The exact engine rebuilds its output from each connection's own vias,
so connections sharing a plane via each wrote a copy: th-eda's flight
controller had 71 spots carrying 2 to 4 vias of one net. Vias are now
written once per net and spot, and never on a via already on the board.
Every pin of a supply drops its own via to the plane, and nothing kept
two of them apart: the flight controller came back with 199 co-located
holes and 109 hole-to-hole errors, nearly all VDD_3V3 and GND. A via now
keeps its drill plus --hole-to-hole (default 0.25 mm, KiCad's) from
every via centre, fixed ones included, except an own-net via at the same
cell, which it reuses; such a via is written once, and none is written
on top of a via already on the board.
rsp2k