Function repack_b_to_padded 

pub fn repack_b_to_padded(
    src_bf16: &[u8],
    out_dim: usize,
    r: usize,
    max_rank: usize,
) -> Vec<u8> 

Row-repack a BF16 B tensor [out_dim, r] into the pool’s padded [out_dim, max_rank] layout: per row, r BF16 elements copied from stride r to stride max_rank; pad columns stay zero. Byte-identical to the disk pack’s B repack. Returns out_dim * max_rank * 2 bytes.