Query nested Matrix entry relations via GraphQL

I’m trying to create a GraphQL query to find nested entries stored in a Matrix field. In my case, I want to find all the albums that have a particular song in its tracklist. According to this comment, Craft 5.x has full support for this.

I’m having trouble finding documentation or examples, though. There’s a short section on the docs page that provides a Twig example using target and field, but the GraphQL docs suggest using relatedToEntries relatedViaField. I also found a GitHub commit comment with an example which looks a lot like what I want, but it’s returning all the albums, not just the ones with the target song in the tracklist.

# Note: $slug here is the slug of the song

query ($slug: [String]) {
  entries(
    section: "albums"
    relatedToEntries: {
      section: "songs"
      slug: $slug
      relatedViaField: "tracklist" <- The album's matrix field
    }
  )
}

What am I missing here?