Unfortunately, there isn’t a bilateral agreement with Mexico on this issue as required by the paragraph you posted.
We do have such a Safe Third Party agreement with Canada, and negotiating one with Mexico may be a way out of this, but for now that section of the Code is a dead letter.
Sure we do. The passage requires only an agreement, not a treaty. Mexico has previously agreed to give the migrants asylum, and Mexico has agreed to cooperate with the U.S. in not allowing the migrants in the caravan to enter the U.S.