If the AP inbox is endpoint-only (can’t be dereferenced) and the servers don’t host an inbox collection, then AP inbox sync is not necessary or possible. A large majority of current AP Fediverse servers do not actually host an inbox collection (all Mastodon servers, for example).
Of course, there may be some kind of non-AP inboxy-like thing internal to a server or server cluster’s implementation, but I assume we’re just talking about AP S2S.
Yes, the inbox collection may not actually exist. The purpose of the mechanism described in FEP-ef61 is to ensure that different servers have the same view of the history of interactions. For example, if one server receives Follow activity, it should forward this activity to other servers where actor’s data is stored.
Hmmm. Shoudn’t a proposal on this include all the functionality currently done in common by Mastodon, Firefish, and others that today (I think) allow migrating followers, following, mutes, bookmarks and blocks without exporting/inporting manually?
And then a future spec that does what Firefish does today, and migrates posts as well?
I don’t know any implementations that automatically migrate following/mutes/etc lists. Streams and Hubzilla may be able to do that, but what they are doing is not a “migration”, strictly speaking.