update on egg-eating solution. unfortunately, they ate up all the mustard-filled eggshells we gave them. even when we mixed in lots of salt & wasabi. so no luck with that strategy
then we had the realization that they *usually* only eat eggs that are laid inside their "sleeping room." they have an "upstairs" sleeping room, where they spend the night, and where we had put the nest boxes. then the chickens mostly decided they prefer to lay "downstairs" in the area of their run that is underneath the sleeping quarters. it's nicer, darker, and has an earthen floor, so i don't blame them. those eggs almost never get eaten.
so, we started letting them out of their upstairs sleeping room a bit earlier in the morning, so they wouldn't be locked up with a tantalizing egg and all the food outside. and when they go out, we shut the upstairs door. they all have to lay their eggs downstairs (and 2 of them aren't happy about it, but what can ya do?). and so far, 2 weeks without an eaten egg!