@lyse@lyse.isobeef.org This looks like a nice way to do it.
Another thought: if clients can’t agree on the url (for example, if we switch to this new way, but some old clients still do it the old way), that could be mitigated by computing many hashes for each twt: one for every url in the feed. So, if a feed has three URLs, every twt is associated with three hashes when it comes time to put threads together.
A client stills need to choose one url to use for the hash when composing a reply, but this might add some breathing room if there’s a period when clients are doing different things.
(From what I understand of jenny, this would be difficult to implement there since each pseudo-email can only have one msgid to match to the in-reply-to headers. I don’t know about other clients.)