feat: implement polling fallback for SSE connection failures and add event deduplication

apps/frontend/src/features/home/home-page.tsx

@@ -172,7 +172,9 @@ export function HomePage() {
     let eventSource: EventSource | null = null;
     let reconnectTimeout: ReturnType<typeof setTimeout> | null = null;
     let reconnectAttempts = 0;
-    const maxReconnectAttempts = 5;
+    const maxReconnectAttempts = 3;
+    let lastEventId: string | null = null;
+    let pollInterval: ReturnType<typeof setInterval> | null = null;
 
     const connect = () => {
       if (eventSource) {
@@ -180,7 +182,8 @@ export function HomePage() {
       }
 
       if (reconnectAttempts >= maxReconnectAttempts) {
-        console.log('[SSE] Max reconnect attempts reached');
+        console.log('[SSE] Max reconnect attempts reached, switching to polling');
+        startPolling();
         return;
       }
 
@@ -191,30 +194,46 @@ export function HomePage() {
       eventSource.onerror = () => {
         if (eventSource?.readyState === EventSource.CLOSED) {
           reconnectAttempts++;
-          const delay = Math.min(1000 * 2 ** reconnectAttempts, 30000);
           console.log(
-            `[SSE] Connection closed, retry ${reconnectAttempts}/${maxReconnectAttempts} in ${delay}ms`
+            `[SSE] Connection closed, retry ${reconnectAttempts}/${maxReconnectAttempts}`
           );
           reconnectTimeout = setTimeout(() => {
             connect();
-          }, delay);
+          }, 2000);
         }
       };
 
       eventSource.addEventListener('message', (event) => {
         if (event.data && event.data !== 'connected' && event.data !== 'ping') {
+          if (event.data !== lastEventId) {
+            lastEventId = event.data;
             reconnectAttempts = 0;
-          void queryClient.invalidateQueries({ queryKey: ['admin-bookings', selectedComplex.id] });
+            void queryClient.invalidateQueries({
+              queryKey: ['admin-bookings', selectedComplex.id],
+            });
+          }
         }
       });
     };
 
+    const startPolling = () => {
+      if (pollInterval) return;
+
+      console.log('[SSE] Starting polling fallback');
+      pollInterval = setInterval(() => {
+        void queryClient.invalidateQueries({ queryKey: ['admin-bookings', selectedComplex.id] });
+      }, 10000);
+    };
+
     connect();
 
     return () => {
       if (reconnectTimeout) {
         clearTimeout(reconnectTimeout);
       }
+      if (pollInterval) {
+        clearInterval(pollInterval);
+      }
       eventSource?.close();
     };
   }, [selectedComplex?.id, queryClient]);