In the editor, it does actually recycle UIDs, to keep them low-ish. (Otherwise if you deleted all your objects and added a new one, it would have a high UID - this way it goes back to being low.) However at runtime UIDs keep incrementing by 1 for every new object, they are never re-used. The limit is the integer limit of Javascript's double-precision floating point numbers, which is 9,007,199,254,740,992 (9 quadrillion I think that's called?). Hopefully high enough
Only recycled in the layout during development.
Unique during runtime.