fix: prevent stale chunk errors after deployments

- Set Cache-Control no-cache on index.html in nginx so browsers always
  fetch fresh chunk references after a deploy
- Auto-reload on chunk load failures (stale deploy detection) with
  loop prevention via sessionStorage
- Show friendly "App Updated" message if auto-reload doesn't resolve it

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

frontend/nginx.conf

@@ -8,12 +8,19 @@ server {
     gzip on;
     gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;
 
+    # index.html — never cache (so deploys serve new chunk references)
+    location = /index.html {
+        add_header Cache-Control "no-cache, no-store, must-revalidate";
+        add_header Pragma "no-cache";
+        add_header Expires "0";
+    }
+
     # Handle SPA routing - serve index.html for all routes
     location / {
         try_files $uri $uri/ /index.html;
     }
 
-    # Cache static assets
+    # Cache hashed static assets (immutable — filenames change on rebuild)
     location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2)$ {
         expires 1y;
         add_header Cache-Control "public, immutable";

frontend/src/components/common/RouteError.tsx

@@ -1,14 +1,44 @@
+import { useEffect } from 'react'
 import { useRouteError, isRouteErrorResponse, useNavigate } from 'react-router-dom'
 import { cn } from '@/lib/utils'
 
+function isChunkLoadError(error: unknown): boolean {
+  if (!(error instanceof Error)) return false
+  const msg = error.message.toLowerCase()
+  return (
+    msg.includes('failed to fetch dynamically imported module') ||
+    msg.includes('importing a module script failed') ||
+    msg.includes('loading chunk') ||
+    msg.includes('loading css chunk')
+  )
+}
+
+const RELOAD_KEY = 'rf_chunk_reload'
+
 export function RouteError() {
   const error = useRouteError()
   const navigate = useNavigate()
 
+  // Auto-reload once on chunk load failures (stale deploy)
+  useEffect(() => {
+    if (isChunkLoadError(error)) {
+      const lastReload = sessionStorage.getItem(RELOAD_KEY)
+      const now = Date.now()
+      // Only auto-reload if we haven't reloaded in the last 10 seconds (prevent loops)
+      if (!lastReload || now - Number(lastReload) > 10_000) {
+        sessionStorage.setItem(RELOAD_KEY, String(now))
+        window.location.reload()
+      }
+    }
+  }, [error])
+
   let errorMessage = 'An unexpected error occurred'
   let errorDetails = ''
 
-  if (isRouteErrorResponse(error)) {
+  if (isChunkLoadError(error)) {
+    errorMessage = 'App Updated'
+    errorDetails = 'A new version was deployed. Please refresh the page.'
+  } else if (isRouteErrorResponse(error)) {
     errorMessage = error.status === 404 ? 'Page not found' : `Error ${error.status}`
     errorDetails = error.statusText || ''
   } else if (error instanceof Error) {