How to serve a static maintenance.html page with angular 19

With Angular 19 and SSR enabled, how to serve a maintenance page via server.ts ?

I have this code from standard Angular 19 with SSR

import { CommonEngine, isMainModule } from '@angular/ssr/node';
import express from 'express';
import { dirname, join, resolve } from 'nodeath';
import { fileURLToPath } from 'node:url';
import bootstrap from './main.server';

const serverDistFolder = dirname(fileURLToPath(import.meta.url));
const browserDistFolder = resolve(serverDistFolder, '../browser');
const indexHtml = join(serverDistFolder, 'index.server.html');

const app = express();
const commonEngine = new CommonEngine();


app.get(
'**',
express.static(browserDistFolder, {
maxAge: '1y',
index: 'index.html',
}),
);

/**
* Handle all other requests by rendering the Angular application.
*/
app.get('**', (req, res, next) => {
const { protocol, originalUrl, headers } = req;

// Rendre le document Angular
commonEngine
.render({
bootstrap,
documentFilePath: indexHtml,
url: `${protocol}://${headers.host}${originalUrl}`,
publicPath: browserDistFolder
})
.then((html) => {

res.send(html);
})
.catch((err) => next(err));
});

/**
* Start the server if this module is the main entry point.
* The server listens on the port defined by the `PORT` environment variable, or defaults to 4000.
*/
if (isMainModule(import.meta.url)) {
const port = process.env['PORT'] || 4000;
app.listen(port, () => {
console.log(`Node Express server listening on http://localhost:${port}`);
});
}

export default app;


I tried this but it doesn't work

app.use((req, res, next) => {
if (process.env['MAINTENANCE'] === 'true') {
return res.status(503).sendFile(resolve(browserDistFolder, '../public/maintenance.html'));
}
next();
});


but It doesn't work, the file doesn't exists but the html is present in public folder

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