Unboxed records are fine, but stack-allocated lists make me nervous. What happens when someone gives you 8 megs of headers, and you run out of stack?

This code seems to put a 32k limit on it, but it's a manual check and error return. What about code that forgets to manually add that limit, or sets it too high? How do you decide when to bump that limit, since 32k is an artificial constraint?

By default in oxcaml, "stack" / local allocations happen in a separate stack on the heap (which the runtime allocates for you). If you allocate enough to exceed that capacity, it will resize it dynamically for you.