The programmer choose what to store where, so you typically store things in arrays by lifetime. Goose gives you many more tools to do that, it can store entire variable sized trees of an enum type in a single array.
You try to avoid having to deallocate in mixed/random order, but if you absolutely must, you can turn arrays into pools, basically.
I'm a bit confused about how you could decide the number of stacks at compile time. I can see you could see how many arrays are lexically in scope. However if the code puts one dynamic array inside another dynamic array I can get to an unbounded number of total stacks without ever needing more than two in lexical scope at once. Do you also add stacks at runtime? Like a stack of stacks?
The spec on your GitHub says: "Two simultaneously-live resizable values never share a stack."
So I surely can't have a dynamic array of dynamic arrays share a single stack? That's an unbounded number of resizeable values sharing a stack?
You could make it work on a single stack but that would involve having non-contiguous memory for each inner array since you can add to any array in any order.
The spec implies that we need one stack per element of the outer dynamic array which would let you have contiguous memory for each inner array, but you wouldn't know how many stacks you needed at compile time.
Depending on your needs you use one of these solutions.