고속 게임 엔진 골격 추가

.gitignore

@@ -9,6 +9,7 @@ wheels/
 
 # Cython-generated sources
 src/coolrl_lost_cities/games/classic/game.c
+src/coolrl_lost_cities/games/classic/engines/fast.c
 
 # Rust build output
 target/

pyproject.toml

@@ -44,6 +44,9 @@ include = ["coolrl_lost_cities*"]
     "fixtures/*.json",
     "docs/*.md",
 ]
+"coolrl_lost_cities.games.classic.engines" = [
+    "*.pyx",
+]
 
 [tool.ruff]
 line-length = 100

setup.py

@@ -13,7 +13,11 @@ extensions = cythonize(
         Extension(
             "coolrl_lost_cities.games.classic.game",
             ["src/coolrl_lost_cities/games/classic/game.pyx"],
-        )
+        ),
+        Extension(
+            "coolrl_lost_cities.games.classic.engines.fast",
+            ["src/coolrl_lost_cities/games/classic/engines/fast.pyx"],
+        ),
     ],
     language_level=3,
     compiler_directives={

src/coolrl_lost_cities/games/classic/engines/__init__.py

@@ -0,0 +1,5 @@
+from __future__ import annotations
+
+from .fast import FastGameState
+
+__all__ = ["FastGameState"]

src/coolrl_lost_cities/games/classic/engines/cards.py

@@ -0,0 +1,31 @@
+from __future__ import annotations
+
+from typing import Any
+
+
+def encode_card(color: int, rank: int, n_ranks: int) -> int:
+    return int(color) * (int(n_ranks) + 1) + int(rank)
+
+
+def decode_card(card: int, n_ranks: int) -> tuple[int, int]:
+    stride = int(n_ranks) + 1
+    return int(card) // stride, int(card) % stride
+
+
+def card_to_snapshot(card: int, n_ranks: int) -> dict[str, int]:
+    color, rank = decode_card(card, n_ranks)
+    return {"color": color, "rank": rank}
+
+
+def encode_card_snapshot(data: Any, n_ranks: int) -> int:
+    if isinstance(data, int):
+        return data
+    if isinstance(data, dict):
+        return encode_card(int(data["color"]), int(data["rank"]), n_ranks)
+    if isinstance(data, (list, tuple)) and len(data) == 2:
+        return encode_card(int(data[0]), int(data[1]), n_ranks)
+    color = getattr(data, "color", None)
+    rank = getattr(data, "rank", None)
+    if color is not None and rank is not None:
+        return encode_card(int(color), int(rank), n_ranks)
+    raise ValueError(f"invalid card snapshot: {data!r}")

