Rust

would not be considered bugs but maybe change requests.

That's just playing with semantics. They are clearly bugs. They are literally called "defect reports".

Without a spec how would you argue that a system/product is safe?

1. Lots of testing, including randomised testing and ideally formal verification.
2. Comprehensive test coverage - both code coverage (lines, branches) and functional coverage (hand written properties).
3. Functional safety features (ECC, redundancy, error reporting & recovery, etc.)
4. Engineering practices known to reduce the chance of bugs (strong static types, version control, CI & nightly tests, rigorous engineering processes - requirement tracking and so on, and yes ideally well written specifications for all the tools you are using).

There are many aspects to safety and it's definitely a good idea to have a spec for a language, but it doesn't automatically mean safety is impossible without it.

Software in itself cannot be safe or unsafe because without hardware it cannot do anything.

The nice thing about abstraction is that you can talk about software without considering the hardware, more or less. If one says "this software is safe", it means it's safe assuming it's running on working hardware.

It doesn't always hold up - sometimes the abstraction leaks, e.g. for things like spectre and rowhammer. And there are sometimes performance concerns. But it's pretty good.