The backend served its settings dataset (including the app actor's private key) to anonymous callers, through the SPARQL endpoint and through the semapps LDP catch-all route, since WebACL is off. An allow-list mounted on every route now exposes only what the app and the pod need (/app, /as/actor/app and its Client ID Document, /catalog, the public key, access needs, the JSON-LD context, nodeinfo, the app inbox and the webhook endpoint); everything else answers 404.
Every watcher-fed service (public read, catalog, attendees, contacts, registration) now decides on the activity and object re-read from the pod as the app, checks they belong to the outbox owner and that the stored object has the expected type, and never acts on the notification body. Decisions for one object are serialized and taken on a read made when acting, with a 30 s bound and an abort check before every write. The anonymous read follows the event's visibility both ways, attendees collection included; Festipod records the grants it makes and revokes only those, leaving any other public share untouched; an unreadable ACL changes nothing. A participant's attendance follows their latest act by the pod's timestamp, not the order notifications arrive. Known limits (no conditional write on the pod, a write in flight at the timeout) are documented in the code.
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