Hm, at least build123d (which I had never heard of, thanks!) can export STEP, which I believe is becoming a necessity if one wants to assemble real-world models with FreeCAD (and nicely also slicers are picking up support to it). I'm on the edge though if I'd really like a proper DSL instead of building it on top of Python, although I can see that too has its benefits (e.g. library access).

Does anyone have idea about the STEP export support status for KCL/µcad? To me it looks like KCL cannot, and I cannot find information on it about µcad. The one tool I'm familiar within this space is OpenSCAD and it cannot. While FreeCAD is able to (sometimes?) convert from STL to STEP, it seems actually working with such models in FreeCAD is quite compute-inefficient.

Fascinating, thanks for sharing!