Function blend_edge_variable 

pub fn blend_edge_variable(
    solid: &BrepSolid,
    edge_id: u64,
    radii: &[(f64, f64)],
    chamfer: bool,
    name: Option<&str>,
) -> Result<BrepSolid, String>

Variable-radius blend (4.9.5): radius stops as (edge fraction, radius) pairs, linearly interpolated along the edge parameter and clamped at the ends. Closed edges must supply matching first/last radii.