Design around one-cycle state transitions

GPC is easier to reason about when main coordinates small stages:

main {
    read_inputs();
    update_mode();
    update_game_state();
    calculate_outputs();
    apply_final_outputs();
    handle_save_request();
}

This is an architectural outline, not a standalone script; each named stage needs a user-function body. Each stage should have a narrow contract. The final-output stage owns writes to the console-facing axes/buttons. Saving is separate from viewing/editing.