Splitting the app with import/export

One file is where backends go to die

The PawWalk backend has walkers, bookings, auth, payments. Pour all of that into one index.ts and every change means scrolling a 2,000-line file, every merge is a conflict, and nobody can find anything. The fix is modules: one file, one job. A walkers module owns walker code; a bookings module owns booking code; each exports what others may use and keeps the rest private.

A module's exports are its public API. Everything you don't export is private by default — the module's implementation detail. That single rule is how a backend stays understandable at 50 files instead of 5.