I agree that it's worth considering other ways of handling concurrency. But we should do so by staying within the realm of reality.

Your understanding of nurseries, conceptually, does not match their capabilities. It's not about any language or implementation, it's that what you think they can do isn't possible. It violates the halting problem.

You can't statically infer whether or not a function will have async side effects without opting into some scheme that describes those effects. If you do that, nurseries provide some guarantees. But those same guarantees are provided by just using async/await, which tracks explicitly which functions are async and which are not.

Nurseries do potentially provide some advantages when dealing with tasks that you want to outlive their scope, which async/await doesn't handle well, and when dealing with an unbounded number of async calls (maybe, I think an `async for` construct handles it too).

But otherwise, most of the advantages you seem to think nurseries provide aren't. And not just by this implementation, but by any implementation. They are provably not providable by any implementation that isn't equivalent to marking your async functions as async.