A thing still missing there is that it sets empty audience for comments on
remote tickets, but that's fine because dev.angeley.es doesn't have such
comments in the database.
I added a migration that creates an ugly fake OutboxItem for messages that
don't have one. I'll try to turn it into a real one. And then very possibly
remove the whole ugly migration, replacing it with addFielfRefRequiredEmpty,
which should work for empty instances.