Pre-warm camera stream on page load if permission already granted

Uses Permissions API (non-prompting) to check camera state on load.
If state === 'granted', silently starts the stream so Scan Label opens
instantly with no browser prompt on subsequent page visits. Falls back
gracefully when Permissions API is unavailable or permission is 'prompt'.

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

src/PowderCoating.Web/wwwroot/js/inventory-label-scan.js

@@ -56,6 +56,10 @@
     if (shutterBtn) shutterBtn.addEventListener('click', captureFrame);
     window.addEventListener('beforeunload', releaseCamera);
 
+    // If the user has already granted camera permission, silently pre-warm the stream
+    // so the next Scan Label click opens instantly without any browser prompt.
+    preWarmCamera();
+
     // ── Open / close ──────────────────────────────────────────────────────
 
     async function openScanner() {
@@ -184,6 +188,24 @@
         rafId = requestAnimationFrame(tick);
     }
 
+    // ── Camera pre-warm ───────────────────────────────────────────────────
+
+    // Check camera permission state without prompting. If already granted, start the stream
+    // silently on page load so Scan Label opens instantly with no browser prompt on this visit.
+    // The idle timer ensures the camera releases if the user never actually scans anything.
+    async function preWarmCamera() {
+        try {
+            if (!navigator.permissions) return;
+            const perm = await navigator.permissions.query({ name: 'camera' });
+            if (perm.state !== 'granted') return;
+            stream = await navigator.mediaDevices.getUserMedia({
+                video: { facingMode: 'environment', width: { ideal: 1280 }, height: { ideal: 720 } }
+            });
+            // Start idle timer — release if user never opens the scanner
+            idleTimer = setTimeout(releaseCamera, IDLE_RELEASE_MS);
+        } catch { /* permission denied or getUserMedia failed — ignore */ }
+    }
+
     function loadJsQR() {
         return new Promise((resolve, reject) => {
             if (window.jsQR) { resolve(); return; }