Fix web camera stuck on "Starting camera…"

getUserMedia (and the awaited play()) could hang indefinitely on iOS when the
scanner mounts after navigation (not in a user-gesture context), leaving the
UI stuck with no recovery. Add a 12s watchdog that surfaces an error + Retry
button (Retry is a fresh gesture iOS honors), stop awaiting play() (fire and
forget), and stop any prior stream before re-requesting.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/components/QRScanner.web.tsx

@@ -24,17 +24,29 @@ export default function QRScanner({ onScan, active }: QRScannerProps) {
   async function start() {
     setError(null);
     setStarting(true);
+    // Stop any previous stream before requesting a new one (Retry / remounts).
+    streamRef.current?.getTracks().forEach((t) => t.stop());
+    streamRef.current = null;
     try {
-      const stream = await navigator.mediaDevices.getUserMedia({
+      // Watchdog: on iOS, getUserMedia can hang indefinitely when it isn't tied
+      // to a user gesture (we navigate here from the name screen). If it doesn't
+      // resolve, surface an error + Retry button (Retry IS a fresh gesture).
+      const stream = await withTimeout(
+        navigator.mediaDevices.getUserMedia({
           video: { facingMode: { ideal: "environment" } },
           audio: false,
-      });
+        }),
+        12000,
+      );
       streamRef.current = stream;
       const video = videoRef.current;
       if (video) {
         video.srcObject = stream;
         video.setAttribute("playsinline", "true");
-        await video.play().catch(() => {});
+        video.muted = true;
+        // Fire-and-forget: awaiting play() can itself hang on iOS. We only need
+        // the stream attached; the tick loop waits for readyState.
+        video.play().catch(() => {});
       }
       const detector = new BarcodeDetector({ formats: ["qr_code"] });
       let busy = false;
@@ -65,12 +77,22 @@ export default function QRScanner({ onScan, active }: QRScannerProps) {
       setStarting(false);
       setError(
         e?.name === "NotAllowedError"
-          ? "Camera permission was denied. Allow camera access and reload."
+          ? "Camera permission was denied. Allow camera access, then tap Retry."
+          : e?.message === "timeout"
+            ? "Camera didn't start. Tap Retry."
             : "Could not open the camera. Make sure you're on HTTPS and no other app is using it.",
       );
     }
   }
 
+  // Reject after `ms` if the promise hasn't settled (used to un-stick getUserMedia).
+  function withTimeout<T>(p: Promise<T>, ms: number): Promise<T> {
+    return Promise.race([
+      p,
+      new Promise<T>((_, reject) => setTimeout(() => reject(new Error("timeout")), ms)),
+    ]);
+  }
+
   useEffect(() => {
     start();
     return () => {