rendering: document managed srp v1 boundaries

managed/XCEngine.ScriptCore/Rendering/Graph/RenderGraphRasterPassBuilder.cs

@@ -12,6 +12,9 @@ namespace XCEngine.Rendering
         FinalColorFullscreen = 3
     }
 
+    // Managed SRP v1 raster recording is intentionally narrow: this builder
+    // only describes fullscreen raster passes that map onto the built-in
+    // ColorScale / ShaderVector / FinalColor executions.
     public sealed class RenderGraphRasterPassBuilder
     {
         private struct TextureBindingRequest
@@ -184,6 +187,8 @@ namespace XCEngine.Rendering
 
         public bool Commit()
         {
+            // Native bridge rejects raster pass recording outside the
+            // fullscreen sequence stages.
             if (m_finalized ||
                 !HasExecutionConfigured() ||
                 !HasAnyColorAttachment())