pub fn append_plain_leader(
positions: &mut Vec<f32>,
colors: &mut Vec<f32>,
a: [f64; 3],
b: [f64; 3],
world_per_pixel: f64,
)Expand description
Append a PLAIN leader line a → b (thin silver rod, NO arrowhead cone / origin
sphere — nothing that reads as grabbable) onto existing (positions, colors)
triangle buffers. The NON-dimensional assembly-constraint overlays (coincident /
parallel / …) draw their anchor-to-anchor leaders through this so the line
styling stays in this ONE home (same silver + screen-constant radius as the
dimension rods, slightly thinner because it carries no handle).