feat(snake): modularize engine and add tournament tools

- Split active strategies, reusable engine code, core classes, and legacy snakes.
- Replace implicit snake imports with explicit module registrations.
- Extract Prism duel, spatial, and survival behavior into focused mixins.
- Improve duel scoring with food races, pressure, caches, and depth metrics.
- Add deterministic arena scenarios and paired seeded engine tournaments.
- Expand benchmark telemetry and bump Prism to version 1.3.0.
- Update documentation and tests for the new package layout and tooling.

README.md

@@ -48,7 +48,7 @@ battlesnake play -W 11 -H 11 --name 'Python Starter Project' --url http://localh
 Continue with the [Battlesnake Quickstart Guide](https://docs.battlesnake.com/quickstart) to customize and improve your Battlesnake's behavior.
 
 ## Included Competitive Snake
-This repo now includes `snakes/BestBattleSnake.py`, a stronger default snake that combines:
+This repo retains `snakes/legacy/BestBattleSnake.py`, a stronger historical snake that combines:
 - collision and head-to-head risk checks
 - flood-fill space evaluation to avoid traps
 - food routing that gets more aggressive as health drops
@@ -66,12 +66,23 @@ BATTLE_SNAKE_DUEL_STYLE=balanced python main.py
 
 Allowed values: `safe`, `balanced`, `aggressive`.
 
+## Snake package layout
+The snake code is split by responsibility:
+- `snakes/strategies/` — actively maintained Apex and Prism entry points
+- `snakes/engine/` — reusable bitboards, spatial mixins, duel search, and survival search
+- `snakes/core/` — shared base classes
+- `snakes/legacy/` — historical snakes retained for compatibility and benchmarks
+
+Snake selection still uses the existing registry names, so deployment values such
+as `SNAKE=PrismBattleSnake_GPT_5_6_Sol` remain unchanged.
+
 ## PrismBattleSnake_GPT_5_6_Sol
 `PrismBattleSnake_GPT_5_6_Sol` is a separate snake that keeps Apex's strategy while
 accelerating hot spatial operations with a Python-integer bitboard engine. It
 also shares duel transpositions across candidate moves, uses principal-variation
-ordering and aspiration windows, and runs a compact adversarial multiplayer
+ordering, aspiration windows, path-aware food races, and a deeper tactical
-rollout with simultaneous enemy responses. Its filename, class, and registry
+horizon, and runs a compact adversarial multiplayer rollout with simultaneous
+enemy responses. Its filename, class, and registry
 key include the model name, while its public Battlesnake API name remains
 `PrismBattleSnake`.
 
@@ -95,11 +106,24 @@ Run the deterministic CI-friendly arena benchmark without a gameplay database:
 just bench-snake-arena positions=100
 ```
 
-It reports latency, reached minimax depth, and move disagreements between Apex
+It rotates through duel, hazard, multiplayer, constrictor, and cramped-endgame
-and Prism. Add `output=data/arena-report.json` to save a machine-readable report.
+positions. It reports latency, completed duel/rollout depth, searched nodes,
+cache hits, deadline exits, and move disagreements between Apex and Prism. Use
+`--scenario hazard` (repeatable) when invoking the Python script to isolate a
+scenario. Add `output=data/arena-report.json` to save a machine-readable report.
 For representative strategy evaluation, provide recorded positions to
-`scripts/benchmark_snake_arena.py --database /path/to/gameplay.sqlite3`, then run
+`scripts/benchmark_snake_arena.py --database /path/to/gameplay.sqlite3`.
-paired seeded games with the local Battlesnake CLI to measure win rate.
+
+Run paired seeded games through the official local Battlesnake rules engine:
+```sh
+just bench-snake-tournament games=20 gametype=standard map=standard
+```
+
+Each seed is played twice with Apex and Prism swapping initial engine slots. The
+report includes wins, draws, win rates, and average game length. Save all
+per-game results with `output=data/tournament-report.json`. The tournament starts
+both snake servers with gameplay persistence disabled, adds the engine identity
+header required by the API, and shuts them down when finished.
 
 ## Compact gameplay database
 New gameplay turns use normalized storage: the turn row stores food, hazards,

justfile

@@ -70,6 +70,14 @@ bench-snake-arena positions="100" output="":
   if [ -n "{{output}}" ]; then args+=(--json-output "{{output}}"); fi
   PYTHONPATH="{{justfile_directory()}}" python "{{justfile_directory()}}/scripts/benchmark_snake_arena.py" "${args[@]}"
 
+bench-snake-tournament games="20" gametype="standard" map="standard" output="":
+  #!/usr/bin/env bash
+  set -euo pipefail
+
+  args=(--games "{{games}}" --gametype "{{gametype}}" --map "{{map}}")
+  if [ -n "{{output}}" ]; then args+=(--json-output "{{output}}"); fi
+  PYTHONPATH="{{justfile_directory()}}" python "{{justfile_directory()}}/scripts/run_seeded_snake_tournament.py" "${args[@]}"
+
 build-battlesnake-cli:
   #!/usr/bin/env bash
   set -euo pipefail

scripts/benchmark_snake_arena.py

@@ -17,34 +17,20 @@ from time import perf_counter
 sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
 
 from scripts.benchmark_snakes_from_db import load_states, percentile
+from scripts.snake_arena_scenarios import SCENARIOS, synthetic_states
 from server.GameBoard import GameBoard
 from snakes import SnakeBuilder
-from tests.bench_best_battle_snake import build_game_state
-
-def synthetic_states(count: int) -> list[tuple[dict, dict]]:
-  states: list[tuple[dict, dict]] = []
-  for index in range(count):
-    payload = build_game_state()
-    payload["game"]["id"] = f"arena-{index}"
-    payload["turn"] = 20 + index
-    # Rotate food deterministically to exercise routing without creating
-    # invalid bodies or relying on private/real network values.
-    payload["board"]["food"] = [
-      {"x": 1 + index % 3, "y": 9},
-      {"x": 9, "y": 1 + (index // 3) % 3},
-    ]
-    states.append((payload["board"], {
-      "game_id": payload["game"]["id"],
-      "source": "custom", "map": "standard",
-      "ruleset": payload["game"]["ruleset"], "turn": payload["turn"],
-      "you": payload["you"],
-    }))
-  return states
 
 def evaluate(name: str, states: list[tuple[dict, dict]]) -> tuple[list[str], dict]:
   moves: list[str] = []
   durations: list[float] = []
-  depths: list[int] = []
+  duel_depths: list[int] = []
+  rollout_depths: list[int] = []
+  duel_nodes = 0
+  rollout_nodes = 0
+  cache_hits = 0
+  deadline_exits = 0
+  scenario_durations: dict[str, list[float]] = {}
   for index, (board_data, metadata) in enumerate(states):
     snake = SnakeBuilder.build(name)
     game_id = f"arena-{name}-{index}-{metadata['game_id']}"
@@ -62,15 +48,32 @@ def evaluate(name: str, states: list[tuple[dict, dict]]) -> tuple[list[str], dic
     })
     started = perf_counter()
     moves.append(snake.choose_move(board))
-    durations.append((perf_counter() - started) * 1000.0)
+    duration = (perf_counter() - started) * 1000.0
+    durations.append(duration)
+    scenario = metadata.get("scenario", "recorded")
+    scenario_durations.setdefault(scenario, []).append(duration)
     history = snake.get_history() if hasattr(snake, "get_history") else []
     if history:
-      depths.append(int(history[-1].get("minimax_depth_reached", 0)))
+      thinking = history[-1]
+      duel_depths.append(int(thinking.get("prism_duel_depth", thinking.get("minimax_depth_reached", 0))))
+      rollout_depths.append(int(thinking.get("prism_rollout_depth", 0)))
+      duel_nodes += int(thinking.get("prism_duel_nodes", 0))
+      rollout_nodes += int(thinking.get("prism_rollout_nodes", 0))
+      cache_hits += int(thinking.get("prism_duel_cache_hits", 0))
+      cache_hits += int(thinking.get("prism_rollout_cache_hits", 0))
+      deadline_exits += int(thinking.get("prism_duel_deadline_exits", 0))
+      deadline_exits += int(thinking.get("prism_rollout_deadline_exits", 0))
   return moves, {
     "snake": name, "positions": len(states),
     "mean_ms": mean(durations), "median_ms": median(durations),
     "p95_ms": percentile(durations, 0.95), "max_ms": max(durations),
-    "mean_minimax_depth": mean(depths) if depths else 0.0,
+    "mean_duel_depth": mean(duel_depths) if duel_depths else 0.0,
+    "mean_rollout_depth": mean(rollout_depths) if rollout_depths else 0.0,
+    "duel_nodes": duel_nodes, "rollout_nodes": rollout_nodes,
+    "cache_hits": cache_hits, "deadline_exits": deadline_exits,
+    "scenario_mean_ms": {
+      scenario: mean(values) for scenario, values in scenario_durations.items()
+    },
   }
 
 def main() -> None:
@@ -79,12 +82,13 @@ def main() -> None:
   parser.add_argument("--database")
   parser.add_argument("--positions", type=int, default=100)
   parser.add_argument("--stride", type=int, default=997)
+  parser.add_argument("--scenario", action="append", choices=sorted(SCENARIOS))
   parser.add_argument("--json-output")
   args = parser.parse_args()
 
   states = (
     load_states(args.database, max(1, args.positions), max(1, args.stride))
-    if args.database else synthetic_states(max(1, args.positions))
+    if args.database else synthetic_states(max(1, args.positions), args.scenario)
   )
   if not states:
     raise SystemExit("No benchmark positions found")
@@ -99,7 +103,10 @@ def main() -> None:
     print(
       f"{name}: mean={report['mean_ms']:.3f} ms, "
       f"p95={report['p95_ms']:.3f} ms, max={report['max_ms']:.3f} ms, "
-      f"depth={report['mean_minimax_depth']:.2f}"
+      f"duel-depth={report['mean_duel_depth']:.2f}, "
+      f"rollout-depth={report['mean_rollout_depth']:.2f}, "
+      f"nodes={report['duel_nodes'] + report['rollout_nodes']}, "
+      f"cache-hits={report['cache_hits']}, deadline-exits={report['deadline_exits']}"
     )
   baseline = names[0]
   disagreements = {
@@ -109,7 +116,25 @@ def main() -> None:
   if disagreements:
     print(f"Move disagreements versus {baseline}: {disagreements}")
 
-  payload = {"reports": reports, "baseline": baseline, "disagreements": disagreements}
+  scenario_disagreements = {}
+  for name in names[1:]:
+    counts: dict[str, int] = {}
+    for index, (baseline_move, candidate_move) in enumerate(
+      zip(move_sets[baseline], move_sets[name])
+    ):
+      if baseline_move != candidate_move:
+        scenario = states[index][1].get("scenario", "recorded")
+        counts[scenario] = counts.get(scenario, 0) + 1
+    scenario_disagreements[name] = counts
+  if any(scenario_disagreements.values()):
+    print(f"Disagreements by scenario: {scenario_disagreements}")
+
+  payload = {
+    "reports": reports,
+    "baseline": baseline,
+    "disagreements": disagreements,
+    "scenario_disagreements": scenario_disagreements,
+  }
   if args.json_output:
     Path(args.json_output).write_text(json.dumps(payload, indent=2) + "\n")
 

scripts/run_seeded_snake_tournament.py

@@ -0,0 +1,238 @@
+#!/usr/bin/env python3
+"""Run paired seeded games through the official local Battlesnake rules engine."""
+
+from __future__ import annotations
+
+import argparse
+import json
+import os
+import re
+import signal
+import subprocess
+import sys
+import tempfile
+import time
+import urllib.error
+import urllib.request
+from collections import Counter
+from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
+from threading import Thread
+from pathlib import Path
+from statistics import mean
+
+ROOT = Path(__file__).resolve().parents[1]
+ENGINE_USER_AGENT = "BattlesnakeEngine/local-tournament"
+RESULT_RE = re.compile(
+  r"Game completed after (\d+) turns\.(?: (.+?) was the winner\.| It was a draw\.)"
