feat: P2 素材库自动匹配 - 支持 all/random/smart 三种素材选取模式

- Schema: 新增 asset_select_mode + asset_select_count 字段
- Domain: GenerationTask 新增 asset_select_mode 字段
- Application: Command/UseCase 透传 asset_select_mode
- Route: _select_assets_from_library() 辅助函数 + 创建任务集成
- SQLAlchemy: Model/Repository 映射 asset_select_mode
- Alembic: 032 号迁移
- Worker: _download_library_assets() 支持 asset_ids 过滤
- 单测: 15 个测试覆盖三种模式 + 边界情况

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

@@ -1,3 +1,4 @@
+import random
 from typing import Any
 
 from app.auth import AuthenticatedUser, get_current_user
@@ -52,6 +53,7 @@ def _to_generation_task_response(task) -> GenerationTaskResponse:
         title_ids=task.title_ids,
         voice_ids=task.voice_ids,
         source_edit_plan_id=task.source_edit_plan_id or "",
+        asset_select_mode=getattr(task, "asset_select_mode", ""),
         status=task.status,
         progress=task.progress,
         result_count=task.result_count,
@@ -86,6 +88,49 @@ def _ensure_library_has_ready_video_assets(assets) -> None:
         )
 
 
+def _select_assets_from_library(
+    assets: list,
+    mode: str,
+    count: int,
+) -> list[str]:
+    """根据选取模式从素材库中选取 ready 状态的视频素材 ID。
+
+    Args:
+        assets: 素材库中所有素材（Asset 实体列表）
+        mode: 选取模式 — all=全部, random=随机, smart=按质量评分
+        count: 选取数量，0 表示全部（仅 random/smart 模式有效）
+
+    Returns:
+        选中的素材 ID 列表
+    """
+    ready_video_assets = [a for a in assets if a.status.value == "ready" and a.mime_type.startswith("video")]
+
+    if not ready_video_assets:
+        return []
+
+    if mode == "random":
+        selected = (
+            ready_video_assets if count <= 0 else random.sample(ready_video_assets, min(count, len(ready_video_assets)))
+        )
+        return [a.id for a in selected]
+
+    if mode == "smart":
+        # 按质量分降序排列（质量分高的优先），质量分相同时按时长降序
+        sorted_assets = sorted(
+            ready_video_assets,
+            key=lambda a: (
+                a.quality_score if a.quality_score is not None else 0.0,
+                a.duration if a.duration is not None else 0.0,
+            ),
+            reverse=True,
+        )
+        selected = sorted_assets if count <= 0 else sorted_assets[:count]
+        return [a.id for a in selected]
+
+    # 默认 all 模式：返回全部 ready 视频素材
+    return [a.id for a in ready_video_assets]
+
+
 def _resolve_project_and_library(
     request: CreateGenerationTaskRequest,
     project_repository: Any,
@@ -137,6 +182,7 @@ def create_generation_task(
     )
 
     # asset_library 存在性校验（仅在提供了 asset_library_id 时）
+    resolved_asset_ids: list[str] = list(request.asset_ids)
     if asset_library_id:
         library = asset_library_repository.get(asset_library_id)
         if library is None or (project_id and library.project_id != project_id):
@@ -145,6 +191,14 @@ def create_generation_task(
         assets = asset_repository.find_by_library(asset_library_id)
         _ensure_library_has_ready_video_assets(assets)
 
+        # 素材库自动匹配：当未显式指定 asset_ids 时，按模式自动选取
+        if not resolved_asset_ids:
+            resolved_asset_ids = _select_assets_from_library(
+                assets,
+                mode=request.asset_select_mode,
+                count=request.asset_select_count,
+            )
+
     use_case = CreateGenerationTaskUseCase(generation_task_repository)
     count = request.count
     created_tasks = []
@@ -157,11 +211,12 @@ def create_generation_task(
                 strategy_id=request.strategy_id,
                 voice_library_id=request.voice_library_id,
                 template_id=request.template_id,
-                asset_ids=request.asset_ids,
+                asset_ids=resolved_asset_ids,
                 title_ids=request.title_ids,
                 voice_ids=request.voice_ids,
                 created_by_user_id=authenticated_user.user.id,
                 source_edit_plan_id=request.source_edit_plan_id,
+                asset_select_mode=request.asset_select_mode,
             )
         )
         celery_app.send_task("worker.generate_video", args=[task.id])
@@ -245,6 +300,7 @@ def retry_generation_task(
             voice_ids=task.voice_ids,
             created_by_user_id=authenticated_user.user.id,
             source_edit_plan_id=task.source_edit_plan_id or "",
+            asset_select_mode=getattr(task, "asset_select_mode", ""),
         )
     )
     celery_app.send_task("worker.generate_video", args=[retried.id])