fix(vtt-thumbnail): [PKG-VTT-THUMB-04] preserve historical type shapes

refactor/tasks.json

@@ -1927,7 +1927,7 @@
         "ENG-06",
         "CORE-07"
       ],
-      "status": "doing",
+      "status": "done",
       "risk": "M",
       "deliverable": "cue/rect/result 和参数可选性保持兼容",
       "acceptance": "严格类型检查、旧消费样例通过；声明路径/导出和同步异步兼容",
@@ -1937,7 +1937,10 @@
         "changes/2026-09-13-PKG-VTT-THUMB-04-public-types.md",
         "baselines/vtt-thumbnail-public-types.json",
         "changes/2026-09-13-PKG-VTT-THUMB-04-module-forms.md",
-        "baselines/vtt-thumbnail-module-forms.json"
+        "baselines/vtt-thumbnail-module-forms.json",
+        "type-compatibility-policy.md",
+        "baselines/vtt-thumbnail-approved-types.json",
+        "changes/2026-09-13-PKG-VTT-THUMB-04-approved-types.md"
       ]
     },
     {