diff --git a/public/js/ar/cv-worker.js b/public/js/ar/cv-worker.js
new file mode 100644
index 0000000..83ccde9
--- /dev/null
+++ b/public/js/ar/cv-worker.js
@@ -0,0 +1,131 @@
+/* cv-worker.js — OpenCV board solve, off the main thread.
+ *
+ * WHY A WORKER: the opencv.js build embeds its ~8MB WASM as a base64 data URI
+ * inside a 10.8MB script. Loading it on the main thread means parsing that
+ * script, decoding the base64, and compiling the WASM synchronously — seconds
+ * of frozen UI and a "page unresponsive" prompt on mobile. In a worker the
+ * whole cost is off-thread, and per-frame solvePnP goes with it.
+ *
+ * Protocol (main <-> worker):
+ *   -> { type:'init' }                          <- { type:'ready' } | { type:'failed', msg }
+ *   -> { type:'solve', id, obj, img, n, W,H,f }  <- { type:'pose', id, ok, C, m3, reproj, n }
+ *   -> { type:'reset' }                          (drop temporal warm start)
+ * obj/img are plain Float64Array payloads (transferred, so no copy).
+ * The worker never touches three.js: it returns the camera position and the
+ * 3x3 world-from-camera rotation, and the client builds the quaternion.
+ */
+
+let cv = null;
+let prev = null;              // { r:[3], t:[3], at } temporal warm start
+const PREV_TTL = 1500;
+const MAX_REPROJ_PX = 8;
+
+// reusable Mats — allocating 7 Mats per frame was a measurable cost
+let bufN = 0;
+let objM = null, imgM = null, rvec = null, tvec = null, R = null, proj = null, jac = null, K = null, dist = null;
+let kW = 0, kH = 0, kF = 0;
+
+function ensureBuffers(n) {
+  if (bufN === n) return;
+  for (const m of [objM, imgM]) if (m) m.delete();
+  objM = new cv.Mat(n, 3, cv.CV_64F);
+  imgM = new cv.Mat(n, 2, cv.CV_64F);
+  bufN = n;
+}
+function ensureIntrinsics(W, H, f) {
+  if (K && kW === W && kH === H && kF === f) return;
+  if (K) { K.delete(); dist.delete(); }
+  K = cv.matFromArray(3, 3, cv.CV_64F, [f, 0, W / 2, 0, f, H / 2, 0, 0, 1]);
+  dist = cv.Mat.zeros(4, 1, cv.CV_64F);
+  kW = W; kH = H; kF = f;
+}
+
+function solve(msg) {
+  const { obj, img, n, W, H, f } = msg;
+  ensureIntrinsics(W, H, f);
+  ensureBuffers(n);
+  objM.data64F.set(obj);
+  imgM.data64F.set(img);
+
+  const fresh = prev && (Date.now() - prev.at) < PREV_TTL;
+  if (fresh) {
+    // warm start: iterative LM from the last frame. Fast, and it resolves
+    // single-marker planar flips by temporal continuity.
+    rvec.data64F.set(prev.r); tvec.data64F.set(prev.t);
+    cv.solvePnP(objM, imgM, K, dist, rvec, tvec, true, cv.SOLVEPNP_ITERATIVE);
+  } else {
+    let ok = false;
+    try { ok = cv.solvePnP(objM, imgM, K, dist, rvec, tvec, false, cv.SOLVEPNP_SQPNP); } catch { ok = false; }
+    if (!ok) { try { ok = cv.solvePnP(objM, imgM, K, dist, rvec, tvec, false, cv.SOLVEPNP_IPPE); } catch { ok = false; } }
+    if (!ok) return { ok: false };
+    cv.solvePnP(objM, imgM, K, dist, rvec, tvec, true, cv.SOLVEPNP_ITERATIVE);
+  }
+
+  // reprojection gate — rejects poisoned frames before they reach the filter
+  cv.projectPoints(objM, rvec, tvec, K, dist, proj, jac);
+  let err = 0;
+  for (let i = 0; i < n; i++) {
+    err += Math.hypot(proj.data64F[2 * i] - img[2 * i], proj.data64F[2 * i + 1] - img[2 * i + 1]);
+  }
+  err /= n;
+  if (err > MAX_REPROJ_PX) { prev = null; return { ok: false, reproj: err }; }
+
+  prev = { r: [...rvec.data64F], t: [...tvec.data64F], at: Date.now() };
+
+  cv.Rodrigues(rvec, R);
+  const d = R.data64F;          // row-major world->cvCam
+  const t = tvec.data64F;
+  // camera position in world: C = -R^T t
+  const C = [
+    -(d[0] * t[0] + d[3] * t[1] + d[6] * t[2]),
+    -(d[1] * t[0] + d[4] * t[1] + d[7] * t[2]),
+    -(d[2] * t[0] + d[5] * t[1] + d[8] * t[2]),
+  ];
+  // world-from-threeCam = R^T * diag(1,-1,-1), row-major for Matrix4.set
+  const m3 = [d[0], -d[3], -d[6], d[1], -d[4], -d[7], d[2], -d[5], -d[8]];
+  return { ok: true, C, m3, reproj: err };
+}
+
+self.onmessage = (ev) => {
+  const msg = ev.data;
+  if (msg.type === 'init') {
+    try {
+      importScripts('/vendor/opencv.js');
+    } catch (e) {
+      self.postMessage({ type: 'failed', msg: 'importScripts: ' + (e && e.message || e) });
+      return;
+    }
+    const mod = self.cv;
+    const finish = (m) => {
+      cv = m;
+      rvec = new cv.Mat(3, 1, cv.CV_64F);
+      tvec = new cv.Mat(3, 1, cv.CV_64F);
+      R = new cv.Mat(); proj = new cv.Mat(); jac = new cv.Mat();
+      self.postMessage({ type: 'ready' });
+    };
+    if (!mod) return self.postMessage({ type: 'failed', msg: 'cv missing after importScripts' });
+    if (mod.Mat) return finish(mod);
+    if (typeof mod.then === 'function') return mod.then(finish, (e) => self.postMessage({ type: 'failed', msg: String(e) }));
+    mod.onRuntimeInitialized = () => finish(self.cv || mod);
+    // safety poll: some builds consume onRuntimeInitialized before we attach
+    const t0 = Date.now();
+    (function poll() {
+      if (cv) return;
+      const m = self.cv;
+      if (m && m.Mat) return finish(m);
+      if (Date.now() - t0 > 60000) return self.postMessage({ type: 'failed', msg: 'init timeout' });
+      setTimeout(poll, 100);
+    })();
+    return;
+  }
+
+  if (msg.type === 'reset') { prev = null; return; }
+
+  if (msg.type === 'solve') {
+    if (!cv) return self.postMessage({ type: 'pose', id: msg.id, ok: false });
+    let out;
+    try { out = solve(msg); }
+    catch (e) { prev = null; out = { ok: false }; }
+    self.postMessage({ type: 'pose', id: msg.id, n: msg.n, ...out });
+  }
+};