diff --git a/cocoscreator_projects/scripts/test/ui-convert.test.mjs b/cocoscreator_projects/scripts/test/ui-convert.test.mjs
index e2a670a..7601d0e 100644
--- a/cocoscreator_projects/scripts/test/ui-convert.test.mjs
+++ b/cocoscreator_projects/scripts/test/ui-convert.test.mjs
@@ -50,11 +50,12 @@ test('convertLayer 识别背景：层内首个 + 满屏 → stretch', () => {
   assert.equal(bg.widget.horizontal, 'stretch');
 });
 
-test('convertLayer 背景判定只认层内首个：非首位的满屏对象不算背景', () => {
+test('convertLayer 背景判定只认层内首个，但拉伸适用于所有满屏对象（spec §2.4）', () => {
   const s = tinySource();
-  // 追加一个非首位、同样满屏的对象——用来钉住"首个 + 满屏"而非"只要满屏"的判定规则
+  // 追加一个非首位、同样满屏的对象（如"创建房间遮罩"那类）——
+  // backgroundNodeId 仍应只认层内首个，但 flags.stretch/widget 对所有满屏对象一视同仁
   s.objects.set(4, {
-    ObjectID: 4, ObjectType: 2, ObjectName: '第二张满屏图', Left: 0, Top: 0, Width: 1280, Height: 720,
+    ObjectID: 4, ObjectType: 2, ObjectName: '第二张满屏遮罩', Left: 0, Top: 0, Width: 1280, Height: 720,
     BelongLayerID: 2, IndexOfLayer: 4, ImageFileID: 1, FrameStyle: 0, FrameIndex: 0,
     L9: 0, T9: 0, R9: 0, B9: 0, GroupID: 5, VoiceFileID: 0, TimerInterval: 0, events: [],
   });
@@ -64,7 +65,8 @@ test('convertLayer 背景判定只认层内首个：非首位的满屏对象不
   const doc = convertLayer(s, s.layers[0], imageBuckets(s));
   assert.equal(doc.backgroundNodeId, 1, '背景仍应是层内首个对象');
   const second = doc.nodes.find((n) => n.id === 4);
-  assert.equal(second.flags.stretch, false, '非首位的满屏对象不应被认作背景');
+  assert.equal(second.flags.stretch, true, '满屏对象都应拉伸，不论是否层内首个');
+  assert.equal(second.widget.horizontal, 'stretch');
 });
 
 test('convertLayer 非背景对象用三区锚点与转换坐标', () => {
@@ -108,6 +110,26 @@ test('convertLayer 保留 legacy 承重字段', () => {
   assert.deepEqual(btn.legacy.events, ['mousedown']);
 });
 
+test('convertLayer 对象引用不存在的图时显式抛错（不兜底），消息可定位对象与图', () => {
+  const s = tinySource();
+  s.objects.set(4, {
+    ObjectID: 4, ObjectType: 2, ObjectName: '缺图对象', Left: 10, Top: 10, Width: 50, Height: 50,
+    BelongLayerID: 2, IndexOfLayer: 4, ImageFileID: 999, FrameStyle: 0, FrameIndex: 0,
+    L9: 0, T9: 0, R9: 0, B9: 0, GroupID: 5, VoiceFileID: 0, TimerInterval: 0, events: [],
+  });
+  s.layers[0].objectIds.push(4);
+  s.groups[0].objectIds.push(4);
+
+  assert.throws(
+    () => convertLayer(s, s.layers[0], imageBuckets(s)),
+    (err) => {
+      assert.ok(err.message.includes('对象 4'), `错误信息应包含对象 ID: ${err.message}`);
+      assert.ok(err.message.includes('999'), `错误信息应包含图 ID: ${err.message}`);
+      return true;
+    },
+  );
+});
+
 test('convertLayer 帧号越界：回退帧 1、标记 flags.frameIndexOutOfRange、收集 warning', () => {
   const s = tinySource();
   // 追加一张 frame_all=2 的图，对象却写着 FrameIndex=3——复现真实数据里 9/40 那类越界
@@ -172,10 +194,23 @@ test('convertAll 的 manifest 含 ObjectID 全局索引（C 的承重依赖）',
 });
 
