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Before every throw, the house commits to its move by publishing sha256(server_seed:round:nonce) in a FistChain transaction. After you choose, it reveals server_seed. The house move is the first byte b < 255 of HMAC-SHA256(server_seed, "client_seed:round:nonce:i"), as b mod 3 → rock / paper / scissors. Everything below runs in your browser.