Right, I've been using variants of
{"code" : "has_status","check" : true,"value" : "celena_bless"}
but can't get it to work. I've tried "has_effect", "e_celena_bless", with or without the check, as both a req and a showupreq, but can't get it to work. Either it doesn't show up, it's always locked, or it's never locked.
Thanks for the information on conflict_class, though, it makes a lot more sense.