Phase 4: Frontend performance optimizations

- AW-2: Scope calendar events fetch to visible date range via start/end
  query params, leveraging existing backend support
- AW-3: Reduce calendar events poll from 5s to 30s (personal organiser
  doesn't need 12 API calls/min)
- AS-4: Gate shared-calendar polling on hasSharedCalendars — saves 12
  wasted API calls/min for personal-only users
- AS-2: Lazy-load all route components with React.lazy() — only
  AdminPortal was previously lazy, now all 10 routes are code-split
- AS-1: Add Vite manualChunks to split FullCalendar (~400KB), React,
  TanStack Query, and UI libs into separate cacheable chunks
- AS-3: Extract clockNow into isolated ClockDisplay memo component —
  prevents all 8 dashboard widgets from re-rendering every minute

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/App.tsx

@@ -3,19 +3,24 @@ import { Routes, Route, Navigate } from 'react-router-dom';
 import { useAuth } from '@/hooks/useAuth';
 import LockScreen from '@/components/auth/LockScreen';
 import AppLayout from '@/components/layout/AppLayout';
-import DashboardPage from '@/components/dashboard/DashboardPage';
-import TodosPage from '@/components/todos/TodosPage';
-import CalendarPage from '@/components/calendar/CalendarPage';
-import RemindersPage from '@/components/reminders/RemindersPage';
-import ProjectsPage from '@/components/projects/ProjectsPage';
-import ProjectDetail from '@/components/projects/ProjectDetail';
-import PeoplePage from '@/components/people/PeoplePage';
-import LocationsPage from '@/components/locations/LocationsPage';
-import SettingsPage from '@/components/settings/SettingsPage';
-import NotificationsPage from '@/components/notifications/NotificationsPage';
 
+// AS-2: Lazy-load all route components to reduce initial bundle parse time
+const DashboardPage = lazy(() => import('@/components/dashboard/DashboardPage'));
+const TodosPage = lazy(() => import('@/components/todos/TodosPage'));
+const CalendarPage = lazy(() => import('@/components/calendar/CalendarPage'));
+const RemindersPage = lazy(() => import('@/components/reminders/RemindersPage'));
+const ProjectsPage = lazy(() => import('@/components/projects/ProjectsPage'));
+const ProjectDetail = lazy(() => import('@/components/projects/ProjectDetail'));
+const PeoplePage = lazy(() => import('@/components/people/PeoplePage'));
+const LocationsPage = lazy(() => import('@/components/locations/LocationsPage'));
+const SettingsPage = lazy(() => import('@/components/settings/SettingsPage'));
+const NotificationsPage = lazy(() => import('@/components/notifications/NotificationsPage'));
 const AdminPortal = lazy(() => import('@/components/admin/AdminPortal'));
 
+const RouteFallback = () => (
+  <div className="flex h-full items-center justify-center text-muted-foreground">Loading...</div>
+);
+
 function ProtectedRoute({ children }: { children: React.ReactNode }) {
   const { authStatus, isLoading } = useAuth();
 
