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Building a Game Engine in a Day

The vellymon.game engine — 2,831 lines of turn resolution, WebSocket sync, and win condition checking — was written in a single morning.

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Phase 6 of the vellymon lobby build was the game server rewrite — a complete engine for simultaneous-action RPG combat. 9 PRs, 2,831 lines, shipped between 10 AM and noon on April 19.

The engine handles:

- Simultaneous command resolution with speed-based priority - Three win conditions: Elimination, Occupation, Energy Accumulation - Energy as a unified team-wide pool - Server-authoritative turn timing with 30-second turns - WebSocket-based real-time state sync

Each module was its own PR: types, config, win conditions, energy, commands, bench/spawn, board, turn timer, and the orchestrator that ties them together.