Support delivery to shared inboxes

[cjslep]

No description provided.

[cjslep]

I'm going to leave this open, but I want to note that I am hesitant to add the sharedInbox optimization at this time.

[aschrijver]

Could you explain a bit more about why you are hesitant as background info? Thanks :)

[cjslep]

Sure, it's simple:

sharedInbox is the only* ActivityPub feature that breaks the Actor model. When you look at any Activity, its addressing (to, bto, cc, bcc, audience) does not align with what bytes actually got shipped to which actors on the network when using sharedInbox. Sending to the sharedInbox isn't sending an Activity to an Actor at all.

*Inbox Forwarding does not count because the entire process still preserves the Actor model: every step of the way is still shipping bytes to the actors directly.

[aschrijver]

Makes perfect sense, thanks!