@@ -57,21 +62,21 @@ function App() {
         }
       >
         <Route index element={<Navigate to="/dashboard" replace />} />
-        <Route path="dashboard" element={<DashboardPage />} />
-        <Route path="todos" element={<TodosPage />} />
-        <Route path="calendar" element={<CalendarPage />} />
-        <Route path="reminders" element={<RemindersPage />} />
-        <Route path="projects" element={<ProjectsPage />} />
-        <Route path="projects/:id" element={<ProjectDetail />} />
-        <Route path="people" element={<PeoplePage />} />
-        <Route path="locations" element={<LocationsPage />} />
-        <Route path="notifications" element={<NotificationsPage />} />
-        <Route path="settings" element={<SettingsPage />} />
+        <Route path="dashboard" element={<Suspense fallback={<RouteFallback />}><DashboardPage /></Suspense>} />
+        <Route path="todos" element={<Suspense fallback={<RouteFallback />}><TodosPage /></Suspense>} />
+        <Route path="calendar" element={<Suspense fallback={<RouteFallback />}><CalendarPage /></Suspense>} />
+        <Route path="reminders" element={<Suspense fallback={<RouteFallback />}><RemindersPage /></Suspense>} />
+        <Route path="projects" element={<Suspense fallback={<RouteFallback />}><ProjectsPage /></Suspense>} />
+        <Route path="projects/:id" element={<Suspense fallback={<RouteFallback />}><ProjectDetail /></Suspense>} />
+        <Route path="people" element={<Suspense fallback={<RouteFallback />}><PeoplePage /></Suspense>} />
+        <Route path="locations" element={<Suspense fallback={<RouteFallback />}><LocationsPage /></Suspense>} />
+        <Route path="notifications" element={<Suspense fallback={<RouteFallback />}><NotificationsPage /></Suspense>} />
+        <Route path="settings" element={<Suspense fallback={<RouteFallback />}><SettingsPage /></Suspense>} />
         <Route
           path="admin/*"
           element={
             <AdminRoute>
-              <Suspense fallback={<div className="flex h-full items-center justify-center text-muted-foreground">Loading...</div>}>
+              <Suspense fallback={<RouteFallback />}>
                 <AdminPortal />
               </Suspense>
             </AdminRoute>

frontend/src/components/calendar/CalendarPage.tsx

@@ -205,13 +205,22 @@ export default function CalendarPage() {
     return () => el.removeEventListener('wheel', handleWheel);
   }, []);
 
+  // AW-2: Track visible date range for scoped event fetching
+  const [visibleRange, setVisibleRange] = useState<{ start: string; end: string } | null>(null);
+
   const { data: events = [] } = useQuery({
-    queryKey: ['calendar-events'],
+    queryKey: ['calendar-events', visibleRange?.start, visibleRange?.end],
     queryFn: async () => {
-      const { data } = await api.get<CalendarEvent[]>('/events');
+      const params: Record<string, string> = {};
+      if (visibleRange) {
+        params.start = visibleRange.start;
+        params.end = visibleRange.end;
+      }
+      const { data } = await api.get<CalendarEvent[]>('/events', { params });
       return data;
     },
-    refetchInterval: 5_000,
+    // AW-3: Reduce from 5s to 30s — personal organiser doesn't need 12 calls/min
+    refetchInterval: 30_000,
   });
 
   const selectedEvent = useMemo(
@@ -467,6 +476,12 @@ export default function CalendarPage() {
   const handleDatesSet = (arg: DatesSetArg) => {
     setCalendarTitle(arg.view.title);
     setCurrentView(arg.view.type as CalendarView);
+    // AW-2: Capture visible range for scoped event fetching
+    const start = arg.start.toISOString().split('T')[0];
+    const end = arg.end.toISOString().split('T')[0];
+    setVisibleRange((prev) =>
+      prev?.start === start && prev?.end === end ? prev : { start, end }
+    );
   };
 
   const navigatePrev = () => calendarRef.current?.getApi().prev();

frontend/src/components/dashboard/DashboardPage.tsx

@@ -1,4 +1,4 @@
-import { useState, useEffect, useRef, useCallback } from 'react';
+import { useState, useEffect, useRef, useCallback, memo } from 'react';
 import { useNavigate } from 'react-router-dom';
 import { useQuery, useQueryClient } from '@tanstack/react-query';
 import { format } from 'date-fns';
@@ -34,6 +34,75 @@ function getGreeting(name?: string): string {
   return `Good night${suffix}`;
 }
 
