refactor: extract SceneThumbnailStrip out of MainWindow.xaml — Phase 2, Commit 16

SceneThumbnailStrip.xaml(.cs) takes the Row 0 scene-picker strip (ItemsControl
over Scenes with staged/live border highlight); Thumbnail_MouseLeftButtonDown
moved into the control, transitioning via DataContext.TransitionToScene.

Zero behavior change; build 0 warnings; 246 pass, only the 2 known failures.
Docs: ViewModels/index.md Phase 2 tracker updated in the same commit.

Controls/SceneThumbnailStrip.xaml

@@ -0,0 +1,54 @@
+<UserControl x:Class="ytLive.Controls.SceneThumbnailStrip"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+    <Border Background="#0d1117" CornerRadius="4" Margin="0,0,0,4" Padding="4">
+        <ItemsControl ItemsSource="{Binding Scenes}">
+            <ItemsControl.ItemsPanel>
+                <ItemsPanelTemplate>
+                    <UniformGrid Rows="1" Columns="5"/>
+                </ItemsPanelTemplate>
+            </ItemsControl.ItemsPanel>
+            <ItemsControl.ItemTemplate>
+                <DataTemplate>
+                    <Border CornerRadius="4" Margin="2" Padding="2"
+                            BorderThickness="2"
+                            BorderBrush="Transparent"
+                            Cursor="Hand"
+                            MouseLeftButtonDown="Thumbnail_MouseLeftButtonDown">
+                        <Border.Style>
+                            <Style TargetType="Border">
+                                <Setter Property="BorderBrush" Value="#333344"/>
+                                <Style.Triggers>
+                                    <DataTrigger Binding="{Binding IsStaged}" Value="True">
+                                        <Setter Property="BorderBrush" Value="#e94560"/>
+                                    </DataTrigger>
+                                    <DataTrigger Binding="{Binding IsLive}" Value="True">
+                                        <Setter Property="BorderBrush" Value="#22c55e"/>
+                                    </DataTrigger>
+                                </Style.Triggers>
+                            </Style>
+                        </Border.Style>
+                        <Grid>
+                            <Grid.RowDefinitions>
+                                <RowDefinition Height="*"/>
+                                <RowDefinition Height="Auto"/>
+                            </Grid.RowDefinitions>
+                            <Border Grid.Row="0" CornerRadius="3"
+                                    Background="#0a0a1a" ClipToBounds="True">
+                                <Image Source="{Binding Snapshot}"
+                                       Stretch="UniformToFill"
+                                       RenderOptions.BitmapScalingMode="LowQuality"/>
+                            </Border>
+                            <TextBlock Grid.Row="1" Foreground="#a0a0b0" FontSize="10"
+                                       HorizontalAlignment="Center"
+                                       Margin="0,2,0,0"
+                                       TextTrimming="CharacterEllipsis">
+                                <Run Text="{Binding Name, Mode=OneWay}"/><Run Text=" "/><Run Text="{Binding HotkeyLabel, Mode=OneWay}" Foreground="#6a6a7a" FontWeight="SemiBold"/>
+                            </TextBlock>
+                        </Grid>
+                    </Border>
+                </DataTemplate>
+            </ItemsControl.ItemTemplate>
+        </ItemsControl>
+    </Border>
+</UserControl>

Controls/SceneThumbnailStrip.xaml.cs

@@ -0,0 +1,21 @@
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Input;
+using ytLive.Models;
+using ytLive.ViewModels;
+
+namespace ytLive.Controls;
+
+public partial class SceneThumbnailStrip : UserControl
+{
+    public SceneThumbnailStrip()
+    {
+        InitializeComponent();
+    }
+
+    private void Thumbnail_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
+    {
+        if (sender is Border { DataContext: Scene scene } && DataContext is MainViewModel vm)
+            vm.TransitionToScene(scene);
+    }
+}

MainWindow.xaml

@@ -93,57 +93,7 @@
             </Grid.ColumnDefinitions>
 
             <!-- ═══ THUMBNAIL STRIP ═══ -->
-            <Border Grid.Row="0" Grid.ColumnSpan="2" Background="#0d1117" CornerRadius="4" Margin="0,0,0,4"
+            <controls:SceneThumbnailStrip Grid.Row="0" Grid.ColumnSpan="2"/>
-                    Padding="4">
-                <ItemsControl ItemsSource="{Binding Scenes}">
-                    <ItemsControl.ItemsPanel>
-                        <ItemsPanelTemplate>
-                            <UniformGrid Rows="1" Columns="5"/>
-                        </ItemsPanelTemplate>
-                    </ItemsControl.ItemsPanel>
-                    <ItemsControl.ItemTemplate>
-                        <DataTemplate>
-                            <Border CornerRadius="4" Margin="2" Padding="2"
-                                    BorderThickness="2"
-                                    BorderBrush="Transparent"
-                                    Cursor="Hand"
-                                    MouseLeftButtonDown="Thumbnail_MouseLeftButtonDown">
-                                <Border.Style>
-                                    <Style TargetType="Border">
-                                        <Setter Property="BorderBrush" Value="#333344"/>
-                                        <Style.Triggers>
-                                            <DataTrigger Binding="{Binding IsStaged}" Value="True">
-                                                <Setter Property="BorderBrush" Value="#e94560"/>
-                                            </DataTrigger>
-                                            <DataTrigger Binding="{Binding IsLive}" Value="True">
-                                                <Setter Property="BorderBrush" Value="#22c55e"/>
-                                            </DataTrigger>
-                                        </Style.Triggers>
-                                    </Style>
-                                </Border.Style>
-                                <Grid>
-                                    <Grid.RowDefinitions>
-                                        <RowDefinition Height="*"/>
-                                        <RowDefinition Height="Auto"/>
-                                    </Grid.RowDefinitions>
-                                    <Border Grid.Row="0" CornerRadius="3"
-                                            Background="#0a0a1a" ClipToBounds="True">
-                                        <Image Source="{Binding Snapshot}"
-                                               Stretch="UniformToFill"
-                                               RenderOptions.BitmapScalingMode="LowQuality"/>
-                                    </Border>
-                                    <TextBlock Grid.Row="1" Foreground="#a0a0b0" FontSize="10"
-                                               HorizontalAlignment="Center"
-                                               Margin="0,2,0,0"
-                                               TextTrimming="CharacterEllipsis">
-                                        <Run Text="{Binding Name, Mode=OneWay}"/><Run Text=" "/><Run Text="{Binding HotkeyLabel, Mode=OneWay}" Foreground="#6a6a7a" FontWeight="SemiBold"/>
-                                    </TextBlock>
-                                </Grid>
-                            </Border>
-                        </DataTemplate>
-                    </ItemsControl.ItemTemplate>
-                </ItemsControl>
-            </Border>
 
