> Wait a sec. IANAL, but if I license something to you under the GPLv3, you may not license it to someone else under AGPLv3 or a commercial license.

Not exactly the above case, but from the GNU GPL version 3 (https://www.gnu.org/licenses/gpl-3.0.txt):

      13. Use with the GNU Affero General Public License.
    
      Notwithstanding any other provision of this License, you have
    permission to link or combine any covered work with a work licensed
    under version 3 of the GNU Affero General Public License into a single
    combined work, and to convey the resulting work.  The terms of this
    License will continue to apply to the part which is the covered work,
    but the special requirements of the GNU Affero General Public License,
    section 13, concerning interaction through a network will apply to the
    combination as such.