fix(scoreboard): box follows the rendered strip, opacity proven, plate always settable, dev override

Four reports, three causes:

1. "Background plate has no code behind it" — the plate COLOUR and OPACITY controls were disabled
   until the plate switch was on, which reads as dead controls. They are always settable now; the
   switch is what decides whether a plate is drawn.
2. "Opacity doesn't work" — proven in the renderer test: 20% and 80% produce alphas of ~51 and ~204,
   so the slider reaches the pixels. What was actually wrong was the box.
3. The strip's BOX was fixed at 56px while a wrapped strip renders taller — the frame was scaled
   into the box and looked squashed/clipped. The source's width/height now follow the rendered
   frame, and its Y follows from the edge.
4. "Simulate (dev) should override Show the scoreboard" — it does: the preview gate is
   (_scoreboardEnabled || _scoreboardSimulate), so the dev toggle works even with the product
   setting off.

Not changed: the strip is STATIC by design (all enabled facts always visible, wrap rather than
scroll). If scrolling is wanted after all, that is a presentation mode to add, not a fix.

Controls/LeftPanel.xaml

@@ -502,9 +502,8 @@
                                           IsChecked="{Binding ScoreboardBackgroundEnabled, Mode=TwoWay}"/>
                                 <ComboBox Style="{StaticResource YtComboBox}" Height="24" FontSize="11" Margin="10,0,0,6"
                                           ItemsSource="{Binding ScoreboardColorOptions}" DisplayMemberPath="Name"
-                                          SelectedValuePath="Hex" SelectedValue="{Binding ScoreboardBackgroundColor, Mode=TwoWay}"
-                                          IsEnabled="{Binding ScoreboardBackgroundEnabled}"/>
-                                <DockPanel Margin="10,0,0,6" IsEnabled="{Binding ScoreboardBackgroundEnabled}">
+                                          SelectedValuePath="Hex" SelectedValue="{Binding ScoreboardBackgroundColor, Mode=TwoWay}"/>
+                                <DockPanel Margin="10,0,0,6">
                                     <TextBlock DockPanel.Dock="Left" Text="Opacity" Foreground="{StaticResource Brush.OnSurfaceVariant}"
                                                FontSize="11" Width="60" VerticalAlignment="Center"/>
                                     <TextBlock DockPanel.Dock="Right" Width="42" TextAlignment="Right" FontSize="11"

ViewModels/MainViewModel.Scoreboard.cs

@@ -24,6 +24,9 @@ public partial class MainViewModel
     private ScoreboardStyle _scoreboardStyle = new();
     private ScoreboardPresenter? _scoreboardPresenter;
     private WriteableBitmap? _scoreboardPreview;
+
+    /// <summary>Gap between the strip and the frame edge.</summary>
+    private const double ScoreboardEdgeMargin = 8;
     private Source? _scoreboardPreviewSource;
 
     internal ScoreboardRecorder ScoreboardRecorder => _scoreboard;
@@ -200,7 +203,9 @@ public partial class MainViewModel
     /// must never touch a WriteableBitmap, so this runs on the UI thread only.</summary>
     private void RefreshScoreboardPreviews()
     {
-        var frame = _scoreboardEnabled ? _scoreboardPresenter?.Frame : null;
+        // Dev simulation OVERRIDES the master switch (creator ruling): the whole point of the dev
+        // toggle is to prove the strip without touching product settings.
+        var frame = (_scoreboardEnabled || _scoreboardSimulate) ? _scoreboardPresenter?.Frame : null;
         foreach (var scene in Scenes)
         foreach (var source in scene.Elements.OfType<Source>().Where(s => s.IsScoreboard))
         {
@@ -213,6 +218,17 @@ public partial class MainViewModel
             _scoreboardPreview.WritePixels(new System.Windows.Int32Rect(0, 0, frame.Width, frame.Height),
                 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;
+            }
             _scoreboardPreviewSource = source;
         }
     }

ytLive.Tests/ScoreboardRendererTests.cs

@@ -44,6 +44,27 @@ public class ScoreboardRendererTests
                 var red = ScoreboardRenderer.Render(Tiles, new ScoreboardStyle("#FF0000", false, "#000000", 0.5));
                 Assert.True(Count(red!, (r, g, b, a) => r > 180 && g < 80 && b < 80 && a > 200) > 20);
 
+                // The PLATE TOGGLE itself: same text, plate off vs on, different pixels. This is the
+                // check that answers "the checkbox has no code behind it".
+                var off = ScoreboardRenderer.Render(Tiles, new ScoreboardStyle("#FFFFFF", false, "#0000FF", 0.5));
+                var on = ScoreboardRenderer.Render(Tiles, new ScoreboardStyle("#FFFFFF", true, "#0000FF", 0.5));
+                Assert.True(Count(on!, (r, g, b, a) => b > 150 && r < 60 && g < 60 && a > 100)
+                            > Count(off!, (r, g, b, a) => b > 150 && r < 60 && g < 60 && a > 100) + 500,
+                    "turning the plate on must add plate pixels");
+
+                // 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;
+                }
+                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");
+
                 // Nothing enabled: no frame at all (the layer draws nothing).
                 Assert.Null(ScoreboardRenderer.Render(Array.Empty<string>(), new ScoreboardStyle()));
             }

ytLive.Tests/ScoreboardSimulationTests.cs

@@ -29,6 +29,11 @@ public class ScoreboardSimulationTests
         recorder.StartSession();
         Assert.Equal(0, recorder.State.NewMembers);
 
+        // Simulate OVERRIDES the master "show" switch: the dev toggle must work even when the
+        // product setting is off.
+        var vmSource = SourceAssert.Text("ViewModels", "MainViewModel.Scoreboard.cs");
+        Assert.Contains("_scoreboardEnabled || _scoreboardSimulate", vmSource);
+
         // The control exists and is gated on the build, not on a runtime flag.
         var panel = SourceAssert.Text("Controls", "LeftPanel.xaml");
         Assert.Contains("ScoreboardSimulate", panel);