Bounded concurrency (backpressure) with a nursery

Create a nursery to limit concurrent spawns:

var {*} = import("slug.channel")
var loadUsers = nursery limit 10 fn(ids) {
    ids
        /> map(fn(id) { spawn { fetchUser(id) } })
        /> map(fn(t) { await(t) })  // join handles
}

Notes:

• limit 10 caps in-flight tasks in this nursery.
• Join is explicit (await each handle), or implicit at nursery exit if you don’t need results.