It's a pretty obscure edge case. You could retain ZWJs when they were between two Unicode points with the Symbol or Emoji Symbol classes, but on further reflect

It's a pretty obscure edge case. You could retain ZWJs when they were between two Unicode points with the Symbol or Emoji Symbol classes, but on further reflection, it would probably be more honest to just strip the ZWJs everywhere and decompose the emojis. EDIT: also what jedanbik said