There was an issue with handling collinear line-segments, which is hopefully now fixed. OpenVoronoi seems to deal OK with most characters from ttt now.
I am still getting some Warnings about numerical instability from LLLSolver, possibly related to these high-degree vertices which don't look quite right (this is a zoom-in inside the circular dot of "j" in the picture above):
I should write a class for extracting offsets next. Then perhaps medial axis (if anyone is interested in v-carving toolpaths).