Mario — arrow keys to walk, up to jump

How it works

The physics is verbatim from the classic Elm-architecture demo. The input handling is the point: arrows are state inside the process and only ticks step the world — holding a key down re-sends the same arrows and moves nothing, so the classic key-repeat double-step cannot happen (it's regression-tested).

for await (const msg of self) {
  if (msg.type === 'arrows') {
    arrows = { x: msg.x, y: msg.y }     // input is state, not a step
  } else {
    m = step(msg.delta, arrows, m)      // only ticks move the world
    yield m
  }
}

The view yields once; two attribute bindings (position style, sprite src) carry every frame. CI asserts the budgets: one view yield total, at most 3 DOM writes per frame, zero node churn — mario.golden.test.ts.