Feature
Identity as a port
next-story asks who a visitor is; it never decides.
The whole identity surface is one function your app supplies: given a request, return an anonymous id and optionally a user id. The default only mints and reads the first-party __ns_aid cookie and never returns a user id.
Links between anonymous and user ids are append-only rows, so adopting a real identity system later is a join, not a migration.