src/coolrl_lost_cities/games/classic/engines/fast.pyx

@@ -0,0 +1,703 @@
+# cython: language_level=3, boundscheck=False, wraparound=False, cdivision=True, initializedcheck=False
+"""C-array based experimental Lost Cities classic engine."""
+
+from collections import Counter
+import random
+
+from libc.stdlib cimport free, malloc
+
+from ..game import IllegalMoveError, LostCitiesConfig, config_from_mapping
+
+
+cdef inline int _phase_card():
+    return 0
+
+
+cdef inline int _phase_draw():
+    return 1
+
+
+cdef class FastGameState:
+    cdef public object config
+    cdef int n_colors
+    cdef int n_ranks
+    cdef int min_rank
+    cdef int n_handshakes
+    cdef int hand_size
+    cdef int expedition_penalty
+    cdef int bonus_threshold
+    cdef int bonus_amount
+    cdef int total_cards
+    cdef int cards_per_color
+    cdef int stride
+
+    cdef int* deck
+    cdef int deck_len
+    cdef int* hands
+    cdef int hand_lens[2]
+    cdef int* expeditions
+    cdef int* expedition_lens
+    cdef int* discards
+    cdef int* discard_lens
+
+    cdef public int current_player
+    cdef int phase_id
+    cdef public int pending_discarded_color
+    cdef public int turn_count
+    cdef public bint terminal
+
+    def __cinit__(self):
+        self.deck = NULL
+        self.hands = NULL
+        self.expeditions = NULL
+        self.expedition_lens = NULL
+        self.discards = NULL
+        self.discard_lens = NULL
+
+    def __init__(self, config=None):
+        config = config or LostCitiesConfig()
+        config.validate()
+        self._configure(config)
+
+    def __dealloc__(self):
+        if self.deck != NULL:
+            free(self.deck)
+        if self.hands != NULL:
+            free(self.hands)
+        if self.expeditions != NULL:
+            free(self.expeditions)
+        if self.expedition_lens != NULL:
+            free(self.expedition_lens)
+        if self.discards != NULL:
+            free(self.discards)
+        if self.discard_lens != NULL:
+            free(self.discard_lens)
+
+    cdef void _configure(self, object config) except *:
+        self.config = config
+        self.n_colors = int(config.n_colors)
+        self.n_ranks = int(config.n_ranks)
+        self.min_rank = int(config.min_rank)
+        self.n_handshakes = int(config.n_handshakes)
+        self.hand_size = int(config.hand_size)
+        self.expedition_penalty = int(config.expedition_penalty)
+        self.bonus_threshold = int(config.bonus_threshold)
+        self.bonus_amount = int(config.bonus_amount)
+        self.total_cards = int(config.deck_size)
+        self.cards_per_color = self.n_ranks + self.n_handshakes
+        self.stride = self.n_ranks + 1
+
+        self.deck = <int*>malloc(self.total_cards * sizeof(int))
+        self.hands = <int*>malloc(2 * self.hand_size * sizeof(int))
+        self.expeditions = <int*>malloc(
+            2 * self.n_colors * self.cards_per_color * sizeof(int)
+        )
+        self.expedition_lens = <int*>malloc(2 * self.n_colors * sizeof(int))
+        self.discards = <int*>malloc(self.n_colors * self.cards_per_color * sizeof(int))
+        self.discard_lens = <int*>malloc(self.n_colors * sizeof(int))
+        if (
+            self.deck == NULL
+            or self.hands == NULL
+            or self.expeditions == NULL
+            or self.expedition_lens == NULL
+            or self.discards == NULL
+            or self.discard_lens == NULL
+        ):
+            raise MemoryError()
+        self._clear()
+
+    cdef void _clear(self) noexcept:
+        cdef int i
+        self.deck_len = 0
+        self.hand_lens[0] = 0
+        self.hand_lens[1] = 0
+        for i in range(2 * self.n_colors):
+            self.expedition_lens[i] = 0
+        for i in range(self.n_colors):
+            self.discard_lens[i] = 0
+        self.current_player = 0
+        self.phase_id = _phase_card()
+        self.pending_discarded_color = -1
+        self.turn_count = 0
+        self.terminal = False
+
+    @classmethod
+    def empty(cls, config=None):
+        return cls(config or LostCitiesConfig())
+
+    @classmethod
+    def new_game(cls, config=None, *, seed=None):
+        config = config or LostCitiesConfig()
+        config.validate()
+        deck = _build_encoded_deck(config)
+        rng = random.Random(config.seed if seed is None else seed)
+        rng.shuffle(deck)
+        return cls.new_game_from_deck(deck, config)
+
+    @classmethod
+    def new_game_from_deck(cls, deck, config=None):
+        config = config or LostCitiesConfig()
+        config.validate()