+)
+
+def wait_for_server(url: str, process: subprocess.Popen, timeout: float = 15.0) -> None:
+  deadline = time.monotonic() + timeout
+  while time.monotonic() < deadline:
+    if process.poll() is not None:
+      raise RuntimeError(f"Snake server exited with status {process.returncode}")
+    try:
+      with urllib.request.urlopen(url, timeout=0.5) as response:
+        if response.status == 200:
+          return
+    except OSError:
+      time.sleep(0.1)
+  raise TimeoutError(f"Snake server did not become ready at {url}")
+
+class _EngineHeaderProxy(BaseHTTPRequestHandler):
+  target: str
+
+  def do_GET(self) -> None:
+    self._forward()
+
+  def do_POST(self) -> None:
+    self._forward()
+
+  def _forward(self) -> None:
+    length = int(self.headers.get("Content-Length", 0))
+    body = self.rfile.read(length) if length else None
+    request = urllib.request.Request(
+      f"{self.target}{self.path}", data=body, method=self.command,
+      headers={
+        "Content-Type": self.headers.get("Content-Type", "application/json"),
+        "User-Agent": ENGINE_USER_AGENT,
+      },
+    )
+    try:
+      with urllib.request.urlopen(request, timeout=2.0) as response:
+        payload = response.read()
+        self.send_response(response.status)
+        self.send_header("Content-Type", response.headers.get("Content-Type", "application/json"))
+    except urllib.error.HTTPError as error:
+      payload = error.read()
+      self.send_response(error.code)
+      self.send_header("Content-Type", error.headers.get("Content-Type", "text/plain"))
+    self.send_header("Content-Length", str(len(payload)))
+    self.end_headers()
+    self.wfile.write(payload)
+
+  def log_message(self, format: str, *args) -> None:
+    pass
+
+def start_proxy(port: int, target_port: int) -> tuple[ThreadingHTTPServer, Thread]:
+  handler = type(
+    f"EngineHeaderProxy{port}",
+    (_EngineHeaderProxy,),
+    {"target": f"http://127.0.0.1:{target_port}"},
+  )
+  server = ThreadingHTTPServer(("127.0.0.1", port), handler)
+  thread = Thread(target=server.serve_forever, daemon=True)
+  thread.start()
+  return server, thread
+
+def start_server(snake: str, port: int) -> subprocess.Popen:
+  env = os.environ.copy()
+  env.update({
+    "HOST": "127.0.0.1",
+    "PORT": str(port),
+    "SNAKE": snake,
+    "DEBUG": "false",
+    "DEBUG_SERVER": "false",
+    "STORE_GAME_HISTORY": "false",
+    "GAMEPLAY_DB_ENABLED": "false",
+    "METRICS_CLEAR_WORKERS_ON_STARTUP": "false",
+  })
+  process = subprocess.Popen(
+    [sys.executable, str(ROOT / "main.py")],
+    cwd=ROOT,
+    env=env,
+    stdin=subprocess.DEVNULL,
+    stdout=subprocess.DEVNULL,
+    stderr=subprocess.DEVNULL,
+    start_new_session=True,
+  )
+  wait_for_server(f"http://127.0.0.1:{port}", process)
+  return process
+
+def stop_server(process: subprocess.Popen) -> None:
+  if process.poll() is not None:
+    return
+  os.killpg(process.pid, signal.SIGTERM)
+  try:
+    process.wait(timeout=5)
+  except subprocess.TimeoutExpired:
+    os.killpg(process.pid, signal.SIGKILL)
+    process.wait(timeout=5)
+
+def run_game(
+  cli: Path,
+  seed: int,
+  game_type: str,
+  map_name: str,
+  players: list[tuple[str, str]],
+  width: int,
+  height: int,
+  timeout_ms: int,
+) -> dict:
+  with tempfile.NamedTemporaryFile(prefix="snake-arena-", suffix=".jsonl") as output:
+    command = [
+      str(cli), "play", "-W", str(width), "-H", str(height),
+      "-g", game_type, "--map", map_name, "--seed", str(seed),
+      "--timeout", str(timeout_ms), "--output", output.name,
+    ]
+    for name, url in players:
+      command.extend(("--name", name, "--url", url))
+    completed = subprocess.run(
+      command, cwd=ROOT, text=True, stdout=subprocess.PIPE,
+      stderr=subprocess.STDOUT, timeout=180, check=False,
+    )
+    if completed.returncode != 0:
+      raise RuntimeError(
+        f"Rules engine failed for seed {seed}:\n{completed.stdout[-2000:]}"
+      )
+    output.seek(0)
+    lines = [json.loads(line) for line in output if line.strip()]
+
+  terminal = lines[-1] if lines else {}
+  match = RESULT_RE.search(completed.stdout)
+  turns = int(match.group(1)) if match else max(0, len(lines) - 2)
+  winner = terminal.get("winnerName") or None
+  draw = bool(terminal.get("isDraw", winner is None))
+  return {"seed": seed, "winner": winner, "draw": draw, "turns": turns}
+
+def main() -> None:
+  parser = argparse.ArgumentParser()
+  parser.add_argument("--games", type=int, default=20, help="Number of unique seeds")
+  parser.add_argument("--seed-start", type=int, default=1)
+  parser.add_argument("--gametype", default="standard")
+  parser.add_argument("--map", default="standard")
+  parser.add_argument("--width", type=int, default=11)
+  parser.add_argument("--height", type=int, default=11)
+  parser.add_argument("--timeout", type=int, default=500)
+  parser.add_argument("--base-port", type=int, default=9301)
+  parser.add_argument("--cli", default=str(ROOT / ".testing/tools/battlesnake-cli/battlesnake"))
+  parser.add_argument("--json-output")
+  args = parser.parse_args()
+
+  cli = Path(args.cli)
+  if not cli.is_file():
+    raise SystemExit(f"Battlesnake CLI not found: {cli}. Run: just build-battlesnake-cli")
+
+  apex_port, prism_port = args.base_port, args.base_port + 1
+  apex_proxy_port, prism_proxy_port = args.base_port + 2, args.base_port + 3
+  servers: list[subprocess.Popen] = []
+  proxies: list[tuple[ThreadingHTTPServer, Thread]] = []
+  results: list[dict] = []
+  started = time.perf_counter()
+  try:
+    servers = [
+      start_server("ApexBattleSnake", apex_port),
+      start_server("PrismBattleSnake_GPT_5_6_Sol", prism_port),
+    ]
+    proxies = [
+      start_proxy(apex_proxy_port, apex_port),
+      start_proxy(prism_proxy_port, prism_port),
+    ]
+    urls = {
+      "Apex": f"http://127.0.0.1:{apex_proxy_port}",
+      "Prism": f"http://127.0.0.1:{prism_proxy_port}",
+    }
+    for offset in range(max(1, args.games)):
+      seed = args.seed_start + offset
+      # Swap engine slots for every seed. This controls for deterministic map
+      # spawn positions and gives each strategy both initial placements.
+      for order in (("Apex", "Prism"), ("Prism", "Apex")):
+        result = run_game(
+          cli=cli, seed=seed, game_type=args.gametype, map_name=args.map,
+          players=[(name, urls[name]) for name in order],
+          width=args.width, height=args.height, timeout_ms=args.timeout,
+        )
+        result["order"] = list(order)
+        results.append(result)
+        print(
+          f"seed={seed} order={'/'.join(order)} winner={result['winner'] or 'draw'} "
+          f"turns={result['turns']}"
+        )
+  finally:
+    for proxy, thread in reversed(proxies):
+      proxy.shutdown()
+      proxy.server_close()
+      thread.join(timeout=2)
+    for server in reversed(servers):
+      stop_server(server)
+
+  wins = Counter(result["winner"] or "draw" for result in results)
+  summary = {
+    "games": len(results),
+    "unique_seeds": max(1, args.games),
+    "gametype": args.gametype,
+    "map": args.map,
+    "wins": dict(wins),
+    "win_rates": {
+      key: value / len(results) for key, value in wins.items()
+    },
+    "mean_turns": mean(result["turns"] for result in results),
+    "elapsed_seconds": time.perf_counter() - started,
+    "results": results,
+  }
+  print(json.dumps({key: value for key, value in summary.items() if key != "results"}, indent=2))
+  if args.json_output:
+    Path(args.json_output).write_text(json.dumps(summary, indent=2) + "\n")
+
+if __name__ == "__main__":
+  main()

scripts/snake_arena_scenarios.py

@@ -0,0 +1,108 @@
+"""Deterministic scenario corpus for the local snake arena."""
+
+from __future__ import annotations
+
+from copy import deepcopy
+
+from tests.bench_best_battle_snake import build_game_state
+
+def _state(payload: dict, scenario: str, index: int) -> tuple[dict, dict]:
+  payload["game"]["id"] = f"arena-{scenario}-{index}"
+  return payload["board"], {
+    "game_id": payload["game"]["id"],
+    "source": "custom",
+    "map": payload["game"].get("map", "standard"),
+    "ruleset": payload["game"]["ruleset"],
+    "turn": payload["turn"],
+    "you": payload["you"],
+    "scenario": scenario,
+  }
+
+def _standard_duel(index: int) -> dict:
+  payload = build_game_state()
+  payload["turn"] = 20 + index
+  payload["board"]["food"] = [
+    {"x": 1 + index % 3, "y": 9},
+    {"x": 9, "y": 1 + (index // 3) % 3},
+  ]
+  return payload
+
+def _hazard_duel(index: int) -> dict:
+  payload = _standard_duel(index)
+  payload["you"]["health"] = 38 + index % 12
+  payload["board"]["snakes"][0]["health"] = payload["you"]["health"]
+  hazard_x = 5 + index % 2
+  payload["board"]["hazards"] = [
+    {"x": hazard_x, "y": y} for y in range(1, 10) if y != 5
+  ]
+  return payload
+
+def _multiplayer(index: int) -> dict:
+  payload = _standard_duel(index)
+  third = {
+    "id": "enemy-2",
+    "name": "enemy-2",
+    "health": 65,
+    "length": 5,
+    "head": {"x": 2, "y": 8},
+    "body": [
+      {"x": 2, "y": 8}, {"x": 2, "y": 9}, {"x": 2, "y": 10},
+      {"x": 1, "y": 10}, {"x": 0, "y": 10},
+    ],
+  }
+  payload["board"]["snakes"].append(third)
+  return payload
+
+def _constrictor(index: int) -> dict:
+  payload = _multiplayer(index)
+  payload["game"]["ruleset"] = deepcopy(payload["game"]["ruleset"])
+  payload["game"]["ruleset"]["name"] = "constrictor"
+  payload["board"]["food"] = []
+  return payload
+
+def _cramped_duel(index: int) -> dict:
+  payload = _standard_duel(index)
+  payload["board"]["width"] = 7
+  payload["board"]["height"] = 7
+  mine = {
+    "id": "me", "name": "me", "health": 72, "length": 7,
+    "head": {"x": 2, "y": 3},
+    "body": [
+      {"x": 2, "y": 3}, {"x": 2, "y": 2}, {"x": 2, "y": 1},
+      {"x": 1, "y": 1}, {"x": 1, "y": 2}, {"x": 1, "y": 3},
+      {"x": 1, "y": 4},
+    ],
+  }
+  enemy = {
+    "id": "enemy", "name": "enemy", "health": 72, "length": 7,
+    "head": {"x": 4, "y": 3},
+    "body": [
+      {"x": 4, "y": 3}, {"x": 4, "y": 2}, {"x": 4, "y": 1},
+      {"x": 5, "y": 1}, {"x": 5, "y": 2}, {"x": 5, "y": 3},
+      {"x": 5, "y": 4},
+    ],
+  }
+  payload["you"] = mine
+  payload["board"]["snakes"] = [mine, enemy]
+  payload["board"]["food"] = [{"x": 3, "y": 5 + index % 2}]
+  payload["board"]["hazards"] = []
+  return payload
+
+SCENARIOS = {
+  "duel": _standard_duel,
+  "hazard": _hazard_duel,
+  "multi": _multiplayer,
+  "constrictor": _constrictor,
+  "cramped": _cramped_duel,
+}
+
+def synthetic_states(count: int, scenarios: list[str] | None = None) -> list[tuple[dict, dict]]:
+  selected = scenarios or list(SCENARIOS)
+  unknown = set(selected) - set(SCENARIOS)
+  if unknown:
+    raise ValueError(f"Unknown arena scenarios: {', '.join(sorted(unknown))}")
+  states: list[tuple[dict, dict]] = []
+  for index in range(count):
+    scenario = selected[index % len(selected)]
+    states.append(_state(SCENARIOS[scenario](index), scenario, index))
+  return states

server/GameBoard.py

@@ -1,4 +1,4 @@
-from snakes.TemplateSnake import TemplateSnake
+from snakes.core.template import TemplateSnake
 from datetime import datetime
 
 class GameBoard:

snakes/PrismBattleSnake_GPT_5_6_Sol.py

@@ -1,663 +0,0 @@
-"""PrismBattleSnake_GPT_5_6_Sol v1.1.0
-
-Built on ApexBattleSnake v1.0.0.  All strategic logic is inherited.
-Performance improvement: all spatial primitives (flood fill, territory,
-articulation detection, distance maps, pathfinding) replaced by a
-bitboard engine that uses integer arithmetic instead of Python sets/deques.
-
-Key speedups:
-  S1: Bitboard flood fill — replaces BFS deque+set with integer bit-expansion.
-      ~60× faster per call, eliminates _neighbors() generator overhead.
-  S2: Bitboard territory — dual-BFS expansion on ints replaces per-cell
-      distance-map comparison loop.
-  S3: Bitboard articulation — partition sizes via bit-flood instead of
-      _bounded_bfs with sets.
-  S4: Bitboard distance map — BFS via bit-expansion + bit-extract.
-  S5: Bitboard path distance — early-exit BFS on ints.
-  S6: Bitboard nearest food — BFS food search on ints.
-  S7: Per-turn BitBoard instance cached for board dimensions.
-  S8: Blocked-set → bitboard conversion cached within a turn to avoid
-      redundant O(n) conversions for the same frozen set.
-  S9: Survival-tree uses bitboards natively — enemy body/attack bits
-      precomputed once at tree root, no per-node set/dict rebuilds.
-  S10: _legal_moves override uses bitboard neighbour mask instead of
-       per-direction Python loop + _in_bounds calls.
-  S11: _future_survival_tree inlines legal-move check with bitboard ops.
-  S12: Duel minimax uses tuple bodies and bitboard move generation.
-  S13: Iterative deepening reuses a transposition table and move-order hints.
-  S14: Candidate duel moves and enemy replies resolve on the same root turn.
-  S15: Candidate moves share one duel transposition/search context per turn.
-  S16: Compact adversarial multiplayer rollout advances plausible enemy replies.
-  S17: Rollout memoization and adaptive depth spend time on ambiguous positions.
