Sad.
The CAM software for my CAD does it for subtractive machining.
Thus circles can be machined with microstep-precision with a minimum of g-code.
For additive machining, the limiting factor is the STL file format. STEP, IGES, ACIS, ProE,... would be so much better.
It never is a curve. In the end it's just discrete microsteps. But that step should always happen in the machine controller when interpreting the g-code.
Projecting a 3D spline onto a 2D plane is just a trivial projection of all it's control point to this plane. In this case it's even just a parallel projection and axis-parallel too.
Bisecting a surace that is defined by 2 3D splines is just a linear interpolation of their control points. Again trivial math.