Correction. Should read: You sidestepped my request. Please try again. I'm asking for documentation from the Philadelphia convention.
In fact, I fully answered your original question, even if you don't like that answer.
Remember, the word "secession" does not appear in the Constitution, or the Federalist Papers or in any other document I know of from that time.
Nor is there explicit discussion of other words which mean "secession", except in the context I've quoted from Madison:
In other words, not just some generalized breach of contract, but specifically, as the Virginia ratification statement says, when Federal powers are:
Again, I would invite you to review all of your vast collection of quotes from Founders -- meaning those who wrote and voted to ratify the Constitution -- to see if any of them answered the secession question as something to be allowed, in Madison's term: "at pleasure".