fix(download): 已入库任务不被 qB 中间态改回（H2）

importing / imported 只由整理侧推进：checkingResumeData / queuedDL / checkingUP / moving 等中间态只更新原始字段，不改回 queued / downloading / completed，completed_at 不重写；这期间也不做无进展判定。

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Cxwgnn2pbzQ7rXv3rq7fei

packages/mapping/src/download.ts

@@ -62,7 +62,9 @@ export function toDomainDownloadStatus(status: DownloadStatus, pauseReason: Paus
 
 /**
  * 同步轮询时合并"下载器观察"与"当前业务状态":
- * - 业务叠加态在其底层下载状态不变时保留(importing/imported 遇 completed、stalled 遇 downloading、submitting 遇 queued);
+ * - importing / imported 只由整理侧推进:下载器的任何中间态(checkingResumeData / queuedDL / checkingUP / moving,
+ *   乃至出错 / 缺文件)都不把它改回下载阶段,同步只更新原始字段;只有 removed(调用方确认移除)例外;
+ * - 其余业务叠加态在其底层下载状态不变时保留(stalled 遇 downloading、submitting 遇 queued);
  * - 暂停原因为 policy/agent 且下载器仍是暂停时保留原因,不被改写成 user;
  * - 其余以观察为准。
  */
@@ -72,7 +74,7 @@ export function mergeObservedDownloadState(
 ): ContractDownloadState {
   const next = TO_CONTRACT[observed];
   const keep =
-    ((current.status === "importing" || current.status === "imported") && observed === "completed") ||
+    ((current.status === "importing" || current.status === "imported") && observed !== "removed") ||
     (current.status === "stalled" && observed === "downloading") ||
     (current.status === "submitting" && observed === "queued");
   if (keep) return { ...current };