Fix iOS camera: require tap gesture before requesting getUserMedia

iOS Safari blocks getUserMedia when called outside a user gesture
context. The useEffect auto-start broke the gesture chain, causing
permission denial without ever showing the prompt. Now on iOS the
scanner shows a "Tap to start camera" button that triggers the
permission request within the tap handler. Non-iOS browsers still
auto-start. Also added a "Try again" button on the error state.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/components/CameraScanner.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useRef, useState } from "react";
+import { useCallback, useEffect, useRef, useState } from "react";
 import { Html5Qrcode } from "html5-qrcode";
 import { Icon } from "./primitives/index.js";
 
@@ -12,18 +12,23 @@ export function CameraScanner({
   const scannerRef = useRef<Html5Qrcode | null>(null);
   const containerRef = useRef<HTMLDivElement>(null);
   const [error, setError] = useState<string | null>(null);
+  const [started, setStarted] = useState(false);
   const [torchOn, setTorchOn] = useState(false);
   const [torchAvailable, setTorchAvailable] = useState(false);
   const lastScan = useRef("");
   const lastScanTime = useRef(0);
 
-  useEffect(() => {
+  const startCamera = useCallback(async () => {
     const id = "apothecary-scanner";
-    const scanner = new Html5Qrcode(id, { verbose: false });
+    let scanner = scannerRef.current;
+    if (!scanner) {
+      scanner = new Html5Qrcode(id, { verbose: false });
       scannerRef.current = scanner;
+    }
+    if (scanner.isScanning) return;
 
-    scanner
-      .start(
+    try {
+      await scanner.start(
         { facingMode: "environment" },
         { fps: 10, qrbox: (w, h) => ({ width: Math.min(w - 40, 280), height: Math.min(h - 40, 280) }) },
         (text) => {
@@ -34,8 +39,8 @@ export function CameraScanner({
           onScan(text);
         },
         () => {},
-      )
-      .then(() => {
+      );
+      setStarted(true);
       try {
         const caps = scanner.getRunningTrackCameraCapabilities();
         if (caps.torchFeature().isSupported()) {
@@ -44,17 +49,24 @@ export function CameraScanner({
       } catch {
         // torch check can fail on some browsers
       }
-      })
-      .catch((err: Error) => {
-        setError(err.message || "Camera access denied");
-      });
+    } catch (err: unknown) {
+      setError(err instanceof Error ? err.message : "Camera access denied");
+    }
+  }, [onScan]);
 
+  // On non-iOS browsers, getUserMedia works fine outside a gesture — auto-start
+  useEffect(() => {
+    const isIOS = /iPad|iPhone|iPod/.test(navigator.userAgent) ||
+      (navigator.platform === "MacIntel" && navigator.maxTouchPoints > 1);
+    if (!isIOS) {
+      startCamera();
+    }
     return () => {
-      if (scanner.isScanning) {
-        scanner.stop().catch(() => {});
+      if (scannerRef.current?.isScanning) {
+        scannerRef.current.stop().catch(() => {});
       }
     };
-  }, []); // eslint-disable-line react-hooks/exhaustive-deps
+  }, [startCamera]);
 
   const toggleTorch = () => {
     try {
@@ -146,6 +158,42 @@ export function CameraScanner({
           id="apothecary-scanner"
           style={{ width: "100%", height: "100%" }}
         />
+        {!started && !error && (
+          <div
+            onClick={startCamera}
+            style={{
+              position: "absolute",
+              inset: 0,
+              display: "flex",
+              flexDirection: "column",
+              alignItems: "center",
+              justifyContent: "center",
+              gap: 16,
+              padding: 32,
+              color: "#fff",
+              textAlign: "center",
+              cursor: "pointer",
+            }}
+          >
+            <div
+              style={{
+                width: 80,
+                height: 80,
+                borderRadius: "50%",
+                background: "var(--sage)",
+                display: "flex",
+                alignItems: "center",
+                justifyContent: "center",
+              }}
+            >
+              <Icon name="camera" size={36} color="#fff" />
+            </div>
+            <div style={{ fontSize: 16, fontWeight: 500 }}>Tap to start camera</div>
+            <div style={{ fontSize: 13, opacity: 0.7, maxWidth: 300 }}>
+              Allow camera access when prompted
+            </div>
+          </div>
+        )}
         {error && (
           <div
             style={{
@@ -164,6 +212,22 @@ export function CameraScanner({
             <Icon name="camera" size={48} color="rgba(255,255,255,0.5)" />
             <div style={{ fontSize: 16, fontWeight: 500 }}>Camera unavailable</div>
             <div style={{ fontSize: 13, opacity: 0.7, maxWidth: 300 }}>{error}</div>
+            <button
+              onClick={() => { setError(null); startCamera(); }}
+              style={{
+                marginTop: 8,
+                padding: "10px 24px",
+                borderRadius: 8,
+                background: "var(--sage)",
+                color: "#fff",
+                border: "none",
+                fontSize: 14,
+                fontWeight: 500,
+                cursor: "pointer",
+              }}
+            >
+              Try again
+            </button>
           </div>
         )}
       </div>