feat: add gameplay stats and restore Zenith rollout depth

- Add read-only gameplay statistics with filters and opponent comparisons.
- Report move-trace latency percentiles and external timeout counts.
- Pair engine latency with the preceding turn to separate timing stages.
- Adjust Zenith rollout deepening for its larger timeout reserve.
- Bump Zenith to 1.2.0 and document the fix and snake-stats command.
- Cover statistics, trace aggregation, rollout depth, and verdict budgets.

tests/snakes/test_ZenithBattleSnake_ClaudeOpus5_5.py

@@ -1,5 +1,8 @@
 import unittest
 from time import perf_counter
+from unittest import mock
+
+from snakes.engine.survival_search import CompactSurvivalSearch
 
 from snakes import SnakeBuilder, get_snake_version
 from snakes.strategies.prism import PrismBattleSnake_GPT_5_6_Sol
@@ -14,8 +17,8 @@ class TestZenithRegistration(unittest.TestCase):
     snake = ZenithBattleSnake_ClaudeOpus5_5()
 
     self.assertEqual(snake.name, "ZenithBattleSnake")
-    self.assertEqual(snake.version, "1.1.0")
-    self.assertEqual(get_snake_version("ZenithBattleSnake_ClaudeOpus5_5"), "1.1.0")
+    self.assertEqual(snake.version, "1.2.0")
+    self.assertEqual(get_snake_version("ZenithBattleSnake_ClaudeOpus5_5"), "1.2.0")
     self.assertIsInstance(snake, PrismBattleSnake_GPT_5_6_Sol)
     self.assertIsInstance(
       SnakeBuilder.build("ZenithBattleSnake_ClaudeOpus5_5"),
@@ -80,5 +83,56 @@ class TestZenithVerdicts(unittest.TestCase):
 
     self.assertEqual(verdicts, {})
 
+def _rollout_depth(snake, remaining_ms: float) -> int:
+  """Depth requested by a 3-snake rollout with ``remaining_ms`` left."""
+  snake._get_bb(11, 11)
+  snake._survival_search_context = None
+  enemies = [
+    {"body": [{"x": 8, "y": 8}, {"x": 8, "y": 9}, {"x": 8, "y": 10}]},
+    {"body": [{"x": 2, "y": 8}, {"x": 2, "y": 9}, {"x": 2, "y": 10}]},
+  ]
+  with mock.patch.object(CompactSurvivalSearch, "search_selected", return_value=0.0) as search:
+    snake._future_rollout_bonus(
+      move="up", safe_moves={"up": {"x": 5, "y": 3}},
+      my_body=[{"x": 5, "y": 2}, {"x": 5, "y": 1}, {"x": 5, "y": 0}],
+      other_snakes=enemies, food_set=set(), is_constrictor=False,
+      width=11, height=11, enemy_can_grow={},
+      deadline=perf_counter() + remaining_ms / 1000,
+    )
+  return search.call_args.kwargs["depth"]
+
+class TestZenithRolloutDepth(unittest.TestCase):
+
+  def test_gate_is_lowered_by_the_extra_timeout_reserve(self):
+    zenith = ZenithBattleSnake_ClaudeOpus5_5()
+    prism = PrismBattleSnake_GPT_5_6_Sol()
+    extra = zenith._get_timeout_buffer_ms() - prism._get_timeout_buffer_ms()
+
+    self.assertEqual(zenith._rollout_deepen_ms, prism._rollout_deepen_ms - extra)
+
+  def test_three_snake_rollout_deepens_after_same_elapsed_time_as_prism(self):
+    # Zenith's budget is 50 ms shorter, so 220 ms left equals 270 ms for Prism.
+    self.assertEqual(_rollout_depth(ZenithBattleSnake_ClaudeOpus5_5(), 220), 3)
+    self.assertEqual(_rollout_depth(PrismBattleSnake_GPT_5_6_Sol(), 270), 3)
+    self.assertEqual(_rollout_depth(PrismBattleSnake_GPT_5_6_Sol(), 220), 2)
+
+  def test_low_budget_still_caps_rollout_depth(self):
+    self.assertEqual(_rollout_depth(ZenithBattleSnake_ClaudeOpus5_5(), 150), 2)
+
+class TestZenithVerdictBudget(unittest.TestCase):
+
+  def test_verdict_pass_skips_when_only_reserve_remains(self):
+    snake = ZenithBattleSnake_ClaudeOpus5_5()
+
+    verdicts = snake._duel_verdicts(
+      safe_moves={"up": {"x": 0, "y": 2}, "right": {"x": 1, "y": 1}},
+      my_body=[{"x": 0, "y": 1}], enemy={"body": [{"x": 4, "y": 4}]},
+      my_health=100, food_set=set(), hazard_set=set(), hazard_damage=15,
+      hazard_count={}, previous_hazard_set=set(), width=5, height=5,
+      deadline=perf_counter() + 0.020,
+    )
+
+    self.assertEqual(verdicts, {})
+
 if __name__ == "__main__":
   unittest.main()