feat: 添加媒体资产测试，验证上传初始化时变体和来源ID的规则

backend/app/services/content_test.go

@@ -195,6 +195,54 @@ func (s *ContentTestSuite) Test_AttachAsset() {
 			So(m.AssetID, ShouldEqual, asset.ID)
 			So(m.Role, ShouldEqual, consts.ContentAssetRoleMain)
 		})
+
+		Convey("preview role 只能绑定 preview variant，且必须有 source_asset_id", func() {
+			previewAsset := &models.MediaAsset{
+				TenantID:  tenantID,
+				UserID:    userID,
+				Type:      consts.MediaAssetTypeVideo,
+				Status:    consts.MediaAssetStatusReady,
+				Provider:  "test",
+				Bucket:    "bucket",
+				ObjectKey: "obj-preview",
+				Meta:      types.JSON([]byte("{}")),
+			}
+			So(previewAsset.Create(ctx), ShouldBeNil)
+
+			// 标记为 preview 产物，但不设置 source_asset_id，应被拒绝。
+			_, err := s.DB.ExecContext(ctx, "UPDATE media_assets SET variant = 'preview', source_asset_id = NULL WHERE tenant_id = $1 AND id = $2", tenantID, previewAsset.ID)
+			So(err, ShouldBeNil)
+
+			_, err = Content.AttachAsset(ctx, tenantID, userID, content.ID, previewAsset.ID, consts.ContentAssetRolePreview, 1, now)
+			So(err, ShouldNotBeNil)
+			var appErr *errorx.AppError
+			So(errors.As(err, &appErr), ShouldBeTrue)
+			So(appErr.Code, ShouldEqual, errorx.ErrPreconditionFailed.Code)
+		})
+
+		Convey("main role 绑定 preview variant 应被拒绝", func() {
+			previewAsset := &models.MediaAsset{
+				TenantID:  tenantID,
+				UserID:    userID,
+				Type:      consts.MediaAssetTypeVideo,
+				Status:    consts.MediaAssetStatusReady,
+				Provider:  "test",
+				Bucket:    "bucket",
+				ObjectKey: "obj-preview2",
+				Meta:      types.JSON([]byte("{}")),
+			}
+			So(previewAsset.Create(ctx), ShouldBeNil)
+
+			// 将该资源标记为 preview 产物，并设置一个合法来源（指向已有 main 资源 asset）。
+			_, err := s.DB.ExecContext(ctx, "UPDATE media_assets SET variant = 'preview', source_asset_id = $1 WHERE tenant_id = $2 AND id = $3", asset.ID, tenantID, previewAsset.ID)
+			So(err, ShouldBeNil)
+
+			_, err = Content.AttachAsset(ctx, tenantID, userID, content.ID, previewAsset.ID, consts.ContentAssetRoleMain, 1, now)
+			So(err, ShouldNotBeNil)
+			var appErr *errorx.AppError
+			So(errors.As(err, &appErr), ShouldBeTrue)
+			So(appErr.Code, ShouldEqual, errorx.ErrPreconditionFailed.Code)
+		})
 	})
 }