The use of the term "currency" in the bills is probably ill-advised for just that reason, but states can, under certain circumstances, issue bank notes that act

The use of the term "currency" in the bills is probably ill-advised for just that reason, but states can, under certain circumstances, issue bank notes that act essentially as currency or bills of credit; Briscoe v. Bank of Commonwealth of Kentucky, 36 U.S. 257 (1837) found such bank notes constitutional so long as they aren't issued under color state sovereignty -- that is, they must trade on "no pledge of the faith of the state, in any form." (The federal government eventually killed off state bank notes, not by attempting to outlaw them directly -- AFAIK! -- but by taxing them aggressively, though I don't believe those laws are on the books any more.) Having said that, the fact that these bills direct the state to establish the program, fixes in law the redemption of the "currency," and directs the state to hold gold reserves for the currency all suggest that this is Constitutionally questionable, because the bill is trading on "the faith of the state." Consider that, if Texas establishes a gold-backed stablecoin then executes a rug-pull, your legal options as an aggrieved party are limited due to state sovereignty, which is precisely the issue that the Constitution seeks to prevent (though at the time the question of sovereign immunity was somewhat less settled in the absence of the Eleventh Amendment).