“The Constitution has no mechanism for secession”
Meaning under the 10th Amendment, it was left to the states to decide. If a power is not specifiacally granted to the Feds, it remains with the states. It’s in plain english.
That is why the constitution only discusses how a state may join the union. When it may leave is automatically left to the state.
But states are required to resolve controversies with the federal government with the supreme court as original jurisdiction.
The 10th amendment doesn’t change that.
That didn’t work so well when it was attempted. Any power exercised inder the Constitution assumes the continued adherence to the charter that granted the power.