fix: duplicate document ingest guard (#15638)

### What problem does this PR solve?
When a document is rerun or updated concurrently, the previous
unconditional update could overwrite a newer task state.
This change adds an `update_time`-based optimistic lock so the update
only succeeds if the record has not been modified by another flow in the
meantime.

### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)

api/db/services/common_service.py

@@ -276,6 +276,26 @@ class CommonService:
         num = cls.model.update(data).where(cls.model.id == pid).execute()
         return num
 
+    @classmethod
+    @DB.connection_context()
+    @retry_db_operation
+    def update_by_id_if_update_time(cls, pid, update_time, data):
+        # Update a single record by ID only if update_time matches the expected value.
+        # Args:
+        #     pid: Record ID
+        #     update_time: Expected update_time value for optimistic locking
+        #     data: Updated field values
+        # Returns:
+        #     Number of records updated
+        data["update_time"] = current_timestamp()
+        data["update_date"] = datetime_format(datetime.now())
+        num = (
+            cls.model.update(data)
+            .where(cls.model.id == pid, cls.model.update_time == update_time)
+            .execute()
+        )
+        return num
+
     @classmethod
     @DB.connection_context()
     def get_by_id(cls, pid):