+// AS-3: Isolated clock component — only this re-renders every minute,
+// not all 8 dashboard widgets.
+const ClockDisplay = memo(function ClockDisplay({ dataUpdatedAt, onRefresh }: {
+  dataUpdatedAt?: number;
+  onRefresh: () => void;
+}) {
+  const [now, setNow] = useState(() => new Date());
+
+  useEffect(() => {
+    let intervalId: ReturnType<typeof setInterval>;
+    let timeoutId: ReturnType<typeof setTimeout>;
+
+    function startClock() {
+      clearTimeout(timeoutId);
+      clearInterval(intervalId);
+      setNow(new Date());
+      const msUntilNextMinute = (60 - new Date().getSeconds()) * 1000 - new Date().getMilliseconds();
+      timeoutId = setTimeout(() => {
+        setNow(new Date());
+        intervalId = setInterval(() => setNow(new Date()), 60_000);
+      }, msUntilNextMinute);
+    }
+
+    startClock();
+    function handleVisibility() {
+      if (document.visibilityState === 'visible') startClock();
+    }
+    document.addEventListener('visibilitychange', handleVisibility);
+    return () => {
+      clearTimeout(timeoutId);
+      clearInterval(intervalId);
+      document.removeEventListener('visibilitychange', handleVisibility);
+    };
+  }, []);
+
+  const updatedAgo = dataUpdatedAt
+    ? (() => {
+        const mins = Math.floor((now.getTime() - dataUpdatedAt) / 60_000);
+        if (mins < 1) return 'just now';
+        if (mins === 1) return '1 min ago';
+        return `${mins} min ago`;
+      })()
+    : null;
+
+  return (
+    <div className="flex items-center gap-2 mt-1">
+      <p className="text-muted-foreground text-sm">
+        <span className="tabular-nums">{format(now, 'h:mm a')}</span>
+        <span className="mx-1.5 text-muted-foreground/30">|</span>
+        {format(now, 'EEEE, MMMM d, yyyy')}
+      </p>
+      {updatedAgo && (
+        <>
+          <span className="text-muted-foreground/40 text-xs">·</span>
+          <span className="text-muted-foreground/60 text-xs">Updated {updatedAgo}</span>
+          <button
+            onClick={onRefresh}
+            className="p-0.5 rounded text-muted-foreground/40 hover:text-accent transition-colors"
+            title="Refresh dashboard"
+            aria-label="Refresh dashboard"
+          >
+            <RefreshCw className="h-3 w-3" />
+          </button>
+        </>
+      )}
+    </div>
+  );
+});
+
 export default function DashboardPage() {
   const navigate = useNavigate();
   const queryClient = useQueryClient();
@@ -42,38 +111,7 @@ export default function DashboardPage() {
   const [quickAddType, setQuickAddType] = useState<'event' | 'todo' | 'reminder' | null>(null);
   const [dropdownOpen, setDropdownOpen] = useState(false);
   const dropdownRef = useRef<HTMLDivElement>(null);
-  const [clockNow, setClockNow] = useState(() => new Date());
-
-  // Live clock — synced to the minute boundary, re-syncs after tab sleep/resume
-  useEffect(() => {
-    let intervalId: ReturnType<typeof setInterval>;
-    let timeoutId: ReturnType<typeof setTimeout>;
-
-    function startClock() {
-      clearTimeout(timeoutId);
-      clearInterval(intervalId);
-      setClockNow(new Date());
-      const msUntilNextMinute = (60 - new Date().getSeconds()) * 1000 - new Date().getMilliseconds();
-      timeoutId = setTimeout(() => {
-        setClockNow(new Date());
-        intervalId = setInterval(() => setClockNow(new Date()), 60_000);
-      }, msUntilNextMinute);
-    }
-
-    startClock();
-
-    // Re-sync when tab becomes visible again (after sleep/background throttle)
-    function handleVisibility() {
-      if (document.visibilityState === 'visible') startClock();
-    }
-    document.addEventListener('visibilitychange', handleVisibility);
-
-    return () => {
-      clearTimeout(timeoutId);
-      clearInterval(intervalId);
-      document.removeEventListener('visibilitychange', handleVisibility);
-    };
-  }, []);
+  // Clock state moved to <ClockDisplay /> (AS-3)
 
   // Click outside to close dropdown
   useEffect(() => {
@@ -191,15 +229,6 @@ export default function DashboardPage() {
     );
   }
 
