> Nothing in the constitution grants the supreme court this power.

Doesn’t matter. They have this power, in actually existing reality.

> Theoretically, congress could act to limit the purview of the supreme court at any time.

Sure, they could try. And the Supreme Court would strike down the law they pass. Then we’re in full-blown Venezuela-level constitutional crisis territory where nobody agrees who legitimately holds power, and it’s impossible to predict what would happen.