coolrl-lost-cities

Focused Lost Cities extraction from the legacy coolrl repository.

The current implementation starts with the classic two-player card game:

• classic 5-expedition rules by default
• Python/Cython game engine
• env wrapper
• random, discard-only, and safe-heuristic bots
• core rule, scoring, mask, env, canonical-state, bot, and GUI smoke tests

Training code, Deep CFR, learned-policy evaluation, GUI, and web client are intentionally outside the first port.

Development

uv run pytest tests/games/classic
uv run lost-cities-classic

For future GUI work, install the optional GUI dependencies:

uv sync --extra gui

Run the classic pygame GUI:

uv run lost-cities-classic-gui --mode pvc --bot safe-heuristic

The GUI uses the in-process Cython game engine.

JAX Rules Engine

lost_cities_jax is a standalone pure rules simulator for one two-player Lost Cities round. It does not contain neural networks, PPO, CFR, MCTS, match wrappers, bots, or rule variants.

Public API:

from lost_cities_jax import (
    OBS_DIM,
    N_ACTIONS,
    State,
    batched_legal_mask,
    batched_obs,
    batched_reset,
    batched_step,
    board_score,
    legal_action_mask,
    observation,
    reset,
    reset_from_order,
    score,
    step,
)

Core functions are pure JAX functions:

• reset(rng) -> State
• reset_from_order(deck_order) -> State
• legal_action_mask(state) -> bool[96]
• step(state, action) -> (State, float32[2], bool)
• score(state) -> float32[2]
• board_score(state) -> float32[2]
• observation(state, player) -> float32[454]

The batched exports are jax.jit(jax.vmap(...)) wrappers. Illegal actions and done-state actions are defined as no-op transitions with zero reward; training code should still sample only from legal_action_mask.

Rule Summary

One round uses 60 cards: five colors, each with three handshakes and ranks 2 through 10. Each player starts with eight cards, then each ply must place one hand card to the matching expedition or discard pile and draw one card from the deck or a discard pile. A player may not draw the card they just discarded.

Expedition numbers must be strictly increasing. Handshakes may be played only before any number in that color. The round ends immediately when the final deck card is drawn, or at MAX_STEPS == 400; forced termination is scored exactly like natural termination.

Scoring per player/color:

empty column: 0
non-empty: (sum(number ranks) - 20) * (1 + handshake_count)
bonus: +20 if total column length >= 8, not multiplied

Encodings

Cards:

Field	Encoding
card_id	color * 12 + slot
color	0..4
slot 0..2	handshake
slot 3..11	ranks 2..10, with rank = slot - 1

Actions (N_ACTIONS == 96):

action_id = hand_slot * 12 + place_type * 6 + draw_source
hand_slot   = 0..7, current player's hand sorted by card_id
place_type  = 0 play, 1 discard
draw_source = 0 deck, 1..5 discard pile color 0..4

Observation (OBS_DIM == 454):

• 60 cards x 7 one-hot channels: my hand, my board, opponent board, discard top, discard non-top, opponent public hand, unknown.
• 34 scalar features: remaining deck /44, opponent unknown hand count /8, step count /400, current-player then opponent col_top /10, col_hs /3, col_len /12, and current board score difference (player - opponent) /780.

Verification

uv run pytest -q tests/lost_cities_jax
uv run pytest -q
uv run ruff check .

Large differential profiles:

# CI profile: 100,000 random legal-policy games
CI=1 uv run pytest -q tests/lost_cities_jax/test_differential.py

# Full profile: 1,000,000 random legal-policy games
uv run pytest -q tests/lost_cities_jax/test_differential.py --full

Throughput benchmark:

flock -n .compute.lock uv run python benchmarks/throughput.py

Measured on 2026-07-04 with CPU JAX backend:

backend=cpu
batch_size=8192
steps=256
elapsed_sec=4.944725
steps_per_sec=424119.01

DECISIONS.md

• Explicit deck_order dealing uses the first eight cards for player 0 and the next eight for player 1. The remaining cards are drawn from index 16. This is equivalent under a uniform shuffle and is fixed by tests.
• After a legal terminal transition, to_move is advanced to the next player, but done=True makes all later steps complete no-ops.
• Terminal reward is emitted only on the transition that reaches done=True. Done-state no-op steps return zero reward.
• Observation scalar normalization is implementation-defined as documented above and locked by the exported OBS_DIM.

Basic Usage

from coolrl_lost_cities.games.classic import GameState, build_bot, classic_config

state = GameState.new_game(classic_config(seed=1))
bot = build_bot("random", seed=1)

while not state.terminal:
    state.apply_action(bot.act(state))

print(state.total_score(0), state.total_score(1))

See classic port notes for the current direction.