-  const updatedAgo = dataUpdatedAt
-    ? (() => {
-        const mins = Math.floor((clockNow.getTime() - dataUpdatedAt) / 60_000);
-        if (mins < 1) return 'just now';
-        if (mins === 1) return '1 min ago';
-        return `${mins} min ago`;
-      })()
-    : null;
-
   return (
     <div className="flex flex-col h-full">
       {/* Header — greeting + date + quick add */}
@@ -208,27 +237,7 @@ export default function DashboardPage() {
           <h1 className="font-heading text-3xl font-bold tracking-tight animate-fade-in">
             {getGreeting(settings?.preferred_name || undefined)}
           </h1>
-          <div className="flex items-center gap-2 mt-1">
-            <p className="text-muted-foreground text-sm">
-              <span className="tabular-nums">{format(clockNow, 'h:mm a')}</span>
-              <span className="mx-1.5 text-muted-foreground/30">|</span>
-              {format(clockNow, 'EEEE, MMMM d, yyyy')}
-            </p>
-            {updatedAgo && (
-              <>
-                <span className="text-muted-foreground/40 text-xs">·</span>
-                <span className="text-muted-foreground/60 text-xs">Updated {updatedAgo}</span>
-                <button
-                  onClick={handleRefresh}
-                  className="p-0.5 rounded text-muted-foreground/40 hover:text-accent transition-colors"
-                  title="Refresh dashboard"
-                  aria-label="Refresh dashboard"
-                >
-                  <RefreshCw className="h-3 w-3" />
-                </button>
-              </>
-            )}
-          </div>
+          <ClockDisplay dataUpdatedAt={dataUpdatedAt} onRefresh={handleRefresh} />
         </div>
         <div className="relative" ref={dropdownRef}>
           <Button

frontend/src/hooks/useCalendars.ts

@@ -1,4 +1,4 @@
-import { useMemo } from 'react';
+import { useMemo, useRef } from 'react';
 import { useQuery } from '@tanstack/react-query';
 import api from '@/lib/api';
 import type { Calendar, SharedCalendarMembership } from '@/types';
@@ -16,16 +16,26 @@ export function useCalendars({ pollingEnabled = false }: UseCalendarsOptions = {
     },
   });
 
+  // AS-4: Gate shared-calendar polling on whether user participates in sharing.
+  // Saves ~12 API calls/min for personal-only users.
+  // Use a ref to latch "has sharing" once discovered, so polling doesn't flicker.
+  const hasSharingRef = useRef(false);
+  const ownsShared = (ownedQuery.data ?? []).some((c) => c.is_shared);
+  if (ownsShared) hasSharingRef.current = true;
+
   const sharedQuery = useQuery({
     queryKey: ['calendars', 'shared'],
     queryFn: async () => {
       const { data } = await api.get<SharedCalendarMembership[]>('/shared-calendars');
       return data;
     },
-    refetchInterval: pollingEnabled ? 5_000 : false,
+    refetchInterval: pollingEnabled && hasSharingRef.current ? 5_000 : false,
     staleTime: 3_000,
   });
 
+  // Also latch if user is a member of others' shared calendars
+  if ((sharedQuery.data ?? []).length > 0) hasSharingRef.current = true;
+
   const allCalendarIds = useMemo(() => {
     const owned = (ownedQuery.data ?? []).map((c) => c.id);
     const shared = (sharedQuery.data ?? []).map((m) => m.calendar_id);

frontend/vite.config.ts

@@ -9,6 +9,25 @@ export default defineConfig({
       '@': path.resolve(__dirname, './src'),
     },
   },
+  build: {
+    rollupOptions: {
+      output: {
+        // AS-1: Split large dependencies into separate chunks for better caching
+        manualChunks: {
+          'vendor-react': ['react', 'react-dom', 'react-router-dom'],
+          'vendor-query': ['@tanstack/react-query'],
+          'vendor-fullcalendar': [
+            '@fullcalendar/react',
+            '@fullcalendar/core',
+            '@fullcalendar/daygrid',
+            '@fullcalendar/timegrid',
+            '@fullcalendar/interaction',
+          ],
+          'vendor-ui': ['sonner', 'lucide-react', 'date-fns'],
+        },
+      },
+    },
+  },
   server: {
     port: 5173,
     proxy: {