srecord noeq RegionHoleBounds(IImageRegion region) {
  new L<Rect> holeBounds;
  BoundsFinder bf;
  
  L<Rect> get() {
    if (region == null) ret holeBounds;
    var borderWalker = new RegionBorder_innerPoints_v2(region);
    borderWalker.onNewTrace(isHole -> {
      if (isHole) {
        if (bf != null) holeBounds.add(bf!);
        bf = new BoundsFinder;
      } else
        bf = null;
    });
    borderWalker.onFoundPoint(p -> { bf?.addPt(p); });
    borderWalker.run();
    if (bf != null) holeBounds.add(bf!);
    ret holeBounds;
  }
}

Began life as a copy of #1034657