and what is PROVABLY FAIR?
your site type:
Game Seed == Server Seed + Client Seed:
19508405357028949
SHA-512(Game Seed) == Sent to client for verification:
8d3c98c78789d564c6f185b4bf0d939e11b74c78d2ea7455e8852bb21b18d7ff
but real SHA-512(19508405357028949) == "8f4a90956ee62a2a28bbaf1e49950867f13aa16ee03cade1b66f40099f35f3dc6b27c59afa4c9ff
0beaefd067d4125a7de10db4478450e98710d0c385cd59938"
and SHA-256(19508405357028949) == "9a9c23521ed79688918363f9e60ac5ad2365ec21cf4a71807d7ba84ffb3bd397"

That's really strange. If you look at the JavaScript you'll see that your browser hashes the raw server seed we send at the end of the game and compares it to the hash of the server seed we sent before the game. If the two don't match an error is thrown.
Can you send me the gameid of a game where you don't think the hash matches? I'd like to investigate.