-"""
-
-from __future__ import annotations
-
-from time import perf_counter
-
-from server.GameBoard import GameBoard
-from snakes.ApexBattleSnake import ApexBattleSnake
-from snakes.bitboard import BitBoard
-from snakes.bitboard_duel_search import BitboardDuelSearch
-from snakes.compact_survival_search import CompactSurvivalSearch
-
-# Direction offsets for coord-dict → tuple conversion
-_DIR_DELTAS = ((0, 1), (0, -1), (-1, 0), (1, 0))
-_DIR_NAMES = ("up", "down", "left", "right")
-
-class PrismBattleSnake_GPT_5_6_Sol(ApexBattleSnake):
-  VERSION = "1.2.0"
-
-  def __init__(self) -> None:
-    super().__init__()
-    self.name = "PrismBattleSnake"
-    self.version = self.VERSION
-
-    # S7: cached BitBoard instance (reused while board dimensions stay the same)
-    self._bb: BitBoard | None = None
-    self._bb_w: int = 0
-    self._bb_h: int = 0
-
-    # S9: precomputed enemy state for survival tree (set per turn in choose_move)
-    self._enemy_body_bits: int = 0          # all enemy body cells as bitboard
-    self._enemy_tail_bits: int = 0          # enemy tails that will vacate
-    self._enemy_attack_danger: int = 0      # tiles where enemy len >= our len
-    self._enemy_attack_opportunity: int = 0 # tiles where enemy len < our len
-
-    # Shared per-turn search contexts. Candidate moves overlap heavily, so
-    # rebuilding their transposition tables wastes most iterative-deepening work.
-    self._duel_search_context: BitboardDuelSearch | None = None
-    self._survival_search_context: CompactSurvivalSearch | None = None
-
-  # ── BitBoard accessor ────────────────────────────────────────────────────
-
-  def _get_bb(self, width: int, height: int) -> BitBoard:
-    """Return (possibly cached) BitBoard for the current dimensions."""
-    if self._bb is None or width != self._bb_w or height != self._bb_h:
-      self._bb = BitBoard(width, height)
-      self._bb_w = width
-      self._bb_h = height
-    return self._bb
-
-  def _blocked_to_bits(self, blocked: set[tuple[int, int]], width: int, height: int) -> int:
-    """Convert blocked cells to bits without stale identity-based caching."""
-    return self._get_bb(width, height).set_to_bits(blocked)
-
-  # ── choose_move override: precompute enemy bits ──────────────────────────
-
-  def choose_move(self, game_data: GameBoard) -> str:
-    bb = self._get_bb(game_data.get_width(), game_data.get_height())
-    self._duel_search_context = None
-    self._survival_search_context = None
-
-    # S9: precompute enemy body / tail / attack bitboards for survival tree
-    other_snakes = game_data.get_other_snakes()
-    my_snake = game_data.get_my_snake()
-    my_len = my_snake.get("length", len(my_snake["body"]))
-    food_set = {(f["x"], f["y"]) for f in game_data.get_food()}
-    all_occupied = {
-      (seg["x"], seg["y"])
-      for snake in [my_snake, *other_snakes]
-      for seg in snake["body"]
-    }
-    game_type = game_data.get_type()
-    is_constrictor = game_type == "constrictor"
-    w = bb.width
-
-    enemy_body_bits = 0
-    enemy_tail_bits = 0
-    enemy_attack_danger = 0
-    enemy_attack_opportunity = 0
-
-    for snake in other_snakes:
-      for seg in snake["body"]:
-        enemy_body_bits |= 1 << (seg["y"] * w + seg["x"])
-      body = snake["body"]
-      # Check if tail will vacate
-      if not is_constrictor and len(body) >= 2:
-        tail_stacked = (body[-1]["x"] == body[-2]["x"] and body[-1]["y"] == body[-2]["y"])
-        if not tail_stacked:
-          can_grow = self._enemy_can_grow_this_turn(snake, food_set, all_occupied)
-          if not can_grow:
-            enemy_tail_bits |= 1 << (body[-1]["y"] * w + body[-1]["x"])
-
-      # Attack map: tiles enemy head can reach in 1 move
-      eh = snake["head"]
-      e_len = snake.get("length", len(body))
-      ehx, ehy = eh["x"], eh["y"]
-      for dx, dy in _DIR_DELTAS:
-        nx, ny = ehx + dx, ehy + dy
-        if 0 <= nx < w and 0 <= ny < bb.height:
-          bit = 1 << (ny * w + nx)
-          if e_len >= my_len:
-            enemy_attack_danger |= bit
-          else:
-            enemy_attack_opportunity |= bit
-
-    self._enemy_body_bits = enemy_body_bits
-    self._enemy_tail_bits = enemy_tail_bits
-    self._enemy_attack_danger = enemy_attack_danger
-    self._enemy_attack_opportunity = enemy_attack_opportunity
-
-    move = super().choose_move(game_data)
-    history = self.get_history()
-    if history:
-      thinking = history[-1]
-      if self._duel_search_context is not None:
-        thinking["prism_duel_nodes"] = self._duel_search_context.nodes
-        thinking["prism_duel_cache_hits"] = self._duel_search_context.cache_hits
-      if self._survival_search_context is not None:
-        thinking["prism_rollout_nodes"] = self._survival_search_context.nodes
-        thinking["prism_rollout_cache_hits"] = self._survival_search_context.cache_hits
-    return move
-
-  # ── S1: Bitboard flood fill ──────────────────────────────────────────────
-
-  def _flood_fill_count(self, start: tuple, blocked: set, width: int, height: int) -> int:
-    bb = self._get_bb(width, height)
-    blocked_bits = self._blocked_to_bits(blocked, width, height)
-    start_idx = bb.idx(start[0], start[1])
-
-    # A7/E2: per-turn transposition cache (kept from Apex)
-    cache_key = (start_idx, blocked_bits, width, height)
-    cached = self._bfs_cache.get(cache_key)
-    if cached is not None:
-      return cached
-
-    result = bb.flood_count(start_idx, blocked_bits)
-
-    if len(self._bfs_cache) < self._bfs_cache_max:
-      self._bfs_cache[cache_key] = result
-    return result
-
-  # ── S2: Bitboard territory ──────────────────────────────────────────────
-
-  def _territory_fast(
-    self, my_pos: tuple, blocked: set, width: int, height: int,
-    deadline: float | None = None,
-  ) -> int:
-    if not self._enemy_heads:
-      return 0
-    bb = self._get_bb(width, height)
-    blocked_bits = self._blocked_to_bits(blocked, width, height)
-    my_idx = bb.idx(my_pos[0], my_pos[1])
-    enemy_idxs = [bb.idx(eh[0], eh[1]) for eh in self._enemy_heads]
-    return bb.territory(my_idx, enemy_idxs, blocked_bits)
-
-  # ── S3: Bitboard articulation penalty ────────────────────────────────────
-
-  def _articulation_penalty(
-    self, point: tuple, blocked: set, width: int, height: int, required_space: int,
-  ) -> float:
-    bb = self._get_bb(width, height)
-    blocked_bits = self._blocked_to_bits(blocked, width, height)
-    point_idx = bb.idx(point[0], point[1])
-
-    sizes = bb.partition_sizes(point_idx, blocked_bits)
-    if not sizes:
-      return 0.0
-
-    min_size = min(sizes)
-    if min_size < required_space:
-      return 1500.0
-    elif min_size < required_space * 2:
-      return 400.0
-    else:
-      return 85.0
-
-  def _bounded_bfs(self, start: tuple, blocked: set, width: int, height: int, limit: int) -> set:
-    """Bitboard-accelerated bounded BFS. Returns a set for API compatibility."""
-    bb = self._get_bb(width, height)
-    blocked_bits = self._blocked_to_bits(blocked, width, height)
-    start_idx = bb.idx(start[0], start[1])
-    reachable_bits = bb.flood_fill(start_idx, blocked_bits)
-
-    result: set[tuple[int, int]] = set()
-    temp = reachable_bits
-    w = bb.width
-    while temp:
-      bit = temp & (-temp)
-      idx = bit.bit_length() - 1
-      result.add((idx % w, idx // w))
-      temp ^= bit
-      if len(result) >= limit:
-        break
-    return result
-
-  # ── S4: Bitboard distance map ───────────────────────────────────────────
-
-  def _distance_map(self, start: tuple, blocked: set, width: int, height: int) -> dict:
-    bb = self._get_bb(width, height)
-    blocked_bits = self._blocked_to_bits(blocked, width, height)
-    start_idx = bb.idx(start[0], start[1])
-    idx_dmap = bb.distance_map(start_idx, blocked_bits)
-    w = bb.width
-    return {(idx % w, idx // w): d for idx, d in idx_dmap.items()}
-
-  # ── S5: Bitboard path distance ──────────────────────────────────────────
-
-  def _path_distance(
-    self, start: tuple, goal: tuple, blocked: set, width: int, height: int,
-  ) -> int | None:
-    bb = self._get_bb(width, height)
-    blocked_bits = self._blocked_to_bits(blocked, width, height)
-    return bb.path_distance(
-      bb.idx(start[0], start[1]),
-      bb.idx(goal[0], goal[1]),
-      blocked_bits,
-    )
-
-  # ── S6: Bitboard nearest food ───────────────────────────────────────────
-
-  def _nearest_food_info(
-    self, start: tuple, food_set: set, blocked: set, width: int, height: int,
-  ) -> tuple[int | None, tuple | None]:
-    if not food_set:
-      return None, None
-    bb = self._get_bb(width, height)
-    blocked_bits = self._blocked_to_bits(blocked, width, height)
-    food_bits = bb.set_to_bits(food_set)
-    start_idx = bb.idx(start[0], start[1])
-    dist, cell_idx = bb.nearest_food(start_idx, food_bits, blocked_bits)
-    if dist is None or cell_idx is None:
-      return None, None
-    return dist, bb.coord(cell_idx)
-
-  # ── Bitboard open-neighbour helpers ──────────────────────────────────────
-
-  def _open_neighbor_count(self, start: tuple, blocked: set, width: int, height: int) -> int:
-    bb = self._get_bb(width, height)
-    blocked_bits = self._blocked_to_bits(blocked, width, height)
-    return bb.open_neighbor_count(bb.idx(start[0], start[1]), blocked_bits)
-
-  def _next_turn_options(self, head: dict, blocked: set, width: int, height: int) -> int:
-    bb = self._get_bb(width, height)
-    blocked_bits = self._blocked_to_bits(blocked, width, height)
-    return bb.open_neighbor_count(bb.idx(head["x"], head["y"]), blocked_bits)
-
-  # ── S12/S13: compact bitboard duel search ───────────────────────────────
-
-  def _new_duel_search(
-    self, food_set: set, hazard_set: set, hazard_count: dict,
-    hazard_damage: int, width: int, height: int, deadline: float | None,
-  ) -> BitboardDuelSearch:
-    if self._duel_search_context is None:
-      self._duel_search_context = BitboardDuelSearch(
-        board=self._get_bb(width, height),
-        food=food_set,
-        hazards=hazard_set,
-        hazard_count=hazard_count,
-        hazard_damage=hazard_damage,
-        deadline=deadline,
-      )
-    return self._duel_search_context
-
-  def _minimax_candidate_id(
-    self, my_body: list, enemy_body: list, my_target: tuple[int, int],
-    food_set: set, hazard_set: set,
-    my_health: int, enemy_health: int, hazard_damage: int, hazard_count: dict,
-    width: int, height: int, max_depth: int, alpha: float, beta: float,
-    deadline: float | None, previous_hazard_set: set | None = None,
-  ) -> tuple[float, int]:
-    """Resolve our selected move and every enemy reply simultaneously."""
-    search = self._new_duel_search(
-      food_set, hazard_set, hazard_count, hazard_damage,
-      width, height, deadline,
-    )
-    adaptive_depth = max_depth
-    remaining = self._remaining_ms(deadline)
-    if remaining > 250:
-      adaptive_depth = min(7, max_depth + 1)
-    elif remaining < 120:
-      adaptive_depth = min(max_depth, 2)
-    return search.search_candidate(
-      my_body=my_body,
-      enemy_body=enemy_body,
-      my_target=my_target,
-      my_health=my_health,
-      enemy_health=enemy_health,
-      max_depth=adaptive_depth,
-      previous_hazards=previous_hazard_set if previous_hazard_set is not None else hazard_set,
-    )
-
-  def _minimax_sim_id(
-    self, my_body: list, enemy_body: list, food_set: set, hazard_set: set,
-    my_health: int, enemy_health: int, hazard_damage: int, hazard_count: dict,
-    width: int, height: int, max_depth: int, alpha: float, beta: float,
-    deadline: float | None, previous_hazard_set: set | None = None,
-  ) -> tuple[float, int]:
-    """Run iterative deepening with one reusable compact search context."""
-    search = self._new_duel_search(
-      food_set, hazard_set, hazard_count, hazard_damage,
-      width, height, deadline,
-    )
-    return search.search(
-      my_body=my_body,
-      enemy_body=enemy_body,
-      my_health=my_health,
-      enemy_health=enemy_health,
-      max_depth=max_depth,
-      previous_hazards=previous_hazard_set if previous_hazard_set is not None else hazard_set,
-    )
-
-  def _minimax_sim(
-    self, my_body: list, enemy_body: list, food_set: set, hazard_set: set,
-    my_health: int, enemy_health: int, hazard_damage: int, hazard_count: dict,
-    width: int, height: int, depth: int, alpha: float, beta: float,
-    deadline: float | None, previous_hazard_set: set | None = None,
-  ) -> float:
-    """Compatibility entry point for tests and callers requesting one depth."""
