Retries and backoff

<div class="n-demo"><div class="n-head"><strong>BACKOFF TIMELINE</strong><span>LIVE TRACE</span></div><div class="n-stage"><div class="back"><div class="back-track"><span id="b0">1</span><span id="b1">2</span><span id="b2">3</span><span id="b3">OK</span></div><div class="back-times mono">0s <span>+1s</span><span>+2s</span><span>+4s</span></div><div id="back-note">attempt 1 failed</div></div></div><div class="n-foot">tap to step · auto replay</div></div>

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let step=0;function advance(){for(let i=0;i<4;i++)document.getElementById('b'+i).classList.toggle('n-on',i===step);document.getElementById('back-note').textContent=step===3?'recovered after delay':'attempt '+(step+1)+' failed';step=(step+1)%4}
const clickTarget=document.querySelector('.n-demo');if(clickTarget&&typeof advance==='function'){advance();const timer=setInterval(advance,1050);clickTarget.addEventListener('pointerdown',()=>{clearInterval(timer);advance()})}