I edited the post because I forgot to include a key constraint to the problem, which is that an attacker can/will be trying to send you false information from “yourself” so you need a way to distinguish. In this case it’s relevant because an attacker could create a false message and force you to swallow the key to that message right before your memories were wiped.
Retrievably swallow the key and salt you used to sign the message :)
I edited the post because I forgot to include a key constraint to the problem, which is that an attacker can/will be trying to send you false information from “yourself” so you need a way to distinguish. In this case it’s relevant because an attacker could create a false message and force you to swallow the key to that message right before your memories were wiped.