I particularly don’t believe that it is possible to have a spec which does a good enough job of explaining what is needed that the implementor doesn’t need to k

I particularly don’t believe that it is possible to have a spec which does a good enough job of explaining what is needed that the implementor doesn’t need to know why. I’ve certainly never encountered such a thing, and all of the best specs I’ve worked with explain the why as well. It’s like claiming that your code doesn’t need any comments saying why things are done because you can see what is happening.