revert(levels): ship round 2's set — contrast selection measurably made it easier

Round 3 tested one hypothesis from round 2's data: levels the agent rated 3
carried 59% more 反差 than the rest, so select for it. With both rounds now at
~100 runs, the answer is in and it is no. The back band went from 2.39 ± 0.10 to
2.19 ± 0.08, roughly two standard errors apart, and the levels averaging 2.5 or
better fell from 11 to 6. Contrast is real and it does correlate with being
rated harder; selecting on it does not produce harder levels.

The low retest reliability does not rescue the change either — r = 0.55 limits
ranking one level against another, not the mean of eighteen levels measured a
hundred times.

So round 2's levels are the ones handed over, rebuilt from its runs via
round-set --emitCampaign. select-50 cannot reproduce them: the pool it drew
from has been rebuilt since, so the same flags now return different levels. The
runs are the record.

Rule bot on the shipped set: 50/50 cleared, dead taps 0.00, blind rotations
0.12, worst blind streak 1. 198 tests pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

bench/board.json

@@ -197,7 +197,7 @@
      "id": "T3.4",
      "title": "收敛判定（难度曲线单调、stuck 达标）",
      "status": "done",
-     "note": "收敛判定完成。机械面：空点 0、不可解态 0、连续空转≤1、终局朝向≥3、三轮全部通关。难度面：三档 2.00 / 2.05 / 2.17，单调但后档低于「刚刚好」的 3 分——上限由深关卡供给决定（见 T1.6），且这项评分复测 r=0.55，本身不足以再往下调。剩下的交人工审核"
+     "note": "收敛判定完成。机械面全部达标：空点 0、不可解态 0、连续空转≤1、终局朝向≥3、三轮全部通关。难度面 2.00/2.05/2.39 单调，后档仍低于「刚刚好」的 3 分，上限由深关卡供给决定（T1.6）。第三轮试图用反差再推一把，被数据否掉并回退"
     }
    ]
   },
@@ -209,7 +209,7 @@
      "id": "T4.1",
      "title": "50 关关卡集",
      "status": "done",
-     "note": "levels/campaign-50.json + src/levels-c50.js，已注册为可玩版本 c50，198 项测试全绿"
+     "note": "交付的是第二版（R2 跑的那一版），从其 run 反建，50 关旋转深度 {1:5,2:5,3:24,4:12,5:4}，家族 weave18/switchback12/v05 10/orbits8/spiral2。198 项测试全绿，规则机器人复核 50/50 通关、空点 0、最长连续盲转 1"
     },
     {
      "id": "T4.2",
@@ -271,6 +271,10 @@
   {
    "at": "一个差点报错的对照",
    "text": "levels/campaign-50-r2.json 本应是 R2 玩的那一版，实际只含 28 个 R2 盘面、46 个 R3 盘面——select-50 原地覆盖同一路径，中间跑过的选关实验把它换掉了。改为从 run 反建（run 自带完整盘面与序号），并删掉该快照"
+  },
+  {
+   "at": "第三轮回退",
+   "text": "按反差选关后，后档评分 2.39±0.10 → 2.19±0.08（约两个标准误），平均分≥2.5 的关从 11 掉到 6。反差确实和「被评得更难」相关，但按它选关造不出更难的关——相关不等于可操纵。已回退到第二版"
   }
  ]
 }