-- in.cue --
root: {
    a: {
        $id: "failure"
        val: "foo"
        out: string
    }
    b: {
        $id: "valToOut"
        $after: a
        val: "bar"
        out: string
    }
}
-- out/run/errors --
error: task failed: failure
-- out/run/t0 --
graph TD
  t0("root.a [Ready]")
  t1("root.b [Waiting]")
  t1-->t0