diff --git a/docs/used/SRP_URP_DefaultRendererCompositionContractPlan_2026-04-22_完成归档.md b/docs/used/SRP_URP_DefaultRendererCompositionContractPlan_2026-04-22_完成归档.md
new file mode 100644
index 00000000..037f16e2
--- /dev/null
+++ b/docs/used/SRP_URP_DefaultRendererCompositionContractPlan_2026-04-22_完成归档.md
@@ -0,0 +1,66 @@
+# SRP / URP Default Renderer Composition Contract Plan
+
+时间：2026-04-22
+
+## 背景
+
+上一阶段已经让 `UniversalRenderPipelineAsset` 在构造时显式创建默认 renderer data list，
+但当前默认组合 contract 仍然不完整：
+
+1. 默认组合仍然被拆成 “rendererDataList + 固定 `defaultRendererIndex = 0`”
+2. `ResetRendererDataToDefault()` 隐式假定默认 renderer 永远在 0 号槽位
+3. 这会限制后续多 renderer variant / renderer preset 的正式表达
+
+如果未来默认组合需要同时带出多个 renderer data，这两个信息本来就应该一起返回。
+
+## 目标
+
+把默认 renderer 资产组合正式收成 composition contract。
+
+阶段完成后要达到：
+
+1. 默认 renderer data list 和默认 renderer index 一起表达
+2. `RendererBackedRenderPipelineAsset` 不再写死默认 index 为 0
+3. `UniversalRenderPipelineAsset` 的默认组合通过正式 composition 工厂返回
+4. 为未来多 renderer variant 的默认组合提供稳定接缝
+
+## 范围
+
+本阶段只处理默认 renderer composition contract，不做：
+
+- deferred renderer
+- editor UI
+- 运行时 renderer selection 语义变更
+- public API 大改
+
+## 实施步骤
+
+### 1. 新增 ScriptableRendererDataComposition
+
+职责：
+
+- 表达默认 renderer data list
+- 表达默认 renderer index
+
+### 2. 接入 RendererBackedRenderPipelineAsset
+
+迁移内容：
+
+- 默认组合创建
+- `ResetRendererDataToDefault()`
+
+### 3. 更新 Universal 默认工厂
+
+目标：
+
+- 明确返回默认 renderer composition
+- 保持当前行为不变，但去掉固定 0 号假设
+
+## 完成标准
+
+满足以下条件才算本阶段收口：
+
+1. 默认 renderer 组合 contract 包含 list + default index
+2. `RendererBackedRenderPipelineAsset` 不再在默认重置时硬编码 `defaultRendererIndex = 0`
+3. `XCEditor` 编译通过
+4. old editor 冒烟至少 10 秒通过
diff --git a/managed/CMakeLists.txt b/managed/CMakeLists.txt
index 169075c3..a6dae341 100644
--- a/managed/CMakeLists.txt
+++ b/managed/CMakeLists.txt
@@ -252,6 +252,7 @@ set(XCENGINE_RENDER_PIPELINES_UNIVERSAL_SOURCES
     ${CMAKE_CURRENT_SOURCE_DIR}/XCEngine.RenderPipelines.Universal/Rendering/Universal/ScriptableRenderer.cs
     ${CMAKE_CURRENT_SOURCE_DIR}/XCEngine.RenderPipelines.Universal/Rendering/Universal/ScriptableRendererData.cs
     ${CMAKE_CURRENT_SOURCE_DIR}/XCEngine.RenderPipelines.Universal/Rendering/Universal/ScriptableRendererDataCollection.cs
+    ${CMAKE_CURRENT_SOURCE_DIR}/XCEngine.RenderPipelines.Universal/Rendering/Universal/ScriptableRendererDataComposition.cs
     ${CMAKE_CURRENT_SOURCE_DIR}/XCEngine.RenderPipelines.Universal/Rendering/Universal/ScriptableRendererFeatureCollection.cs
     ${CMAKE_CURRENT_SOURCE_DIR}/XCEngine.RenderPipelines.Universal/Rendering/Universal/ScriptableRendererFeature.cs
     ${CMAKE_CURRENT_SOURCE_DIR}/XCEngine.RenderPipelines.Universal/Rendering/Universal/StageColorData.cs
diff --git a/managed/XCEngine.RenderPipelines.Universal/Rendering/Universal/RendererBackedRenderPipelineAsset.cs b/managed/XCEngine.RenderPipelines.Universal/Rendering/Universal/RendererBackedRenderPipelineAsset.cs
index 8f0c4b8e..2df35b2e 100644
--- a/managed/XCEngine.RenderPipelines.Universal/Rendering/Universal/RendererBackedRenderPipelineAsset.cs
+++ b/managed/XCEngine.RenderPipelines.Universal/Rendering/Universal/RendererBackedRenderPipelineAsset.cs
@@ -152,6 +152,19 @@ namespace XCEngine.Rendering.Universal
                 : Array.Empty<ScriptableRendererData>();
         }
 
