Which is a reminder: If you are going to do unethical things, make sure you can prove that your bosses ordered it. Otherwise, in addition to being a rat, you will likely twist in the wind.
"Let's take this offline"
"Just to recap our conversation earlier..."
take the notes, conspicuously, and accompanied by several "come again please, i'm taking notes" if over the phone, ostensibly to make sure that you're doing it to carry the Leader's order in all the glorious details. Kind of James Comey or North Korea style. Years ago, an acquaintance, a former captain of Soviet Army who served at the place pretty intense even during the peace time, had some funny stories how such habit saved his bacon on various occasions and it made me remember that advice.
Yes. Take notes, then send them back via email or some other mechanism that can be discovered later.
I once worked on a startup founded by lawyers and they would do this all the time. Never put things in writing that they might be flexible on later. I hated that part.
Follow up with an email (or message or whatever the medium is) confirming the agreed-upon outcome of the offline discussion? This is good practice anyway, summarising what was said over an hour long discussion can often reveal people came away with very different interpretation of what was agreed upon
Yup, always note your concerns and objections via email and make sure to CC the appropriate people.