Function intervals_intersect 

pub fn intervals_intersect(
    a: &[(f64, f64)],
    b: &[(f64, f64)],
) -> Result<Vec<(f64, f64)>, IoError>

Intersect two interval lists — e.g. pause == 0 ∩ beam_power > 1.5 MW.

Inputs may be unsorted/overlapping (each side is normalised by sort-and-merge first, the same policy as crate::nexus::load_nexus_bank_spectrum’s keep_intervals); every pair must be finite with t_end > t_start. Output is sorted, non-overlapping, and drops empty intersections.

Errors

IoError::InvalidParameter on a non-finite or empty/inverted pair.