This is the operation the existing subtract_2d could not stand in for: it
returns one shape per island, where subtract_2d collapses to the largest
(correct for a single extrusion profile, silent geometry loss anywhere else).
b may hold any number of rings; they subtract as their union, so there is
no separate "difference against many" entry point.
a - b, keeping EVERY disjoint remnant.This is the operation the existing
subtract_2dcould not stand in for: it returns one shape per island, wheresubtract_2dcollapses to the largest (correct for a single extrusion profile, silent geometry loss anywhere else).bmay hold any number of rings; they subtract as their union, so there is no separate "difference against many" entry point.