fix: P2 API异常信息泄露 + P3-1 逐素材下载日志

P2: generation_tasks.py:260 异常detail改为通用消息，避免泄露内部错误
P3-1: _download_library_assets 添加逐素材日志(asset_id/耗时/大小/成功失败)
      通过 gen_task.append_log 持久化到任务日志，前端可查

apps/api/app/api/routes/generation_tasks.py

@@ -259,7 +259,7 @@ def create_generation_task(
             )
     except Exception as e:
         logger.error("[生成任务] 创建失败: %s", e, exc_info=True)
-        raise HTTPException(status_code=500, detail=f"创建生成任务失败: {e}")
+        raise HTTPException(status_code=500, detail="创建生成任务失败，请稍后重试或查看任务日志")
 
     items = [_to_generation_task_response(t) for t in created_tasks]
     return BatchGenerationTaskResponse(items=items, total=len(items))

apps/worker/worker_app/tasks/generation.py

@@ -343,6 +343,8 @@ def _download_library_assets(
     asset_ids: list[str] | None = None,
     video_extensions: tuple = (".mp4", ".mov", ".avi", ".mkv", ".webm"),
     strict: bool = True,
+    task_id: str = "",
+    gen_task=None,
 ) -> list[Path]:
     """下载视频素材 — 同时支持素材库模式和项目级模式。
 
@@ -442,19 +444,65 @@ def _download_library_assets(
                 storage_key = asset.file_url if asset.file_url else None
                 if not storage_key:
                     failed_assets.append(f"{asset.name}({asset.id})")
-                    logger.warning("素材缺少 file_url, 跳过: asset_id=%s name=%s", asset.id, asset.name)
+                    logger.warning(
+                        "[task_id=%s] 素材缺少 file_url, 跳过: asset_id=%s name=%s", task_id, asset.id, asset.name
+                    )
+                    if gen_task:
+                        gen_task.append_log(
+                            "下载素材",
+                            f"素材缺少file_url, 跳过",
+                            level="WARN",
+                            asset_id=asset.id,
+                            asset_name=asset.name,
+                            success=False,
+                            file_size=0,
+                            duration=0.0,
+                        )
                     if strict:
                         raise RuntimeError(f"素材缺少 file_url: asset_id={asset.id}, name={asset.name}")
                     continue
 
                 ext = Path(storage_key).suffix or ".mp4"
                 local_file = temp_path / f"asset_{i:03d}_{asset.id}{ext}"
-                if download_asset(storage_key, local_file):
+                asset_start = time.monotonic()
+                download_ok = download_asset(storage_key, local_file)
+                asset_elapsed = time.monotonic() - asset_start
+
+                if download_ok:
+                    file_size = local_file.stat().st_size if local_file.exists() else 0
                     downloaded.append(local_file)
-                    logger.info("Downloaded asset: %s -> %s", asset.name, local_file)
+                    logger.info(
+                        "[task_id=%s] Downloaded asset: %s -> %s (size=%d, time=%.1fs)",
+                        task_id,
+                        asset.name,
+                        local_file,
+                        file_size,
+                        asset_elapsed,
+                    )
+                    if gen_task:
+                        gen_task.append_log(
+                            "下载素材",
+                            f"下载成功: {asset.name}",
+                            asset_id=asset.id,
+                            asset_name=asset.name,
+                            success=True,
+                            file_size=file_size,
+                            duration=round(asset_elapsed, 2),
+                        )
                 else:
                     failed_assets.append(f"{asset.name}({asset.id})")
-                    logger.warning("Failed to download asset: %s (id=%s)", asset.name, asset.id)
+                    logger.warning("[task_id=%s] Failed to download asset: %s (id=%s)", task_id, asset.name, asset.id)
+                    if gen_task:
+                        gen_task.append_log(
+                            "下载素材",
+                            f"下载失败: {asset.name}",
+                            level="WARN",
+                            asset_id=asset.id,
+                            asset_name=asset.name,
+                            success=False,
+                            file_size=0,
+                            duration=round(asset_elapsed, 2),
+                        )
                     if strict:
                         raise RuntimeError(f"素材下载失败: asset_id={asset.id}, name={asset.name}")
 
@@ -598,6 +646,8 @@ def generate_video(self, task_id: str) -> dict:
                 asset_library_id=asset_library_id,
                 project_id=project_id,
                 asset_ids=task_asset_ids or None,
+                task_id=task_id,
+                gen_task=gen_task,
             )
             download_elapsed = time.monotonic() - download_start
             logger.info(