Function fixed_reference_sweep_exact

pub fn fixed_reference_sweep_exact(
    profile: &Profile,
    path: &[Point3],
    reference_direction: Vec3,
    tolerance: Tolerance,
) -> GeomResult<ExactBRep>

Sweep a supported profile along a straight path with a fixed reference.

A fixed-reference sweep along a STRAIGHT directrix keeps the profile’s orientation constant, so the swept solid is exactly a linear extrusion along that segment. Rather than build a second implementation that could drift from it, this delegates to extrude_profile_exact, which is the same solid by construction.

A curved directrix is refused: the profile then rotates along the path and the walls become general swept surfaces, not planes and cylinders. That is the curved-surface work this issue explicitly puts out of scope.