Function helix_sample_points 

pub fn helix_sample_points(
    axis_origin: Vec3,
    axis_direction: Vec3,
    reference: Option<Vec3>,
    start_radius: f64,
    end_radius: f64,
    pitch: f64,
    turns: f64,
    start_angle: f64,
    left_handed: bool,
) -> Result<(Vec<Vec3>, Vec<f64>), String>

Helical sweep (§5.7): sweep a CLOSED PLANAR profile loop along a helix of helix_radius about the axis through axis_origin with direction axis_direction, rising pitch per revolution for turns revolutions.

Sample a helix — turns revolutions about axis_direction from axis_origin, starting at angle start_angle (radians, measured from the axis frame’s u) and rising pitch per turn, the radius running linearly from start_radius to end_radius — uniformly in angle: 64 stations per turn (at least 9, at most 4097 in total, so beyond 64 turns the per-turn density thins). Returns the points and their chord parameters s ∈ [0,1] (uniform-in-angle IS chord-length for a constant-radius helix, which is what the averaged-knot interpolation assumes). left_handed winds the angle the other way. The axis frame is w = axis, u = the component of reference perpendicular to the axis (so angle zero points AT the reference — the helix feature’s local +X, or its start point), falling back to w.perpendicular() when there is no usable reference, and v = w × u. Shared by sweep_profile_helix and the HX feature, so the coil a sweep builds and the edge a helix feature publishes agree exactly.

Errors on a degenerate axis, non-finite inputs, turns ≤ 0, more than 256 turns, a negative radius or pitch, or a helix that is a single point (both radii AND the pitch zero).