+        encoded = [_encode_card_snapshot(card, config) for card in deck]
+        if Counter(encoded) != Counter(_build_encoded_deck(config)):
+            raise ValueError("deck must contain exactly the cards defined by config")
+
+        cdef int i
+        cdef int player
+        cdef FastGameState state = cls(config)
+        state.deck_len = len(encoded)
+        for i, card in enumerate(encoded):
+            state.deck[i] = <int>card
+        for _ in range(config.hand_size):
+            for player in range(2):
+                state.deck_len -= 1
+                state.hands[state._hand_index(player, state.hand_lens[player])] = state.deck[
+                    state.deck_len
+                ]
+                state.hand_lens[player] += 1
+        state.validate_invariants()
+        return state
+
+    @classmethod
+    def from_snapshot(cls, snapshot, *, validate=True):
+        config = config_from_mapping(snapshot["config"])
+        cdef FastGameState state = cls(config)
+        cdef int player
+        cdef int color
+        cdef int index
+        cdef list cards
+
+        cards = [_encode_card_snapshot(card, config) for card in snapshot["deck"]]
+        state.deck_len = len(cards)
+        for index, card in enumerate(cards):
+            state.deck[index] = <int>card
+
+        for player in range(2):
+            cards = [
+                _encode_card_snapshot(card, config) for card in snapshot["hands"][player]
+            ]
+            state.hand_lens[player] = len(cards)
+            for index, card in enumerate(cards):
+                state.hands[state._hand_index(player, index)] = <int>card
+
+        for player in range(2):
+            for color in range(state.n_colors):
+                cards = [
+                    _encode_card_snapshot(card, config)
+                    for card in snapshot["expeditions"][player][color]
+                ]
+                state.expedition_lens[state._expedition_len_index(player, color)] = len(cards)
+                for index, card in enumerate(cards):
+                    state.expeditions[state._expedition_index(player, color, index)] = <int>card
+
+        for color in range(state.n_colors):
+            cards = [_encode_card_snapshot(card, config) for card in snapshot["discards"][color]]
+            state.discard_lens[color] = len(cards)
+            for index, card in enumerate(cards):
+                state.discards[state._discard_index(color, index)] = <int>card
+
+        state.current_player = int(snapshot.get("current_player", 0))
+        state.phase = snapshot.get("phase", "card")
+        pending = snapshot.get("pending_discarded_color")
+        state.pending_discarded_color = -1 if pending is None else int(pending)
+        state.turn_count = int(snapshot.get("turn_count", 0))
+        state.terminal = bool(snapshot.get("terminal", False))
+        if validate:
+            state.validate_invariants()
+        return state
+
+    @property
+    def phase(self):
+        return "card" if self.phase_id == _phase_card() else "draw"
+
+    @phase.setter
+    def phase(self, value):
+        if value == "card":
+            self.phase_id = _phase_card()
+        elif value == "draw":
+            self.phase_id = _phase_draw()
+        else:
+            raise ValueError(f"invalid phase: {value!r}")
+
+    @property
+    def card_action_size(self):
+        return 2 * self.hand_size
+
+    @property
+    def draw_action_size(self):
+        return 1 + self.n_colors
+
+    @property
+    def action_size(self):
+        return self.card_action_size + self.draw_action_size
+
+    def to_snapshot(self):
+        return {
+            "config": self.config.to_snapshot(),
+            "deck": [self._card_snapshot(self.deck[i]) for i in range(self.deck_len)],
+            "hands": [
+                [
+                    self._card_snapshot(self.hands[self._hand_index(player, i)])
+                    for i in range(self.hand_lens[player])
+                ]
+                for player in range(2)
+            ],
+            "expeditions": [
+                [
+                    [
+                        self._card_snapshot(
+                            self.expeditions[self._expedition_index(player, color, i)]
+                        )
+                        for i in range(
+                            self.expedition_lens[
+                                self._expedition_len_index(player, color)
+                            ]
+                        )
+                    ]
+                    for color in range(self.n_colors)
