changes to the Scanning processing

Web/app.py

@@ -4276,6 +4276,7 @@ def api_library_scan_action():
     - scan student card id
     - scan media code (ISBN/Code_4)
     - borrow if available, otherwise return (toggle behavior)
+    - action='borrow' can be used by scan modes that must never return an item
     """
     if 'username' not in session:
         return jsonify({'ok': False, 'message': 'Nicht angemeldet.'}), 401
@@ -4285,6 +4286,7 @@ def api_library_scan_action():
         return jsonify({'ok': False, 'message': 'Schülerausweis-Modul ist deaktiviert.'}), 403
 
     payload = request.get_json(silent=True) or {}
+    requested_action = str(payload.get('action') or 'toggle').strip().lower()
     student_card_id = us.normalize_student_card_id(payload.get('student_card_id') or payload.get('card_id'))
     item_code_raw = str(payload.get('item_code') or payload.get('code') or '').strip()
     duration_raw = str(payload.get('borrow_duration_days') or '').strip()
@@ -4388,6 +4390,12 @@ def api_library_scan_action():
                 'message': f"{item_doc.get('Name', 'Medium')} wurde ausgeliehen."
             }), 200
 
+        if requested_action == 'borrow':
+            return jsonify({
+                'ok': False,
+                'message': f"Medium ist bereits ausgeliehen und wurde nicht verändert.",
+            }), 409
+
         # Toggle back: item is currently borrowed -> return
         current_borrower = str(item_doc.get('User') or '').strip()
         current_permissions = us.get_effective_permissions(session['username'])

Web/templates/library_table.html

@@ -1414,7 +1414,8 @@
                 },
                 body: JSON.stringify({
                     student_card_id: activeStudentCardId,
-                    item_code: scannedCode
+                    item_code: scannedCode,
+                    action: 'borrow'
                 })
             });