Function graph_kv_read_rows 

pub fn graph_kv_read_rows(
    _kv_id: u64,
    _reqs: &[(usize, usize, usize)],
    _nkv: usize,
    _hd: usize,
) -> Option<Vec<(Vec<f32>, Vec<f32>)>>

Copy rows back from the wgpu token graph’s K/V mirrors in one submit: for each (layer, from, to) the K and V rows [from..to), position-major ([(to − from) × nkv × hd] each).