             <!-- LEFT PANEL: one panel, two states.
                  Offline (edit mode): LAYERS + PROPERTIES

MainWindow.xaml.cs

@@ -164,13 +164,6 @@ public partial class MainWindow : Window
         }
     }
 
-    // ─── Preview image selection / move / resize ───
-    private void Thumbnail_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
-    {
-        if (sender is Border { DataContext: Scene scene })
-            _viewModel.TransitionToScene(scene);
-    }
-
 
     private void Window_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
     {

ViewModels/index.md

@@ -57,7 +57,8 @@ Progress (Commit N/12 · tag):
 - [x] **Commit 12 · `refactor-commit-12`** — **BottomBar** → `Controls/BottomBar.xaml(.cs)` (gear menu + stream stats + quality dropdown; `GearButton_Click` moved to the control's code-behind).
 - [x] **Commit 13 · `refactor-commit-13`** — **HealthBanner** → `Controls/HealthBanner.xaml` (Row 1). Also promoted the 7 value↔visibility converters out of `MainWindow.Window.Resources` into `Themes/Controls.xaml` so extracted controls can resolve them (app-level, not window-level).
 - [x] **Commit 14 · `refactor-commit-14`** — **TopBar** → `Controls/TopBar.xaml(.cs)` (Row 0: logo, REC/ON-AIR pills + signs, avatar, Sign In/Start/End buttons). Avatar fetch moved (async-preserved) into the control; window exposes `_topBar.RefreshAvatar()` invoked on `IsConnected`/`AccountAvatarUrl` changes.
-- [x] **Commit 15 · `refactor-commit-15`** — **PreviewPane** → `Controls/PreviewPane.xaml(.cs)` (Row 1 Col 1 center preview pane). Moved the 1920×1080 canvas (OverlayCanvas/SelectionOverlay/BrandFlashLayer/SocialBarElement), text pull-out, and the live-controls row (TRAX/game/mic meters + sliders + speakers + socials button). Code-behind moved: preview drag/select/resize/hit-test (Preview_Mouse*, HitHandle, HitElement), webcam-context-menu handlers (WebcamMenu_*), social-bar glow (SocialBar_*, SocialsButton_*, SocialGlowTick), audio sliders/speakers (VolumeSlider_*, GameVolumeSlider_*, MicSpeaker_*, GameSpeaker_*, SetSliderValueFromClick, FindParent), TraxButton_*. Window keeps the source-list left panel + thumbnail strip + edit UI, and routes selection-overlay via `_previewPane.UpdateSelectionOverlay(bool)` plus `_previewPane.IsClickInsidePreview/Drawer`. `BackgroundMenu_*` stayed in the window (used by the left-panel source context menu). Pending: thumbnail strip, left scene/chat panel, overlay host.
+- [x] **Commit 15 · `refactor-commit-15`** — **PreviewPane** → `Controls/PreviewPane.xaml(.cs)` (Row 1 Col 1 center preview pane). Moved the 1920×1080 canvas (OverlayCanvas/SelectionOverlay/BrandFlashLayer/SocialBarElement), text pull-out, and the live-controls row (TRAX/game/mic meters + sliders + speakers + socials button). Code-behind moved: preview drag/select/resize/hit-test (Preview_Mouse*, HitHandle, HitElement), webcam-context-menu handlers (WebcamMenu_*), social-bar glow (SocialBar_*, SocialsButton_*, SocialGlowTick), audio sliders/speakers (VolumeSlider_*, GameVolumeSlider_*, MicSpeaker_*, GameSpeaker_*, SetSliderValueFromClick, FindParent), TraxButton_*. Window keeps the source-list left panel + thumbnail strip + edit UI, and routes selection-overlay via `_previewPane.UpdateSelectionOverlay(bool)` plus `_previewPane.IsClickInsidePreview/Drawer`. `BackgroundMenu_*` stayed in the window (used by the left-panel source context menu).
+- [x] **Commit 16 · `refactor-commit-16`** — **SceneThumbnailStrip** → `Controls/SceneThumbnailStrip.xaml(.cs)` (Row 0 scene-picker strip). `Thumbnail_MouseLeftButtonDown` moved into the control (transitions via `DataContext.TransitionToScene`). Pending: left scene/chat panel, overlay host.
 
 The partial `.cs` files land next to `MainViewModel.cs` in this folder as the split
 proceeds; each partial carries its own `using`s and re-declares nothing from core.