修复BQ自动路由劫持暴力搜索基线的问题

- 新增 force_brute_force 字段：显式禁用自动BQ路由，确保基准测试对照组可靠
- 修复 pipeline.rs 路由逻辑：use_bq 增加 !force_brute_force 前置判断
- 修复所有benchmark：brute_cfg 统一加 force_brute_force: true
  (bench_medium / bq_vs_brute / bench_500k)
- 根因：原 total_nodes > 20_000 会无视 enable_bq_coarse_search: false，
  导致所有 >20K 节点的 BruteForce vs BQ 对比数据完全失真

Author: YoKONCy

benches/bench_500k.rs

@@ -337,6 +337,7 @@ fn main() {
     let brute_cfg = SearchConfig {
         top_k,
         enable_bq_coarse_search: false,
+        force_brute_force: true,
         ..Default::default()
     };
     let bq_cfg = SearchConfig {

benches/bench_medium.rs

@@ -227,6 +227,7 @@ fn main() {
     let brute_cfg = SearchConfig {
         top_k: TOP_K,
         enable_bq_coarse_search: false,
+        force_brute_force: true,
         ..Default::default()
     };
     let t_brute = Instant::now();

benches/bq_vs_brute.rs

@@ -193,6 +193,7 @@ fn run_precision_report(n: usize, dim: usize, top_k: usize, num_queries: usize)
     let brute_config = SearchConfig {
         top_k,
         enable_bq_coarse_search: false,
+        force_brute_force: true,
         ..Default::default()
     };
     eprintln!(
@@ -360,6 +361,7 @@ fn bench_brute_vs_bq(c: &mut Criterion) {
     let brute_cfg = SearchConfig {
         top_k: 10,
         enable_bq_coarse_search: false,
+        force_brute_force: true,
         ..Default::default()
     };
     let mut group = c.benchmark_group("BQ_Rocket_vs_Brute_200k_dim1536");

src/database/config.rs

@@ -65,6 +65,9 @@ pub struct SearchConfig {
     pub enable_bq_coarse_search: bool,
     /// BQ 粗筛候选集占总数据量的比例
     pub bq_candidate_ratio: f32,
+    /// 强制使用暴力搜索，禁用自动 BQ 路由（用于基准测试和需要精确结果的场景）
+    /// 当为 true 时，即使 node_count > 20,000 也不会自动切换到 BQ 管线
+    pub force_brute_force: bool,
 
     // --- 混合倒排与文本检索 (Hybrid Search) ---
     /// 启用文本混合查询时，决定文本匹配的分数提权倍率 (Boost)
@@ -98,6 +101,7 @@ impl Default for SearchConfig {
             lateral_inhibition_threshold: 0,
             enable_bq_coarse_search: false,
             bq_candidate_ratio: 0.05,
+            force_brute_force: false,
             text_boost: 1.5,
             enable_text_hybrid_search: false,
             bm25_k1: 1.2,

src/database/pipeline.rs

@@ -276,12 +276,14 @@ fn recall_vector<T: VectorType>(
 
     // ═══════════════════════════════════════════════════════
     // 动态引擎路由：基于数据规模的自适应多级管线
-    // 1. N <= 20,000 => 暴力全扫 (AVX2 极限)
-    // 2. 20,000 < N <= 100,000 => BQ 双级管线
-    // 3. 100,000 < N => BQ 三级火箭
+    // 1. force_brute_force == true => 暴力全扫（无视数据量，用于基准测试）
+    // 2. N <= 20,000 => 暴力全扫 (AVX2 极限)
+    // 3. 20,000 < N <= 100,000 => BQ 双级管线
+    // 4. 100,000 < N => BQ 三级火箭
     // ═══════════════════════════════════════════════════════
     let total_nodes = mt.node_count();
-    let use_bq = config.enable_bq_coarse_search || total_nodes > 20_000;
+    let use_bq = !config.force_brute_force
+        && (config.enable_bq_coarse_search || total_nodes > 20_000);
     let use_int8_rocket = total_nodes > 100_000;
 
     let vector_hits: Vec<SearchHit> = if use_bq {