use cache 경계

<section class="stage"><div class="heading">USE CACHE <span class="hint">same input, reused result</span></div><div class="pair"><div class="tile list"><b>PRODUCTS</b><span>A · B · C</span><small>cache hit</small></div><div class="tile cart"><b>CART</b><span id="cart-count">0 items</span><small>new request</small></div></div><div class="caption">One boundary is stable while another changes</div></section>

.stage{width:min(94vw,780px);height:min(88vh,322px);padding:clamp(12px,3vmin,20px);border:1px solid var(--line);border-radius:16px;background:var(--surface);box-shadow:0 12px 36px #0001;display:flex;flex-direction:column;gap:clamp(7px,2vmin,14px);font:500 clamp(12px,3.5vmin,17px)/1.3 var(--font-sans,system-ui,sans-serif);overflow:hidden}.heading{display:flex;justify-content:space-between;align-items:center;gap:8px;font-weight:750;color:var(--accent)}.hint{color:var(--muted);font-size:clamp(12px,3.2vmin,14px);font-weight:500}.caption{margin-top:auto;color:var(--muted);font-size:clamp(12px,3.2vmin,14px)}.row{display:flex;gap:clamp(5px,1.5vmin,12px);align-items:center}.tile{padding:clamp(6px,1.8vmin,13px);border:1px solid var(--line);border-radius:9px;background:var(--bg);text-align:center;min-width:0}.arrow{color:var(--accent);font-weight:800}.stage [data-on]{transition:background .3s,border-color .3s,opacity .3s,transform .3s}.stage .on{border-color:var(--accent);background:color-mix(in srgb,var(--accent) 14%,var(--surface));color:var(--accent)}.pair{display:flex;flex:1;align-items:stretch;justify-content:center;gap:clamp(8px,3vmin,24px);min-height:75px}.pair .tile{width:42%;max-width:220px;display:flex;flex-direction:column;justify-content:space-around}.pair b{color:var(--accent);font-size:.85em}.pair small{color:var(--muted);font:600 .72em ui-monospace,monospace}.list{border-color:var(--accent)!important}.list::after{content:"";display:block;height:4px;background:var(--accent);border-radius:3px}.cart{border-color:var(--accent-3)!important}.stage[data-step="1"] .cart,.stage[data-step="2"] .cart{background:color-mix(in srgb,var(--accent-3) 18%,var(--surface))}.stage small,.stage button,.stage .cards b,.stage .phase b,.stage .pair b,.stage .tree-mini b{font-size:clamp(12px,3.2vmin,14px)!important}

const stage=document.querySelector(".stage"),count=document.getElementById("cart-count");let step=0;function tick(){stage.dataset.step=String(step);count.textContent=step+" items";step=(step+1)%3}tick();let timer=setInterval(tick,900);stage.addEventListener("pointerdown",()=>{clearInterval(timer);tick()})