so public_recips and allowed_public_recips is working so much better than before, but was still not quite right. We seem to be getting all the right results for top-level posts now, but comments aren't getting through on channels for which we've allowed them to send us their stream, but not comment on our posts. The reason is we were seeing if they could comment - and we only need to do that if we own the post. If they own the post, we only need to check if they can send us their stream.