+                ]
+                for player in range(2)
+            ],
+            "discards": [
+                [
+                    self._card_snapshot(self.discards[self._discard_index(color, i)])
+                    for i in range(self.discard_lens[color])
+                ]
+                for color in range(self.n_colors)
+            ],
+            "current_player": self.current_player,
+            "phase": self.phase,
+            "pending_discarded_color": (
+                None if self.pending_discarded_color < 0 else self.pending_discarded_color
+            ),
+            "turn_count": self.turn_count,
+            "terminal": self.terminal,
+        }
+
+    cpdef FastGameState clone(self):
+        cdef FastGameState other = FastGameState(self.config)
+        cdef int i
+        other.deck_len = self.deck_len
+        for i in range(self.deck_len):
+            other.deck[i] = self.deck[i]
+        for i in range(2 * self.hand_size):
+            other.hands[i] = self.hands[i]
+        other.hand_lens[0] = self.hand_lens[0]
+        other.hand_lens[1] = self.hand_lens[1]
+        for i in range(2 * self.n_colors * self.cards_per_color):
+            other.expeditions[i] = self.expeditions[i]
+        for i in range(2 * self.n_colors):
+            other.expedition_lens[i] = self.expedition_lens[i]
+        for i in range(self.n_colors * self.cards_per_color):
+            other.discards[i] = self.discards[i]
+        for i in range(self.n_colors):
+            other.discard_lens[i] = self.discard_lens[i]
+        other.current_player = self.current_player
+        other.phase_id = self.phase_id
+        other.pending_discarded_color = self.pending_discarded_color
+        other.turn_count = self.turn_count
+        other.terminal = self.terminal
+        return other
+
+    cpdef list legal_card_mask(self):
+        cdef list mask = [False] * (2 * self.hand_size)
+        cdef int slot
+        cdef int card
+        if self.terminal:
+            return mask
+        for slot in range(self.hand_lens[self.current_player]):
+            card = self.hands[self._hand_index(self.current_player, slot)]
+            mask[2 * slot] = self.can_play_encoded_card(self.current_player, card)
+            mask[2 * slot + 1] = True
+        return mask
+
+    cpdef list legal_draw_mask(self):
+        cdef list mask = [False] * (1 + self.n_colors)
+        cdef int color
+        if self.terminal:
+            return mask
+        mask[0] = self.deck_len > 0
+        for color in range(self.n_colors):
+            mask[1 + color] = (
+                self.discard_lens[color] > 0
+                and (self.pending_discarded_color < 0 or color != self.pending_discarded_color)
+            )
+        return mask
+
+    cpdef list legal_mask(self):
+        if self.phase_id == _phase_card():
+            return self.legal_card_mask()
+        return self.legal_draw_mask()
+
+    cpdef list unified_legal_mask(self):
+        cdef list result
+        if self.phase_id == _phase_card():
+            result = self.legal_card_mask()
+            result.extend([False] * (1 + self.n_colors))
+            return result
+        result = [False] * (2 * self.hand_size)
+        result.extend(self.legal_draw_mask())
+        return result
+
+    cpdef int from_unified_action(self, int action_id):
+        cdef int card_action_size = 2 * self.hand_size
+        cdef int action_size = card_action_size + 1 + self.n_colors
+        if action_id < 0 or action_id >= action_size:
+            raise IllegalMoveError(f"action {action_id} is out of range")
+        if self.phase_id == _phase_card():
+            if action_id >= card_action_size:
+                raise IllegalMoveError(
+                    f"card action {action_id} is illegal during card phase"
+                )
+            return action_id
+        if action_id < card_action_size:
+            raise IllegalMoveError(
+                f"card action {action_id} is illegal during draw phase"
+            )
+        return action_id - card_action_size
+
+    def to_unified_action(self, int action_id, phase=None):
+        cdef object p = self.phase if phase is None else phase
+        if p == "card":
+            if action_id < 0 or action_id >= 2 * self.hand_size:
+                raise IllegalMoveError(f"card action {action_id} is out of range")
+            return action_id
+        if action_id < 0 or action_id >= 1 + self.n_colors:
+            raise IllegalMoveError(f"draw action {action_id} is out of range")
+        return 2 * self.hand_size + action_id
