rendering: close out backend contract phase 4.1

engine/include/XCEngine/Rendering/Pipelines/ManagedScriptableRenderPipelineAsset.h

@@ -20,7 +20,9 @@ namespace Pipelines {
 
 enum class ManagedPipelineRendererAssetPolicy {
     Unspecified = 0,
+    // Runtime resolved a concrete shared native backend asset.
     ExplicitAsset = 1,
+    // Runtime explicitly uses the engine default native scene backend.
     DefaultNativeBackend = 2,
 };
 
@@ -110,6 +112,9 @@ public:
     GetPipelineRendererAsset() const {
         return nullptr;
     }
+    // Optional shared native backend asset for the managed pipeline runtime.
+    // Current Mono-backed SRP assets typically return nullptr here and rely on
+    // DefaultNativeBackend instead.
     virtual std::shared_ptr<const RenderPipelineAsset>
     GetSharedPipelineBackendAsset() const {
         return GetPipelineRendererAsset();