Drop variant B, adopt Black-belt Exam defender, add one-sidedness metrics

- Remove variant B (Brown cap, +1 for higher beating lower) from rules,
  engine, bots and simulator; a higher belt beating a lower one gains 0.
- Final Exam: the defender fights as a Black belt (RULES.md v0.7). Ties to
  the defender and best-of-3 stay as simulator switches (`--exam`).
- Report stripe income per source as gains and losses.
- Add ten one-sidedness measures sampled at turn ends (lead gap, winner
  margin and lead share, halfway leader, last lead change, contention,
  rank swaps, leader Kumite losses, Exam challengers, winner pace).
- Plan: decisions D28-D33 and the detailed Phase 6.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tests/test_sim.py

@@ -2,6 +2,7 @@ from pathlib import Path
 
 import pytest
 
+from dojo.rules import RulesConfig
 from dojo.sim import BoardFiles, Scenario, matrix, run
 
 BOARD = Path(__file__).parent.parent / "board"
@@ -10,16 +11,35 @@ LINEUP = ("balanced", "random")
 
 
 def test_matrix_crosses_every_axis() -> None:
-    scenarios = matrix(["A", "B"], [3, 4], [2, 1], [0], [LINEUP])
+    scenarios = matrix(["none", "acd"], [3, 4], [2, 1], [0], [LINEUP])
 
     assert len(scenarios) == 8
-    assert scenarios[0].name == "A p3 kiai+2 start0 balanced,random"
-    assert scenarios[-1].config.kiai_bonus == 1
-    assert scenarios[-1].config.brown_requires_kumite
+    assert scenarios[0].name == "exam:none p3 kiai+2 start0 balanced,random"
+    assert scenarios[0].config == RulesConfig(exam_defender_black=False)
+    assert scenarios[-1].config == RulesConfig(
+        exam_ties_to_defender=True, exam_defender_black=True, exam_rounds=3, kiai_bonus=1
+    )
+
+
+@pytest.mark.parametrize(
+    ("exam", "ties", "black", "rounds"),
+    [
+        ("none", False, False, 1),
+        ("a", True, False, 1),
+        ("c", False, True, 1),
+        ("d", False, False, 3),
+        ("cd", False, True, 3),
+    ],
+)
+def test_exam_options_map_to_rules(exam: str, ties: bool, black: bool, rounds: int) -> None:
+    config = Scenario(exam, 4, 2, 0, LINEUP).config
+
+    assert (config.exam_ties_to_defender, config.exam_defender_black) == (ties, black)
+    assert config.exam_rounds == rounds
 
 
 def test_lineup_fills_the_seats_and_rotates_each_game() -> None:
-    scenario = Scenario("A", 3, 2, 0, LINEUP)
+    scenario = Scenario("none", 3, 2, 0, LINEUP)
 
     assert scenario.seating(0) == ("balanced", "random", "balanced")
     assert scenario.seating(1) == ("random", "balanced", "balanced")
@@ -27,23 +47,25 @@ def test_lineup_fills_the_seats_and_rotates_each_game() -> None:
 
 
 @pytest.mark.parametrize(
-    ("variant", "players", "lineup", "message"),
+    ("exam", "players", "lineup", "message"),
     [
-        ("C", 4, LINEUP, "unknown variant"),
-        ("A", 4, ("balanced", "cheater"), "unknown bots"),
-        ("A", 4, (), "unknown bots"),
-        ("A", 9, LINEUP, "supported range"),
+        ("b", 4, LINEUP, "unknown Exam options"),
+        ("aa", 4, LINEUP, "unknown Exam options"),
+        ("", 4, LINEUP, "unknown Exam options"),
+        ("none", 4, ("balanced", "cheater"), "unknown bots"),
+        ("none", 4, (), "unknown bots"),
+        ("none", 9, LINEUP, "supported range"),
     ],
 )
 def test_invalid_scenarios_are_rejected(
-    variant: str, players: int, lineup: tuple[str, ...], message: str
+    exam: str, players: int, lineup: tuple[str, ...], message: str
 ) -> None:
     with pytest.raises(ValueError, match=message):
-        Scenario(variant, players, 2, 0, lineup)
+        Scenario(exam, players, 2, 0, lineup)
 
 
 def test_runs_are_reproducible_and_independent_of_worker_count() -> None:
-    scenarios = matrix(["A", "B"], [3], [2], [0], [LINEUP])
+    scenarios = matrix(["none", "acd"], [3], [2], [0], [LINEUP])
 
     serial = run(FILES, scenarios, games=2, seed=5, jobs=1)
     parallel = run(FILES, scenarios, games=2, seed=5, jobs=2)