Face lines, structural butt joints, hull caps, concave fillets, the
derived bore, ring fit, ring envelope and section assembly. N-generic
throughout, as the reference is.
Junctions are structural, not cosmetic: one sleeve runs through its
neighbour and is cut flush against that member the far surface, so the
two share a full-width overlap whether or not a fillet is applied on
top. The bore is derived from the members own inside-wall lines rather
than a separately scaled shape, which is what makes the declared inside
wall exactly what remains beside each cavity.
43 tests. Mutation testing found two of the reference own warnings to be
load-bearing and untested by me. A bore that has turned inside out can
carry over a square millimetre of area, so the area guard alone accepts
it and only the interior-side test rejects it. And the ring fit really
does have a spurious lower branch: a thin triangle meets a 1.2 mm web at
relative scale 0.425, where members overhang their own corners and the
solve looks converged. Both now covered.
A third mutation was malformed on my part rather than a gap -- cutting
the cavities twice is idempotent -- and was replaced with one that does
change behaviour. Nine mutations caught.
Oracle acceptance still skips; 236 unchanged.
