I think you can subscribe to the on_player_toggled_map_editor event to archive this, see the docs: https://lua-api.factorio.com/latest/events.html#on_player_toggled_map_editor

Ahh thank you! I never noticed that. It must have been added at the same time as the LuaPlayer::toggle_map_editor() that I use, but wasn't in the changelog.

Thanks very much - I will make an update that makes use of that soon, hopefully in the next 24 hours.

Just to let you know that I have - very belatedly - updated the mod to make use of this event :) Thanks again for pointing me to it.