If that treaty can trump the Constitution then all treaties can trump the Constitution. And if that is true then Texas has rights under the Constitution denied to other states. I don't agree with that.
No, it doesn’t mean that Texas has rights under the Constitution that other states don’t have. The admission of any new states formed from Texas must be admitted according to the Constitution. There is no doubt about that.
There was/is no treaty. There was a joint resolution and order of annexation, neither of which trumps or conflicts with the Constitution.