Nachrichten: kein Pushover wenn Empfänger aktiv im Chat

frontend/src/tools/nachrichten.jsx

@@ -95,6 +95,40 @@ export default function Nachrichten({ toast, mobile }) {
   const bottomRef = useRef(null);
   const pollRef   = useRef(null);
   const pickerRef = useRef(null);
+  const heartbeatRef = useRef(null);
+
+  // Presence Heartbeat: solange Nachrichten offen + Tab sichtbar → aktiv
+  useEffect(() => {
+    const sendPresence = (active) => api('/tools/nachrichten/presence', { method:'POST', body:{ active } }).catch(()=>{});
+
+    const start = () => {
+      if (document.visibilityState === 'visible') {
+        sendPresence(true);
+        heartbeatRef.current = setInterval(() => {
+          if (document.visibilityState === 'visible') sendPresence(true);
+        }, 30000);
+      }
+    };
+
+    const onVisibility = () => {
+      if (document.visibilityState === 'visible') {
+        sendPresence(true);
+        if (!heartbeatRef.current) heartbeatRef.current = setInterval(() => sendPresence(true), 30000);
+      } else {
+        sendPresence(false);
+        clearInterval(heartbeatRef.current);
+        heartbeatRef.current = null;
+      }
+    };
+
+    start();
+    document.addEventListener('visibilitychange', onVisibility);
+    return () => {
+      sendPresence(false);
+      clearInterval(heartbeatRef.current);
+      document.removeEventListener('visibilitychange', onVisibility);
+    };
+  }, []);
 
   useEffect(() => {
     if (!showPicker) return;