feat(product-suite): make image pulls cancellable

docs/api.md

@@ -378,12 +378,14 @@ create_job(project_id, source_asset_id=None, job_type="main", prompt="", ...) ->
 list_jobs(project_id, statuses=None, path=None) -> list[ImageStudioJob]
 list_resumable_jobs(project_id=None, include_failed_downloads=False, path=None) -> list[ImageStudioJob]
 replace_selections(project_id, selection_type, asset_ids, path=None) -> list[ImageStudioSelection]
-pull_remote_main_image_urls(account_or_alias, item_id, path=None, config=None) -> dict
+pull_remote_main_image_urls(account_or_alias, item_id, path=None, config=None,
+                            should_stop=None) -> dict
 
 # app/image_studio_images.py
 download_remote_image(url, max_bytes=..., timeout=(connect, read)) -> RemoteImage
 load_thumbnail(url, key=None, max_size=220) -> ThumbnailResult
-download_original_asset(asset_id, path=None, config=None) -> ImageStudioAsset
+download_original_asset(asset_id, path=None, config=None,
+                        should_stop=None) -> ImageStudioAsset
 import_original_files(project_id, file_paths, path=None, config=None) -> dict
 import_original_bytes(project_id, content, filename_hint="clipboard.png", ...) -> ImageStudioAsset
 trash_generated_asset(asset_id, path=None, config=None) -> dict
@@ -433,7 +435,7 @@ class GenerateWorker(BaseWorker)           # ② 后台生成：ai.generate_batc
 class ApplyWorker(BaseWorker)              # ③ 后台更新：账号就绪预检 -> 检查或按批调用 editor.apply_task(...) -> db.set_applied/mark_skipped
 class WriteBackWorker(BaseWorker)          # ①/③ 后台回写：旧字段或更新结果写回原 Excel
 class AIModelTestWorker(BaseWorker)        # ⑤ 后台测试 AI 模型连接：appconfig.test_ai_model
-class ImageStudioPullImagesWorker(BaseWorker)      # ⑥ 后台只读拉蝦皮原主图 URL
+class ImageStudioPullImagesWorker(BaseWorker)      # ⑥ 后台只读拉蝦皮原主图 URL；安全边界协作停止
 class ImageStudioDownloadOriginalWorker(BaseWorker)# ⑥ 后台下载远程原图
 class ImageStudioGenerateJobsWorker(BaseWorker)    # ⑥ 后台提交/查询/下载 cmhub 生图 job
 class ImageStudioResumeJobsWorker(BaseWorker)      # ⑥ 后台恢复已有 task_id 的生图 job