on_mount set by the router macro: injects into each LiveView the list of domains, the mount base, and the current actor (resolved from the session).

Without an explicit domains: passed to the macro, the list is read on every request from Application.get_env(otp_app, :ash_domains, []) — a domain added afterward (via the Ash generators, which already maintain this config) therefore appears immediately, with no reinstallation needed.