Files
turnstone/examples/door-game/understone/engine/__init__.py
Patrick Buckley 99e7dc17ec feat(examples): Understone — a BBS door game as a standalone MCP server
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.
2026-06-13 04:40:40 -07:00

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Python

"""Game engine — pure stdlib mechanics with injectable clock and RNG.
This package has no knowledge of MCP, persistence, or rendering. Every
function takes its inputs explicitly (world, player, rng, clock) so the
mechanics are deterministic under test.
"""