Source access enforcement (the catalog): 10-source catalog + per-scene access matrix enforced by SceneAccessPolicy; Add-Source menu is one ItemsSource rebuilt per scene (Screen = Live-only, BG/Image/Text every scene), webcam row always present + greys out; Chatbox/Alerts/Socials are inert SourceType rows ready for their features; Text queued as a ship step (countdown + credits modes); Monetization notes socialBar free = YouTube + 1, unlimited with the paid key (79 tests passing)

Services/SceneAccessPolicy.cs

@@ -0,0 +1,32 @@
+using ytLive.Models;
+
+namespace ytLive.Services;
+
+/// <summary>
+/// The per-scene source access matrix (see the source catalog in TASKS.md).
+/// One source's availability in a scene is a product decision, enforced by
+/// scene name on every place a source can be added. Countdown and Credits are
+/// Text *modes*, not source types: their scene restrictions gate the mode when
+/// the Text ship step lands. Chatbox / Alerts / Socials are inert values until
+/// their features ship — the rows are live from today.
+/// </summary>
+public static class SceneAccessPolicy
+{
+    public static bool Allows(string? sceneName, SourceType type)
+    {
+        if (!SceneCatalog.IsCanonical(sceneName)) return false;
+
+        return type switch
+        {
+            SourceType.DisplayCapture or SourceType.WindowCapture =>
+                SceneCatalog.Is(sceneName, SceneCatalog.Live),
+            SourceType.Background or SourceType.Image or SourceType.TextOverlay or
+            SourceType.Alerts or SourceType.Socials => true,
+            SourceType.Chatbox =>
+                SceneCatalog.Is(sceneName, SceneCatalog.Live)
+                || SceneCatalog.Is(sceneName, SceneCatalog.Brb)
+                || SceneCatalog.IsChat(sceneName),
+            _ => false,
+        };
+    }
+}