The sorting logic works only when elements are listed vertically

Is this reproducible without using code components aka without <astro-slot>?

RE : #3 I have reproduced this.

The good news is, the issue appears to be in code we control, not in the depths of sortableJS and I think on my first look that it's a visual issue more than anything more fundamentally unsupported.

Just linking this here for future reference - some exploration into building a "dropzone overlay" that integrates with our overlay that would go further to prevent us having to interfere with the iFrame document contents

https://jsfiddle.net/marmite/fmop190z/

Resolved in 📌 Investigate drag-and-drop solution that removes the need to drop items into the preview iFrame Active