 test('convertAll 在真实数据上覆盖全部对象与界面（回归护栏）', () => {
-  const { layers, manifest, warnings } = convertAll(loadSource(REAL_SOURCE));
+  const source = loadSource(REAL_SOURCE);
+  const { layers, manifest, warnings } = convertAll(source);
   assert.equal(layers.length, 55, '界面数');
   const total = layers.reduce((s, l) => s + l.nodes.length, 0);
   assert.equal(total, 991, '节点总数必须等于对象总数——不得丢对象');
   assert.equal(Object.keys(manifest.objectIndex).length, 991, 'ObjectID 索引必须完整');
   assert.equal(warnings.length, 10, '已知的帧号越界对象必须恰为 10 个——数量漂移应被人工关注');
+
+  // 内容级校验（不只是条数）：objectIndex 每条的 layerId 必须等于该对象真实所属的层
+  // （source 里的 BelongLayerID）。全量遍历能杀掉"全部条目被写成同一个 layerId"
+  // 这类变异——55 个不同层里任何一层的对象被错误映射，都会在此处失败。
+  for (const [idStr, entry] of Object.entries(manifest.objectIndex)) {
+    const obj = source.objects.get(Number(idStr));
+    assert.equal(
+      entry.layerId,
+      obj.BelongLayerID,
+      `ObjectID ${idStr} 的 objectIndex.layerId(${entry.layerId}) 应等于其 BelongLayerID(${obj.BelongLayerID})`,
+    );
+  }
 });
diff --git a/cocoscreator_projects/scripts/ui-migration/convert.mjs b/cocoscreator_projects/scripts/ui-migration/convert.mjs
index 946a34b..e7e87a6 100644
--- a/cocoscreator_projects/scripts/ui-migration/convert.mjs
+++ b/cocoscreator_projects/scripts/ui-migration/convert.mjs
@@ -55,7 +55,10 @@ function spriteBlock(obj, image, bucket, warnings) {
   return { block, outOfRange };
 }
 
-function toNode(obj, source, imageBucketMap, isBackground, warnings) {
+function toNode(obj, source, imageBucketMap, warnings) {
+  // 拉伸(四边置0)适用于全部满屏对象(spec §2.4: 实测 52 个)，不论是否层内首个。
+  // backgroundNodeId(层内唯一)是另一件事：仅用于"首个+满屏"的背景判定，与此处解耦。
+  const stretch = isFullScreen(obj.Width, obj.Height);
   const node = {
     id: obj.ObjectID,
     name: obj.ObjectName,
@@ -63,9 +66,9 @@ function toNode(obj, source, imageBucketMap, isBackground, warnings) {
     position: toCocosPosition(obj.Left, obj.Top, obj.Width, obj.Height),
     size: { width: obj.Width, height: obj.Height },
     siblingIndex: obj.IndexOfLayer,
-    widget: isBackground ? stretchWidget() : inferWidget(obj.Left, obj.Width),
+    widget: stretch ? stretchWidget() : inferWidget(obj.Left, obj.Width),
     flags: {
-      stretch: isBackground,
+      stretch,
       offscreen: isOffscreen(obj.Left, obj.Top, obj.Width, obj.Height),
       animation: obj.FrameStyle === 1,
       frameIndexOutOfRange: false,
@@ -111,7 +114,7 @@ export function convertLayer(source, layer, imageBucketMap) {
 
   const warnings = [];
   const nodes = objs
-    .map((o) => toNode(o, source, imageBucketMap, o.ObjectID === backgroundNodeId, warnings))
+    .map((o) => toNode(o, source, imageBucketMap, warnings))
     .sort((a, b) => a.siblingIndex - b.siblingIndex);
 
   const nodeIdSet = new Set(nodes.map((n) => n.id));