Why a slip

You start a Svelte app. Vite defaults to 5173. You start another. It gets 5174. That is fine until you reboot and start them in the other order. The ports swap. The bookmark, the firewall hole, and the phone all follow the number, not the app.

A name holds the number still. foo is 5173. bar is 5174. The agent or the app calls the CLI (localberth get foo) instead of taking whatever is free.

The same miss shows up when an app moves from 5173 to 5193 and the firewall rule stays on 5173. The phone times out. LocalBerth is local DNS for ports: a name for a number you still type.