CamBam / FreeCAD 2D/3D MOP question Please help

[Robin Hewitt]

But you aren't trying to cut a semi-circular slot, you are trying to cut a semi-circular slot with something at the ends so the software knows what to do when it gets there. The tool needs to know where it can overhang.
Given half a chance any self respecting software will not view this as a pocket sinking exercise. That way it can cut the outline when it reaches the end. Simples.
The easiest way is to write a quick program that spits out a G code, that way you can be sure you get a finishing cut that increments to the face rather than the depth.