Switch WHO this thread's email sends as — any current unusual.ai admin — then rewrite the live draft so it reads naturally as the new sender (a takeover, not an identity fiction). Two cases share the door: correcting a mis-derived seat, and a real handover (Sarah picking up Will's thread). On a handover the ORIGINAL seat is stamped once in channel_refs and stays CC'd on every email send after; the campaign alias is never CC'd.

Allowed wherever the pending message sends as an email: campaign-email threads, and LinkedIn threads whose draft is a direct email. A pure LinkedIn reply's sender is structural (the conversation belongs to one seat's account).