return a list of posts with any unpublished drafts at the top, where if a published post has a pending draft, that takes its place instead.

*[
  _type == "post" 
  && (
  	// either is a draft
    (_id in path("drafts.**")) ||
    // or is published and doesn't have an equivalent draft
    (
      !(_id in path("drafts.**")) &&
      (count(*[
        _type == "post"
        && (_id in path("drafts.**"))
        && (slug.current == ^.slug.current)
      ]) == 0)
    )
  )
]{
  _id,  
  title,
  slug,
  publishedAt,
} | order(select(defined(publishedAt) => 1,  0) asc, publishedAt desc)