E503 - Cannot infer edge side (slides not on same row or column)

Cause

An edge omitted its side, and scrolly tried to infer it from the slide positions — but the two slides are diagonal (different row and different column), so there's no unique side to pick.

Example

{ slides: [
  { id: "a", position: [0, 0], source: "a.slide.json" },
  { id: "b", position: [1, 1], source: "b.slide.json" }
], edges: [["a", "b"]] }   // a → b is diagonal

How to fix

Specify the side explicitly on at least one endpoint: ["a|right", "b|left"] or similar.