diff --git a/package.json b/package.json
index 442cfffe..e9e3f210 100644
--- a/package.json
+++ b/package.json
@@ -129,7 +129,7 @@
   },
   "dependencies": {
     "@apollo/server": "^5.5.1",
-    "@as-integrations/express4": "^1.1.2",
+    "@as-integrations/express": "^3.0.0",
     "@aztec/bb.js": "^0.87.9",
     "@opentelemetry/api": "^1.9.0",
     "@opentelemetry/auto-instrumentations-node": "^0.67.0",
@@ -144,7 +144,7 @@
     "buffer": "^6.0.3",
     "cors": "^2.8.5",
     "dataloader": "^2.2.3",
-    "express": "^4.21.0",
+    "express": "^5.0.0",
     "express-rate-limit": "^8.6.2",
     "fuse.js": "^7.5.0",
     "ioredis": "^5.4.1",
diff --git a/server/graphql/server.ts b/server/graphql/server.ts
index 945453da..ea93d150 100644
--- a/server/graphql/server.ts
+++ b/server/graphql/server.ts
@@ -1,8 +1,8 @@
 /**
- * server/graphql/server.ts — Apollo Server wiring for Express (#528)
+ * server/graphql/server.ts — Apollo Server 5 wiring for Express 5 (#751)
  */
 import { ApolloServer } from '@apollo/server'
-import { expressMiddleware } from '@as-integrations/express4'
+import { expressMiddleware } from '@as-integrations/express'
 import { ApolloServerPluginLandingPageDisabled } from '@apollo/server/plugin/disabled'
 import { GraphQLError, Kind, type ValidationRule } from 'graphql'
 import type { NextFunction, Request, RequestHandler, Response } from 'express'
diff --git a/server/middleware/cors.js b/server/middleware/cors.js
index 35aed9a1..5e0f15e0 100644
--- a/server/middleware/cors.js
+++ b/server/middleware/cors.js
@@ -86,6 +86,8 @@ export function createCorsMiddleware(opts = {}) {
     res.setHeader("Access-Control-Allow-Origin", origin);
     res.setHeader("Access-Control-Allow-Methods", methods.join(", "));
     res.setHeader("Access-Control-Allow-Headers", headers.join(", "));
+    // #753: Allow credentials for wallet postMessage flows
+    res.setHeader("Access-Control-Allow-Credentials", "true");
     if (req.method === "OPTIONS") {
       res.setHeader("Access-Control-Max-Age", String(maxAge));
       return res.status(204).end();
diff --git a/server/middleware/cors.ts b/server/middleware/cors.ts
index 6df614dc..f665dcc4 100644
--- a/server/middleware/cors.ts
+++ b/server/middleware/cors.ts
@@ -125,8 +125,8 @@ export function createCorsMiddleware(opts: CorsOptions = {}) {
 
     // Allowed origin – set CORS headers
     res.setHeader('Access-Control-Allow-Origin', origin)
-    // Credentials are not needed for ZK prover (no cookies), keep false to avoid extra complexity
-    // If you need credentials, set Access-Control-Allow-Credentials: true and mirror origin
+    // #753: Allow credentials for Stellar wallet popups with postMessage
+    res.setHeader('Access-Control-Allow-Credentials', 'true')
     res.setHeader('Access-Control-Allow-Methods', methods.join(', '))
     res.setHeader('Access-Control-Allow-Headers', headers.join(', '))
     // Only set Max-Age on preflight responses (per spec, but also harmless on simple requests)
diff --git a/src/i18n.ts b/src/i18n.ts
index 837caa0c..4789af0a 100644
--- a/src/i18n.ts
+++ b/src/i18n.ts
@@ -1,29 +1,33 @@
 import i18n from 'i18next'
-import HttpBackend from 'i18next-http-backend'
 import { initReactI18next } from 'react-i18next'
 
 export const SUPPORTED_LANGUAGES = ['en', 'ar'] as const
 export const DEFAULT_LNG = 'en'
 export const DEFAULT_NS = 'common'
 
-const ready = i18n
-  .use(HttpBackend)
-  .use(initReactI18next)
-  .init({
-    lng: DEFAULT_LNG,
-    fallbackLng: DEFAULT_LNG,
-    supportedLngs: [...SUPPORTED_LANGUAGES],
-    nonExplicitSupportedLngs: true,
-    load: 'languageOnly',
-    defaultNS: DEFAULT_NS,
-    ns: [DEFAULT_NS],
-    backend: {
-      loadPath: '/locales/{{lng}}/{{ns}}.json',
-      requestOptions: { cache: 'no-cache' },
-    },
-    interpolation: { escapeValue: false },
-    react: { useSuspense: false },
-  })
+const ready = (async () => {
+  // Lazy-load HttpBackend to reduce initial bundle (#744)
+  const { default: HttpBackend } = await import('i18next-http-backend')
+
+  return i18n
+    .use(HttpBackend)
+    .use(initReactI18next)
+    .init({
+      lng: DEFAULT_LNG,
+      fallbackLng: DEFAULT_LNG,
+      supportedLngs: [...SUPPORTED_LANGUAGES],
+      nonExplicitSupportedLngs: true,
+      load: 'languageOnly',
+      defaultNS: DEFAULT_NS,
+      ns: [DEFAULT_NS],
+      backend: {
+        loadPath: '/locales/{{lng}}/{{ns}}.json',
+        requestOptions: { cache: 'no-cache' },
+      },
+      interpolation: { escapeValue: false },
+      react: { useSuspense: false },
+    })
+})()
 
 function syncDocumentLocale(language: string): void {
   if (typeof document === 'undefined') return
diff --git a/src/service-worker.js b/src/service-worker.js
index 5e87163c..0b4a1582 100644
--- a/src/service-worker.js
+++ b/src/service-worker.js
@@ -54,6 +54,15 @@ self.addEventListener("fetch", (event) => {
   const { request } = event;
   const url = new URL(request.url);
 
+  // #742: Skip caching for HMR and dev server requests to avoid stale-while-revalidate
+  if (
+    url.searchParams.has("t") || // Vite HMR timestamp query
+    /\/@vite\//.test(url.pathname) || // Vite HMR module
+    /\.hmr(?:\.json)?$/.test(url.pathname) // HMR manifest
+  ) {
+    return; // Let fetch proceed normally, don't cache
+  }
+
   if (
     request.method === "GET" &&
     url.origin === self.location.origin &&
diff --git a/vite.config.ts b/vite.config.ts
index 0e13355f..2061aac3 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -243,6 +243,13 @@ export default defineConfig(({ mode }) => ({
       "Cross-Origin-Opener-Policy": "same-origin",
       "Cross-Origin-Embedder-Policy": "credentialless",
     },
+    hmr: {
+      // #742: Explicit HMR config prevents stale-cache issues with service worker
+      protocol: "ws",
+      host: "localhost",
+      port: 3000,
+      timeout: 5000,
+    },
     proxy: {
       "/zk": {
         target: "http://127.0.0.1:3001",