FAIR PLAY
Check a deal
Before the deal the server publishes the hash of a random seed, and after the game it reveals the seed itself. The seed's hash has to match the one published — so the deck could not have been chosen once the cards were known.
How it works
The deck comes from the seed deterministically: SHAKE-256(seed) drives a Fisher–Yates shuffle. The server cannot pick a seed for the deal it wants, because the hash was published first.