-    search = self._new_duel_search(
-      food_set, hazard_set, hazard_count, hazard_damage,
-      width, height, deadline,
-    )
-    return search.search_depth(
-      my_body=my_body,
-      enemy_body=enemy_body,
-      my_health=my_health,
-      enemy_health=enemy_health,
-      depth=depth,
-      previous_hazards=previous_hazard_set if previous_hazard_set is not None else hazard_set,
-    )
-
-  # ── S16/S17: compact adversarial survival rollout ───────────────────────
-
-  def _future_rollout_bonus(
-    self, move: str, safe_moves: dict, my_body: list, other_snakes: list,
-    food_set: set, is_constrictor: bool, width: int, height: int,
-    enemy_can_grow: dict, deadline: float | None,
-  ) -> float:
-    pos = safe_moves.get(move)
-    if pos is None:
-      return -250.0
-    # Duel minimax already advances the opponent exactly. Keep the much faster
-    # bitboard-native solo rollout here instead of paying for the same response
-    # model twice. Constrictor and multiplayer still use adversarial rollouts.
-    if len(other_snakes) == 1 and not is_constrictor:
-      return super()._future_rollout_bonus(
-        move, safe_moves, my_body, other_snakes, food_set, is_constrictor,
-        width, height, enemy_can_grow, deadline,
-      )
-    if self._survival_search_context is None:
-      remaining = self._remaining_ms(deadline)
-      enemy_branch = 2 if len(other_snakes) <= 2 and remaining > 100 else 1
-      self._survival_search_context = CompactSurvivalSearch(
-        board=self._get_bb(width, height),
-        food=food_set,
-        is_constrictor=is_constrictor,
-        deadline=deadline,
-        branch=self._planning_branch,
-        enemy_branch=enemy_branch,
-        response_cap=8 if remaining > 150 else 4,
-      )
-    remaining = self._remaining_ms(deadline)
-    depth = min(self._planning_depth, 2 if len(other_snakes) > 1 else 3)
-    if remaining < 90:
-      depth = min(depth, 2)
-    elif remaining > 250 and len(other_snakes) <= 2:
-      depth = min(4, depth + 1)
-    raw = self._survival_search_context.search_selected(
-      my_body=my_body,
-      enemies=other_snakes,
-      target=(pos["x"], pos["y"]),
-      depth=depth,
-    )
-    return raw * 0.15
-
-  # ── S9: Optimised survival tree (compatibility fallback) ────────────────
-
-  def _future_position_score(
-    self, my_body: list, other_snakes: list, food_set: set, is_constrictor: bool,
-    width: int, height: int, enemy_can_grow: dict, deadline: float | None,
-  ) -> float:
-    """S9: Bitboard-native position scoring for the survival tree.
-
-    Builds blocked bitboard directly from body lists (no intermediate set).
-    Uses precomputed enemy bits instead of rebuilding attack map per node.
-    """
-    if deadline is not None and perf_counter() >= deadline:
-      return 0.0
-
-    bb = self._bb  # already initialised in choose_move
-    w = bb.width
-    head = my_body[0]
-    hx, hy = head["x"], head["y"]
-    head_idx = hy * w + hx
-    head_bit = 1 << head_idx
-    body_len = len(my_body)
-
-    # ── Build blocked bitboard directly (no set) ──────────────────────
-    my_bits = 0
-    for seg in my_body:
-      my_bits |= 1 << (seg["y"] * w + seg["x"])
-
-    # Own tail vacates unless stacked or constrictor
-    if not is_constrictor and body_len >= 2:
-      t, t2 = my_body[-1], my_body[-2]
-      if not (t["x"] == t2["x"] and t["y"] == t2["y"]):
-        my_bits &= ~(1 << (t["y"] * w + t["x"]))
-
-    # Enemy body (precomputed) minus vacating tails
-    en_bits = self._enemy_body_bits & ~self._enemy_tail_bits
-
-    blocked_bits = (my_bits | en_bits) & ~head_bit
-
-    # ── Reachable space ───────────────────────────────────────────────
-    reachable = bb.flood_count(head_idx, blocked_bits)
-    required = body_len + max(3, body_len // 6) if is_constrictor else body_len
-    if reachable < required:
-      return -5000.0
-
-    # ── Open neighbours (liberties) ───────────────────────────────────
-    nb_free = bb._neighbor_masks[head_idx] & ~blocked_bits & bb.board_mask
-    liberties = nb_free.bit_count()
-    if liberties == 0:
-      return -5000.0
-
-    # ── Safe next options (enemy-attack aware) ────────────────────────
-    # Rebuild danger for the simulated length. The root-turn danger mask is
-    # stale after eating and includes enemy moves blocked in this future body.
-    danger_here = 0
-    for enemy in other_snakes:
-      enemy_len = enemy.get("length", len(enemy["body"]))
-      if enemy_len < body_len:
-        continue
-      enemy_head = enemy["head"]
-      enemy_idx = enemy_head["y"] * w + enemy_head["x"]
-      danger_here |= bb._neighbor_masks[enemy_idx]
-    danger_here &= ~blocked_bits
-    safe_nb = nb_free & ~danger_here
-    en_safe = safe_nb.bit_count()
-
-    if en_safe == 0:
-      return -4000.0
-
-    next_opts = liberties
-    sc = reachable * 1.9 + liberties * 14.0 + next_opts * 11.0 + en_safe * 26.0
-    if en_safe == 1:
-      sc -= 420.0
-    return sc
-
-  def _future_survival_tree(
-    self, my_body: list, other_snakes: list, food_set: set, is_constrictor: bool,
-    width: int, height: int, enemy_can_grow: dict,
-    depth: int, branch: int, deadline: float | None,
-  ) -> float:
-    """S9/S11: Bitboard-accelerated survival tree.
-
-    Inlines legal-move check with bitboard ops instead of per-direction
-    Python loops.  Uses the bitboard-native _future_position_score.
-    """
-    if depth <= 0 or (deadline is not None and perf_counter() >= deadline):
-      return 0.0
-
-    bb = self._bb
-    w = bb.width
-    head = my_body[0]
-    hx, hy = head["x"], head["y"]
-    head_idx = hy * w + hx
-    body_len = len(my_body)
-
-    # ── Build occupied bitboard for legal-move check ──────────────────
-    occupied_bits = 0
-    for seg in my_body:
-      occupied_bits |= 1 << (seg["y"] * w + seg["x"])
-    occupied_bits |= self._enemy_body_bits
-
-    # Own tail can be stepped on if not stacked/constrictor
-    passable = 0
-    if not is_constrictor and body_len >= 2:
-      t, t2 = my_body[-1], my_body[-2]
-      if not (t["x"] == t2["x"] and t["y"] == t2["y"]):
-        passable |= 1 << (t["y"] * w + t["x"])
-
-    # Enemy vacating tails are also steppable
-    passable |= self._enemy_tail_bits
-
-    # Legal moves: free neighbours OR passable tiles
-    legal_bits = bb._neighbor_masks[head_idx] & ((~occupied_bits & bb.board_mask) | passable)
-
-    if not legal_bits:
-      return -5000.0
-
-    # ── Precompute food bitboard once ─────────────────────────────────
-    food_bits_local = 0
-    for fx, fy in food_set:
-      food_bits_local |= 1 << (fy * w + fx)
-
-    # ── Score each legal move ─────────────────────────────────────────
-    scored: list[tuple[float, list]] = []
-    temp = legal_bits
-    while temp:
-      if deadline is not None and perf_counter() >= deadline:
-        break
-      bit = temp & (-temp)
-      temp ^= bit
-      idx = bit.bit_length() - 1
-      nx, ny = idx % w, idx // w
-      pos = {"x": nx, "y": ny}
-      ate = bool(bit & food_bits_local)
-      fb = self._future_body(my_body, pos, ate, is_constrictor)
-      sc = self._future_position_score(
-        fb, other_snakes, food_set, is_constrictor,
-        width, height, enemy_can_grow, deadline,
-      )
-      scored.append((sc, fb))
-
-    if not scored:
-      return -5000.0
-
-    DEATH = self._TREE_DEATH_THRESHOLD
-    viable = [(sc, fb) for sc, fb in scored if sc > DEATH]
-    if not viable:
-      return max(sc for sc, _ in scored)
-
-    viable.sort(key=lambda x: x[0], reverse=True)
-
-    if depth == 1:
-      return viable[0][0]
-
-    best = viable[0][0]
-    for sc, fb in viable[:branch]:
-      if deadline is not None and perf_counter() >= deadline:
-        break
-      cont = self._future_survival_tree(
-        fb, other_snakes, food_set, is_constrictor,
-        width, height, enemy_can_grow, depth - 1, branch, deadline,
-      )
-      total = sc + cont * 0.72
-      if total > best:
-        best = total
-    return best
-
-  # ── S10: Bitboard legal moves ────────────────────────────────────────────
-
-  def _legal_moves(
-    self, my_head, my_body: list, other_snakes: list,
-    food_set: set, is_constrictor: bool, width: int, height: int,
-    enemy_can_grow: dict | None = None,
-  ):
-    """S10: Bitboard-accelerated legal move generation."""
-    bb = self._get_bb(width, height)
-    w = bb.width
-
-    # Build occupied bitboard
-    occupied = 0
-    for seg in my_body:
-      occupied |= 1 << (seg["y"] * w + seg["x"])
-    for snake in other_snakes:
-      for seg in snake["body"]:
-        occupied |= 1 << (seg["y"] * w + seg["x"])
-
-    hx, hy = my_head["x"], my_head["y"]
-    head_idx = hy * w + hx
-
-    # Own tail can be stepped on
-    passable = 0
-    if not is_constrictor and len(my_body) >= 2:
-      t, t2 = my_body[-1], my_body[-2]
-      if not (t["x"] == t2["x"] and t["y"] == t2["y"]):
-        passable |= 1 << (t["y"] * w + t["x"])
-
-    # Enemy tails that will vacate
-    if not is_constrictor:
-      for snake in other_snakes:
-        sbody = snake["body"]
-        if len(sbody) < 2:
-          continue
-        st, st2 = sbody[-1], sbody[-2]
-        if st["x"] == st2["x"] and st["y"] == st2["y"]:
-          continue  # stacked
-        sid = snake.get("id")
-        can_grow = None
-        if enemy_can_grow is not None and sid is not None:
-          can_grow = enemy_can_grow.get(sid)
-        if can_grow is None:
-          can_grow = self._enemy_can_grow_this_turn(snake, food_set)
-        if not can_grow:
-          passable |= 1 << (st["y"] * w + st["x"])
-
-    legal = bb._neighbor_masks[head_idx] & ((~occupied & bb.board_mask) | passable)
-
-    safe: dict[str, dict[str, int]] = {}
-    for name, (dx, dy) in self.DIRECTIONS.items():
-      nx, ny = hx + dx, hy + dy
-      if 0 <= nx < w and 0 <= ny < bb.height:
-        if (1 << (ny * w + nx)) & legal:
-          safe[name] = {"x": nx, "y": ny}
-    return safe
-
-  # ── Enemy confinement (uses bitboard flood) ──────────────────────────────
-
-  def _enemy_confinement_metrics(
-    self, enemy_head: tuple, blocked: set, width: int, height: int,
-  ) -> tuple[int, int]:
-    bb = self._get_bb(width, height)
-    blocked_bits = self._blocked_to_bits(blocked, width, height)
-    eh_idx = bb.idx(enemy_head[0], enemy_head[1])
-    eb_bits = blocked_bits & ~(1 << eh_idx)
-    space = bb.flood_count(eh_idx, eb_bits)
-    options = bb.open_neighbor_count(eh_idx, eb_bits)
-    return space, options
-
-  def _enemy_constrictor_projection(
-    self, other_snakes: list, blocked: set, width: int, height: int,
-  ) -> tuple[int, int]:
-    bb = self._get_bb(width, height)
-    blocked_bits = self._blocked_to_bits(blocked, width, height)
-    best_space = 0
-    total_opts = 0
-    for enemy in other_snakes:
-      eh = (enemy["head"]["x"], enemy["head"]["y"])
-      eh_idx = bb.idx(eh[0], eh[1])
-      nb = bb.neighbors_of(eh_idx) & ~blocked_bits & bb.board_mask
-      temp = nb
-      while temp:
-        total_opts += 1
-        bit = temp & (-temp)
-        n_idx = bit.bit_length() - 1
-        sp = bb.flood_count(n_idx, blocked_bits | bit)
-        if sp > best_space:
-          best_space = sp
-        temp ^= bit
-    return best_space, total_opts

snakes/__init__.py

@@ -1,40 +1,61 @@
 import importlib
+from dataclasses import dataclass
 
+@dataclass(frozen=True, slots=True)
+class SnakeRegistration:
+  module: str
+  version: str
+
+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"
+  ),
+  "DummSnake": SnakeRegistration("snakes.legacy.DummSnake", "1.0.0"),
+  "LogicSnake": SnakeRegistration("snakes.legacy.LogicSnake", "1.1.0"),
+  "MasterSnake": SnakeRegistration("snakes.legacy.MasterSnake", "1.2.0"),
+  "BetterMasterSnake": SnakeRegistration("snakes.legacy.BetterMasterSnake", "1.3.0"),
+  "BestBattleSnake": SnakeRegistration("snakes.legacy.BestBattleSnake", "2.6.0"),
+  "TrainedBattleSnake": SnakeRegistration(
+    "snakes.legacy.TrainedBattleSnake", "0.1.0"
+  ),
+  "UltimateBattleSnake": SnakeRegistration(
+    "snakes.legacy.UltimateBattleSnake", "4.5.0"
+  ),
+  "SupremeBattleSnake_ClaudeOpus4_6": SnakeRegistration(
+    "snakes.legacy.SupremeBattleSnake_ClaudeOpus4_6",
+    "1.0.0",
+  ),
+}
+
+# Backward-compatible public version map.
