Stress-test a small multiplayer game server, then write a minimal crash reproducer and a fix that holds up under hidden stress tests

# Stress-test a small multiplayer game server, find the bug that crashes it, write a minimal reproducer and fix it `game/` is a small synthetic multiplayer city-builder server that runs in-process, with no network and no ports; `SPEC.md` says how it must behave. Players report that the server sometimes crashes during busy sessions. Everything is synthetic and offline; don't open any network port. Rules: - You may edit files under `game/` (that is the fix) as well as writing under `out/`; this overrides the general rule below. - Find the crash: a sequence of client messages (several clients may send in the same tick) that makes `Server.process` raise. There is one such bug. - Reproducer: write `out/repro.py`, at most 60 lines, that drives the server through `game.server` or `game.sim` (it is run from the folder root with the folder on PYTHONPATH, as `python3 out/repro.py`). On the code as shipped, it must crash with the server's own uncaught exception, raised inside `game/`. Once the bug is fixed, it must run cleanly and exit 0. - Fix: edit the code under `game/` so that the server never raises and follows SPEC.md, including on your reproducer's input. A rejected request must change nothing, so swallowing exceptions is not a fix if it leaves half-done changes. Keep the public API unchanged. - No regression: behaviour on normal sessions must stay exactly as it was (same replies and the same `world.snapshot()` after every tick). - Write `out/bug.json`: `{"exception": "<exception type raised>", "crash_module": "<path of the game/ file where it is raised, e.g. game/x.py>", "trigger": "<one sentence>"}`. ## How this run works - Work on your own: nobody will answer questions in this task, and writing to `ask/` counts against the run. - Write only under `out/`. Create `out/` if it is missing. Inputs are synthetic; don't fetch anything from the network. - Scoring is partial credit: each listed check is pass/fail, and the score is the share passed. Numbers are compared to within 0.005 unless the task says otherwise.