my assumption is the only way you will be able to stop any bot from double spend attack is to multisig the puzzle address when its solved so any transaction there forth would need your main wallets or any wallet that you set up to need its signature or signature(s) if using multiple before any transactions are made but you will need to be quick about it maybe even setting up your own script or bot to do so i find it wild that the solver didn't think that someone could swoop in and take the reward i multisig all my addresses for that very reason and yes i know a lot about mutisig it's impossible to use a double spend attack with that set up