I started working on the NaroCAD code in a new repository, using the most recent code, from here.
After a few small fixes so everything would build and start, I tested the 2D drawing tools and found some problems for the two types of arcs, the drawing for splines and the trim function.
The arcs were not displayed correctly because the plane axis was not passed correctly after the new sketch mode was added. After adding this, the CSE arc was drawn correctly. The SER arc was previewed correctly but when the drawing was finalized it was sometimes reversed (if we previewed the minor arc, the major one was drawn).
The previewing was done using FunctionNames.Arc3P and the drawing was done with FunctionNames.Arc. I've changed the drawing to use the same one as the preview, but since the CSE arc uses FunctionNames.Arc, I'll try to adapt the preview to use it, as well.
You can find the changes here.