Show the production domain while recording demos against a local server: Chromium --host-resolver-rules MAP

import { chromium } from "playwright";
const REAL = process.env.BASE || "http://localhost:3000";          // local server
const BASE = process.env.NOMAP ? REAL : "http://app.example.com";  // what the viewer sees
const MAPARG = `--host-resolver-rules=MAP app.example.com:80 127.0.0.1:${new URL(REAL).port}`;
const br = await chromium.launch({ channel: "chrome", headless: true, args: [MAPARG] });
const ctx = await br.newContext({ viewport: { width: 1440, height: 810 } });
await ctx.addCookies([{ name: "session", value: token, url: BASE }]);  // cookies for the displayed host
const pg = await ctx.newPage();
await pg.goto(BASE + "/");

Chromium resolves app.example.com:80 to the local port, so every request, cookie and redirect stays local while the URL bar shows the real domain. Use plain http://. With https the local server would need a certificate for the production name.