what happens when one moves next to another?

Does the older one die, or live?

I bet it will be about the order of creation again.
let's wait for the developers to answer.

Both agents dies.

I don't understand how this is the correct answer. It seems like, as with every other effect, they should be processed in the usual order causing one to kill the other (presumably the older killing the younger). After one dies, the remaining one is no longer next to an agent of death.

On a meta level, how was this behavior implemented? I'm assuming that there is generally some sort of list of effects to check that is processed and that effects related to entities that have previously been removed are ignored. Is this then special cased differently so that it is processed despite the agent having been removed? Or is there some kind of notification system that things listen on and invoke handlers?

Yes, there's list and it updates only between events (or when cycle repeats is case of dying order when for example Purtrid Zombie might explode, kill another Zombie and so on). I hope it is clear now. And anyway death to both Agents looks correct.

Well, ok

Wasn't what I was expecting

Just wondering, shouldn't the older on move first, and so kill the other before it can be killed?