 SNAKE_REGISTRY = {
-  "TemplateSnake": "1.0.0",
+  name: registration.version for name, registration in SNAKE_REGISTRATIONS.items()
-  "DummSnake": "1.0.0",
-  "LogicSnake": "1.1.0",
-  "MasterSnake": "1.2.0",
-  "BetterMasterSnake": "1.3.0",
-  "BestBattleSnake": "2.6.0",
-  "TrainedBattleSnake": "0.1.0",
-  "UltimateBattleSnake": "4.5.0",
-  "ApexBattleSnake": "1.0.0",
-  "SupremeBattleSnake_ClaudeOpus4_6": "1.0.0",
-  "PrismBattleSnake_GPT_5_6_Sol": "1.2.0",
 }
 
 DEFAULT_SNAKE_CONFIG = {
-  'apiversion': '1',
+  "apiversion": "1",
-  'author': '',
+  "author": "",
-  'color': '#888888',
+  "color": "#888888",
-  'head': 'default',
+  "head": "default",
-  'tail': 'default',
+  "tail": "default",
 }
 
+
 def build_snake(selected_snake: str):
-  if selected_snake not in SNAKE_REGISTRY:
+  registration = SNAKE_REGISTRATIONS.get(selected_snake)
+  if registration is None:
     raise ValueError(f"Unknown snake: {selected_snake}")
 
-  snake_module = importlib.import_module(f"snakes.{selected_snake}")
+  snake_module = importlib.import_module(registration.module)
   snake_class = getattr(snake_module, selected_snake)
   return snake_class()
 
 def get_snake_version(selected_snake: str) -> str | None:
-  version = SNAKE_REGISTRY.get(selected_snake)
+  registration = SNAKE_REGISTRATIONS.get(selected_snake)
-  if version is None:
+  return registration.version if registration is not None else None
-    return None
+
-  return str(version)
 
 class SnakeBuilder:
   @classmethod

snakes/core/__init__.py

@@ -0,0 +1,5 @@
+"""Shared snake base classes."""
+
+from snakes.core.template import TemplateSnake
+
+__all__ = ("TemplateSnake",)

snakes/engine/__init__.py

@@ -0,0 +1,18 @@
+"""Reusable high-performance board and search engines for competitive snakes."""
+
+from snakes.engine.bitboard import BitBoard
+from snakes.engine.duel import BitboardDuelMixin
+from snakes.engine.duel_search import BitboardDuelSearch, DuelState
+from snakes.engine.spatial import BitboardSpatialMixin
+from snakes.engine.survival import BitboardSurvivalMixin
+from snakes.engine.survival_search import CompactSurvivalSearch
+
+__all__ = (
+  "BitBoard",
+  "BitboardDuelMixin",
+  "BitboardDuelSearch",
+  "BitboardSpatialMixin",
+  "BitboardSurvivalMixin",
+  "CompactSurvivalSearch",
+  "DuelState",
+)

snakes/engine/duel.py

@@ -0,0 +1,89 @@
+"""Reusable compact duel-search integration for Apex-style snakes."""
+
+from __future__ import annotations
+
+from snakes.engine.duel_search import BitboardDuelSearch
+
+class BitboardDuelMixin:
+  def _new_duel_search(
+      self, food_set: set, hazard_set: set, hazard_count: dict,
+      hazard_damage: int, width: int, height: int, deadline: float | None,
+    ) -> BitboardDuelSearch:
+      if self._duel_search_context is None:
+        self._duel_search_context = BitboardDuelSearch(
+          board=self._get_bb(width, height),
+          food=food_set,
+          hazards=hazard_set,
+          hazard_count=hazard_count,
+          hazard_damage=hazard_damage,
+          deadline=deadline,
+        )
+      return self._duel_search_context
+
+  def _minimax_candidate_id(
+      self, my_body: list, enemy_body: list, my_target: tuple[int, int],
+      food_set: set, hazard_set: set,
+      my_health: int, enemy_health: int, hazard_damage: int, hazard_count: dict,
+      width: int, height: int, max_depth: int, alpha: float, beta: float,
+      deadline: float | None, previous_hazard_set: set | None = None,
+    ) -> tuple[float, int]:
+      """Resolve our selected move and every enemy reply simultaneously."""
+      search = self._new_duel_search(
+        food_set, hazard_set, hazard_count, hazard_damage,
+        width, height, deadline,
+      )
+      adaptive_depth = max_depth
+      remaining = self._remaining_ms(deadline)
+      if remaining > 250:
+        adaptive_depth = min(7, max_depth + 1)
+      elif remaining < 120:
+        adaptive_depth = min(max_depth, 2)
+      return search.search_candidate(
+        my_body=my_body,
+        enemy_body=enemy_body,
+        my_target=my_target,
+        my_health=my_health,
+        enemy_health=enemy_health,
+        max_depth=adaptive_depth,
+        previous_hazards=previous_hazard_set if previous_hazard_set is not None else hazard_set,
+      )
+
+  def _minimax_sim_id(
+      self, my_body: list, enemy_body: list, food_set: set, hazard_set: set,
+      my_health: int, enemy_health: int, hazard_damage: int, hazard_count: dict,
+      width: int, height: int, max_depth: int, alpha: float, beta: float,
+      deadline: float | None, previous_hazard_set: set | None = None,
+    ) -> tuple[float, int]:
+      """Run iterative deepening with one reusable compact search context."""
+      search = self._new_duel_search(
+        food_set, hazard_set, hazard_count, hazard_damage,
+        width, height, deadline,
+      )
+      return search.search(
+        my_body=my_body,
+        enemy_body=enemy_body,
+        my_health=my_health,
+        enemy_health=enemy_health,
+        max_depth=max_depth,
+        previous_hazards=previous_hazard_set if previous_hazard_set is not None else hazard_set,
+      )
+
+  def _minimax_sim(
+      self, my_body: list, enemy_body: list, food_set: set, hazard_set: set,
+      my_health: int, enemy_health: int, hazard_damage: int, hazard_count: dict,
+      width: int, height: int, depth: int, alpha: float, beta: float,
+      deadline: float | None, previous_hazard_set: set | None = None,
+    ) -> float:
+      """Compatibility entry point for tests and callers requesting one depth."""
+      search = self._new_duel_search(
+        food_set, hazard_set, hazard_count, hazard_damage,
+        width, height, deadline,
+      )
+      return search.search_depth(
+        my_body=my_body,
+        enemy_body=enemy_body,
+        my_health=my_health,
+        enemy_health=enemy_health,
+        depth=depth,
+        previous_hazards=previous_hazard_set if previous_hazard_set is not None else hazard_set,
+      )

snakes/engine/duel_search.py

@@ -6,7 +6,7 @@ from collections.abc import Iterable
 from dataclasses import dataclass
 from time import perf_counter
 
-from snakes.bitboard import BitBoard
+from snakes.engine.bitboard import BitBoard
 
 Body = tuple[int, ...]
 
@@ -51,8 +51,12 @@ class BitboardDuelSearch:
     self.killer_moves: dict[int, int] = {}
     self.history: dict[int, int] = {}
     self._body_bits_cache: dict[Body, int] = {}
+    self._evaluation_cache: dict[DuelState, float] = {}
     self.nodes = 0
     self.cache_hits = 0
+    self.evaluation_cache_hits = 0
+    self.completed_depth = 0
+    self.deadline_exits = 0
 
   def body_from_dicts(self, body: list[dict]) -> Body:
     return tuple(self.board.idx(seg["x"], seg["y"]) for seg in body)
@@ -90,6 +94,7 @@ class BitboardDuelSearch:
       result = value
       completed_depth = depth
 
+    self.completed_depth = max(self.completed_depth, completed_depth)
     return result, completed_depth
 
   def search_candidate(
@@ -135,6 +140,7 @@ class BitboardDuelSearch:
         break
       result = value
       completed_depth = depth
+    self.completed_depth = max(self.completed_depth, completed_depth)
     return result, completed_depth
 
   def search_depth(
@@ -154,7 +160,9 @@ class BitboardDuelSearch:
       enemy_health=enemy_health,
       previous_hazard_bits=self.board.set_to_bits(set(previous_hazards)),
     )
-    value, _ = self._search(state, depth, -float("inf"), float("inf"))
+    value, completed = self._search(state, depth, -float("inf"), float("inf"))
+    if completed:
+      self.completed_depth = max(self.completed_depth, depth)
     return value
 
   def _search_selected_move(
@@ -344,6 +352,11 @@ class BitboardDuelSearch:
     return sorted(moves, key=score, reverse=True)
 
   def _evaluate(self, state: DuelState) -> float:
+    cached = self._evaluation_cache.get(state)
+    if cached is not None:
+      self.evaluation_cache_hits += 1
+      return cached
+
     my_blocked = self._body_bits(state.my_body[1:]) | self._body_bits(state.enemy_body[1:])
     my_head, enemy_head = state.my_body[0], state.enemy_body[0]
     my_space = self.board.flood_count(my_head, my_blocked)
@@ -356,14 +369,48 @@ class BitboardDuelSearch:
     tail_score = (12.0 if my_tail_path is not None else -24.0) - (12.0 if enemy_tail_path is not None else -24.0)
     my_hazard = self._hazard_cost(my_head, state.previous_hazard_bits)
     enemy_hazard = self._hazard_cost(enemy_head, state.previous_hazard_bits)
-    length_score = (len(state.my_body) - len(state.enemy_body)) * 20.0
+    length_delta = len(state.my_body) - len(state.enemy_body)
+    length_score = length_delta * 20.0
     health_score = (state.my_health - state.enemy_health) * 0.18
     forced_score = (my_liberties > 1) * 10.0 - (enemy_liberties > 1) * 10.0
-    return (
+
+    # Food races matter most when health is low or eating changes head-to-head
+    # priority. Compare actual path lengths rather than Manhattan distance so a
+    # food tile behind a body wall is not treated as reachable.
+    food_score = 0.0
+    if state.food_bits:
+      my_food = self.board.nearest_food(my_head, state.food_bits, my_blocked)
+      enemy_food = self.board.nearest_food(enemy_head, state.food_bits, my_blocked)
+      my_distance = my_food[0] if my_food[0] is not None else 200
+      enemy_distance = enemy_food[0] if enemy_food[0] is not None else 200
+      my_urgency = max(0.0, (55.0 - state.my_health) / 55.0)
+      enemy_urgency = max(0.0, (55.0 - state.enemy_health) / 55.0)
+      food_score += (enemy_distance - my_distance) * 2.5
+      food_score -= my_distance * my_urgency * 5.0
+      food_score += enemy_distance * enemy_urgency * 3.0
+      if length_delta == 0 and my_distance < enemy_distance:
+        food_score += 14.0
+      elif length_delta < 0 and my_distance <= enemy_distance:
+        food_score += 20.0
+
+    # Reward maintaining safe pressure around the opposing head. This captures
+    # two-turn head traps that raw territory and flood counts often score as a
+    # neutral position.
+    head_distance = self.board.path_distance(my_head, enemy_head, my_blocked)
+    pressure_score = 0.0
+    if head_distance is not None and head_distance <= 3:
+      pressure = (4 - head_distance) * 6.0
+      pressure_score = pressure if length_delta > 0 else -pressure if length_delta < 0 else 0.0
+
+    value = (
       (my_space - enemy_space) * 1.5 + territory * 1.2
       + (my_liberties - enemy_liberties) * 14.0 + length_score + health_score
-      + tail_score + forced_score + (enemy_hazard - my_hazard) * 0.8
+      + tail_score + forced_score + food_score + pressure_score
+      + (enemy_hazard - my_hazard) * 0.8
     )
+    if len(self._evaluation_cache) < 32_768:
+      self._evaluation_cache[state] = value
+    return value
 
   def _hazard_cost(self, target: int, previous_hazard_bits: int) -> int:
     bit = 1 << target
@@ -400,4 +447,7 @@ class BitboardDuelSearch:
   def _out_of_time(self, reserve_ms: float = 0.0) -> bool:
     if self.deadline is None:
       return False
-    return perf_counter() + reserve_ms / 1000.0 >= self.deadline
+    expired = perf_counter() + reserve_ms / 1000.0 >= self.deadline
+    if expired:
+      self.deadline_exits += 1
+    return expired

snakes/engine/spatial.py

@@ -0,0 +1,216 @@
+"""Bitboard-backed spatial primitives shared by competitive snakes."""
+
+from __future__ import annotations
+
+from snakes.engine.bitboard import BitBoard
+
+class BitboardSpatialMixin:
+  def _get_bb(self, width: int, height: int) -> BitBoard:
+      """Return (possibly cached) BitBoard for the current dimensions."""
+      if self._bb is None or width != self._bb_w or height != self._bb_h:
+        self._bb = BitBoard(width, height)
+        self._bb_w = width
+        self._bb_h = height
+      return self._bb
+
+  def _blocked_to_bits(self, blocked: set[tuple[int, int]], width: int, height: int) -> int:
+      """Convert blocked cells to bits without stale identity-based caching."""
