Given your example, I am convinced you've never written any Rust. Of course it does stop you doing shit like that. But in this example, even Java does it properly, since the constructor runs to completion before any Object is accessible to any Thread, not just the one creating it. You need to validate the state of the object in the constructor to prevent that, but TBH why are we talking about this, it's almost completely unrelated to concurrency models.

I agree that messy reality can intervene, in the medium term (for about a decade) we'll need to handle leap seconds

But we can do a lot without challenging the messy reality. 61 second minutes are (regrettably) a thing in some time systems, but negative 1 million second minutes are not a thing, there's no need for this to be a signed integer!