I have to assume I got whatever Costco warranties that were standard since road hazard wasn't specifically excluded. We've bought a lot of tires at Costco but the only ones that have been ruined by road hazards (e.g. nails near tread edge, curb strikes that damaged sidewalls) have been tires that came on the vehicles when new. The requirement to sign releases at Costco when buying H-rated tires for cars that have top speeds above 130 mph has been more like a routine formality - just something they need to do. I've never found road hazard warranties to have much benefit the way they are pro-rated off the tire's retail price but more importantly because its almost always only one tire that gets ruined by a road hazard - then it is best to also replace the other three for consistent handling if all the tires are more than half way through their tread lives.
I recently made a pro-rated claim, and they seemed to push really hard when measuring the remaining tread depth...
The Prius is fairly stable up to 100 mph on highway 5 between farms in CA, so.... No Prius can't go 130 mph even on the best tires. Unless you're going down hill ... With a death wish.