fix(scoreboard): the strip and the social bar now really share the frame

Reported: the ticker was painting OVER the socials. The coupling rule existed and was tested
(ScoreboardLayout.ResolveEdges) but nothing ever CALLED it — the strip's Y still came from its own
preference, so both bars landed on the south edge.

Now the resolution runs at publish time: the social bar keeps its side, the scoreboard takes the
other one, and its Y follows from that edge. The pair re-sorts whenever the social bar moves (the
preview click-toggle) or shows/hides, because the rule is "resolve from what is visible", not a
stored pairing.

The layer also gains an Edge preference (Top/Bottom) in its properties, labelled "socials take the
other" — a preference, never a claim on an occupied edge.

Also stabilised the opacity assertion: it samples a plate-only pixel 5px from the left edge instead
of the first semi-transparent pixel it finds (which could be anti-aliased text).

Controls/LeftPanel.xaml

@@ -473,6 +473,12 @@
                                 <CheckBox Style="{StaticResource YtCheckBox}" Margin="0,0,0,4"
                                           Content="Show the scoreboard" IsChecked="{Binding ScoreboardEnabled, Mode=TwoWay}"
                                           ToolTip="Off hides the strip in every scene AND stops the channel polling."/>
+                                <TextBlock Text="Edge (socials take the other)" Foreground="{StaticResource Brush.OnSurfaceVariant}"
+                                           FontSize="11" Margin="10,0,0,2"/>
+                                <ComboBox Style="{StaticResource YtComboBox}" Height="24" FontSize="11" Margin="10,0,0,6"
+                                          ItemsSource="{Binding ScoreboardEdgeOptions}"
+                                          SelectedItem="{Binding ScoreboardEdge, Mode=TwoWay}"/>
+
                                 <TextBlock Text="Facts" Foreground="{StaticResource Brush.OnSurfaceVariant}" FontSize="11" FontWeight="SemiBold" Margin="0,0,0,4"/>
                                 <WrapPanel Margin="10,0,0,0">
                                     <CheckBox Style="{StaticResource YtCheckBox}" Content="Subscribers" Margin="0,0,10,4"

ViewModels/MainViewModel.Scoreboard.cs

@@ -27,6 +27,22 @@ public partial class MainViewModel
 
     /// <summary>Gap between the strip and the frame edge.</summary>
     private const double ScoreboardEdgeMargin = 8;
+
+    private BarEdge _scoreboardPreferredEdge = BarEdge.Bottom;
+
+    /// <summary>The edge the creator asked for. It is only a PREFERENCE: the resolver gives the
+    /// scoreboard the edge the social bar does not hold (creator ruling, resolved at render time).</summary>
+    public BarEdge ScoreboardEdge
+    {
+        get => _scoreboardPreferredEdge;
+        set
+        {
+            if (!SetProperty(ref _scoreboardPreferredEdge, value)) return;
+            RefreshScoreboardPreviews();
+        }
+    }
+
+    public IReadOnlyList<BarEdge> ScoreboardEdgeOptions { get; } = new[] { BarEdge.Top, BarEdge.Bottom };
     private Source? _scoreboardPreviewSource;
 
     internal ScoreboardRecorder ScoreboardRecorder => _scoreboard;
@@ -219,16 +235,18 @@ public partial class MainViewModel
                 frame.BgraPixels, frame.Width * 4, 0);
             source.VideoImageSource = _scoreboardPreview;
 
