[Poison Pill]

It does not prohibit the state taxing exports.

The power to regulate this falls to Congress, not the states, not SCOTUS and not POTUS

Article I, Section 8, Clause 3:[3]

[The Congress shall have Power] To regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes;

[Labyrinthos]

They are two different provisions with two different meanings.