WilliamIsMe1/StarcaveEngine ? reverse-engineered prompt

Build me the core of a Java sandbox game called Starcave, focused on exploration, building, and multiplayer from the start.

I want the game to generate an infinite world in all directions with caves, sky islands, and huge mountains, and I want basic colored lighting so the world feels alive. Please set up a simple but solid engine foundation that can handle physics for things like rigid blocks, ropes, springs, and moving vehicles later on. Also add the start of a combat and character system where bodies can have separate parts like a head and limbs, so things like headshots and limb damage can work.

If you can, include the beginnings of a crafting system where tools are made from parts like a handle and head, and make the code easy to extend for mods later. Keep it playable and clean, not just a demo. Look up current Java and graphics docs online if you need to.