I've switched the water-trail effect back to cauldron; it only needs to be CAULDRON_ITEM to work.
Added sanity check so 'ground finder' won't drop endlessly into the void if there's no bedrock.
I've done cleanup on the BoxSnowballLogic; it can now be made to fill the interior with something other than air, or not fill the interior at all, and with subclassing it can be made to replace everything, or things other than air and liquids.

I've also changed it to for-loops for iteration, and introduced more correct clamping logic.