Clipping rectangle with open path

[rath3t]

Hi Clipper2 community, thanks for this awesome library.
I though about a very simple problem clipping away parts of a rectangle with open paths with C++

At then end I want the right-hand side a closed path, where the lower right hand part is gone and replaced by the red line.

I have three questions here:

1. Since Clipperlib2 only supports subjects to be open, my scenario is not working out of the box, is it?
2. As a fallback I can construct at least the lines that trims my rectangle ( the bold red line). To store all the information i need later, to reconstruct by hand my clipped rectangle I'm using the USINGZ feature. This I do by the following code:

using namespace Clipper2Lib;

    // create rectangle
    PathsD rectPath;
    rectPath.push_back({});
    for (int i=0; i<4 ; ++i)
      rectPath[0].push_back({corners[i][0],corners[i][1],i+1}); // flag indices of rectangle

    ClipperD c(5);
    int intersectionCounter= 5;

   std::map<int,std::tuple<int,int,PointD>> tracker;

    c.SetZCallback([&](const PointD& e1bot, const PointD& e1top,
  const PointD& e2bot, const PointD& e2top, PointD& pt) {

      tracker.insert({{intersectionCounter++},{e2top.z,e2bot.z,PointD({pt.x,pt.y})}});
      pt.z=intersectionCounter++; // not needed since the rectangle is gone anyway at the end
    });

    PathsD trimmingCurve;
    // ... create curve

    c.AddOpenSubject(trimmingCurve);
    c.AddClip(rectPath);
    PathsD clippedOpenEdges;
    PathsD clippedClosedEdges;
    PolyTreeD tree;
    // c.Execute(ClipType::Intersection,FillRule::NonZero,tree); // returns empty tree, is this expected?
    c.Execute(ClipType::Intersection,FillRule::EvenOdd,clippedClosedEdges,clippedOpenEdges)
   //clippedClosedEdges is empty 
   // clippedOpenEdges contains red line

   //reconstruct clipped rectangle with tracker and clippedOpenEdges 

Now with my tracker, I can reconstruct the full trimmed rectangle, from the information how I pierced my edges of the rectangle.

I feel this is quite overengineered and I wonder if there is an easier solution.
3. Since my solutions depends on setting a ZCallback on my rectangle path, I cannot use RectClipLines for my scenario, can I?

Thanks for your time.