ADR-0004 · accepted

One press reaches one step

Amended by ADR-0010 on 2026-11-04: GameLoop.frame runs this step order under either budget, endFrame runs once per frame call that ran a step, and packages/runtime/src/loop.test.ts now checks the order and both behaviors.

Amended by ADR-0012 on 2026-11-04: on a lockstep peer, the engine samples the local device source on its own schedule and calls its endStep and endFrame; GameLoop reads the buffer of merged inputs.

Amended on 2026-11-06: GameDriver is gone; makeGameEngine's attach is the requestAnimationFrame adapter, see the note on ADR-0010.

A slow frame runs up to five catch-up steps, and presses used to be reset once per frame, so one press moved push-puzzle's player up to five cells and one undo undid up to five turns (#15, finding 1). GameDriver now calls InputSource.endStep after every step, and endFrame once per frame that ran a step. A source that needs one press to reach one step resets its presses in endStep, as push-puzzle does with InputController.consumePresses().

Considered Options

• Call endFrame after every step. It was tried in #4 and reverted. It keeps the hook's name and type but changes when it runs, so the compiler can't flag it. Per-frame work in a source would then run up to five times a frame, and InputController.endFrame polls the gamepads.
• Make read report each press once. Every input source would then have to do this itself, as push-puzzle's first workaround did.

Consequences

• For each step the driver calls read, step, then endStep. endFrame follows the frame's last endStep. packages/runtime/src/runtime.test.ts checks this order and both behaviors.
• A press made during a frame that runs no step waits for the next step.
• Survivors reads only axes, so it needs no endStep.
• #25 sends each step's input to the other peers. A press lands in exactly one step's input, so every peer applies it once.
• endFrame is tied to frames that ran a step. If #25 moves stepping off requestAnimationFrame (ADR-0003), it has to say when endFrame runs.