+
+    cpdef apply_action(self, int action_id):
+        if self.terminal:
+            raise IllegalMoveError("game is already terminal")
+        cdef list mask = self.legal_mask()
+        if action_id < 0 or action_id >= len(mask) or not mask[action_id]:
+            raise IllegalMoveError(
+                f"illegal action {action_id} in phase {self.phase} "
+                f"for player {self.current_player}"
+            )
+        if self.phase_id == _phase_card():
+            self._apply_card_action(action_id)
+        else:
+            self._apply_draw_action(action_id)
+
+    cpdef apply_unified_action(self, int action_id):
+        self.apply_action(self.from_unified_action(action_id))
+
+    cpdef object apply_action_with_undo(self, int action_id):
+        if self.terminal:
+            raise IllegalMoveError("game is already terminal")
+        cdef list mask = self.legal_mask()
+        if action_id < 0 or action_id >= len(mask) or not mask[action_id]:
+            raise IllegalMoveError(
+                f"illegal action {action_id} in phase {self.phase} "
+                f"for player {self.current_player}"
+            )
+        cdef object undo
+        if self.phase_id == _phase_card():
+            undo = self._card_action_undo(action_id)
+            self._apply_card_action(action_id)
+        else:
+            undo = self._draw_action_undo(action_id)
+            self._apply_draw_action(action_id)
+        return undo
+
+    cpdef object apply_unified_action_with_undo(self, int action_id):
+        return self.apply_action_with_undo(self.from_unified_action(action_id))
+
+    cpdef undo_action(self, object undo):
+        cdef str phase = undo[0]
+        if phase == "card":
+            self._undo_card_action(undo)
+            return
+        if phase == "draw":
+            self._undo_draw_action(undo)
+            return
+        raise ValueError(f"invalid undo phase: {phase!r}")
+
+    cpdef bint can_play_encoded_card(self, int player, int card):
+        cdef int color = self._card_color(card)
+        cdef int rank = self._card_rank(card)
+        cdef int last_numeric
+        if color < 0 or color >= self.n_colors:
+            return False
+        if rank < 0 or rank > self.n_ranks:
+            return False
+        last_numeric = self.last_numeric_rank(player, color)
+        if rank == 0:
+            return last_numeric == 0
+        return rank > last_numeric
+
+    cpdef int last_numeric_rank(self, int player, int color):
+        cdef int length = self.expedition_lens[self._expedition_len_index(player, color)]
+        cdef int i
+        cdef int rank
+        cdef int best = 0
+        for i in range(length):
+            rank = self._card_rank(self.expeditions[self._expedition_index(player, color, i)])
+            if rank > best:
+                best = rank
+        return best
+
+    cpdef int expedition_score(self, int player, int color):
+        cdef int length = self.expedition_lens[self._expedition_len_index(player, color)]
+        cdef int handshakes = 0
+        cdef int numeric_sum = 0
+        cdef int i
+        cdef int rank
+        cdef int score
+        if length == 0:
+            return 0
+        for i in range(length):
+            rank = self._card_rank(self.expeditions[self._expedition_index(player, color, i)])
+            if rank == 0:
+                handshakes += 1
+            else:
+                numeric_sum += self.min_rank + rank - 1
+        score = (numeric_sum + self.expedition_penalty) * (handshakes + 1)
+        if length >= self.bonus_threshold:
+            score += self.bonus_amount
+        return score
+
+    cpdef int total_score(self, int player):
+        cdef int total = 0
+        cdef int color
+        for color in range(self.n_colors):
+            total += self.expedition_score(player, color)
+        return total
+
+    cpdef int score_diff(self, int player=0):
+        return self.total_score(player) - self.total_score(1 - player)
+
+    def validate_invariants(self):
+        self.config.validate()
+        if self.current_player not in (0, 1):
+            raise ValueError("current_player must be 0 or 1")
+        if self.phase_id not in (_phase_card(), _phase_draw()):
+            raise ValueError("invalid phase")
+        if self.pending_discarded_color >= self.n_colors:
+            raise ValueError("pending_discarded_color is out of range")
+        if self.hand_lens[0] > self.hand_size or self.hand_lens[1] > self.hand_size:
+            raise ValueError("hand exceeds hand_size")
