perf(snake): cache survival rollout state

- Cache occupancy bitboards for repeated multiplayer rollout positions.
- Memoize position evaluations to avoid duplicate flood-fill calculations.
- Reuse shared values while ranking simultaneous enemy responses.
- Include evaluation hits in Prism rollout telemetry.
- Document the optimization and bump Prism to version 1.4.0.

README.md

@@ -82,7 +82,7 @@ accelerating hot spatial operations with a Python-integer bitboard engine. It
 also shares duel transpositions across candidate moves, uses principal-variation
 ordering, aspiration windows, path-aware food races, and a deeper tactical
 horizon, and runs a compact adversarial multiplayer rollout with simultaneous
-enemy responses. Its filename, class, and registry
+enemy responses and cached occupancy/evaluation states. Its filename, class, and registry
 key include the model name, while its public Battlesnake API name remains
 `PrismBattleSnake`.
 

snakes/__init__.py

@@ -10,7 +10,7 @@ SNAKE_REGISTRATIONS = {
   "TemplateSnake": SnakeRegistration("snakes.core.template", "1.0.0"),
   "ApexBattleSnake": SnakeRegistration("snakes.strategies.apex", "1.0.0"),
   "PrismBattleSnake_GPT_5_6_Sol": SnakeRegistration(
-    "snakes.strategies.prism", "1.3.0"
+    "snakes.strategies.prism", "1.4.0"
   ),
   "DummSnake": SnakeRegistration("snakes.legacy.DummSnake", "1.0.0"),
   "LogicSnake": SnakeRegistration("snakes.legacy.LogicSnake", "1.1.0"),

snakes/engine/survival_search.py

@@ -10,6 +10,7 @@ from snakes.engine.bitboard import BitBoard
 Body = tuple[int, ...]
 EnemyBodies = tuple[Body, ...]
 StateKey = tuple[Body, EnemyBodies, int, int]
+EvaluationKey = tuple[Body, EnemyBodies]
 
 class CompactSurvivalSearch:
   """Small paranoid beam search with simultaneous enemy responses.
@@ -39,9 +40,12 @@ class CompactSurvivalSearch:
     self.enemy_branch = max(1, enemy_branch)
     self.response_cap = max(1, response_cap)
     self.cache: dict[StateKey, float] = {}
+    self.evaluation_cache: dict[EvaluationKey, float] = {}
+    self.occupied_cache: dict[EvaluationKey, int] = {}
     self.body_bits_cache: dict[Body, int] = {}
     self.nodes = 0
     self.cache_hits = 0
+    self.evaluation_cache_hits = 0
     self.completed_depth = 0
     self.deadline_exits = 0
 
@@ -102,9 +106,8 @@ class CompactSurvivalSearch:
       return cached
 
     occupied = self._occupied(mine, enemies)
-    targets = list(self._iter_bits(self.board.neighbors_of(mine[0])))
     ranked: list[tuple[float, int]] = []
-    for target in targets:
+    for target in self._iter_bits(self.board.neighbors_of(mine[0])):
       # Collision legality is finalized simultaneously because eating controls
       # whether tails vacate.
       ate = bool((1 << target) & food_bits)
@@ -152,6 +155,8 @@ class CompactSurvivalSearch:
       return []
     choices: list[list[int]] = []
     my_length_after = len(mine) + int(bool((1 << my_target) & food_bits))
+    occupied = self._occupied(mine, enemies)
+    mx, my = self.board.coord(my_target)
     for enemy in enemies:
       ranked: list[tuple[float, int]] = []
       for target in self._iter_bits(self.board.neighbors_of(enemy[0])):
@@ -161,9 +166,8 @@ class CompactSurvivalSearch:
         if target == my_target:
           score += 1000.0 if enemy_length_after >= my_length_after else -1000.0
         tx, ty = self.board.coord(target)
-        mx, my = self.board.coord(my_target)
         score -= abs(tx - mx) + abs(ty - my)
-        score += self.board.open_neighbor_count(target, self._occupied(mine, enemies)) * 3.0
+        score += self.board.open_neighbor_count(target, occupied) * 3.0
         score += 20.0 if ate else 0.0
         ranked.append((score, target))
       ranked.sort(reverse=True)
@@ -225,6 +229,12 @@ class CompactSurvivalSearch:
     return next_mine, tuple(surviving), food_bits & ~eaten
 
