Function mtp_attn_meta_dev 

pub fn mtp_attn_meta_dev(
    base: DevicePtr,
    max_blocks_per_seq: u32,
) -> AttnMetadataDev

2026-09-25: Pack one MTP attention-metadata slab, or return an error when it would not fit region_bytes.

Layout: position u32 at 0, global_slot i64 at 8, seq_len i32 at 16, then the block table from MTP_META_HEADER_BYTES, four little-endian bytes per entry. region_bytes is what the caller owns at the destination: the per-sequence stride for the batched propose, or scratch_bytes - MTP_META_OFFSET for the single-sequence callers. 2026-09-29: The attention metadata pack_mtp_attn_meta lays out at base (position @0, slot @8, sequence length @16, block table @MTP_META_HEADER_BYTES), for one row.