Buy the token, then call claim. 300,000 $CLAW is destroyed, not collected. In exchange the contract writes down your address and the current block, and one crab is held in reserve for you so the last claims cannot be sold a crab that is already owed. Nothing is minted yet.

The draw is anchored to the hash of the next block, which did not exist while you were signing. You cannot look at the crab first and decide whether to pay. Nobody can, including us. On this chain that block is an Ethereum block, so the wait is about twenty-three seconds and the window to draw stays open about forty-five minutes.

Call reveal, or let anybody call it for you. The draw indexes into a lazy Fisher-Yates shuffle over the ids nobody holds yet, so the crab is uniform over whatever is left and no id can come out twice. The whole image order was hashed on chain before the first claim, so which crab is rare was fixed before anyone could act on it.

If nobody drew your commit before the blockhash went out of reach, the claim is not lost and it is not paid for twice. Re-anchoring moves it to the current block and costs nothing but gas, because the $CLAW was already destroyed when you committed.