RDak, I hope this answers your question:
Article IV, Section 3
New States may be admitted by the Congress into this Union; but no new States shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress.
The Congress shall have Power to dispose of and make all needful Rules and Regulations respecting the Territory or other Property belonging to the United States; and nothing in this Constitution shall be so construed as to Prejudice any Claims of the United States, or of any particular State.
The above section of the Constitution does 2 things.
The first clause allows for the admittance of new States into the union, with restrictions on making new States out of existing States. Exactly how this should be done is not specified.
The second clause grants power to the Congress to administer all Federal lands that are not States; Such as making a territory into a State or States.
The enabling Act of 1802 became the precedence of how a new State is to be admitted. It set forth the rules by which a people (of a territory or other possession of the US) could elect representatives and vote on Statehood; Write their own Constitution and petition the Congress for admittance.
It is not a contract, agreement or compact (in the sense of the original 13 colonies under the Articles of Confederation), but a series of official legislative acts by the Congress relative to the people of the proposed State.
Under the Articles of Confederation, the union of the Colonies/States were declared to "be perpetual." The Constitution was ordained "to form a more perfect union." The logic then holds that since it took the States of the Union (via the Congress) to admit another State into Union, therefore said State was placed in perpetual union with all other States. That is, the new State was incorporated into the body politic. Such a thing is more than a mere compact, agreement or contract.
To dissolve the incorporation (union) requires that the corporation (union) agree to such dissolution. In other words, How a State became a State (by consent and Acts of the Congress) is exactly how a State would shed its union (by consent and further Acts of Congress). That conforms to Article IV Section 1 of the Constitution.
Any State that had signing documents that seemed to say something different, have no force of law, once admitted into union with the other States.