+        protected virtual ScriptableRendererDataComposition
+        CreateDefaultRendererDataComposition()
+        {
+            ScriptableRendererData[] defaultRendererDataList =
+                CreateDefaultRendererDataList() ??
+                Array.Empty<ScriptableRendererData>();
+            return new ScriptableRendererDataComposition(
+                defaultRendererDataList,
+                defaultRendererDataList.Length > 0
+                    ? 0
+                    : -1);
+        }
+
         protected virtual bool UsesExplicitFullscreenStagePlanning()
         {
             return true;
@@ -159,11 +172,11 @@ namespace XCEngine.Rendering.Universal
 
         protected void ResetRendererDataToDefault()
         {
-            ScriptableRendererData[] defaultRendererDataList =
-                CreateDefaultRendererDataList() ??
-                Array.Empty<ScriptableRendererData>();
-            rendererDataList = defaultRendererDataList;
-            defaultRendererIndex = 0;
+            ScriptableRendererDataComposition composition =
+                CreateDefaultRendererDataComposition();
+            rendererDataList = composition.rendererDataList;
+            defaultRendererIndex =
+                composition.defaultRendererIndex;
         }
 
         internal ScriptableRendererData GetDefaultRendererData()
diff --git a/managed/XCEngine.RenderPipelines.Universal/Rendering/Universal/ScriptableRendererDataComposition.cs b/managed/XCEngine.RenderPipelines.Universal/Rendering/Universal/ScriptableRendererDataComposition.cs
new file mode 100644
index 00000000..114af8ea
--- /dev/null
+++ b/managed/XCEngine.RenderPipelines.Universal/Rendering/Universal/ScriptableRendererDataComposition.cs
@@ -0,0 +1,21 @@
+using System;
+
+namespace XCEngine.Rendering.Universal
+{
+    public struct ScriptableRendererDataComposition
+    {
+        public readonly ScriptableRendererData[] rendererDataList;
+        public readonly int defaultRendererIndex;
+
+        public ScriptableRendererDataComposition(
+            ScriptableRendererData[] rendererDataList,
+            int defaultRendererIndex)
+        {
+            this.rendererDataList =
+                rendererDataList ??
+                Array.Empty<ScriptableRendererData>();
+            this.defaultRendererIndex =
+                defaultRendererIndex;
+        }
+    }
+}
diff --git a/managed/XCEngine.RenderPipelines.Universal/Rendering/Universal/UniversalDefaultRendererDataFactory.cs b/managed/XCEngine.RenderPipelines.Universal/Rendering/Universal/UniversalDefaultRendererDataFactory.cs
index d2d448cb..7d77d4f1 100644
--- a/managed/XCEngine.RenderPipelines.Universal/Rendering/Universal/UniversalDefaultRendererDataFactory.cs
+++ b/managed/XCEngine.RenderPipelines.Universal/Rendering/Universal/UniversalDefaultRendererDataFactory.cs
@@ -22,5 +22,13 @@ namespace XCEngine.Rendering.Universal
                 rendererData
             };
         }
+
+        public static ScriptableRendererDataComposition
+        CreateDefaultRendererDataComposition()
+        {
+            return new ScriptableRendererDataComposition(
+                CreateDefaultRendererDataList(),
+                0);
+        }
     }
 }
diff --git a/managed/XCEngine.RenderPipelines.Universal/Rendering/Universal/UniversalRenderPipelineAsset.cs b/managed/XCEngine.RenderPipelines.Universal/Rendering/Universal/UniversalRenderPipelineAsset.cs
index 262b607c..aa19a3e8 100644
--- a/managed/XCEngine.RenderPipelines.Universal/Rendering/Universal/UniversalRenderPipelineAsset.cs
+++ b/managed/XCEngine.RenderPipelines.Universal/Rendering/Universal/UniversalRenderPipelineAsset.cs
@@ -92,11 +92,11 @@ namespace XCEngine.Rendering.Universal
                 .CreateDefaultRendererData();
         }
 
-        protected override ScriptableRendererData[]
-        CreateDefaultRendererDataList()
+        protected override ScriptableRendererDataComposition
+        CreateDefaultRendererDataComposition()
         {
             return UniversalDefaultRendererDataFactory
-                .CreateDefaultRendererDataList();
+                .CreateDefaultRendererDataComposition();
         }
 
         protected override int ResolveRendererIndex(