diff --git a/tools/deploy.sh b/tools/deploy.sh
index 71a7aba..e8c2d76 100755
--- a/tools/deploy.sh
+++ b/tools/deploy.sh
@@ -94,5 +94,25 @@ echo "      · $LIVE (no slash) -> HTTP $REDIR (301/302 to /gutsy/ expected)"
 
 [ "$fail" = "0" ] || { echo "      ✗ DEPLOY UNVERIFIED"; exit 1; }
 echo "      ✓ deployed: $LIVE/"
-echo
-echo "Cloudflare fronts partly.party — purge the cache if you redeploy over existing files."
+
+# ---------------------------------------------------------------------
+# THE CHECK ABOVE VERIFIES A URL NOBODY VISITS.
+# Every check() appends ?v=$BUST, which is precisely what makes it bypass Cloudflare's edge
+# cache — so all six can pass while every actual player is still being served the PREVIOUS
+# build from a POP. The script's answer to that was a line of prose at the end telling a human
+# to remember. This asks the question properly: fetch a module the way a browser does, with no
+# query string, and compare it to the bytes we just shipped.
+# ---------------------------------------------------------------------
+echo "[5/5] Checking what a PLAYER gets (no cache-buster) ..."
+EDGE="$(curl -fsS --max-time 20 "$LIVE/js/boot.js" 2>/dev/null || true)"
+if [ -z "$EDGE" ]; then
+  echo "      ⚠ could not fetch $LIVE/js/boot.js un-busted — cannot tell whether the edge is stale"
+elif [ "$EDGE" = "$(cat "$ROOT/web/js/boot.js")" ]; then
+  echo "      ✓ edge is serving this build"
+else
+  echo "      ✗ STALE EDGE — players are still being served the previous build."
+  echo "        Cloudflare has partly.party/gutsy/js/*.js cached. Purge it:"
+  echo "        Cloudflare dashboard -> partly.party -> Caching -> Configuration -> Purge Everything"
+  echo "        (or Custom Purge on $LIVE/js/). Then re-run this script to confirm."
+  exit 1
+fi
diff --git a/web/js/boot.js b/web/js/boot.js
index 4cbb35b..a206366 100644
--- a/web/js/boot.js
+++ b/web/js/boot.js
@@ -45,7 +45,11 @@ addEventListener('error', (e) => fail('script error', e?.message));
 addEventListener('unhandledrejection', (e) => fail('failed to load', e?.reason?.message ?? e?.reason));
 
 const renderer = new THREE.WebGLRenderer({ antialias: true, preserveDrawingBuffer: true });
-renderer.setPixelRatio(Math.min(devicePixelRatio, 2));
+// THE ONE PERF LEVER WORTH HAVING. Device pixel ratio is quadratic in fill cost, so a
+// retina laptop was rendering 4x the pixels of a 1x one with no way for its owner to say no.
+// Capped at 1 on `low`: everything else in this game is geometry-light and fill-heavy (fogged
+// tube, additive glows, a full-screen damage layer), so this is the lever that moves.
+renderer.setPixelRatio(Math.min(devicePixelRatio, store.load().quality === 'low' ? 1 : 2));
 renderer.setSize(innerWidth, innerHeight);
 document.getElementById('game').appendChild(renderer.domElement);
 // A laptop sleeping or a display being hotplugged takes the GL context away; without this the
diff --git a/web/js/core/save.js b/web/js/core/save.js
index 5976496..285f68d 100644
--- a/web/js/core/save.js
+++ b/web/js/core/save.js
@@ -15,7 +15,7 @@ const KEY = 'guts.save';
 // beats the one on file.
 const RANK = ['none', 'bronze', 'silver', 'gold', 'platinum'];
 
-const EMPTY = () => ({ v: 1, diff: 'normal', cleared: 0, best: {} });
+const EMPTY = () => ({ v: 1, diff: 'normal', quality: 'high', cleared: 0, best: {} });
 
 export function load() {
   try {
@@ -36,7 +36,8 @@ export function save(s) {
   return s;
 }
 
-export function setDiff(id) { const s = load(); s.diff = id; return save(s); }
+/** Set one option. Generic because there are two of them now and there will be three. */
+export function setOpt(key, value) { const s = load(); s[key] = value; return save(s); }
 
 /**
  * File a finished run.
@@ -88,9 +89,11 @@ if (typeof process !== 'undefined' && process.argv?.[1]?.endsWith('save.js') &&
   ok(load().best.L1_mouth.medal === 'platinum', 'a better medal replaces');
   ok(load().best.L1_mouth.score === 1500, 'a worse score does not');
 
-  setDiff('hard');
+  setOpt('diff', 'hard');
   ok(load().diff === 'hard', 'difficulty persists');
-  ok(load().best.L1_mouth, 'setDiff does not clobber records');
+  ok(load().best.L1_mouth, 'setOpt does not clobber records');
+  setOpt('quality', 'low');
+  ok(load().quality === 'low' && load().diff === 'hard', 'options do not clobber each other');
   clearCampaign(); clearCampaign();
   ok(load().cleared === 2, 'clears count');
 
diff --git a/web/js/ui/cards.js b/web/js/ui/cards.js
index 02164fe..b780a1c 100644
--- a/web/js/ui/cards.js
+++ b/web/js/ui/cards.js
@@ -446,11 +446,23 @@ export function createCards({
     paintDiff();
     dBtn.addEventListener('click', () => {
       S.diff = dOrder[(dOrder.indexOf(S.diff) + 1) % dOrder.length];
-      store.setDiff(S.diff);
+      store.setOpt('diff', S.diff);
       paintDiff();
       go({ diff: null });   // drop any ?diff= override so the save is what takes effect
     });
 
+    // Quality. Same reload path as difficulty for the same reason — the renderer's pixel ratio
+    // is set once at boot, before anything this card can reach exists.
+    const qBtn = el('button', 'chip', menu);
+    qBtn.type = 'button';
+    qBtn.style.color = C.soft;
+    qBtn.textContent = `quality · ${S.quality === 'low' ? 'performance' : 'full'}`;
+    qBtn.title = 'caps the render resolution — the one lever that moves the frame rate on a laptop';
+    qBtn.addEventListener('click', () => {
+      store.setOpt('quality', S.quality === 'low' ? 'high' : 'low');
+      go({});
+    });
+
     // The one thing a save is FOR: proof you finished. Nothing in this game acknowledged a
     // completed campaign anywhere the player could see it.
     if (S.cleared > 0) {