+      return self._get_bb(width, height).set_to_bits(blocked)
+
+  def _flood_fill_count(self, start: tuple, blocked: set, width: int, height: int) -> int:
+      bb = self._get_bb(width, height)
+      blocked_bits = self._blocked_to_bits(blocked, width, height)
+      start_idx = bb.idx(start[0], start[1])
+
+      # A7/E2: per-turn transposition cache (kept from Apex)
+      cache_key = (start_idx, blocked_bits, width, height)
+      cached = self._bfs_cache.get(cache_key)
+      if cached is not None:
+        return cached
+
+      result = bb.flood_count(start_idx, blocked_bits)
+
+      if len(self._bfs_cache) < self._bfs_cache_max:
+        self._bfs_cache[cache_key] = result
+      return result
+
+  def _territory_fast(
+      self, my_pos: tuple, blocked: set, width: int, height: int,
+      deadline: float | None = None,
+    ) -> int:
+      if not self._enemy_heads:
+        return 0
+      bb = self._get_bb(width, height)
+      blocked_bits = self._blocked_to_bits(blocked, width, height)
+      my_idx = bb.idx(my_pos[0], my_pos[1])
+      enemy_idxs = [bb.idx(eh[0], eh[1]) for eh in self._enemy_heads]
+      return bb.territory(my_idx, enemy_idxs, blocked_bits)
+
+  def _articulation_penalty(
+      self, point: tuple, blocked: set, width: int, height: int, required_space: int,
+    ) -> float:
+      bb = self._get_bb(width, height)
+      blocked_bits = self._blocked_to_bits(blocked, width, height)
+      point_idx = bb.idx(point[0], point[1])
+
+      sizes = bb.partition_sizes(point_idx, blocked_bits)
+      if not sizes:
+        return 0.0
+
+      min_size = min(sizes)
+      if min_size < required_space:
+        return 1500.0
+      elif min_size < required_space * 2:
+        return 400.0
+      else:
+        return 85.0
+
+  def _bounded_bfs(self, start: tuple, blocked: set, width: int, height: int, limit: int) -> set:
+      """Bitboard-accelerated bounded BFS. Returns a set for API compatibility."""
+      bb = self._get_bb(width, height)
+      blocked_bits = self._blocked_to_bits(blocked, width, height)
+      start_idx = bb.idx(start[0], start[1])
+      reachable_bits = bb.flood_fill(start_idx, blocked_bits)
+
+      result: set[tuple[int, int]] = set()
+      temp = reachable_bits
+      w = bb.width
+      while temp:
+        bit = temp & (-temp)
+        idx = bit.bit_length() - 1
+        result.add((idx % w, idx // w))
+        temp ^= bit
+        if len(result) >= limit:
+          break
+      return result
+
+  def _distance_map(self, start: tuple, blocked: set, width: int, height: int) -> dict:
+      bb = self._get_bb(width, height)
+      blocked_bits = self._blocked_to_bits(blocked, width, height)
+      start_idx = bb.idx(start[0], start[1])
+      idx_dmap = bb.distance_map(start_idx, blocked_bits)
+      w = bb.width
+      return {(idx % w, idx // w): d for idx, d in idx_dmap.items()}
+
+  def _path_distance(
+      self, start: tuple, goal: tuple, blocked: set, width: int, height: int,
+    ) -> int | None:
+      bb = self._get_bb(width, height)
+      blocked_bits = self._blocked_to_bits(blocked, width, height)
+      return bb.path_distance(
+        bb.idx(start[0], start[1]),
+        bb.idx(goal[0], goal[1]),
+        blocked_bits,
+      )
+
+  def _nearest_food_info(
+      self, start: tuple, food_set: set, blocked: set, width: int, height: int,
+    ) -> tuple[int | None, tuple | None]:
+      if not food_set:
+        return None, None
+      bb = self._get_bb(width, height)
+      blocked_bits = self._blocked_to_bits(blocked, width, height)
+      food_bits = bb.set_to_bits(food_set)
+      start_idx = bb.idx(start[0], start[1])
+      dist, cell_idx = bb.nearest_food(start_idx, food_bits, blocked_bits)
+      if dist is None or cell_idx is None:
+        return None, None
+      return dist, bb.coord(cell_idx)
+
+  def _open_neighbor_count(self, start: tuple, blocked: set, width: int, height: int) -> int:
+      bb = self._get_bb(width, height)
+      blocked_bits = self._blocked_to_bits(blocked, width, height)
+      return bb.open_neighbor_count(bb.idx(start[0], start[1]), blocked_bits)
+
+  def _next_turn_options(self, head: dict, blocked: set, width: int, height: int) -> int:
+      bb = self._get_bb(width, height)
+      blocked_bits = self._blocked_to_bits(blocked, width, height)
+      return bb.open_neighbor_count(bb.idx(head["x"], head["y"]), blocked_bits)
+
+  def _legal_moves(
+      self, my_head, my_body: list, other_snakes: list,
+      food_set: set, is_constrictor: bool, width: int, height: int,
+      enemy_can_grow: dict | None = None,
+    ):
+      """S10: Bitboard-accelerated legal move generation."""
+      bb = self._get_bb(width, height)
+      w = bb.width
+
+      # Build occupied bitboard
+      occupied = 0
+      for seg in my_body:
+        occupied |= 1 << (seg["y"] * w + seg["x"])
+      for snake in other_snakes:
+        for seg in snake["body"]:
+          occupied |= 1 << (seg["y"] * w + seg["x"])
+
+      hx, hy = my_head["x"], my_head["y"]
+      head_idx = hy * w + hx
+
+      # Own tail can be stepped on
+      passable = 0
+      if not is_constrictor and len(my_body) >= 2:
+        t, t2 = my_body[-1], my_body[-2]
+        if not (t["x"] == t2["x"] and t["y"] == t2["y"]):
+          passable |= 1 << (t["y"] * w + t["x"])
+
+      # Enemy tails that will vacate
+      if not is_constrictor:
+        for snake in other_snakes:
+          sbody = snake["body"]
+          if len(sbody) < 2:
+            continue
+          st, st2 = sbody[-1], sbody[-2]
+          if st["x"] == st2["x"] and st["y"] == st2["y"]:
+            continue  # stacked
+          sid = snake.get("id")
+          can_grow = None
+          if enemy_can_grow is not None and sid is not None:
+            can_grow = enemy_can_grow.get(sid)
+          if can_grow is None:
+            can_grow = self._enemy_can_grow_this_turn(snake, food_set)
+          if not can_grow:
+            passable |= 1 << (st["y"] * w + st["x"])
+
+      legal = bb._neighbor_masks[head_idx] & ((~occupied & bb.board_mask) | passable)
+
+      safe: dict[str, dict[str, int]] = {}
+      for name, (dx, dy) in self.DIRECTIONS.items():
+        nx, ny = hx + dx, hy + dy
+        if 0 <= nx < w and 0 <= ny < bb.height:
+          if (1 << (ny * w + nx)) & legal:
+            safe[name] = {"x": nx, "y": ny}
+      return safe
+
+  def _enemy_confinement_metrics(
+      self, enemy_head: tuple, blocked: set, width: int, height: int,
+    ) -> tuple[int, int]:
+      bb = self._get_bb(width, height)
+      blocked_bits = self._blocked_to_bits(blocked, width, height)
+      eh_idx = bb.idx(enemy_head[0], enemy_head[1])
+      eb_bits = blocked_bits & ~(1 << eh_idx)
+      space = bb.flood_count(eh_idx, eb_bits)
+      options = bb.open_neighbor_count(eh_idx, eb_bits)
+      return space, options
+
+  def _enemy_constrictor_projection(
+      self, other_snakes: list, blocked: set, width: int, height: int,
+    ) -> tuple[int, int]:
+      bb = self._get_bb(width, height)
+      blocked_bits = self._blocked_to_bits(blocked, width, height)
+      best_space = 0
+      total_opts = 0
+      for enemy in other_snakes:
+        eh = (enemy["head"]["x"], enemy["head"]["y"])
+        eh_idx = bb.idx(eh[0], eh[1])
+        nb = bb.neighbors_of(eh_idx) & ~blocked_bits & bb.board_mask
+        temp = nb
+        while temp:
+          total_opts += 1
+          bit = temp & (-temp)
+          n_idx = bit.bit_length() - 1
+          sp = bb.flood_count(n_idx, blocked_bits | bit)
+          if sp > best_space:
+            best_space = sp
+          temp ^= bit
+      return best_space, total_opts

snakes/engine/survival.py

@@ -0,0 +1,214 @@
+"""Reusable bitboard and adversarial survival rollouts."""
+
+from __future__ import annotations
+
+from time import perf_counter
+
+from snakes.engine.survival_search import CompactSurvivalSearch
+
+class BitboardSurvivalMixin:
+  def _future_rollout_bonus(
+      self, move: str, safe_moves: dict, my_body: list, other_snakes: list,
+      food_set: set, is_constrictor: bool, width: int, height: int,
+      enemy_can_grow: dict, deadline: float | None,
+    ) -> float:
+      pos = safe_moves.get(move)
+      if pos is None:
+        return -250.0
+      # Duel minimax already advances the opponent exactly. Keep the much faster
+      # bitboard-native solo rollout here instead of paying for the same response
+      # model twice. Constrictor and multiplayer still use adversarial rollouts.
+      if len(other_snakes) == 1 and not is_constrictor:
+        return super()._future_rollout_bonus(
+          move, safe_moves, my_body, other_snakes, food_set, is_constrictor,
+          width, height, enemy_can_grow, deadline,
+        )
+      if self._survival_search_context is None:
+        remaining = self._remaining_ms(deadline)
+        enemy_branch = 2 if len(other_snakes) <= 2 and remaining > 100 else 1
+        self._survival_search_context = CompactSurvivalSearch(
+          board=self._get_bb(width, height),
+          food=food_set,
+          is_constrictor=is_constrictor,
+          deadline=deadline,
+          branch=self._planning_branch,
+          enemy_branch=enemy_branch,
+          response_cap=8 if remaining > 150 else 4,
+        )
+      remaining = self._remaining_ms(deadline)
+      depth = min(self._planning_depth, 2 if len(other_snakes) > 1 else 3)
+      if remaining < 90:
+        depth = min(depth, 2)
+      elif remaining > 250 and len(other_snakes) <= 2:
+        depth = min(4, depth + 1)
+      raw = self._survival_search_context.search_selected(
+        my_body=my_body,
+        enemies=other_snakes,
+        target=(pos["x"], pos["y"]),
+        depth=depth,
+      )
+      return raw * 0.15
+
+  def _future_position_score(
+      self, my_body: list, other_snakes: list, food_set: set, is_constrictor: bool,
+      width: int, height: int, enemy_can_grow: dict, deadline: float | None,
+    ) -> float:
+      """S9: Bitboard-native position scoring for the survival tree.
+
+      Builds blocked bitboard directly from body lists (no intermediate set).
+      Uses precomputed enemy bits instead of rebuilding attack map per node.
+      """
+      if deadline is not None and perf_counter() >= deadline:
+        return 0.0
+
+      bb = self._bb  # already initialised in choose_move
+      w = bb.width
+      head = my_body[0]
+      hx, hy = head["x"], head["y"]
+      head_idx = hy * w + hx
+      head_bit = 1 << head_idx
+      body_len = len(my_body)
+
+      # ── Build blocked bitboard directly (no set) ──────────────────────
+      my_bits = 0
+      for seg in my_body:
+        my_bits |= 1 << (seg["y"] * w + seg["x"])
+
+      # Own tail vacates unless stacked or constrictor
+      if not is_constrictor and body_len >= 2:
+        t, t2 = my_body[-1], my_body[-2]
+        if not (t["x"] == t2["x"] and t["y"] == t2["y"]):
+          my_bits &= ~(1 << (t["y"] * w + t["x"]))
+
+      # Enemy body (precomputed) minus vacating tails
+      en_bits = self._enemy_body_bits & ~self._enemy_tail_bits
+
+      blocked_bits = (my_bits | en_bits) & ~head_bit
+
+      # ── Reachable space ───────────────────────────────────────────────
+      reachable = bb.flood_count(head_idx, blocked_bits)
+      required = body_len + max(3, body_len // 6) if is_constrictor else body_len
+      if reachable < required:
+        return -5000.0
+
+      # ── Open neighbours (liberties) ───────────────────────────────────
+      nb_free = bb._neighbor_masks[head_idx] & ~blocked_bits & bb.board_mask
+      liberties = nb_free.bit_count()
+      if liberties == 0:
+        return -5000.0
+
+      # ── Safe next options (enemy-attack aware) ────────────────────────
+      # Rebuild danger for the simulated length. The root-turn danger mask is
+      # stale after eating and includes enemy moves blocked in this future body.
+      danger_here = 0
+      for enemy in other_snakes:
+        enemy_len = enemy.get("length", len(enemy["body"]))
+        if enemy_len < body_len:
+          continue
+        enemy_head = enemy["head"]
+        enemy_idx = enemy_head["y"] * w + enemy_head["x"]
+        danger_here |= bb._neighbor_masks[enemy_idx]
+      danger_here &= ~blocked_bits
+      safe_nb = nb_free & ~danger_here
+      en_safe = safe_nb.bit_count()
+
+      if en_safe == 0:
+        return -4000.0
+
+      next_opts = liberties
+      sc = reachable * 1.9 + liberties * 14.0 + next_opts * 11.0 + en_safe * 26.0
+      if en_safe == 1:
+        sc -= 420.0
+      return sc
+
+  def _future_survival_tree(
+      self, my_body: list, other_snakes: list, food_set: set, is_constrictor: bool,
+      width: int, height: int, enemy_can_grow: dict,
+      depth: int, branch: int, deadline: float | None,
+    ) -> float:
+      """S9/S11: Bitboard-accelerated survival tree.
+
+      Inlines legal-move check with bitboard ops instead of per-direction
+      Python loops.  Uses the bitboard-native _future_position_score.
