Function select_candidate_blocks 

pub fn select_candidate_blocks(
    logits: &[f32],
    queries: usize,
    width: usize,
    compress_lens: &[usize],
    topk_blocks: usize,
    block: usize,
) -> Vec<bool>

2026-09-25: Candidate blocks: per query, score each block-wide block of logits[queries][width] (unreachable positions at -inf) by its max, pin the block holding position compress_lens[q] - 1, keep the top topk_blocks blocks that are not all -inf. Returns the keep mask [queries][width].