+        if Counter(_all_cards_from_snapshot(self.to_snapshot())) != Counter(
+            _build_encoded_deck(self.config)
+        ):
+            raise ValueError("card conservation failed")
+        if self.phase_id == _phase_card() and self.pending_discarded_color >= 0:
+            raise ValueError("pending_discarded_color must be None during card phase")
+        if self.pending_discarded_color >= 0 and self.discard_lens[self.pending_discarded_color] == 0:
+            raise ValueError("pending discard color must have a discard pile card")
+        any_legal = any(self.unified_legal_mask())
+        if self.terminal and any_legal:
+            raise ValueError("terminal state must have no legal actions")
+        if not self.terminal and not any_legal:
+            raise ValueError("non-terminal state must have at least one legal action")
+
+    cdef object _card_action_undo(self, int action_id):
+        cdef int slot = action_id // 2
+        cdef bint play = action_id % 2 == 0
+        cdef int card = self.hands[self._hand_index(self.current_player, slot)]
+        return (
+            "card",
+            self.current_player,
+            action_id,
+            self.pending_discarded_color,
+            self.terminal,
+            slot,
+            play,
+            card,
+        )
+
+    cdef object _draw_action_undo(self, int action_id):
+        cdef int card
+        if action_id == 0:
+            card = self.deck[self.deck_len - 1]
+        else:
+            card = self.discards[self._discard_index(action_id - 1, self.discard_lens[action_id - 1] - 1)]
+        return (
+            "draw",
+            self.current_player,
+            action_id,
+            self.pending_discarded_color,
+            self.terminal,
+            self.turn_count,
+            card,
+        )
+
+    cdef void _apply_card_action(self, int action_id) except *:
+        cdef int slot = action_id // 2
+        cdef bint play = action_id % 2 == 0
+        cdef int player = self.current_player
+        cdef int card = self.hands[self._hand_index(player, slot)]
+        cdef int color = self._card_color(card)
+        cdef int i
+        cdef int length_index
+        for i in range(slot, self.hand_lens[player] - 1):
+            self.hands[self._hand_index(player, i)] = self.hands[self._hand_index(player, i + 1)]
+        self.hand_lens[player] -= 1
+        if play:
+            length_index = self._expedition_len_index(player, color)
+            self.expeditions[self._expedition_index(player, color, self.expedition_lens[length_index])] = card
+            self.expedition_lens[length_index] += 1
+        else:
+            self.discards[self._discard_index(color, self.discard_lens[color])] = card
+            self.discard_lens[color] += 1
+            self.pending_discarded_color = color
+        self.phase_id = _phase_draw()
+        if self.deck_len == 0 and not self._has_any_legal_draw():
+            self.terminal = True
+
+    cdef void _apply_draw_action(self, int action_id) except *:
+        cdef int player = self.current_player
+        cdef int card
+        cdef int color
+        if action_id == 0:
+            self.deck_len -= 1
+            card = self.deck[self.deck_len]
+        else:
+            color = action_id - 1
+            self.discard_lens[color] -= 1
+            card = self.discards[self._discard_index(color, self.discard_lens[color])]
+        self.hands[self._hand_index(player, self.hand_lens[player])] = card
+        self.hand_lens[player] += 1
+        self.pending_discarded_color = -1
+        self.turn_count += 1
+        if self.deck_len == 0:
+            self.terminal = True
+            return
+        self.current_player = 1 - self.current_player
+        self.phase_id = _phase_card()
+
+    cdef void _undo_card_action(self, object undo) except *:
+        cdef int player = <int>undo[1]
+        cdef int pending_before = <int>undo[3]
+        cdef bint terminal_before = <bint>undo[4]
+        cdef int slot = <int>undo[5]
+        cdef bint play = <bint>undo[6]
+        cdef int card = <int>undo[7]
+        cdef int color = self._card_color(card)
+        cdef int moved
+        cdef int i
+        cdef int length_index
+        if play:
+            length_index = self._expedition_len_index(player, color)
+            self.expedition_lens[length_index] -= 1
+            moved = self.expeditions[self._expedition_index(player, color, self.expedition_lens[length_index])]
+        else:
+            self.discard_lens[color] -= 1
