So, the clown car wrecked ~10 dorfs who were in the caverns where I had the mining accident: lesson learned; The hollow tube can be placed above squares containing candy. I didn't realize it could wind around like that. The good news: I had 2 artifact doors in place on that mining area.
Right now I have all non-essential fortress operations turned off while I extract strands, smelt wafers, smith arms and armor, and prepare for the circus ring show. I'm also using all my spare copper to make spikes so that I can fill a gigantic winding hallway will hundreds of them. I'll have raising bridges to close them in and repeat spike lever for several hundred tiles. I also have it set up so I can drain the water cavern above into it. Will the clowns destroy a bridge that's in the "down" position?
Next good news: I found two other veins of candy. I'm mining them out now with my new knowledge. I should at least be able to get everyone candy axes, swords, and spears. Do candy helms help, or are the clowns too playful for them? Masterwork Steel helms were like paper against them.
In other news, my awesome mayor who only ever wanted me to make warhammers was out cutting trees when a goblin ambush got near him. I'm fairly sure he was one of the seven too.