fix(import): harden automatic incremental imports

docs/cn/standard/chatlab-import.md

@@ -371,7 +371,7 @@ ChatLab 不为调用方维护游标。推荐结构：
 
 ### 并发约束
 
-当前版本：**同一 session 同一时刻仅允许一个导入任务**。对同一 sessionId 的并发请求会收到 `IMPORT_IN_PROGRESS` (409) 错误；不同 session 的并发导入互不影响。
+当前版本：**同一用户数据目录同一时刻仅允许一个写入型导入任务**。如果 Desktop、CLI、Web 或 Push API 已在向该数据目录导入，后续请求即使目标 sessionId 不同，也会收到 `IMPORT_IN_PROGRESS` (409) 错误。格式检测、导入分析等只读操作不受此限制。
 
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docs/en/standard/chatlab-import.md

@@ -371,7 +371,7 @@ After each successful batch, update the cursor with `session.lastTimestamp` from
 
 ### Concurrency
 
-Current version: **only one import task is allowed at a time per session**. Concurrent requests to the same sessionId return `IMPORT_IN_PROGRESS` (409); imports to different sessions run independently.
+Current version: **only one write import task is allowed at a time per user data directory**. If Desktop, CLI, Web, or the Push API is already importing into that data directory, later requests return `IMPORT_IN_PROGRESS` (409) even when they target a different sessionId. Read-only format detection and import analysis are not blocked.
 
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