feat(lotto): select_winner_by_lift + ε-게이팅

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lotto/tests/test_weight_evolver.py

@@ -120,3 +120,18 @@ def test_decide_base_update_cold_start_returns_default():
     )
     assert new_base == winner_W
     assert reason == "winner_4plus"
+
+
+def test_select_winner_by_lift_gating():
+    # engine_w 3개 + random_null 기준. lift = engine 등수점수 − random 등수점수
+    per_w = [
+        {"trial_id": 1, "day_of_week": 0, "weight": [0.2]*5, "prize_score": 5.0},
+        {"trial_id": 2, "day_of_week": 1, "weight": [0.3,0.2,0.2,0.2,0.1], "prize_score": 9.0},
+        {"trial_id": 3, "day_of_week": 2, "weight": [0.1,0.3,0.2,0.2,0.2], "prize_score": 4.0},
+    ]
+    # random baseline이 8.0이면 lift는 +1, +1, -4 → 노이즈 ε=2 안에서 게이팅
+    winner = we.select_winner_by_lift(per_w, random_score=8.0, epsilon=2.0)
+    assert winner["gated"] is True       # 최대 lift(+1) < ε(2) → 게이팅
+    winner2 = we.select_winner_by_lift(per_w, random_score=3.0, epsilon=2.0)
+    assert winner2["gated"] is False
+    assert winner2["trial_id"] == 2      # prize 9 → lift +6