fix: resolve 9 P0+P1 review findings (bills decorators, campus isolation bypass, ding raw crash, batch import counter, SSE multi-tab, interval leak, dept permissions, cycle prevention, tree depth)

apps/admin/src/components/NotificationBell.tsx

@@ -58,6 +58,7 @@ const NotificationBell: React.FC = () => {
   };
   const openRef = useRef(open);
   openRef.current = open;
+  const retryRef = useRef<number | null>(null);
 
   // SSE connection — decoupled from popover open state
   useEffect(() => {
@@ -74,9 +75,14 @@ const NotificationBell: React.FC = () => {
     };
     es.onerror = () => {
       es.close();
-      setInterval(fetchUnread, 60_000);
+      if (retryRef.current !== null) clearInterval(retryRef.current);
+      retryRef.current = window.setInterval(fetchUnread, 60_000);
+    };
+    return () => {
+      es.close();
+      clearInterval(retryRef.current ?? undefined);
+      retryRef.current = null;
     };
-    return () => es.close();
   }, []);
 
   const handleOpen = (visible: boolean) => {