+            moved = self.discards[self._discard_index(color, self.discard_lens[color])]
+        if moved != card:
+            raise ValueError("undo card mismatch")
+        for i in range(self.hand_lens[player], slot, -1):
+            self.hands[self._hand_index(player, i)] = self.hands[self._hand_index(player, i - 1)]
+        self.hands[self._hand_index(player, slot)] = card
+        self.hand_lens[player] += 1
+        self.current_player = player
+        self.phase_id = _phase_card()
+        self.pending_discarded_color = pending_before
+        self.terminal = terminal_before
+
+    cdef void _undo_draw_action(self, object undo) except *:
+        cdef int player = <int>undo[1]
+        cdef int action_id = <int>undo[2]
+        cdef int pending_before = <int>undo[3]
+        cdef bint terminal_before = <bint>undo[4]
+        cdef int turn_count_before = <int>undo[5]
+        cdef int card = <int>undo[6]
+        cdef int moved
+        cdef int color
+        self.hand_lens[player] -= 1
+        moved = self.hands[self._hand_index(player, self.hand_lens[player])]
+        if moved != card:
+            raise ValueError("undo draw mismatch")
+        if action_id == 0:
+            self.deck[self.deck_len] = card
+            self.deck_len += 1
+        else:
+            color = action_id - 1
+            self.discards[self._discard_index(color, self.discard_lens[color])] = card
+            self.discard_lens[color] += 1
+        self.current_player = player
+        self.phase_id = _phase_draw()
+        self.pending_discarded_color = pending_before
+        self.turn_count = turn_count_before
+        self.terminal = terminal_before
+
+    cdef bint _has_any_legal_draw(self):
+        cdef int color
+        if self.deck_len > 0:
+            return True
+        for color in range(self.n_colors):
+            if (
+                self.discard_lens[color] > 0
+                and (self.pending_discarded_color < 0 or color != self.pending_discarded_color)
+            ):
+                return True
+        return False
+
+    cdef inline int _hand_index(self, int player, int slot):
+        return player * self.hand_size + slot
+
+    cdef inline int _expedition_len_index(self, int player, int color):
+        return player * self.n_colors + color
+
+    cdef inline int _expedition_index(self, int player, int color, int index):
+        return (player * self.n_colors + color) * self.cards_per_color + index
+
+    cdef inline int _discard_index(self, int color, int index):
+        return color * self.cards_per_color + index
+
+    cdef inline int _encode_card(self, int color, int rank):
+        return color * self.stride + rank
+
+    cdef inline int _card_color(self, int card):
+        return card // self.stride
+
+    cdef inline int _card_rank(self, int card):
+        return card % self.stride
+
+    cdef object _card_snapshot(self, int card):
+        return {"color": self._card_color(card), "rank": self._card_rank(card)}
+
+
+def _build_encoded_deck(config):
+    deck = []
+    stride = int(config.n_ranks) + 1
+    for color in range(int(config.n_colors)):
+        for _ in range(int(config.n_handshakes)):
+            deck.append(color * stride)
+        for rank in range(1, int(config.n_ranks) + 1):
+            deck.append(color * stride + rank)
+    return deck
+
+
+def _encode_card_snapshot(data, config):
+    stride = int(config.n_ranks) + 1
+    if isinstance(data, int):
+        return int(data)
+    if isinstance(data, dict):
+        return int(data["color"]) * stride + int(data["rank"])
+    if isinstance(data, (list, tuple)) and len(data) == 2:
+        return int(data[0]) * stride + int(data[1])
+    color = getattr(data, "color", None)
+    rank = getattr(data, "rank", None)
+    if color is not None and rank is not None:
+        return int(color) * stride + int(rank)
+    raise ValueError(f"invalid card snapshot: {data!r}")
+
+
+def _all_cards_from_snapshot(snapshot):
+    cards = []
+    config = config_from_mapping(snapshot["config"])
+    for card in snapshot["deck"]:
+        cards.append(_encode_card_snapshot(card, config))
+    for hand in snapshot["hands"]:
+        for card in hand:
+            cards.append(_encode_card_snapshot(card, config))
+    for player_expeditions in snapshot["expeditions"]:
+        for expedition in player_expeditions:
+            for card in expedition:
+                cards.append(_encode_card_snapshot(card, config))
+    for discard in snapshot["discards"]:
+        for card in discard:
+            cards.append(_encode_card_snapshot(card, config))
+    return cards

