Function resolve_edge 

pub fn resolve_edge(
    csg: &CsgLeaves,
    a: (usize, FaceTag),
    b: (usize, FaceTag),
) -> Result<(EdgeGeom, Convexity), EdgeReject>

Resolve the edge where faces (leaf_a, face_a) and (leaf_b, face_b) meet on the final solid. See the module docs for what resolves and why things reject.

Anisotropically scaled round leaves make the evaluation-frame attempt reject with EdgeReject::NonUniformScale; the resolution is then retried in each round face’s leaf frame (where that leaf’s surfaces are canonical), and the result is mapped back — circles keep the frame (CircularEdge::frame), straight cap creases map exactly.