It also doesn't work at all, because next to no user of this facility
wants the contract evaluation semantic configuration to turn this
assert completely off.

Maybe you don't want it, but it sounds a lot like OP wants something along those lines. As Jonathan said, when __OPTIMIZE__ is not defined, all the compile_asserts go away.

That's exactly the kind of global configuration that I'm thinking of. Of course, you may want to make decisions differently for different contract assertions/preconditions, and there are proposals that allow for that.

And they certainly don't want the act of turning off runtime checks to
also turn off all compile-time checks.

But people doing that is the status quo. Ignore semantic with contracts gets rid of any runtime check, and also offers no compile-time check (other than static analysis in the future). The new "proof" semantic would allow you to turn off runtime checks and turn them into compile-time checks.

Of course, once again, there is still the issue of granularity; you can only switch globally, and that's presumably going to be fixed in C++29.