fix: SDF nan/edge cases + B-Rep vertex index → ID fix + IGES 1-based DE + STEP cleanup

include/vde/sdf/sdf_primitives.h

@@ -46,7 +46,12 @@ using core::Vector3D;
 [[nodiscard]] inline double capsule(const Point3D& p, const Point3D& a, const Point3D& b, double radius) {
     Point3D pa = p - a;
     Point3D ba = b - a;
-    double h = std::clamp(pa.dot(ba) / ba.squaredNorm(), 0.0, 1.0);
+    double ba_sq = ba.squaredNorm();
+    if (ba_sq < 1e-30) {
+        // Degenerate to sphere
+        return pa.norm() - radius;
+    }
+    double h = std::clamp(pa.dot(ba) / ba_sq, 0.0, 1.0);
     return (pa - ba * h).norm() - radius;
 }
 
@@ -75,6 +80,10 @@ using core::Vector3D;
     double k1 = Point3D(p.x() / (radii.x() * radii.x()),
                          p.y() / (radii.y() * radii.y()),
                          p.z() / (radii.z() * radii.z())).norm();
+    if (k1 < 1e-30) {
+        // Degenerate: point at origin → distance = -min(radii)
+        return -std::min({radii.x(), radii.y(), radii.z()});
+    }
     return k0 * (k0 - 1.0) / k1;
 }