lambda account, token, client_config=None: ok_client)
        with Session(db_engine, expire_on_commit=False) as db:
            f = _seed_sendable(db)
            unsub_token = f["recipient"].unsub_token
            cid, crid, acc_email = f["campaign"].id, f["cr"].id, f["account"].email
            cr_email = f["cr"].email
            subj_text = f["subject"].subject
        out = _call(st, cid, crid)
        assert out == {"ok": True, "status": "sent", "message_id": "MSG-FAKE-123",
                       "thread_id": "TH-FAKE-456"}
        # MIME captured by the fake transport — assert real headers/content
        assert len(ok_client.sent) == 1
        mime = ok_client.sent[0]
        assert mime["From"] == acc_email            # never spoofed
        assert mime["To"] == cr_email
        assert mime["Subject"] == subj_text
        lu = mime["List-Unsubscribe"]
        assert unsub_token in lu and lu.startswith("<http")
        assert mime["List-Unsubscribe-Post"] == "List-Unsubscribe=One-Click"
        body = mime.as_string()
        # MIMEText uses base64 CTE — decode payload parts before searching