Add update-available banner via periodic health version check

Backend /health now returns a build version; frontend polls it every
2 minutes (and on tab focus) and shows a reload banner when it changes.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/src/index.js

@@ -5,6 +5,7 @@ import { initDb } from './db.js'
 import { noticeRoutes } from './routes/notices.js'
 
 const app = Fastify({ logger: true, trustProxy: true })
+const startedAt = Date.now()
 
 await app.register(cookie)
 await app.register(cors, {
@@ -12,7 +13,7 @@ await app.register(cors, {
   credentials: true,
 })
 
-app.get('/health', async () => ({ status: 'healthy' }))
+app.get('/health', async () => ({ status: 'healthy', version: process.env.BUILD_VERSION || String(startedAt) }))
 
 await app.register(noticeRoutes)
 

frontend/src/App.tsx

@@ -1,10 +1,16 @@
 import { AuthGate } from './components/AuthGate'
 import { NoticeBoard } from './components/NoticeBoard'
+import { UpdateBanner } from './components/UpdateBanner'
+import { useVersionCheck } from './hooks/useVersionCheck'
 
 export default function App() {
+  const updateAvailable = useVersionCheck('/notices/health')
   return (
-    <AuthGate>
-      {user => <NoticeBoard user={user} />}
-    </AuthGate>
+    <>
+      <AuthGate>
+        {user => <NoticeBoard user={user} />}
+      </AuthGate>
+      <UpdateBanner visible={updateAvailable} />
+    </>
   )
 }

frontend/src/components/UpdateBanner.tsx

@@ -0,0 +1,44 @@
+import { RefreshCw } from 'lucide-react'
+
+export function UpdateBanner({ visible }: { visible: boolean }) {
+  if (!visible) return null
+  return (
+    <div style={{
+      position: 'fixed',
+      bottom: 0,
+      left: 0,
+      right: 0,
+      zIndex: 9999,
+      background: 'var(--sidebar)',
+      color: 'var(--text-light)',
+      display: 'flex',
+      alignItems: 'center',
+      justifyContent: 'center',
+      gap: '12px',
+      padding: '10px 16px',
+      fontSize: '14px',
+      boxShadow: '0 -2px 8px rgba(0,0,0,0.3)',
+    }}>
+      <span>A new version is available.</span>
+      <button
+        onClick={() => window.location.reload()}
+        style={{
+          display: 'flex',
+          alignItems: 'center',
+          gap: '6px',
+          background: 'var(--accent)',
+          color: 'var(--sidebar)',
+          border: 'none',
+          borderRadius: '4px',
+          padding: '6px 14px',
+          fontWeight: 600,
+          cursor: 'pointer',
+          fontSize: '13px',
+        }}
+      >
+        <RefreshCw size={14} strokeWidth={1.75} />
+        Reload
+      </button>
+    </div>
+  )
+}

frontend/src/hooks/useVersionCheck.ts

@@ -0,0 +1,43 @@
+import { useEffect, useState } from 'react'
+
+const POLL_MS = 2 * 60 * 1000
+
+export function useVersionCheck(healthUrl: string) {
+  const [updateAvailable, setUpdateAvailable] = useState(false)
+
+  useEffect(() => {
+    let seenVersion: string | null = null
+
+    async function check() {
+      try {
+        const res = await fetch(healthUrl, { cache: 'no-store' })
+        if (!res.ok) return
+        const data = await res.json()
+        const v: string | undefined = data.version
+        if (!v) return
+        if (seenVersion === null) {
+          seenVersion = v
+        } else if (v !== seenVersion) {
+          setUpdateAvailable(true)
+        }
+      } catch {
+        // network error — skip silently
+      }
+    }
+
+    check()
+    const interval = setInterval(check, POLL_MS)
+
+    function onVisible() {
+      if (document.visibilityState === 'visible') check()
+    }
+    document.addEventListener('visibilitychange', onVisible)
+
+    return () => {
+      clearInterval(interval)
+      document.removeEventListener('visibilitychange', onVisible)
+    }
+  }, [healthUrl])
+
+  return updateAvailable
+}