The running proxy: routes table + Finch pool + Bandit listener, one supervision tree started by the CLI (or embedded by a host app).

On start it records {port} in the state file so clients (Cherrypicker.register/2, the CLI verbs) can find the control API without configuration; the file is removed on clean shutdown.

The default port is 80 — that is what makes http://myapp.localhost pretty — but binding 80 needs privileges on Unix, so :port is honest configuration, not a hidden sudo. port: 0 binds an ephemeral port, which the state file then advertises.