@mikedev @deadsuperhero Synchronization definitely needs more thinking, but the general idea has been laid out in "Inboxes and outboxes" section: https://codeberg.org/fediverse/fep/src/branch/main/fep/ef61/fep-ef61.md#inboxes-and-outboxes
When actor creates an activity, it should be sent to all servers where outboxes of actor's clones are located. This can be done by a primary server, or it can be done directly from a client.