JMAP: setMailboxes does not do (topological) sort of creations

[rjbs]

I issue creates to setMailboxes like this:

{ x: { name: "foo" }, y: { name: "bar", parentId: "#x" } }

...and I get inconsistent results. I feel fairly certain that this is an ordering issue. If it tries to create y first, it fails because #x can't be resolved.

[brong]

Fixed for setMailboxes particularly