rather than allowing edits for invisible edits for X minutes, couldn’t your client just delay actually sending it for X minutes allowing to cancel or edit freely until that point?
Gmail allows a similar feature and it seems safer in a distributed system than relying on everyone else to respect what happens after you send a raw message and an edit right after
Correct, though to be pedantic anyone can be a CA- you just generate a cert with the right bits to say it’s a ca certificate and then use it to sign any other certificate you want.
But the only devices that will consider your signature worth anything are ones you also install your ca certificate on. So it’s useful and common in internal networks but isn’t really what is being asked here.
The hard part is getting in the root CA store of operating systems and browsers. As far as I know they are all maintained independently with their own requirements.