refactor(render): extract world scene frame owner

Move fallback and PView world drawing, shared alpha, particles, visibility, selection, and diagnostics behind focused frame owners. Make exceptional frames failure-atomic by restoring the shared GL baseline and preserving primary alpha failures through cleanup.

Co-authored-by: Codex <codex@openai.com>

src/AcDream.App/Rendering/Selection/RetailSelectionScene.cs

@@ -9,7 +9,19 @@ namespace AcDream.App.Rendering.Selection;
 /// The renderer builds one frame while input queries the previously completed
 /// frame, avoiding partial visibility state during multi-slice portal drawing.
 /// </summary>
-internal sealed class RetailSelectionScene : IRetailSelectionRenderSink, IRetailSelectionLightingSource
+internal interface IWorldSceneSelectionFrame
+{
+    void BeginFrame();
+
+    void CompleteFrame();
+
+    void AbortFrame();
+}
+
+internal sealed class RetailSelectionScene :
+    IRetailSelectionRenderSink,
+    IRetailSelectionLightingSource,
+    IWorldSceneSelectionFrame
 {
     private readonly IRetailSelectionGeometrySource _geometry;
     private readonly RetailSelectionLightingPulse _lightingPulse;
@@ -100,6 +112,15 @@ internal sealed class RetailSelectionScene : IRetailSelectionRenderSink, IRetail
         (_published, _building) = (_building, _published);
     }
 
+    /// <summary>Discards the incomplete building frame and preserves the last
+    /// completely published selection product.</summary>
+    public void AbortFrame()
+    {
+        _building.Clear();
+        _buildingKeys.Clear();
+        _viewFrustum = null;
+    }
+
     public RetailSelectionHit? Pick(
         float mouseX,
         float mouseY,