Moving client projects from the Pages Router to the Next.js App Router sounded like a routine upgrade — until it wasn't. Every migration I've done has surfaced the same handful of breakages. Here are the four that cost me real hours, and how I fix them now. 1. getServerSideProps doesn't exist anymore The first thing that breaks is data fetching. There is no getServerSideProps in the App Router — server components fetch directly: // app/dashboard/page.jsx export d...