Your agent reads team channels safely
Your agent can read team channels and draft posts through a broker that fences every message as untrusted, and messages to an offline Mac wait sealed.
Team channels are useful context and a risk: anyone can write in them. Your agent now reads them through a broker that marks every message as untrusted, so text in a channel cannot instruct it.
An offline mailbox
Messages to a Mac that is offline are sealed to that Mac's key and wait as ciphertext until it comes back. A recovery envelope stays in your account.