exp: 轮次45——tie(等长安全前缀按沿路最小间隙定夺)判掉

两臂 n=256 同 seed 背靠背(配方=轮次42 K8+cert_batch=1+inc_cap=1)：到达 0.5234→0.5039
(-1.95pp，逐题配对丢6赢1净-5，McNemar 精确 p=0.125 与零不可分)，时限内 +1.17pp、
刹停 -9%、行程比 -0.076、执行碰撞仍为 0(判据未放松)。丢的 6 题 5 题在 A 类(开阔区)
=买余量卖进度的签名。

仪表与离线数交叉验证：改选率 5.58% 对上轮次44 独立测得的"执行点间隙落在 0.2–0.5mm 占
5.6%"，并列率 79.0% 对上"满前缀 79.4%" ⇒ 分辨率上界被宽相位截顶 gcap=max(0.5,margin+0.5)
锁死，5.6% 是这个家族在 cap=0.5 下的天花板，不是实现没调好。

结构性发现：#24 作用在错的人群——tie 只在 maxlen>0 触发，而失败主人群是全拒(maxlen=0，
未到达题 22% 的规划)；全拒那条已由 backoff(轮次43)判掉。前置条件记为 #28(gcap 与
gap_margin 解耦)。

实现账：新增 tie 与触发计数器(生产端 per 数组+dump 键、消费端汇总 tie_* 同批改完，
tie=0 时 22/22 老键逐位复现)；修掉 tie 分支局部名 nmax 顶掉主循环总步数的遮蔽 bug，
守卫单测做过变异检查；计数器正对照可手算(tie_opp=tie_changed=n_plans)。47 项测试绿。

docs/experiment_round45_tie0.json

@@ -0,0 +1,108 @@
+{
+  "config": {
+    "ckpt": "ml/runs/base_dag2_dag1/best.pt",
+    "samples": "ml/data/samples",
+    "tasks": null,
+    "split": "val",
+    "n": 256,
+    "K": 8,
+    "commit": 2,
+    "fb": 2.2,
+    "ki": 0.0,
+    "fb_scale": 0.0,
+    "fb_near": 0.2,
+    "fb_fallback": 0.0,
+    "kdecay": 0.9,
+    "kimax": 0.5,
+    "fb_every": 1,
+    "safety_try": 0,
+    "sel_w": 0.1,
+    "dls_safety": 1,
+    "fb_clear": 0.0,
+    "fb_cmin": 0.3,
+    "sub_refresh": 0,
+    "fb_block_gain": 0.5,
+    "dump": "ml/runs/round45_tie0_rows.json",
+    "out": "docs/experiment_round45_tie0.json",
+    "trace": null,
+    "select": "endpoint",
+    "replan": "empty",
+    "safety": 1,
+    "partial": 1,
+    "inc_cap": 1,
+    "gap_margin": 0.0,
+    "cert_batch": 1,
+    "steps": 1,
+    "z_scale": 1.0,
+    "len_w": 0.0,
+    "tie": 0,
+    "backoff": 0,
+    "max_sec": null,
+    "seed": 0,
+    "dls": "analytic",
+    "device": "cuda"
+  },
+  "batch_size": 256,
+  "batch_seed_rule": "same seed per batch",
+  "checkpoint_sha256": "f7f686fd8ee92fb6948fbcc4ee954636065ad87bb54f661c4f8f575bc16c2ce1",
+  "tasks_sha256": "249bd93457825cda98c59e64d9a096d3473c69aeb3553de1dea6d9e56be71772",
+  "kin_fp": "2ebcbf17",
+  "act_scale": 1.0,
+  "metrics": {
+    "n": 256,
+    "n_ref": 256,
+    "success": 0.5234375,
+    "collision_free_success": 0.5234375,
+    "time_ok_1p3": 0.265625,
+    "collision_rate": 0.0,
+    "collision_steps_mean": 0.0,
+    "travel_ratio_median": 2.615795850753784,
+    "time_mean_s": 2.486567258834839,
+    "brakes_mean": 19.5546875,
+    "start_fail": 0.0,
+    "goal_ratio_2s": 0.27920001745224,
+    "err_fail_med": 204.71360778808594,
+    "err_success_med": 0.21751396358013153,
+    "dls_share": 0.61328125,
+    "time_budget": "teacher×2(≥3 s)",
+    "speed_ratio_p50": 1.0000016689300537,
+    "speed_ratio_p95": 1.0000101327896118,
+    "speed_ratio_max": 1.0000101327896118,
+    "over_vmax_rate": 0.0,
+    "accel_ratio_p95": 1.0000016689300537,
+    "accel_ratio_max": 1.0000101327896118,
+    "reverse_p50": 0.24741201102733612,
+    "reverse_mean": 0.25991496443748474,
+    "reverse_moving_p50": 0.32581019401550293,
+    "moving_share_p50": 0.9587156176567078,
+    "brake_rate_mean": 0.10028044879436493,
+    "brake_rate_p50": 0.0051282052882015705,
+    "brake_rate_p90": 0.3153846263885498,
+    "stuck_share": 0.234375,
+    "n_plans_mean": 195.0,
+    "success_reachable": 0.5514403581619263,
+    "by_cat": {
+      "A": [
+        128,
+        96
+      ],
+      "B": [
+        74,
+        20
+      ],
+      "C": [
+        32,
+        11
+      ],
+      "D": [
+        13,
+        0
+      ],
+      "Dr": [
+        9,
+        7
+      ]
+    }
+  },
+  "simulation_wall_s": 317.56223549999413
+}