GameManager, matchmaking, the game clock, live game snapshots, saving
finished games and live previews, ported from the Node backend with its
tests. Snapshots keep the Node backend's format; a test restores one the
Node backend wrote. Valkey writes and saves run off the game loop.
Quarkus 3.40 on Java 25, built with the Maven wrapper. The engine is a
line-by-line port of packages/mancala.js; a parity test replays games
recorded with the TypeScript engine, including illegal moves, and
compares every board, turn, error and the game JSON.
