diff --git a/backend/app/services/product_service.py b/backend/app/services/product_service.py
index f661562..a304140 100644
--- a/backend/app/services/product_service.py
+++ b/backend/app/services/product_service.py
@@ -136,6 +136,24 @@ async def get_product_by_serial(db: AsyncSession, serial_number: str) -> Product
         t.created_by = creator_map.get(t.id)
         if t.created_by: assignee_ids.add(t.created_by)
 
+    # 🔧 兜底：在库/入库任务无创建日志时，用该产品在库前最近一道主工序的负责人作为「转入人」
+    all_mains: list = []
+    def _collect_main(tasks):
+        for t in tasks:
+            if not t.parent_task_id or t.task_type in ("TRANSFER", "RECOVERY"):
+                all_mains.append(t)
+            if t.child_tasks:
+                _collect_main(t.child_tasks)
+    _collect_main(task_tree)
+    all_mains.sort(key=lambda t: t.created_at)
+    for t in all_mains:
+        is_w = t.task_name and ("在库" in t.task_name or "入库" in t.task_name)
+        if is_w and not t.created_by:
+            prev = [m for m in all_mains if m.created_at < t.created_at and m.assignee_id]
+            if prev:
+                t.created_by = prev[-1].assignee_id
+                assignee_ids.add(t.created_by)
+
     # 🔧 中文名映射（负责人 + 创建人，供前端显示"谁转入在库"等）
     assignee_names = _lookup_display_names(list(assignee_ids))