Function permutation_search 

pub fn permutation_search(
    stego_bytes: &[u8],
    mask: &BinMask,
    config: &SearchConfig,
    seed: u64,
) -> Permutation

Find the lowest-detectability permutation within config.max_iterations.

seed must be derived from the crypto key — never use a fresh random seed (the receiver needs to reconstruct the same permutation for extraction).

Uses a random-restart hill-climb: each iteration proposes a swap of two positions and accepts it if it lowers the chi-square score.