fix(model): do not treat no-op system task state writes as lock loss (#7135)

model/system_task.go

@@ -322,7 +322,23 @@ func UpdateSystemTaskState(taskID string, lockedBy string, state any) error {
 	if result.Error != nil {
 		return result.Error
 	}
-	if result.RowsAffected == 0 {
+	if result.RowsAffected > 0 {
+		return nil
+	}
+	// MySQL counts changed rows, not matched rows. A no-op persist of the same
+	// state in the same second therefore returns RowsAffected == 0 even while
+	// the lease is still held. Confirm the lock before treating this as loss.
+	// Reuse `now` from the UPDATE so a clock tick cannot reintroduce false
+	// lock-loss; a lease that expires during the write is caught by the next heartbeat.
+	var held int64
+	err = DB.Model(&SystemTask{}).
+		Where("task_id = ? AND status = ? AND locked_by = ?", taskID, SystemTaskStatusRunning, lockedBy).
+		Where("EXISTS (SELECT 1 FROM system_task_locks WHERE system_task_locks.task_id = system_tasks.task_id AND system_task_locks.locked_by = ? AND system_task_locks.locked_until >= ?)", lockedBy, now).
+		Count(&held).Error
+	if err != nil {
+		return err
+	}
+	if held == 0 {
 		return ErrSystemTaskLockLost
 	}
 	return nil