+      """
+      if depth <= 0 or (deadline is not None and perf_counter() >= deadline):
+        return 0.0
+
+      bb = self._bb
+      w = bb.width
+      head = my_body[0]
+      hx, hy = head["x"], head["y"]
+      head_idx = hy * w + hx
+      body_len = len(my_body)
+
+      # ── Build occupied bitboard for legal-move check ──────────────────
+      occupied_bits = 0
+      for seg in my_body:
+        occupied_bits |= 1 << (seg["y"] * w + seg["x"])
+      occupied_bits |= self._enemy_body_bits
+
+      # Own tail can be stepped on if not stacked/constrictor
+      passable = 0
+      if not is_constrictor and body_len >= 2:
+        t, t2 = my_body[-1], my_body[-2]
+        if not (t["x"] == t2["x"] and t["y"] == t2["y"]):
+          passable |= 1 << (t["y"] * w + t["x"])
+
+      # Enemy vacating tails are also steppable
+      passable |= self._enemy_tail_bits
+
+      # Legal moves: free neighbours OR passable tiles
+      legal_bits = bb._neighbor_masks[head_idx] & ((~occupied_bits & bb.board_mask) | passable)
+
+      if not legal_bits:
+        return -5000.0
+
+      # ── Precompute food bitboard once ─────────────────────────────────
+      food_bits_local = 0
+      for fx, fy in food_set:
+        food_bits_local |= 1 << (fy * w + fx)
+
+      # ── Score each legal move ─────────────────────────────────────────
+      scored: list[tuple[float, list]] = []
+      temp = legal_bits
+      while temp:
+        if deadline is not None and perf_counter() >= deadline:
+          break
+        bit = temp & (-temp)
+        temp ^= bit
+        idx = bit.bit_length() - 1
+        nx, ny = idx % w, idx // w
+        pos = {"x": nx, "y": ny}
+        ate = bool(bit & food_bits_local)
+        fb = self._future_body(my_body, pos, ate, is_constrictor)
+        sc = self._future_position_score(
+          fb, other_snakes, food_set, is_constrictor,
+          width, height, enemy_can_grow, deadline,
+        )
+        scored.append((sc, fb))
+
+      if not scored:
+        return -5000.0
+
+      DEATH = self._TREE_DEATH_THRESHOLD
+      viable = [(sc, fb) for sc, fb in scored if sc > DEATH]
+      if not viable:
+        return max(sc for sc, _ in scored)
+
+      viable.sort(key=lambda x: x[0], reverse=True)
+
+      if depth == 1:
+        return viable[0][0]
+
+      best = viable[0][0]
+      for sc, fb in viable[:branch]:
+        if deadline is not None and perf_counter() >= deadline:
+          break
+        cont = self._future_survival_tree(
+          fb, other_snakes, food_set, is_constrictor,
+          width, height, enemy_can_grow, depth - 1, branch, deadline,
+        )
+        total = sc + cont * 0.72
+        if total > best:
+          best = total
+      return best

snakes/engine/survival_search.py

@@ -5,7 +5,7 @@ from __future__ import annotations
 from itertools import product
 from time import perf_counter
 
-from snakes.bitboard import BitBoard
+from snakes.engine.bitboard import BitBoard
 
 Body = tuple[int, ...]
 EnemyBodies = tuple[Body, ...]
@@ -42,6 +42,8 @@ class CompactSurvivalSearch:
     self.body_bits_cache: dict[Body, int] = {}
     self.nodes = 0
     self.cache_hits = 0
+    self.completed_depth = 0
+    self.deadline_exits = 0
 
   def body_from_dicts(self, body: list[dict]) -> Body:
     return tuple(self.board.idx(segment["x"], segment["y"]) for segment in body)
@@ -58,17 +60,24 @@ class CompactSurvivalSearch:
     target_idx = self.board.idx(*target)
     if not self.board.neighbors_of(mine[0]) & (1 << target_idx):
       return self.DEATH
-    return self._selected_root(mine, enemy_bodies, self.food_bits, target_idx, depth)
+    value, completed = self._selected_root(
+      mine, enemy_bodies, self.food_bits, target_idx, depth,
+    )
+    if completed:
+      self.completed_depth = max(self.completed_depth, depth)
+    return value
 
   def _selected_root(
     self, mine: Body, enemies: EnemyBodies, food_bits: int, target: int, depth: int,
-  ) -> float:
+  ) -> tuple[float, bool]:
     replies = self._enemy_responses(enemies, mine, target, food_bits)
     if not replies:
       replies = [()]
     worst = float("inf")
+    completed = True
     for response in replies:
       if self._out_of_time():
+        completed = False
         break
       child = self._advance(mine, enemies, target, response, food_bits)
       if child is None:
@@ -79,7 +88,8 @@ class CompactSurvivalSearch:
         if depth > 1 and value > self.DEATH:
           value += self._search(next_mine, next_enemies, next_food, depth - 1) * 0.72
       worst = min(worst, value)
-    return self._evaluate(mine, enemies) if worst == float("inf") else worst
+    value = self._evaluate(mine, enemies) if worst == float("inf") else worst
+    return value, completed
 
   def _search(self, mine: Body, enemies: EnemyBodies, food_bits: int, depth: int) -> float:
     self.nodes += 1
@@ -260,4 +270,7 @@ class CompactSurvivalSearch:
       bits ^= bit
 
   def _out_of_time(self) -> bool:
-    return self.deadline is not None and perf_counter() >= self.deadline
+    expired = self.deadline is not None and perf_counter() >= self.deadline
+    if expired:
+      self.deadline_exits += 1
+    return expired

snakes/legacy/BestBattleSnake.py

@@ -7,7 +7,7 @@ import os
 from quart_common.web.env import env_int
 from server.dataset.RLBootstrapDataset import RLBootstrapDataset
 
-from snakes.TemplateSnake import TemplateSnake
+from snakes.core.template import TemplateSnake
 from server.GameBoard import GameBoard
 
 class BestBattleSnake(TemplateSnake):

snakes/legacy/BetterMasterSnake.py

@@ -1,4 +1,4 @@
-from snakes.TemplateSnake import TemplateSnake
+from snakes.core.template import TemplateSnake
 from server.GameBoard import GameBoard
 from collections import deque
 

snakes/legacy/DummSnake.py

@@ -1,4 +1,4 @@
-from snakes.TemplateSnake import TemplateSnake
+from snakes.core.template import TemplateSnake
 
 import random
 

snakes/legacy/LogicSnake.py

@@ -1,4 +1,4 @@
-from snakes.TemplateSnake import TemplateSnake
+from snakes.core.template import TemplateSnake
 
 import random
 from scipy import spatial

snakes/legacy/MasterSnake.py

@@ -1,4 +1,4 @@
-from snakes.TemplateSnake import TemplateSnake
+from snakes.core.template import TemplateSnake
 
 class MasterSnake(TemplateSnake):
   VERSION = "1.2.0"

snakes/legacy/SupremeBattleSnake_ClaudeOpus4_6.py

@@ -29,8 +29,8 @@ from __future__ import annotations
 from typing import Any
 from time import perf_counter
 
-from snakes.ApexBattleSnake import ApexBattleSnake
+from snakes.strategies.apex import ApexBattleSnake
-from snakes.bitboard import BitBoard
+from snakes.engine.bitboard import BitBoard
 from server.GameBoard import GameBoard
 
 # Direction offsets for coord-dict → tuple conversion

snakes/legacy/TrainedBattleSnake.py

@@ -3,7 +3,7 @@ from typing import Any
 import random, json, os
 
 from server.TrainBattleSnakeAI import MOVES, extract_feature_values
-from snakes.TemplateSnake import TemplateSnake
+from snakes.core.template import TemplateSnake
 
 class TrainedBattleSnake(TemplateSnake):
   VERSION = "0.1.0"

snakes/legacy/UltimateBattleSnake.py

@@ -6,7 +6,7 @@ import heapq, os
 
 from quart_common.web.env import env_int
 
-from snakes.TemplateSnake import TemplateSnake
+from snakes.core.template import TemplateSnake
 from server.GameBoard import GameBoard
 from server.dataset.RLBootstrapDataset import RLBootstrapDataset
 

snakes/legacy/__init__.py

@@ -0,0 +1 @@
+"""Historical snake strategies retained for replay and comparison."""

snakes/strategies/__init__.py

@@ -0,0 +1,6 @@
+"""Actively maintained competitive snake strategies."""
+
+from snakes.strategies.apex import ApexBattleSnake
+from snakes.strategies.prism import PrismBattleSnake_GPT_5_6_Sol
+
+__all__ = ("ApexBattleSnake", "PrismBattleSnake_GPT_5_6_Sol")

snakes/strategies/apex.py

@@ -7,7 +7,7 @@ import heapq, os
 from quart_common.web.env import env_int
 
 from server.dataset.RLBootstrapDataset import RLBootstrapDataset
-from snakes.TemplateSnake import TemplateSnake
+from snakes.core.template import TemplateSnake
 from server.GameBoard import GameBoard
 
 class ApexBattleSnake(TemplateSnake):

snakes/strategies/prism.py

@@ -0,0 +1,169 @@
+"""PrismBattleSnake_GPT_5_6_Sol v1.3.0
+
+Built on ApexBattleSnake v1.0.0.  All strategic logic is inherited.
+Performance improvement: all spatial primitives (flood fill, territory,
+articulation detection, distance maps, pathfinding) replaced by a
+bitboard engine that uses integer arithmetic instead of Python sets/deques.
+
+Key speedups:
+  S1: Bitboard flood fill — replaces BFS deque+set with integer bit-expansion.
+    ~60× faster per call, eliminates _neighbors() generator overhead.
+  S2: Bitboard territory — dual-BFS expansion on ints replaces per-cell
+    distance-map comparison loop.
+  S3: Bitboard articulation — partition sizes via bit-flood instead of
+    _bounded_bfs with sets.
+  S4: Bitboard distance map — BFS via bit-expansion + bit-extract.
+  S5: Bitboard path distance — early-exit BFS on ints.
+  S6: Bitboard nearest food — BFS food search on ints.
+  S7: Per-turn BitBoard instance cached for board dimensions.
+  S8: Blocked-set → bitboard conversion cached within a turn to avoid
+    redundant O(n) conversions for the same frozen set.
+  S9: Survival-tree uses bitboards natively — enemy body/attack bits
+    precomputed once at tree root, no per-node set/dict rebuilds.
+  S10: _legal_moves override uses bitboard neighbour mask instead of
+     per-direction Python loop + _in_bounds calls.
+  S11: _future_survival_tree inlines legal-move check with bitboard ops.
+  S12: Duel minimax uses tuple bodies and bitboard move generation.
+  S13: Iterative deepening reuses a transposition table and move-order hints.
+  S14: Candidate duel moves and enemy replies resolve on the same root turn.
+  S15: Candidate moves share one duel transposition/search context per turn.
+  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.
+"""
+
+from __future__ import annotations
+
+from server.GameBoard import GameBoard
+from snakes.engine.bitboard import BitBoard
+from snakes.engine.duel import BitboardDuelMixin
+from snakes.engine.duel_search import BitboardDuelSearch
+from snakes.engine.spatial import BitboardSpatialMixin
+from snakes.engine.survival import BitboardSurvivalMixin
+from snakes.engine.survival_search import CompactSurvivalSearch
+from snakes.strategies.apex import ApexBattleSnake
+
+# Direction offsets for coord-dict → tuple conversion
+_DIR_DELTAS = ((0, 1), (0, -1), (-1, 0), (1, 0))
+_DIR_NAMES = ("up", "down", "left", "right")
+
+class PrismBattleSnake_GPT_5_6_Sol(
+  BitboardDuelMixin,
+  BitboardSurvivalMixin,
+  BitboardSpatialMixin,
+  ApexBattleSnake,
+):
+  VERSION = "1.3.0"
+
+  def __init__(self) -> None:
+    super().__init__()
+    self.name = "PrismBattleSnake"
+    self.version = self.VERSION
+
+    # Prism's compact state search is fast enough to inspect one additional
+    # turn. The existing deadline checks and Apex timeout reserve still cap the
+    # work on difficult positions.
+    self._planning_depth = max(self._planning_depth, 4)
+
+    # S7: cached BitBoard instance (reused while board dimensions stay the same)
+    self._bb: BitBoard | None = None
+    self._bb_w: int = 0
+    self._bb_h: int = 0
+
+    # S9: precomputed enemy state for survival tree (set per turn in choose_move)
+    self._enemy_body_bits: int = 0  # all enemy body cells as bitboard
+    self._enemy_tail_bits: int = 0  # enemy tails that will vacate
+    self._enemy_attack_danger: int = 0  # tiles where enemy len >= our len
+    self._enemy_attack_opportunity: int = 0  # tiles where enemy len < our len
+
+    # Shared per-turn search contexts. Candidate moves overlap heavily, so
+    # rebuilding their transposition tables wastes most iterative-deepening work.
