I think I detected the general area of the source of the bleeding-feet syndrome. It's all around the moat. I think. Ironically, dwarfs seem to generally die much faster in the area, while animals manage to walk twice the distance before dropping dead.
It's getting serious, too. Only one swollen and blistered foot is enough to kill anyone before they can enter the fort.
I can consider the following options:
-quarantine the general area and builds floors/fortifications over it
-enlarge the moat and channel out the risky tiles
=> both of these are very risky for the workers
-weaponize the deadly blood leftovers, wherever that is, and force goblins to take that path... since they have no mounts anymore and are usually wearing socks/sandals, this might be fruitless
-waste several hours of my life in a painful way by enrolling all 160+ dorfs just to force them to wear sock/shoes (I didn't think I'd have to say it ever), and witness the inevitable tantrum spirals that will occur once all of the 15+ kids will have died painfully.
-magma. DFhack will be my friend once again, as I haven't seen a drop of magma yet, and it's gonna be extremely long and painful getting it to the surface through a full aquifer and a few partial ones. Sadly, it seems to be my best solution.
All of that because fucking gobbos decided to elect a demon with deadly blood as their leader, assault him, and walk confidently to my fort with their stuff spayed in goo. If their strategy was killing everyone in the long term, I must say it's working; loyalty cascade almost makes sense there. And almost everyone has a friend, a lover, a family, or a combination of any of the above. Urnflashes of Autumn will end in a fucking tantrum spiral, I know it. Must say I'm very upset by that shit, as the only Forgotten Beast that appeared so far is a fire-breathing ape that ate many olm men and lizardmen but showed no interest in meeting dwarfs.
I fucking hate goblins so much. I'll execute as many as I can before everyone dies, and with a little luck, I'll survive until the freezing season and encase some of them in ice.