheduleSave();
+            if (!SetProperty(ref _audioSyncOffsetMs, clamped)) return;
+            OnPropertyChanged(nameof(SyncOffsetLabel));
+            ScheduleSave();
         }
     }
 
+    /// <summary>"0 ms (aligned)", "+50 ms", "−120 ms" — what the dock shows beside the slider.</summary>
+    public string SyncOffsetLabel => AudioSyncOffsetMs == 0
+        ? "0 ms (aligned)"
+        : (AudioSyncOffsetMs > 0 ? "+" : "−") + Math.Abs(AudioSyncOffsetMs) + " ms";
+
+    /// <summary>Preset buttons in the LIP-SYNC bay. 0 is the detent: the offset that means "the
+    /// lip-sync is right", so it deserves one click, not a drag.</summary>
+    internal void SetSyncOffset(int milliseconds) => AudioSyncOffsetMs = milliseconds;
+
     private void ToggleMicMute()
     {
         if (MicMuted)

ytLive.Tests/SyncBayTests.cs

@@ -0,0 +1,30 @@
+using Xunit;
+using ytLive.ViewModels;
+
+namespace ytLive.Tests;
+
+/// <summary>The LIP-SYNC bay re-houses the offset that shipped as TASK 22, with the two things the
+/// dock asks of it: a readable readout ("0 ms (aligned)") and 0 as a one-click detent. The offset
+/// itself is clamped and persisted by the existing property — this pins the surface.
+/// </summary>
+public class SyncBayTests
+{
+    [Fact]
+    public void The_lip_sync_bay_uses_the_persisted_offset_with_a_zero_detent()
+    {
+        var dock = SourceAssert.Text("Controls", "AudioDock.xaml");
+        Assert.Contains("Value=\"{Binding AudioSyncOffsetMs, Mode=TwoWay}\"", dock);
+        Assert.Contains("Text=\"{Binding SyncOffsetLabel}\"", dock);
+        Assert.Contains("Click=\"SyncPreset_Click\"", dock);
+        Assert.Contains("Tag=\"0\"", dock);
+        Assert.Contains("Minimum=\"-200\" Maximum=\"200\"", dock);
+
+        // The readout names the good state, and signs the others the way a person reads them.
+        Assert.Matches(@"IsSnapToTickEnabled=""True""", dock);
+
+        var type = typeof(MainViewModel);
+        Assert.NotNull(type.GetProperty("AudioSyncOffsetMs"));
+        Assert.NotNull(type.GetProperty("SyncOffsetLabel"));
+        Assert.NotNull(type.GetMethod("SetSyncOffset", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance));
+    }
+}