CORS preflight

<div class="n-demo"><div class="n-head"><strong>CORS GATE</strong><span>LIVE TRACE</span></div><div class="n-stage"><div class="cors-flow"><div class="n-box mono" id="c0">OPTIONS /api</div><div class="cors-gate" id="c1">ALLOW?</div><div class="n-box mono" id="c2">POST /api</div><div class="cors-note" id="c3">checking policy</div></div></div><div class="n-foot">tap to step · auto replay</div></div>

.n-demo{width:min(94vw,760px);height:min(88vh,324px);padding:clamp(9px,2.2vmin,18px);border:1px solid var(--line);border-radius:13px;background:var(--surface);display:flex;flex-direction:column;gap:clamp(5px,1.3vmin,10px);font:600 clamp(12px,2.4vmin,16px)/1.3 "Pretendard Variable",Pretendard,-apple-system,BlinkMacSystemFont,"Apple SD Gothic Neo",sans-serif;overflow:hidden}.n-head,.n-foot{display:flex;justify-content:space-between;align-items:center;color:var(--muted)}.n-head strong{color:var(--accent)}.n-head span,.n-foot{font-size:12px}.n-stage{flex:1;min-height:0;position:relative;display:flex;align-items:center;justify-content:center;gap:clamp(4px,1vmin,10px)}.mono{font-family:ui-monospace,SFMono-Regular,Consolas,monospace}.n-box{padding:clamp(5px,1.5vmin,11px);border:1px solid var(--line);border-radius:8px;background:var(--bg);text-align:center}.n-on{border-color:var(--accent)!important;color:var(--accent)!important;background:color-mix(in srgb,var(--accent) 12%,var(--surface))!important}.n-muted{color:var(--muted)}@media(max-width:400px){.n-head span{display:none}}.cors-flow{width:95%;display:grid;grid-template-columns:1fr .8fr 1fr;align-items:center;gap:6px}.cors-gate{border:2px solid var(--line);border-radius:50%;padding:12px 3px;text-align:center}.cors-flow .n-box{padding:9px 2px}.cors-note{grid-column:1/-1;text-align:center;color:var(--muted)}

let step=0;function advance(){const notes=['send preflight','allow origin + method','send actual request','deny: stop at browser'];for(let i=0;i<3;i++)document.getElementById('c'+i).classList.toggle('n-on',i===Math.min(step,2)&&step!==3);document.getElementById('c3').textContent=notes[step];document.getElementById('c1').textContent=step===3?'DENY':'ALLOW?';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()})}