Per-request nursery (server pattern)

Put limits at the right scope: connection, request, or whole server.

var {*} = import("slug.channel")
var handleRequest = nursery limit 20 fn(req) {
    // at most 20 concurrent spawns inside this request
    var userT  = spawn { fetchUser(req.id) }
    var postsT = spawn { fetchPosts(req.id) }

    var user  = await(userT, 200)
    var posts = await(postsT, 400)

    render(user, posts)
}

This gives request-local backpressure without affecting the whole server.