feat: N-side filling + G3 continuity

include/vde/curves/nurbs_operations.h

@@ -237,4 +237,18 @@ using core::Vector3D;
 [[nodiscard]] NurbsSurface extend_surface(const NurbsSurface& surf,
     int edge, double length);
 
+/// Fill an N-sided hole with a smooth surface
+/// @param boundary_curves N boundary curves forming a closed loop
+/// @param continuity Desired continuity (1=G1 tangent, 2=G2 curvature)
+/// @return Filling NURBS surface
+[[nodiscard]] NurbsSurface fill_n_sided(const std::vector<NurbsCurve>& boundary_curves,
+                                         int continuity = 1);
+
+/// Check G3 (torsion) continuity between two surfaces along a shared boundary
+[[nodiscard]] bool is_g3_continuous(const NurbsSurface& surf_a,
+    const NurbsSurface& surf_b, int edge, int samples = 10);
+
+/// Compute torsion of a surface at a point
+[[nodiscard]] double surface_torsion(const NurbsSurface& surf, double u, double v);
+
 } // namespace vde::curves