refactor(vtt-thumbnail): [PKG-VTT-THUMB-04] type runtime data and resource boundaries

refactor/tasks.json

@@ -1921,11 +1921,14 @@
         "ENG-06",
         "CORE-07"
       ],
-      "status": "todo",
+      "status": "doing",
       "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",
-      "evidence": []
+      "evidence": [
+        "changes/2026-09-13-PKG-VTT-THUMB-04-runtime-types.md",
+        "baselines/vtt-thumbnail-runtime-types.json"
+      ]
     },
     {
       "id": "PKG-VTT-THUMB-05",