- surface_curvature: mean (H) and Gaussian (K) curvature via
first/second fundamental forms with analytic first derivatives
and finite-difference second derivatives
- is_g2_continuous: G0/G1/G2 continuity check along shared boundary
with proper parameter range extraction and reverse-parameter
matching on opposite edges
- extend_surface: tangent-aligned surface extension along any edge
(umin/umax/vmin/vmax) with knot vector propagation
茂之钳