diff --git a/Web/templates/library_table.html b/Web/templates/library_table.html
index a26af68..ad0e00f 100644
--- a/Web/templates/library_table.html
+++ b/Web/templates/library_table.html
@@ -805,74 +805,92 @@
         deleteLibraryItem(itemId);
     }
 
-    // =========================================================================
-    // 3. CORE SCANNER ROUTING ENGINE (QUAGGA2)
-    // =========================================================================
-    function startScanner(targetCallback) {
-        const readerWrap = document.getElementById('scanReaderWrap');
+    async function startScanner(callback = null) {
+        if (scannerRunning) {
+            console.warn("Scanner is already running. Stopping it first...");
+            await stopScanner();
+        }
+
+        activeScannerCallback = callback;
+
+        const scannerWrap = document.querySelector('.library-scan-reader-wrap');
         const toggleBtn = document.getElementById('toggleScannerBtn');
 
-        activeScannerCallback = targetCallback;
+        // 1. CRITICAL FIX: Make the container visible BEFORE Quagga initializes
+        // Quagga cannot calculate video dimensions if display is 'none'
+        if (scannerWrap) {
+            scannerWrap.style.display = 'block';
+        }
 
-        if (readerWrap) readerWrap.style.display = 'block';
-        setScanStatus('Initializing camera...', 'warn');
-        
-        const scannerContainer = document.querySelector('.library-scan-reader-wrap');
-        scannerContainer.style.display = 'block';
+        setScanStatus('Starte Kamera...', 'warn');
 
-        Quagga.init({
-            inputStream: {
-                name: "Live",
-                type: "LiveStream",
-                target: document.querySelector('.library-scan-reader'),
-                constraints: {
-                    width: 640,
-                    height: 480,
-                    facingMode: "environment"
+        // 2. Initialize Quagga with a slight delay to allow the DOM to render the block
+        setTimeout(() => {
+            Quagga.init({
+                inputStream: {
+                    name: "Live",
+                    type: "LiveStream",
+                    // This MUST match the inner div where the video should appear
+                    target: document.querySelector('.library-scan-reader'), 
+                    constraints: {
+                        width: 640,
+                        height: 480,
+                        facingMode: "environment" // Prefer back camera on mobile
+                    }
                 },
-            },
-            decoder: {
-                readers: [
-                    "code_128_reader",
-                    "ean_reader",
-                    "code_39_reader",
-                    "upc_reader",
-                    "codabar_reader",
-                    "i2of5_reader"
-                ]
-            }
-        }, function(err) {
-            if (err) {
-                console.error('Scanner start failed:', err);
-                if (readerWrap) readerWrap.style.display = 'none';
-                const detail = (err && (err.message || err.name)) ? ` (${err.message || err.name})` : '';
-                setScanStatus(`Scanner konnte nicht gestartet werden${detail}`, 'error');
-                return;
-            }
+                locator: {
+                    patchSize: "medium",
+                    halfSample: true
+                },
+                decoder: {
+                    // Keep only the barcode types you actually use to improve performance
+                    readers: ["code_128_reader", "ean_reader", "code_39_reader"] 
+                },
+                locate: true
+            }, function(err) {
+                if (err) {
+                    // This will finally log the actual error (e.g., NotAllowedError) if permissions fail
+                    console.error("Quagga initialization failed:", err);
+                    setScanStatus('Kamera-Fehler: ' + (err.name || err), 'error');
 
-            Quagga.start();
-            scannerRunning = true;
+                    if (scannerWrap) scannerWrap.style.display = 'none';
+                    scannerRunning = false;
+                    return;
+                }
 
-            if (!targetCallback && toggleBtn) {
-                toggleBtn.textContent = 'Scanner stoppen';
-            }
-            setScanStatus('Scanner aktiv. Jetzt Code scannen.', 'warn');
-        });
+                Quagga.start();
+                scannerRunning = true;
+                setScanStatus('Scanner bereit.', 'ok');
+
+                if (toggleBtn) {
+                    toggleBtn.textContent = 'Scanner stoppen';
+                }
+            });
+        }, 50);
     }
 
-    function stopScanner() {
+    async function stopScanner() {
         if (!scannerRunning) return;
 
-        const readerWrap = document.getElementById('scanReaderWrap');
-        const toggleBtn = document.getElementById('toggleScannerBtn');
+        try {
+            Quagga.stop();
+        } catch (e) {
+            console.warn("Error stopping Quagga (it may not have been running):", e);
+        }
 
-        Quagga.stop();
         scannerRunning = false;
         activeScannerCallback = null;
 
-        if (readerWrap) readerWrap.style.display = 'none';
-        if (toggleBtn) toggleBtn.textContent = 'Scanner starten';
-        setScanStatus('Scanner gestoppt.', 'warn');
+        // Hide the container to free up UI space
+        const scannerWrap = document.querySelector('.library-scan-reader-wrap');
+        if (scannerWrap) {
+            scannerWrap.style.display = 'none';
+        }
+
+        const toggleBtn = document.getElementById('toggleScannerBtn');
+        if (toggleBtn) {
+            toggleBtn.textContent = 'Kamera Scanner'; // Reset button text
+        }
     }
 
     async function isStudentCardBarcode(code) {