The forge you have should refund all its materials if you destroy/deconstruct it. Just temporarily relocate it, then put it back to where it originaly was. It's a... questionable system that you can't build something at the existing one and like carry it to where it needs to be. But it's not like you have to do everything from scratch again. You're somewhat exaggerating.

And even if you don't feel like replacing the existing forge, this is your motivation to get some reserve copper that you are perhaps wise to have anyway. After I upgraded my bronze gear I went outside one more time with a karve or longship and filled it to the brim with copper and now a troll could do to me what he did to you tons of times over.

How did you build the sconce the first time around? It must mean you must have had a forge near there at least once. Why did you use up the bronze from that forge? I'm sorry, but if you are so notoriously low on bronze, then that's perhaps on you, at least partly so.

And regarding future trolls, just extend the distance with spikes, trenches/ditches, more walls... I don't know... I would take this as an inspiration and motivation for other building projects... not sure why you're this pissed at that. Maybe it's the wrong game for you if you hate some unforseen things happening. I'll agree that a troll glitching its weapon through walls is a rather poor reason... but come on, calm down and just get to it... learn from that for the future when building something... and then move on... I'm not a dev myself, but it might be just too hard to adjust the reach of the troll per-se or or of its weapon in different circumstances. Maybe they could somehow make it that when hitting a certain kind of material or a certain height of walls that only the initial piece of structure takes damage... Dunno... Maybe they'll fix that one day. But if not then it's not like the world is collapsing from you having to adapt to that a little.