Why my single Next.js app runs 4 different domains (and how the proxy.ts decides who sees what)

> TL;DR — I run four different domains off one Next.js codebase: a marketing site at pagestrike.com, an authenticated app at app.pagestrike.com, a public publishing domain at pagestrike.app, and customer-owned domains. The trick isn't deploying four apps — it's a single proxy.ts that reads the host and rewrites/redirects/passes-through per-request. This post walks through why I chose this shape, the parts I got wrong, and the cookie-domain trick that makes it all stick. Stack: Next.js 16 Ap...