feat: create端点兜底复用预览产物 + confirm同步标题

- create_generation_task: source_edit_plan_id非空且is_preview=False时，
  查询该plan下已完成的预览任务，分辨率一致则直接mark_confirmed返回（秒出），
  不创建新任务、不入队
- confirm_generation: ConfirmGenerationRequest增加custom_title字段，
  mark_confirmed时同步更新title_config，并回写EditPlan.config
- GenerationTask.mark_confirmed: 增加title_config参数
- 8个回归测试覆盖兜底复用/分辨率不匹配/预览请求跳过/标题同步

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

@@ -293,6 +293,89 @@ def create_generation_task(
                     detail="当前项目没有符合条件的视频素材，请先上传并等待导入完成后再生成。",
                 )
 
+    # ── 兜底复用预览产物 ──
+    # 前端刷新后 previewTaskId 丢失，降级调 create 接口时，
+    # 如果同一 edit_plan 有已完成的预览任务，直接复用（秒出）。
+    if request.source_edit_plan_id and not request.is_preview:
+        try:
+            from packages.adapters.sqlalchemy_impl.models import (
+                GenerationTaskModel,
+            )
+
+            _preview_model = (
+                db.query(GenerationTaskModel)
+                .filter(
+                    GenerationTaskModel.source_edit_plan_id == request.source_edit_plan_id,
+                    GenerationTaskModel.is_preview.is_(True),
+                    GenerationTaskModel.status == "completed",
+                    GenerationTaskModel.created_by_user_id == authenticated_user.user.id,
+                )
+                .order_by(GenerationTaskModel.created_at.desc())
+                .first()
+            )
+            if _preview_model is not None:
+                # 校验分辨率一致性（与 confirm 端点逻辑相同）
+                req_w = request.output_width or 0
+                req_h = request.output_height or 0
+                src_w = getattr(_preview_model, "output_width", 0) or 0
+                src_h = getattr(_preview_model, "output_height", 0) or 0
+                resolution_match = (req_w == 0 or req_w == src_w) and (req_h == 0 or req_h == src_h)
+
+                if resolution_match:
+                    from packages.adapters.sqlalchemy_impl.generation_task_repository import (
+                        _to_domain,
+                    )
+
+                    preview_task = _to_domain(_preview_model)
+
+                    # 如果传了标题，更新 title_config
+                    fallback_title_config = None
+                    if request.title_config and request.title_config.get("text", "").strip():
+                        fallback_title_config = dict(preview_task.title_config or {})
+                        fallback_title_config.update(request.title_config)
+
+                    preview_task.mark_confirmed(
+                        cover_url=request.cover_url or preview_task.cover_url,
+                        output_width=request.output_width or preview_task.output_width,
+                        output_height=request.output_height or preview_task.output_height,
+                        title_config=fallback_title_config,
+                    )
+                    generation_task_repository.update(preview_task)
+
+                    # 同步标题到 EditPlan.config
+                    if fallback_title_config:
+                        _writeback_edit_plan_config(
+                            plan_id=request.source_edit_plan_id,
+                            task_id=preview_task.id,
+                            title_config=fallback_title_config,
+                            db=db,
+                        )
+
+                    logger.info(
+                        "[生成任务] 兜底复用预览产物: preview_task_id=%s, plan_id=%s",
+                        preview_task.id,
+                        request.source_edit_plan_id,
+                    )
+                    return BatchGenerationTaskResponse(
+                        items=[_to_generation_task_response(preview_task)],
+                        total=1,
+                    )
+                else:
+                    logger.info(
+                        "[生成任务] 兜底复用跳过（分辨率不一致）: plan_id=%s, src=%sx%s, req=%sx%s",
+                        request.source_edit_plan_id,
+                        src_w,
+                        src_h,
+                        req_w,
+                        req_h,
+                    )
+        except Exception:
+            logger.warning(
+                "[生成任务] 兜底复用预览产物异常（不影响主流程）: plan_id=%s",
+                request.source_edit_plan_id,
+                exc_info=True,
+            )
+
     use_case = CreateGenerationTaskUseCase(generation_task_repository)
     count = request.count
     created_tasks = []
@@ -445,6 +528,7 @@ def confirm_generation(
     authenticated_user: AuthenticatedUser = Depends(get_current_user),
     generation_task_repository: Any = Depends(get_generation_task_repository),
     project_repository: Any = Depends(get_project_repository),
+    db: Session = Depends(get_db_session),
 ) -> BatchGenerationTaskResponse:
     """确认生成 -- 复用预览渲染产物（预览与正式品质一致）。
 
@@ -473,12 +557,29 @@ def confirm_generation(
         resolution_match = (req_w == 0 or req_w == src_w) and (req_h == 0 or req_h == src_h)
 
         if resolution_match:
+            # 如果用户传了 custom_title，同步更新 title_config
+            confirmed_title_config = None
+            if request.custom_title and request.custom_title.strip():
+                confirmed_title_config = dict(getattr(source_task, "title_config", {}) or {})
+                confirmed_title_config["text"] = request.custom_title.strip()
+
             source_task.mark_confirmed(
                 cover_url=request.cover_url,
                 output_width=request.output_width,
                 output_height=request.output_height,
+                title_config=confirmed_title_config,
             )
             generation_task_repository.update(source_task)
+
+            # 同步标题到 EditPlan.config
+            if confirmed_title_config and source_task.source_edit_plan_id:
+                _writeback_edit_plan_config(
+                    plan_id=source_task.source_edit_plan_id,
+                    task_id=source_task.id,
+                    title_config=confirmed_title_config,
+                    db=db,
+                )
+
             logger.info(
                 "[确认生成] 复用预览产物: task_id=%s, user_id=%s",
                 task_id,

apps/api/app/schemas/generation_task.py

@@ -10,6 +10,7 @@ class ConfirmGenerationRequest(BaseModel):
     output_width: int = Field(default=1080, ge=100, description="输出视频宽度")
     output_height: int = Field(default=1920, ge=100, description="输出视频高度")
     cover_url: str = Field(default="", description="自定义封面图片 URL")
+    custom_title: str = Field(default="", description="用户自定义标题文本，非空时同步到任务和编辑计划")
 
 
 class CreateGenerationTaskRequest(BaseModel):