feat: add bucket score global router

tests/smoke.rs

@@ -385,3 +385,69 @@ fn bucketed_configs_are_rejected_by_legacy_fixed_placement_paths() {
     .expect_err("bucketed replay should fail");
     assert!(err.to_string().contains("cluster.buckets"));
 }
+
+#[test]
+fn bucket_score_can_deviate_from_strict_length_bucket() {
+    let tmp = std::env::temp_dir().join("kvcache_sim_bucket_score");
+    let _ = std::fs::remove_dir_all(&tmp);
+    std::fs::create_dir_all(&tmp).unwrap();
+    let trace_path = tmp.join("trace.jsonl");
+
+    let mut f = std::fs::File::create(&trace_path).unwrap();
+    for req_id in 0..3 {
+        writeln!(
+            f,
+            "{}",
+            serde_json::json!({
+                "chat_id": req_id,
+                "parent_chat_id": -1,
+                "timestamp": 0.0,
+                "input_length": 24,
+                "output_length": 16,
+                "type": "text",
+                "turn": 0,
+                "hash_ids": [100 + req_id, 200 + req_id]
+            })
+        )
+        .unwrap();
+    }
+
+    let mut strict_cfg = bucketed_config(
+        trace_path.to_str().unwrap(),
+        tmp.to_str().unwrap(),
+        RouterMode::LeastLoaded,
+    );
+    strict_cfg.cluster.buckets = vec![
+        BucketConfig {
+            name: "short".into(),
+            input_length_min: 0,
+            input_length_max: 32,
+            num_instances: 1,
+        },
+        BucketConfig {
+            name: "long".into(),
+            input_length_min: 33,
+            input_length_max: 96,
+            num_instances: 1,
+        },
+    ];
+    strict_cfg.cluster.global_router.mode = GlobalRouterMode::StrictInputLength;
+
+    let mut score_cfg = strict_cfg.clone();
+    score_cfg.cluster.global_router.mode = GlobalRouterMode::BucketScore;
+    score_cfg.cluster.global_router.length_penalty_weight = 1.0;
+    score_cfg.cluster.global_router.load_weight = 10.0;
+    score_cfg.cluster.global_router.cache_weight = 0.0;
+
+    let _ = driver::run(&strict_cfg, Some("strict_score_cmp")).expect("strict run");
+    let _ = driver::run(&score_cfg, Some("bucket_score_cmp")).expect("bucket score run");
+
+    let strict_log =
+        std::fs::read_to_string(tmp.join("strict_score_cmp/routing_log.jsonl")).unwrap();
+    let score_log =
+        std::fs::read_to_string(tmp.join("bucket_score_cmp/routing_log.jsonl")).unwrap();
+
+    assert!(strict_log.contains("\"chosen_bucket\":0"));
+    assert!(score_log.contains("\"global_mode\":\"bucket_score\""));
+    assert!(score_log.contains("\"chosen_bucket\":1"));
+}