审批请求已有客户图纸，设计单保存内部图纸后，再补充客户图纸时部分图纸从页面消失。客户图纸和内部图纸应合并展示，而非互相覆盖。

// BizApprovalRequestServiceImpl.java
public DrawingAggregation getDrawingAggregation(String requestNo, String designTaskId) {
    List<BizDrawing> externalDrawings = drawingMapper.selectByRequestNo(requestNo);
    List<BizDrawing> internalDrawings = drawingMapper.selectByDesignTaskId(designTaskId);

    // BUG: 直接覆盖而非合并
    // 后补外部图纸时重建 payload，已有的内部图纸查询被覆盖
    DrawingAggregation result = new DrawingAggregation();
    if (CollectionUtils.isNotEmpty(externalDrawings)) {
        result.setDrawings(externalDrawings);  // 整列表替换
    }
    if (CollectionUtils.isNotEmpty(internalDrawings)) {
        result.setDrawings(internalDrawings);  // 再次替换，外部图纸丢失
    }
    return result;
}