Function gdn_wy4_fold 

pub fn gdn_wy4_fold(
    gpu: &dyn GpuBackend,
    kernel: KernelHandle,
    h_table: DevicePtr,
    stash: DevicePtr,
    na_tab: DevicePtr,
    hi_tables: DevicePtr,
    slab_entries: u32,
    engaged_flag: DevicePtr,
    k_rows: u32,
    batch_size: u32,
    num_k_heads: u32,
    num_v_heads: u32,
    k_dim: u32,
    v_dim: u32,
    stash_seq_floats: u32,
    stream: u64,
) -> Result<()>

2026-09-25: Post-verdict fold (gated_delta_rule_wy4_fold). When the engaged word is set, it applies stashed rows 0..na_tab[b] to H, reading and writing H once. Otherwise the parent kernel ran, and a partial accept (na < k_rows) restores Hi(na - 1) from hi_tables.