src/coolrl_lost_cities/games/classic/game.pyx

@@ -1,4 +1,11 @@
 # cython: language_level=3, boundscheck=False, wraparound=False, cdivision=True, initializedcheck=False
+"""Deprecated compatibility rules engine for Lost Cities classic.
+
+This module remains the public engine while the replacement fast engine is
+developed under ``coolrl_lost_cities.games.classic.engines``. New traversal,
+simulation, and training work should target the fast engine once it exists.
+"""
+
 from collections import Counter
 from dataclasses import dataclass, fields
 import random
@@ -10,6 +17,7 @@ cimport cython
 
 
 Phase = Literal["card", "draw"]
+DEPRECATED_ENGINE = True
 
 
 class IllegalMoveError(ValueError):

tests/games/classic/engines/test_fast_parity.py

@@ -0,0 +1,105 @@
+from __future__ import annotations
+
+import random
+
+from coolrl_lost_cities.games.classic.game import Card, GameState, LostCitiesConfig
+
+from coolrl_lost_cities.games.classic.engines import FastGameState
+
+
+def _small_config() -> LostCitiesConfig:
+    return LostCitiesConfig(
+        n_colors=2,
+        n_ranks=2,
+        min_rank=1,
+        n_handshakes=0,
+        hand_size=1,
+        expedition_penalty=0,
+        bonus_threshold=99,
+        bonus_amount=0,
+    )
+
+
+def test_fast_new_game_from_deck_matches_game_state_snapshot() -> None:
+    config = _small_config()
+    deck = [
+        Card(0, 1),
+        Card(0, 2),
+        Card(1, 1),
+        Card(1, 2),
+    ]
+
+    classic = GameState.new_game_from_deck(deck, config)
+    fast = FastGameState.new_game_from_deck(deck, config)
+
+    assert fast.to_snapshot() == classic.to_snapshot()
+    fast.validate_invariants()
+
+
+def test_fast_snapshot_roundtrip_preserves_snapshot() -> None:
+    config = LostCitiesConfig(seed=11)
+    classic = GameState.new_game(config)
+    fast = FastGameState.from_snapshot(classic.to_snapshot())
+
+    assert fast.to_snapshot() == classic.to_snapshot()
+    restored = FastGameState.from_snapshot(fast.to_snapshot())
+    assert restored.to_snapshot() == fast.to_snapshot()
+
+
+def test_fast_random_action_sequence_matches_game_state() -> None:
+    config = LostCitiesConfig(
+        n_colors=3,
+        n_ranks=5,
+        min_rank=2,
+        n_handshakes=1,
+        hand_size=5,
+    )
+    for seed in range(48):
+        classic = GameState.new_game(config, seed=seed)
+        fast = FastGameState.new_game(config, seed=seed)
+        rng = random.Random(seed ^ 0xF457)
+        steps = 0
+
+        while True:
+            assert fast.to_snapshot() == classic.to_snapshot()
+            assert fast.unified_legal_mask() == classic.unified_legal_mask()
+            assert fast.score_diff(0) == classic.score_diff(0)
+            if classic.terminal:
+                break
+
+            legal = [
+                index for index, is_legal in enumerate(classic.unified_legal_mask()) if is_legal
+            ]
+            action = rng.choice(legal)
+            classic.apply_unified_action(action)
+            fast.apply_unified_action(action)
+            steps += 1
+            assert steps < 1000
+
+
+def test_fast_apply_undo_restores_every_legal_action() -> None:
+    config = LostCitiesConfig(
+        n_colors=3,
+        n_ranks=5,
+        min_rank=2,
+        n_handshakes=1,
+        hand_size=5,
+    )
+    for seed in range(32):
+        state = FastGameState.new_game(config, seed=seed)
+        rng = random.Random(seed ^ 0xFA57A11)
+        steps = 0
+
+        while not state.terminal:
+            legal = [index for index, is_legal in enumerate(state.unified_legal_mask()) if is_legal]
+            for action in legal:
+                candidate = state.clone()
+                before = candidate.to_snapshot()
+                undo = candidate.apply_unified_action_with_undo(action)
+                candidate.undo_action(undo)
+                assert candidate.to_snapshot() == before
+                candidate.validate_invariants()
+
+            state.apply_unified_action(rng.choice(legal))
+            steps += 1
+            assert steps < 1000