Documentation

Return the id of the user's newest notification, if any.

Useful as a pagination anchor (since): instead of relying on a short notificationTTL to expire pre-existing notifications (e.g. the welcome notification) before querying, we page from the newest existing one.

The welcome notification is pushed asynchronously on user creation, so it may not have landed yet when we first look. We therefore poll until the set of pre-existing notifications stabilizes (two consecutive reads agree) before anchoring on the newest id. This restores the "wait for the welcome notification" duty of the old fixed sleep without the TTL-expiry race: the previous approach set a 2s TTL and slept for 2.1s, racing the anchor to expiry before the final since query (gundeck returns 404 by design when the since cursor is gone).