Resolve an EdgeRef in shape: resolve its two face-roles to current faces,
then return the edge they share. One shared edge → exact; several (the two
faces meet along more than one edge) → disambiguate by hint; none, or a
missing bounding face → broken.
Resolve an EdgeRef in
shape: resolve its two face-roles to current faces, then return the edge they share. One shared edge → exact; several (the two faces meet along more than one edge) → disambiguate by hint; none, or a missing bounding face → broken.