[jasode]

>which is _intended_ to be unconditionally true of safe Rust code,

I emphasized "intended" because it seems like we're talking past each other.

You: re-emphasizing Rust's specified design goal.

Me: emphasizing the current state of Rust compiler as reality which makes the statement "safe Rust has no undefined behavior" as not true.

(In other words, I emphasize the unintentional UB whereas you do not.)

>, because your conditional is equivalent to saying "if you write valid code".

If you look at the github issue, "1.04E+17 as u8" is valid safe Rust code which invokes UB.