What is the adjective for "supersedure" or "primacy"?

I would imagine the simplest way to do it would be simply superseding; but since you’re looking for more legalistic-sounding terms, there is:

The ruling demonstrated disregard for the supersessory constitution/law/legal right.

The OED defines supersessory (or its synonym, supersessive) as:

Having the quality or character of supersession; taking the place of something or someone displaced

– and gives a citation that appears to me (who am not very well-versed in US law, I should note!) to be quite parallel to what you’re looking for:

His decrees are always in the form of rescripts, which conclude with a general supercessory clause, contrariis quibuscunque non obstantibus. (The Monthly Review (London), Sept. 205, 1789)

Consider the term preemption

a doctrine in conflicts of law: when a superior government (as of a state) has undertaken to regulate a subject its laws supersede those of an inferior government (as of a municipality).

According to the doctrine of preemption, federal law supersedes state law when federal law is in conflict with a state law on a subject or when there is congressional intent to regulate a subject to the exclusion of the states. Federal preemption is based on the supremacy clause of the U.S. Constitution and is closely related to the powers granted Congress in the commerce clause.

The adjectival form is preemptive.

Perhaps 'overarching' ? Not strictly related to legal matters of course.

I'd go with 'ultimate' as in the 'ultimate authority.'

Alternatively, 'fundamental' may be more in line with your example sentence.