It's the other way around. Rust has always had contexts that are guaranteed to be compile-time (const and static items), and gradually added the ability to run

It's the other way around. Rust has always had contexts that are guaranteed to be compile-time (const and static items), and gradually added the ability to run some subset of the language at compile-time (const fn) specifically to accommodate const/static items (e.g. to replace the old lazy_static with the modern LazyLock), and naturally also allows these functions to run at runtime if you want (and in what would otherwise be a runtime context, you can enforce compile-time evaluation with a const block).