BLOCK_SIZE = 16

def block_hashes(token_ids, salt=None):
    """Chain-hash a token sequence into per-block keys."""

    hashes, parent = [], hash(salt)

    # Only complete blocks are hashed. A partial tail block is skipped.
    for start in range(0, len(token_ids) - BLOCK_SIZE + 1, BLOCK_SIZE):
        block = tuple(token_ids[start : start + BLOCK_SIZE])
        parent = hash((parent, block))
        hashes.append(parent)

    return hashes