Function extract_view_into 

fn extract_view_into<'v, 'p, K, V, T, R>(
    view: BorrowedOf<'v, ((K, V), T, R)>,
    probes: BorrowedOf<'p, K>,
    probe_index: &mut usize,
    staging: &mut <((K, V), T, R) as Columnar>::Container,
)
where
    K: Columnar,
    V: Columnar,
    T: Columnar,
    R: Columnar,
    for<'b> Ref<'b, K>: Copy + Ord,

Append every update in view whose key matches a probe at or after *probe_index into staging, per the UnloadChunk consume-index protocol: probes strictly below the view’s last key are consumed, a probe equal to it is extracted but left for the next chunk.