Kill stringly-typed command tokens: Add Source menu passes SourceType enum via x:Static CommandParameter (typos break the build, not silently add an Image); webcam gets its own AddWebcamCommand; AddSource keeps Enum.TryParse fallback; docs updated (65 tests passing)

MainWindow.xaml

@@ -4,6 +4,7 @@
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
         xmlns:vm="clr-namespace:ytLive.ViewModels"
+        xmlns:models="clr-namespace:ytLive.Models"
         xmlns:Helpers="clr-namespace:ytLive.Helpers"
         mc:Ignorable="d"
         Title="{Binding WindowTitle}" Height="720" Width="1280"
@@ -249,13 +250,13 @@
                                 Click="AddSourceButton_Click">
                             <Button.ContextMenu>
                                 <ContextMenu DataContext="{Binding PlacementTarget.DataContext, RelativeSource={RelativeSource Self}}">
-                                    <MenuItem Header="Webcam" Command="{Binding AddSourceCommand}" CommandParameter="webcam"
+                                    <MenuItem Header="Webcam" Command="{Binding AddWebcamCommand}"
                                               IsEnabled="{Binding CanAddWebcamToActiveScene}"
                                               ToolTip="One webcam at a time — it's already in your stream"/>
-                                    <MenuItem Header="Screen" Command="{Binding AddSourceCommand}" CommandParameter="screen"/>
-                                    <MenuItem Header="Background" Command="{Binding AddSourceCommand}" CommandParameter="background"/>
+                                    <MenuItem Header="Screen" Command="{Binding AddSourceCommand}" CommandParameter="{x:Static models:SourceType.DisplayCapture}"/>
+                                    <MenuItem Header="Background" Command="{Binding AddSourceCommand}" CommandParameter="{x:Static models:SourceType.Background}"/>
                                     <MenuItem Header="Image" Command="{Binding AddImageCommand}"/>
-                                    <MenuItem Header="Text" Command="{Binding AddSourceCommand}" CommandParameter="text"/>
+                                    <MenuItem Header="Text" Command="{Binding AddSourceCommand}" CommandParameter="{x:Static models:SourceType.TextOverlay}"/>
                                 </ContextMenu>
                             </Button.ContextMenu>
                             <Path Data="M12,4 L12,20 M4,12 L20,12" Stroke="#e94560" StrokeThickness="2"

ViewModels/MainViewModel.cs

@@ -525,6 +525,7 @@ public class MainViewModel : ViewModelBase
     public ICommand RemoveSceneCommand { get; }
     public ICommand ToggleSceneVisibilityCommand { get; }
     public ICommand AddSourceCommand { get; }
+    public ICommand AddWebcamCommand { get; }
     public ICommand AddImageCommand { get; }
     public ICommand RemoveSourceCommand { get; }
     public ICommand ChangeWebcamCommand { get; }
@@ -577,7 +578,8 @@ public class MainViewModel : ViewModelBase
         EditSceneCommand = new RelayCommand(scene => BeginEditScene(scene as Scene));
         RemoveSceneCommand = new RelayCommand(scene => RemoveScene(scene as Scene));
         ToggleSceneVisibilityCommand = new RelayCommand(scene => ToggleSceneVisibility(scene as Scene));
-        AddSourceCommand = new RelayCommand(type => AddSource(type as string));
+        AddSourceCommand = new RelayCommand(parameter => AddSource(parameter));
+        AddWebcamCommand = new RelayCommand(_ => _ = AddWebcamToActiveSceneAsync());
         AddImageCommand = new RelayCommand(_ => AddImage());
         RemoveSourceCommand = new RelayCommand(element => RemoveElement(element as SceneElement));
         ChangeWebcamCommand = new RelayCommand(_ => _ = ChangeWebcamAsync(), _ => CanChangeWebcam);
@@ -1060,25 +1062,14 @@ public class MainViewModel : ViewModelBase
             ActiveScene = Scenes.FirstOrDefault();
     }
 
-    private void AddSource(string? type)
+    private void AddSource(object? parameter)
     {
         var scene = ActiveScene;
         if (scene == null) return;
 
-        if (string.Equals(type, "webcam", StringComparison.OrdinalIgnoreCase))
-        {
-            _ = AddWebcamToActiveSceneAsync();
-            return;
-        }
-
-        var sourceType = type?.ToLowerInvariant() switch
-        {
-            "screen" => SourceType.DisplayCapture,
-            "window" => SourceType.WindowCapture,
-            "background" => SourceType.Background,
-            "text" => SourceType.TextOverlay,
-            _ => SourceType.Image,
-        };
+        var sourceType = parameter is SourceType typed
+            ? typed
+            : Enum.TryParse<SourceType>(parameter?.ToString(), true, out var parsed) ? parsed : SourceType.Image;
         var baseName = sourceType switch
         {
             SourceType.DisplayCapture => "Screen",

ai.md

@@ -95,7 +95,7 @@ C# / WPF (.NET 8) following MVVM:
 ### Key patterns
 
 - `ViewModelBase.SetProperty<T>()` for property change notifications
-- `RelayCommand` for all button actions; commands gate on state (e.g. Start only when Offline)
+- `RelayCommand` for all button actions; commands gate on state (e.g. Start only when Offline). **Typed `CommandParameter`s — no stringly-typed command tokens:** menu items that pick a source type pass the enum value itself (`CommandParameter="{x:Static models:SourceType.DisplayCapture}"`), so a typo breaks the build instead of silently adding an Image; `AddSource` still falls back to `Enum.TryParse<SourceType>(..., true)` for safety. The webcam item is its own `AddWebcamCommand` (it greys out via `CanAddWebcamToActiveScene` and isn't a `SourceType` — webcams are `WebcamSceneConfig`, not `Source` rows)
 - ViewModels are constructed in XAML (`<vm:MainViewModel/>` as DataContext)
 - Services are currently instantiated in MainViewModel's constructor — no DI container yet
 - Layout persists to SQLite (`Microsoft.Data.Sqlite`); scenes/sources/asset bytes stored in the DB, asset identity is a SHA-256 content hash (1:M reuse, no file paths — assets are always available)