A stable reference to a vertex, identified by the roles of the faces meeting
at it. A solid corner is where ≥3 faces meet at a point; two faces meet
along an edge (two endpoints → ambiguous), so a vertex needs ≥3 face-roles.
Resolves by finding the vertex common to those roles' current faces.
A stable reference to a vertex, identified by the roles of the faces meeting at it. A solid corner is where ≥3 faces meet at a point; two faces meet along an edge (two endpoints → ambiguous), so a vertex needs ≥3 face-roles. Resolves by finding the vertex common to those roles' current faces.