url metadata field unequivocally treated as the canon feed url when calculating hashes, or are they ignored if they're not at least proper urls? do you just tolerate it if they're impersonating someone else's feed, or pointing to something that isn't even a feed at all?
@zvava@twtxt.net Yes, the specification defines the first url to be used for hashing. No matter if it points to a different feed or whatever. Just unsubscribe from malicious feeds and you’re done.
Since the first url is used for hashing, it must never change. Otherwise, it will break threading, as you already noticed. If your feed moves and you wanna keep the old messages in the same new feed, you still have to point to the old url location and keep that forever. But you can add more urls. As I said several times in the past, in hindsight, using the first url was a big mistake. It would have been much better, if the last encountered url were used for hashing onwards. This way, feed moves would be relatively straightforward. However, that ship has sailed. Luckily, feeds typically don’t relocate.