Forgive me if I misunderstand, but I thought Signal's protocol prevented anyone, including Signal from intercepting messages, as these are encrypted end-to-end.

Forgive me if I misunderstand, but I thought Signal's protocol prevented anyone, including Signal from intercepting messages, as these are encrypted end-to-end. The threat model is that someone else is impersonating your correspondent. This is not message interception but identity verification. Your communication with whoever is on the other end is secure within Signal, but your correspondent may do whatever they wish with the messages.