[CuriousCosmic]

An ABI also has a concept of defined and undefined behaviour. You can design an ABI that is fully protected against abuse but often the performance penalty for that will be huge.

Instead what you'll do is specify the constrained inputs and expected output behaviour. From there you can out anything that violates those constraints as non-conformant. As long as you maintain those constraints between versions, there's no ABI breakage.

Also you can absolutely have constant references in an ABI. There may be ways of ignoring the const depending on how you design the ABI but they will be obvious abuse.