+    self._duel_search_context: BitboardDuelSearch | None = None
+    self._survival_search_context: CompactSurvivalSearch | None = None
+
+  # ── choose_move override: precompute enemy bits ──────────────────────────
+
+  def choose_move(self, game_data: GameBoard) -> str:
+    bb = self._get_bb(game_data.get_width(), game_data.get_height())
+    self._duel_search_context = None
+    self._survival_search_context = None
+
+    # S9: precompute enemy body / tail / attack bitboards for survival tree
+    other_snakes = game_data.get_other_snakes()
+    my_snake = game_data.get_my_snake()
+    my_len = my_snake.get("length", len(my_snake["body"]))
+    food_set = {(f["x"], f["y"]) for f in game_data.get_food()}
+    all_occupied = {
+      (seg["x"], seg["y"])
+      for snake in [my_snake, *other_snakes]
+      for seg in snake["body"]
+    }
+    game_type = game_data.get_type()
+    is_constrictor = game_type == "constrictor"
+    w = bb.width
+
+    enemy_body_bits = 0
+    enemy_tail_bits = 0
+    enemy_attack_danger = 0
+    enemy_attack_opportunity = 0
+
+    for snake in other_snakes:
+      for seg in snake["body"]:
+        enemy_body_bits |= 1 << (seg["y"] * w + seg["x"])
+      body = snake["body"]
+      # Check if tail will vacate
+      if not is_constrictor and len(body) >= 2:
+        tail_stacked = (
+          body[-1]["x"] == body[-2]["x"] and body[-1]["y"] == body[-2]["y"]
+        )
+        if not tail_stacked:
+          can_grow = self._enemy_can_grow_this_turn(
+            snake, food_set, all_occupied
+          )
+          if not can_grow:
+            enemy_tail_bits |= 1 << (body[-1]["y"] * w + body[-1]["x"])
+
+      # Attack map: tiles enemy head can reach in 1 move
+      eh = snake["head"]
+      e_len = snake.get("length", len(body))
+      ehx, ehy = eh["x"], eh["y"]
+      for dx, dy in _DIR_DELTAS:
+        nx, ny = ehx + dx, ehy + dy
+        if 0 <= nx < w and 0 <= ny < bb.height:
+          bit = 1 << (ny * w + nx)
+          if e_len >= my_len:
+            enemy_attack_danger |= bit
+          else:
+            enemy_attack_opportunity |= bit
+
+    self._enemy_body_bits = enemy_body_bits
+    self._enemy_tail_bits = enemy_tail_bits
+    self._enemy_attack_danger = enemy_attack_danger
+    self._enemy_attack_opportunity = enemy_attack_opportunity
+
+    move = super().choose_move(game_data)
+    history = self.get_history()
+    if history:
+      thinking = history[-1]
+      if self._duel_search_context is not None:
+        thinking["prism_duel_depth"] = self._duel_search_context.completed_depth
+        thinking["prism_duel_nodes"] = self._duel_search_context.nodes
+        thinking["prism_duel_cache_hits"] = (
+          self._duel_search_context.cache_hits
+          + self._duel_search_context.evaluation_cache_hits
+        )
+        thinking["prism_duel_deadline_exits"] = (
+          self._duel_search_context.deadline_exits
+        )
+      if self._survival_search_context is not None:
+        thinking["prism_rollout_depth"] = (
+          self._survival_search_context.completed_depth
+        )
+        thinking["prism_rollout_nodes"] = self._survival_search_context.nodes
+        thinking["prism_rollout_cache_hits"] = (
+          self._survival_search_context.cache_hits
+        )
+        thinking["prism_rollout_deadline_exits"] = (
+          self._survival_search_context.deadline_exits
+        )
+    return move

tests/bench_best_battle_snake.py

@@ -3,7 +3,7 @@ import argparse
 import time
 
 from server.GameBoard import GameBoard
-from snakes.BestBattleSnake import BestBattleSnake
+from snakes.legacy.BestBattleSnake import BestBattleSnake
 
 def build_game_state() -> dict:
   return {

tests/scripts/test_run_seeded_snake_tournament.py

@@ -0,0 +1,54 @@
+import io
+import unittest
+from unittest.mock import patch
+
+from scripts.run_seeded_snake_tournament import ENGINE_USER_AGENT, run_game
+
+class _Completed:
+  returncode = 0
+  stdout = "INFO Game completed after 42 turns. Prism was the winner.\n"
+
+class _OutputFile:
+
+  def __init__(self, *args, **kwargs):
+    self.file = io.BytesIO(
+      b'{"turn":0}\n'
+      b'{"winnerId":"snake-id","winnerName":"Prism","isDraw":false}\n'
+    )
+    self.name = "arena-output.jsonl"
+
+  def __enter__(self):
+    return self
+
+  def __exit__(self, *args):
+    self.file.close()
+
+  def seek(self, offset):
+    return self.file.seek(offset)
+
+  def __iter__(self):
+    return iter(self.file)
+
+class TestSeededSnakeTournament(unittest.TestCase):
+
+  def test_proxy_identifies_requests_as_battlesnake_engine(self):
+    self.assertIn("BattlesnakeEngine", ENGINE_USER_AGENT)
+
+  @patch("scripts.run_seeded_snake_tournament.subprocess.run", return_value=_Completed())
+  @patch("scripts.run_seeded_snake_tournament.tempfile.NamedTemporaryFile", _OutputFile)
+  def test_run_game_reads_official_engine_result(self, run):
+    result = run_game(
+      cli="battlesnake", seed=7, game_type="standard", map_name="standard",
+      players=[("Apex", "http://host:9001"), ("Prism", "http://host:9002")],
+      width=11, height=11, timeout_ms=500,
+    )
+
+    self.assertEqual(result, {
+      "seed": 7, "winner": "Prism", "draw": False, "turns": 42,
+    })
+    command = run.call_args.args[0]
+    self.assertIn("--seed", command)
+    self.assertIn("--output", command)
+
+if __name__ == "__main__":
+  unittest.main()

tests/scripts/test_snake_arena_scenarios.py

@@ -0,0 +1,31 @@
+import unittest
+
+from scripts.snake_arena_scenarios import SCENARIOS, synthetic_states
+
+class TestSnakeArenaScenarios(unittest.TestCase):
+
+  def test_default_corpus_rotates_through_every_scenario(self):
+    states = synthetic_states(len(SCENARIOS))
+
+    self.assertEqual(
+      {metadata["scenario"] for _, metadata in states},
+      set(SCENARIOS),
+    )
+
+  def test_scenario_filter_is_deterministic(self):
+    first = synthetic_states(3, ["hazard"])
+    second = synthetic_states(3, ["hazard"])
+
+    self.assertEqual(first, second)
+    self.assertTrue(all(metadata["scenario"] == "hazard" for _, metadata in first))
+
+  def test_generated_you_is_present_on_board(self):
+    for board, metadata in synthetic_states(20):
+      with self.subTest(scenario=metadata["scenario"]):
+        ids = {snake["id"] for snake in board["snakes"]}
+        self.assertIn(metadata["you"]["id"], ids)
+        self.assertGreater(board["width"], 0)
+        self.assertGreater(board["height"], 0)
+
+if __name__ == "__main__":
+  unittest.main()

tests/snakes/test_PrismBattleSnake_GPT_5_6_Sol.py

@@ -2,11 +2,11 @@ import unittest
 from time import perf_counter
 
 from snakes import SnakeBuilder, get_snake_version
-from snakes.ApexBattleSnake import ApexBattleSnake
+from snakes.engine.bitboard import BitBoard
-from snakes.bitboard import BitBoard
+from snakes.engine.duel_search import BitboardDuelSearch
-from snakes.bitboard_duel_search import BitboardDuelSearch
+from snakes.engine.survival_search import CompactSurvivalSearch
-from snakes.compact_survival_search import CompactSurvivalSearch
+from snakes.strategies.apex import ApexBattleSnake
-from snakes.PrismBattleSnake_GPT_5_6_Sol import PrismBattleSnake_GPT_5_6_Sol
+from snakes.strategies.prism import PrismBattleSnake_GPT_5_6_Sol
 
 class TestBitBoard(unittest.TestCase):
 
@@ -52,8 +52,9 @@ class TestPrismBattleSnake_GPT_5_6_Sol(unittest.TestCase):
     snake = PrismBattleSnake_GPT_5_6_Sol()
 
     self.assertEqual(snake.name, "PrismBattleSnake")
-    self.assertEqual(snake.version, "1.2.0")
+    self.assertEqual(snake.version, "1.3.0")
-    self.assertEqual(get_snake_version("PrismBattleSnake_GPT_5_6_Sol"), "1.2.0")
+    self.assertEqual(get_snake_version("PrismBattleSnake_GPT_5_6_Sol"), "1.3.0")
+    self.assertGreaterEqual(snake._planning_depth, 4)
     self.assertIsInstance(SnakeBuilder.build("PrismBattleSnake_GPT_5_6_Sol"), PrismBattleSnake_GPT_5_6_Sol)
 
   def test_bitboard_primitives_match_apex(self):
@@ -175,6 +176,21 @@ class TestPrismBattleSnake_GPT_5_6_Sol(unittest.TestCase):
 
     self.assertIs(snake._duel_search_context, first_context)
     self.assertGreater(first_context.nodes, 0)
+    self.assertGreater(first_context.completed_depth, 0)
+
+  def test_duel_evaluation_prioritizes_reachable_food_when_starving(self):
+    board = BitBoard(5, 3)
+    search = BitboardDuelSearch(
+      board=board, food={(2, 1)}, hazards=set(), hazard_count={},
+      hazard_damage=15, deadline=None,
+    )
+    my_body = [{"x": 0, "y": 1}, {"x": 0, "y": 0}]
+    enemy_body = [{"x": 4, "y": 1}, {"x": 4, "y": 0}]
+
+    hungry = search.search_depth(my_body, enemy_body, 15, 100, 0, set())
+    healthy = search.search_depth(my_body, enemy_body, 100, 100, 0, set())
+
+    self.assertLess(hungry, healthy)
 
   def test_compact_rollout_models_lethal_enemy_head_response(self):
     board = BitBoard(3, 3)
@@ -205,6 +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.assertGreaterEqual(search.completed_depth, 3)
 
   def test_bitboard_duel_search_reuses_transpositions(self):
     board = BitBoard(5, 5)

tests/snakes/test_SnakePackageLayout.py

@@ -0,0 +1,35 @@
+import unittest
+
+from snakes import SNAKE_REGISTRATIONS, SnakeBuilder
+from snakes.engine import (
+  BitBoard,
+  BitboardDuelMixin,
+  BitboardSpatialMixin,
+  BitboardSurvivalMixin,
+)
+from snakes.strategies.prism import PrismBattleSnake_GPT_5_6_Sol
+
+class TestSnakePackageLayout(unittest.TestCase):
+
+  def test_registry_uses_explicit_package_modules(self):
+    for name, registration in SNAKE_REGISTRATIONS.items():
+      with self.subTest(name=name):
+        self.assertTrue(registration.module.startswith("snakes."))
+        self.assertNotEqual(registration.module, f"snakes.{name}")
+
+  def test_registry_builds_active_strategies_after_package_move(self):
+    for name in ("ApexBattleSnake", "PrismBattleSnake_GPT_5_6_Sol"):
+      with self.subTest(name=name):
+        snake = SnakeBuilder.build(name)
+        self.assertEqual(snake.__class__.__name__, name)
+
+  def test_prism_composes_reusable_engine_mixins(self):
+    snake = PrismBattleSnake_GPT_5_6_Sol()
+
+    self.assertIsInstance(snake, BitboardDuelMixin)
+    self.assertIsInstance(snake, BitboardSpatialMixin)
+    self.assertIsInstance(snake, BitboardSurvivalMixin)
+    self.assertIsInstance(snake._get_bb(11, 11), BitBoard)
+
+if __name__ == "__main__":
+  unittest.main()

tests/snakes/test_SupremeBattleSnake.py

@@ -5,8 +5,8 @@ and that the bitboard engine itself is sound.
 """
 import unittest
 
-from snakes.SupremeBattleSnake_ClaudeOpus4_6 import SupremeBattleSnake_ClaudeOpus4_6 as SupremeBattleSnake
+from snakes.legacy.SupremeBattleSnake_ClaudeOpus4_6 import SupremeBattleSnake_ClaudeOpus4_6 as SupremeBattleSnake
-from snakes.bitboard import BitBoard
+from snakes.engine.bitboard import BitBoard
 from server.GameBoard import GameBoard
 
 # ── Helpers ───────────────────────────────────────────────────────────────────
@@ -348,7 +348,7 @@ class TestParityWithApex(unittest.TestCase):
 
   def test_trapped_corner(self):
     """Both snakes should survive a forced single-exit scenario."""
-    from snakes.ApexBattleSnake import ApexBattleSnake
+    from snakes.strategies.apex import ApexBattleSnake
 
     state = gs(my_body=[(1, 1), (1, 2), (2, 2), (2, 1)],
                other_bodies=[], foods=[(5, 5)], width=7, height=7)

tests/snakes/test_UltimateBattleSnake.py

@@ -1,6 +1,6 @@
 import unittest
 
-from snakes.UltimateBattleSnake import UltimateBattleSnake
+from snakes.legacy.UltimateBattleSnake import UltimateBattleSnake
 from server.GameBoard import GameBoard
 
 # ── Helpers ───────────────────────────────────────────────────────────────────

tests/test_BestBattleSnake.py

@@ -1,6 +1,6 @@
 import unittest
 
-from snakes.BestBattleSnake import BestBattleSnake
+from snakes.legacy.BestBattleSnake import BestBattleSnake
 from server.GameBoard import GameBoard
 
 def make_board(game_state):

tests/test_MasterSnake.py

@@ -1,5 +1,5 @@
 import unittest
-from snakes.MasterSnake import MasterSnake
+from snakes.legacy.MasterSnake import MasterSnake
 
 class TestMasterSnake(unittest.TestCase):
     def setUp(self):

tests/tests.py

@@ -12,7 +12,7 @@ in the folder where this file exists:
 """
 import unittest
 
-from snakes.LogicSnake import avoid_my_neck
+from snakes.legacy.LogicSnake import avoid_my_neck
 
 
 class AvoidNeckTest(unittest.TestCase):