   def _evaluate(self, mine: Body, enemies: EnemyBodies) -> float:
+    key = (mine, enemies)
+    cached = self.evaluation_cache.get(key)
+    if cached is not None:
+      self.evaluation_cache_hits += 1
+      return cached
+
     blocked = self._occupied(mine, enemies) & ~(1 << mine[0])
     space = self.board.flood_count(mine[0], blocked)
     liberties = self.board.open_neighbor_count(mine[0], blocked)
@@ -238,12 +248,21 @@ class CompactSurvivalSearch:
       enemy_pressure += max(0, 3 - enemy_liberties) * 18.0
       if len(mine) > len(enemy):
         enemy_pressure += max(0, 8 - enemy_space) * 8.0
-    return space * 1.9 + liberties * 32.0 + enemy_pressure - len(enemies) * 4.0
+    value = space * 1.9 + liberties * 32.0 + enemy_pressure - len(enemies) * 4.0
+    if len(self.evaluation_cache) < 32_768:
+      self.evaluation_cache[key] = value
+    return value
 
   def _occupied(self, mine: Body, enemies: EnemyBodies) -> int:
+    key = (mine, enemies)
+    cached = self.occupied_cache.get(key)
+    if cached is not None:
+      return cached
     occupied = self._body_bits(mine)
     for enemy in enemies:
       occupied |= self._body_bits(enemy)
+    if len(self.occupied_cache) < 32_768:
+      self.occupied_cache[key] = occupied
     return occupied
 
   def _body_bits(self, body: Body) -> int:

snakes/strategies/prism.py

@@ -1,4 +1,4 @@
-"""PrismBattleSnake_GPT_5_6_Sol v1.3.0
+"""PrismBattleSnake_GPT_5_6_Sol v1.4.0
 
 Built on ApexBattleSnake v1.0.0.  All strategic logic is inherited.
 Performance improvement: all spatial primitives (flood fill, territory,
@@ -30,6 +30,7 @@ Key speedups:
   S16: Compact adversarial multiplayer rollout advances plausible enemy replies.
   S17: Rollout memoization and adaptive depth spend time on ambiguous positions.
   S18: Prism uses a deeper tactical horizon while retaining Apex's timeout reserve.
+  S19: Rollout occupancy and evaluation caches avoid repeated flood-fill work.
 """
 
 from __future__ import annotations
@@ -53,7 +54,7 @@ class PrismBattleSnake_GPT_5_6_Sol(
   BitboardSpatialMixin,
   ApexBattleSnake,
 ):
-  VERSION = "1.3.0"
+  VERSION = "1.4.0"
 
   def __init__(self) -> None:
     super().__init__()
@@ -162,6 +163,7 @@ class PrismBattleSnake_GPT_5_6_Sol(
         thinking["prism_rollout_nodes"] = self._survival_search_context.nodes
         thinking["prism_rollout_cache_hits"] = (
           self._survival_search_context.cache_hits
+          + self._survival_search_context.evaluation_cache_hits
         )
         thinking["prism_rollout_deadline_exits"] = (
           self._survival_search_context.deadline_exits

tests/snakes/test_PrismBattleSnake_GPT_5_6_Sol.py

@@ -52,8 +52,8 @@ class TestPrismBattleSnake_GPT_5_6_Sol(unittest.TestCase):
     snake = PrismBattleSnake_GPT_5_6_Sol()
 
     self.assertEqual(snake.name, "PrismBattleSnake")
-    self.assertEqual(snake.version, "1.3.0")
+    self.assertEqual(snake.version, "1.4.0")
-    self.assertEqual(get_snake_version("PrismBattleSnake_GPT_5_6_Sol"), "1.3.0")
+    self.assertEqual(get_snake_version("PrismBattleSnake_GPT_5_6_Sol"), "1.4.0")
     self.assertGreaterEqual(snake._planning_depth, 4)
     self.assertIsInstance(SnakeBuilder.build("PrismBattleSnake_GPT_5_6_Sol"), PrismBattleSnake_GPT_5_6_Sol)
 
@@ -221,6 +221,7 @@ class TestPrismBattleSnake_GPT_5_6_Sol(unittest.TestCase):
     search.search_selected(mine, enemies, (2, 1), depth=3)
 
     self.assertGreater(search.cache_hits, hits_before)
+    self.assertGreater(search.evaluation_cache_hits, 0)
     self.assertGreaterEqual(search.completed_depth, 3)
 
   def test_bitboard_duel_search_reuses_transpositions(self):