Your analysis of the issue of not being able to pass arrays as arguments is compelling, but I'm not so sure about "All it needs is a little new syntax" as a sol

Your analysis of the issue of not being able to pass arrays as arguments is compelling, but I'm not so sure about "All it needs is a little new syntax" as a solution: you say how to keep backwards compatibility with existing C standards you need a #if cpp-directive: that's already a code health and maintenance problem that isn't going to go away. Regehr's suggestion of using assertions hidden in code avoids that: isn't it better? You could have just a comment directive like @ arraycast char* a \represents char a[..] and then you wouldn't need any cpp-directives.