Function build_seq_slot_host 

pub fn build_seq_slot_host(
    adapter_slots: &[i32],
    padded_n: usize,
    active: i32,
) -> Vec<i32>

2026-09-25: The host seq_slot[padded_n] buffer the bgmv reads, one entry per row: row i < n: adapter_slots[i] if >= 0, else active (a negative slot means the active adapter); row i >= n (padding): -1, which lora_bgmv.cu treats as no delta.