fix(cover): 修复预览视频存储路径错误导致封面生成 500

修复两个导致封面生成 MediaKit 404 的存储路径 bug：

Bug 1: 统一渲染引擎 storage_key 路径不匹配
- RenderAdapter 实际上传到 rendered/{plan_id}/{job_id}.mp4
- 但 edit_plan_generation.py 硬编码存储 rendered/{plan_id}/output.mp4
- cover.py 通过 storage_key 构造的 URL 指向不存在的文件 → 404
- 修复：从 adapter 返回的 output_url 提取实际 storage_key

Bug 2: Worker _upload_and_record 双斜杠路径
- project_id 为空时（模板编辑器草稿），f'generated/projects/{project_id}/tasks/...'
  产生 projects//tasks/ 双斜杠
- MediaKit HTTP 客户端规范化 URL（合并 //）→ 404
- 修复：过滤空路径段，新文件不再产生 //

apps/worker/worker_app/tasks/edit_plan_generation.py

@@ -241,9 +241,15 @@ def _render_with_unified(
         return {"status": "error", "message": result.error_message or "渲染失败"}
 
     output_path = result.output_path or Path("")
-    output_url = result.output_url
+    output_url = result.output_url or ""
     thumbnail_url = result.thumbnail_url or ""
-    storage_key = f"rendered/{plan_id}/output.mp4"
+    # adapter 上传到 rendered/{plan_id}/{job_id}.mp4，从 URL 提取实际 key
+    # 不能用 output.mp4 硬编码，否则 cover 等下游通过 key 构造的 URL 指向不存在的文件
+    if output_url:
+        from packages.shared.storage import get_shared_storage_service
+        storage_key = get_shared_storage_service().normalize_storage_key(output_url)
+    else:
+        storage_key = f"rendered/{plan_id}/{generation_task_id or plan_id}.mp4"
 
     # 用 adapter 返回的 clip 明细（以 adapter 的结果为准）
     rendered_clip_ids = result.rendered_clip_ids or []

apps/worker/worker_app/tasks/generation.py

@@ -1262,7 +1262,9 @@ def _upload_and_record(
     Returns:
         (file_url, duration, file_size, video_count)
     """
-    storage_key = f"generated/projects/{project_id}/tasks/{task_id}/{output_path.name}"
+    # project_id 可能为空（模板编辑器草稿不属于任何项目），过滤空段避免 OSS key 出现 //
+    path_parts = [p for p in ("generated", "projects", project_id, "tasks", task_id, output_path.name) if p]
+    storage_key = "/".join(path_parts)
     file_size = output_path.stat().st_size
 
     # 上传 OSS

tests/unit/test_mediakit_cover.py

@@ -342,3 +342,4 @@ class TestGenerateCover:
         assert result["type"] == "ai_frame"
         call_kwargs = mock_cover_service.call_args[1]
         assert call_kwargs["primary_video_url"] is None
+