Shapely has no corner rounding, so the round_corners -> _circlecorner ->
arc -> segs chain is transcribed from BOSL2 at the pinned commit
92d697c2, read from source rather than recalled. Also deduplicate,
path_merge_collinear, is_collinear and approx, which the cleanup path
depends on.
Segment counts are contract, not a quality setting. An arc becomes
straight segments and the count sets the enclosed area, compared against
the oracle at 1e-3 mm2 -- and the extruded solid is those segments, so
this is the definition of the surface. Both generators set $fn = facets
with facets = 48 and no oracle case overrides it, so segmentation
depends on swept angle alone. A right angle gives 12 points.
round_corners raises where BOSL2 asserts, rather than clamping: silently
fitting a roundover the reference refused would diverge without any
visible failure. sb_corner_radii exists to derive safe radii up front.
33 tests. The exact-fit boundary raises rather than passing, because
tan(45) is under 1 in both languages -- a test asserting the tidy
behaviour would have looked right and been wrong. Mutation run found a
real gap: nothing exercised the three-point floor on blunt corners until
a 170-degree case was added. Seven mutations now caught.
Oracle acceptance still skips; 236 unchanged.
