"Holos doesn't really implement ActivityPub."S2S is implemented. HTTP Signatures, WebFinger, inbox/outbox, Accept, Reject, Move, Flag, NodeInfo 2.1. The publicly reachable inbox lives on the relay because that's where the stable URL is. Signing and identity come from the device. Tested with Mastodon, Pleroma, Misskey, Pixelfed, GoToSocial.