Festipod's create path now addresses events and meeting points to the ActivityStreams Public collection (to: as:Public), and the backend grants acl:Read to foaf:Agent on a created as:Event only when it carries that public intent (one predicate, hasPublicIntent, in backend/services/public-intent.js). Before this, every as:Event written to a user's outbox would have been made world-readable, including other apps' events and events addressed to a single friend. The grant is idempotent (it reads the ACL first) and never throws into the webhook path.
The attendees service overrides the collections mixin so that an event posted with apods:attendees already attached no longer reaches new URL(undefined) and takes the whole backend process down. Attendee lists stay world-readable as the pod creates them; whether they should is an open product question.
Sylvain Duchesne