Function interpolate_position_and_velocity 

pub fn interpolate_position_and_velocity(
    points: &[TrajectoryPoint],
    target_dist_m: f64,
) -> Option<(f64, f64)>

Linearly interpolate (position.y, velocity_magnitude) at horizontal distance target_dist_m from a solved trajectory’s points (position.x = downrange). Mirrors cli_api::fit_value_at’s interpolation (private to that module), but resolves both quantities from the same bracketing pair in one pass since the dsf verb needs drop AND Mach at the identical range. None if the trajectory never reaches target_dist_m.