Farwilder worlds are rebuilt from their seed, and a save stores what has changed. That keeps saves small, but it has a sharp edge. If the world generator changes, the same seed produces a different landscape, and an old save’s changes would be applied to ground they no longer describe.
So a save records the generator version, and a mismatch is refused with a clear reason. It is labeled incompatible rather than corrupt, and a test checks that exact label, because telling someone their save is damaged when it is simply older is its own kind of bug. Saves also never silently drop data they do not understand.
During development the generator changes often, and each change makes older worlds unloadable. Carrying saves across those changes would need a migration step that does not exist yet.
