Function unwrap_one_echo 

fn unwrap_one_echo(
    phase: &[f64],
    mag: &[f64],
    mask: &[u8],
    config: &FieldMappingConfig,
    nx: usize,
    ny: usize,
    nz: usize,
    vsx: f64,
    vsy: f64,
    vsz: f64,
) -> Vec<f64>

One echo’s phase, unwrapped. Laplacian: as on the multi-echo path, the phase is zeroed outside the mask first (a global Poisson solve otherwise carries the noise there into the brain; not with laplacian_unmasked).