diff --git a/frontend-s2s/config/launcher.integration.ts b/frontend-s2s/config/launcher.integration.ts
index 0aeeb66..2720a82 100644
--- a/frontend-s2s/config/launcher.integration.ts
+++ b/frontend-s2s/config/launcher.integration.ts
@@ -20,6 +20,7 @@ const args = process.argv.slice(2);
 writeFileSync(root + "/" + role + ".pid", String(process.pid));
 writeFileSync(root + "/" + role + ".json", JSON.stringify({
   args, target: process.env.S2S_BACKEND_URL, hosts: process.env.S2S_DEV_ALLOWED_HOSTS,
+  nodeEnv: process.env.NODE_ENV,
 }));
 if (process.env.S2S_TEST_FAIL === role) process.exit(37);
 const worker = spawn(process.execPath, ["-e",
@@ -95,6 +96,7 @@ async function launcher(context: TestContext, env: Record<string, string> = {})
       ...process.env,
       UI_PORT: String(publicPort),
       UI_HOST: "0.0.0.0",
+      NODE_ENV: "production",
       S2S_BACKEND_PORT: "1",
       S2S_BACKEND_URL: "http://wrong-target.invalid",
       S2S_TEST_ROOT: root,
@@ -133,6 +135,7 @@ for (const signal of ["SIGINT", "SIGTERM"] as const) {
         args: ["--host", "0.0.0.0", "--port", String(run.publicPort), "--strictPort"],
         target: `http://127.0.0.1:${run.backendPort}`,
         hosts: "s2s.test",
+        nodeEnv: "development",
       });
       assert.equal(run.output().includes("Installing"), false);
       run.child.kill(signal);
diff --git a/start_ui.sh b/start_ui.sh
index 3e18dbd..8381a5d 100755
--- a/start_ui.sh
+++ b/start_ui.sh
@@ -146,6 +146,8 @@ fi
 
 (
   cd "$FRONTEND_DIR"
+  # Keep React Fast Refresh enabled even if PM2 exports NODE_ENV=production.
+  export NODE_ENV=development
   exec setsid node node_modules/vite/bin/vite.js --host "$UI_HOST" --port "$UI_PORT" --strictPort
 ) &
 frontend_pid=$!