A shared-world, classic-door-game-style door game in examples/door-game/: a pure-stdlib
game engine (tile overworld + location menus, seeded combat, daily turn
budget, leveling, shop, event log, leaderboard) behind nine sync door_*
FastMCP tools returning monochrome box-drawing frames. The connecting
session's LLM plays dungeon master — tool descriptions plus a door_help
manual teach a cold model to run the game with zero setup, while the server
owns all dice and state, so the DM narrates around facts it cannot bend.
Non-obvious decisions:
- engine/screen/world/persistence import stdlib only; server.py is the only
mcp import. All nine handlers are sync def: on mcp 1.27 they execute
inline on the event loop (verified against func_metadata), so tool bodies
serialize and one SQLite connection (WAL, per-action commit) is safe.
check_same_thread=False exists only because the Store may be constructed
on a different thread than the serving loop.
- Streamable HTTP serves ONE process = one shared world (players appear on
each other's maps; async "while you were away" event feed); stdio is the
solo-world fallback.
- The economy is content, not code: daily_turns, costs, xp curve, bestow
budget, and dungeon tiers live in world.json settings, band-validated by
the loader. door_bestow gives the DM capped, event-audited largesse
(gold/heal only, never turns) so story generosity cannot melt the shared
leaderboard.
- Player names and bestow reasons are sanitized (printable-only, length
caps) because they flow into the shared event log and from there into
other players' DM context — embedded newlines would forge log lines.
- Daily turn/bestow pools lazy-reset per UTC day on every consuming path
(injectable clock); the dungeon gauntlet is a fixed boss ladder by design.
Tests: 109 — engine units with seeded RNG + frozen clock, hand-authored
golden frames paired with structural asserts, loader band rejections, and
one real-wire integration test (uvicorn + streamablehttp_client) with a
two-session shared-world assertion. Negative-tested by reverting the guard
and watching the suite fail: the daily turn-budget guard, the bestow cap,
and the sanitizer's isprintable clause.
Patrick Buckley