AcGeIntersectPrimitive:
    | AcGeIntersectPrimitiveBase & {
        extent: AcGeCurveExtent;
        kind: "line";
        line: AcGeLine3d;
    }
    | AcGeIntersectPrimitiveBase & { arc: AcGeCircArc3d; kind: "circArc" }
    | AcGeIntersectPrimitiveBase & {
        arc: AcGeEllipseArc3d;
        kind: "ellipseArc";
    }
    | AcGeIntersectPrimitiveBase & { kind: "spline"; spline: AcGeSpline3d }

A WCS curve primitive used by acgeIntersectCurves.

Linear primitives carry an AcGeCurveExtent. Arcs and ellipses use their stored start/end angles; when extended they are treated as the full circle or ellipse.