-            // The strip's height follows what was RENDERED (one line or two). A fixed 56px box
-            // squashed a wrapped strip instead of showing it, and its Y follows from the edge.
-            if (Math.Abs(source.Height - frame.Height) > 0.5)
-            {
-                source.Width = frame.Width;
-                source.Height = frame.Height;
-                source.Y = _scoreboardStyle is var _ && source.Y > 540
-                    ? 1080 - frame.Height - ScoreboardEdgeMargin
-                    : ScoreboardEdgeMargin;
-            }
+            // The strip's box follows what was RENDERED (one or two lines), and its edge comes
+            // from the SHARED rule: the social bar keeps its side, the scoreboard takes the other.
+            var socialEdge = _socials?.BarPosition == SocialBarPosition.Top ? BarEdge.Top : BarEdge.Bottom;
+            var (_, resolved) = ScoreboardLayout.ResolveEdges(
+                socialVisible: SocialBarVisible, socialPreferred: socialEdge,
+                scoreboardVisible: true, scoreboardPreferred: _scoreboardPreferredEdge);
+
+            source.Width = frame.Width;
+            source.Height = frame.Height;
+            source.Y = resolved == BarEdge.Top
+                ? ScoreboardEdgeMargin
+                : 1080 - frame.Height - ScoreboardEdgeMargin;
             _scoreboardPreviewSource = source;
         }
     }

ViewModels/MainViewModel.Socials.cs

@@ -224,6 +224,7 @@ public partial class MainViewModel
     private void NotifySocialsChanged()
     {
         RenderSocialBarFrame();
+        RefreshScoreboardPreviews();   // the pair re-sorts when the social bar shows/hides
         OnPropertyChanged(nameof(SocialBarTextBrush));
         OnPropertyChanged(nameof(SocialBarBackgroundBrush));
         OnPropertyChanged(nameof(HasSocials));
@@ -238,6 +239,8 @@ public partial class MainViewModel
         if (_socials == null || _socials.BarPosition == position) return;
         _socials.BarPosition = position;
         OnPropertyChanged(nameof(SocialBarTop));
+        // Coupled pair: moving the social bar moves the scoreboard to the other edge.
+        RefreshScoreboardPreviews();
         ScheduleSave();
     }
 

ytLive.Tests/ScoreboardRendererTests.cs

@@ -55,12 +55,9 @@ public class ScoreboardRendererTests
                 // Opacity: 20% and 80% must produce visibly different plate transparency.
                 var faint = ScoreboardRenderer.Render(Tiles, new ScoreboardStyle("#FFFFFF", true, "#0000FF", 0.2));
                 var solid = ScoreboardRenderer.Render(Tiles, new ScoreboardStyle("#FFFFFF", true, "#0000FF", 0.8));
-                int AlphaOf(VideoFrame f)
-                {
-                    for (var i = 3; i < f.BgraPixels.Length; i += 4)
-                        if (f.BgraPixels[i] is > 10 and < 245) return f.BgraPixels[i];
-                    return 0;
-                }
+                // Sample a plate-only pixel (5px in from the left edge, vertical middle): the text is
+                // centred, so nothing anti-aliased can pollute the alpha reading.
+                static int AlphaOf(VideoFrame f) => f.BgraPixels[((f.Height / 2) * f.Width + 5) * 4 + 3];
                 Assert.InRange(AlphaOf(faint!), 35, 70);     // ~20% of 255
                 Assert.InRange(AlphaOf(solid!), 190, 220);   // ~80% of 255
                 Assert.True(AlphaOf(solid!) > AlphaOf(faint!) + 100, "the opacity slider must move the alpha");

ytLive.Tests/ScoreboardSimulationTests.cs

@@ -43,7 +43,6 @@ public class ScoreboardSimulationTests
         Assert.NotNull(type.GetProperty("ScoreboardSimulate"));
         Assert.NotNull(type.GetProperty("IsDevelopmentBuild"));
         // DEBUG-gated at compile time, so a Release build has no dev control at all.
-        var vmSource = SourceAssert.Text("ViewModels", "MainViewModel.Scoreboard.cs");
         Assert.Contains("#if DEBUG", vmSource);
         Assert.Contains("private const bool DevelopmentBuild = true;", vmSource);
         Assert.Contains("private const bool DevelopmentBuild = false;", vmSource);