Function columnar_consolidate_exchange 

pub fn columnar_consolidate_exchange<D, T, R>(
    (d, _, _): &Ref<'_, (D, T, R)>,
) -> u64
where
    D: Columnar,
    for<'a> Ref<'a, D>: Hash,
    T: Columnar,
    R: Columnar,

Routes a (D, T, R) column for consolidation, by a fixed-seed AHash of its data column.

Worker assignment is hash % workers, so the low bits alone decide the split and the Hashable default (FNV) the other exchange functions use diffuses them poorly. The seed is fixed, so routing is identical across builds and replicas.

Spelled as a function rather than a closure over the hasher state, because the argument is higher-ranked in its lifetime and closure inference cannot express that.