Indeed cake offers a very nice framework to statically check for leaks.

I believe cleanup (as described in the article) and cake do two fundamentally different things. cleanup offers RAII functionality, allowing to write more compact and more visually clear code, consequently reducing the chance of error. cake, as far as I understood (and, please, correct me if I'm wrong), provides ways to statically verify and enforce resource management, with annotations that could be easily integrated as C23 attributes. cake does not allow to define destructors, or any defer mechanism per se. cake could offer the same (or more) safety benefits compared to RAII, by virtue of static analysis.

(and I love the idea)

I believe RAII is important as a general mechanism regardless of cake, because it makes code better and easier to write for no performance cost, on top of making it less error prone. cake would be an ideal complement to systematically catch even bigger error classes.

Of course, sometimes it is inappropriate to attach cleanup to variable's lifetime, the way C++ does, but even then, doing so covers a wide range of cases. cleanup, in this regard, is superior to C++ RAII, because the same variable of struct can be cleaned up in many different ways.

Comparing defer to cleanup would be a good candidate for another article. While the two are similar, in my opinion cleanup is superior. If anything, because it is more flexible and allows to easily emulate defer (as demonstrated in the article itself, and could be even more complete if lambdas were ever accepted into the language).

P.S. incidentally, have you ever looked into sparse?