So I said screw it and skimmed the damn thing. Article 7 of the treaty mentions borders, but only serves to clarify that the preexisting borders will continue to exist and that they “be natural and convenient for one and another nations”.

Interestingly, article 5 says that black slaves will not cross the borders, and escaped slaves will be returned to their respective country. Turns out that Brazil did not ban slavery until 1888! Peru never had slaves so I’m not who the Brazilians would need to return