Combat in CF is clearly defined an identifiable by looking at someone and seeing who they are fighting, even via the scan command.

If they're not fighting, they're not fighting.

Negotiating a fight, prepping, and spelling up a slept character do not count as combat.

As being IN combat is one of the rules used to determine whether or not parity applies, if you're not IN combat, you MAY be fair game.

It's different than you both being low HP for the following reason:

If your HP is low enough (I'd consider it pretty crappy to attack a mage who was lower than small cuts, but I try to not attack unless they're at perfect health) then it's unacceptable for a Villager to attack you.

Again, though, if you are not in combat and at perfect health, you're fair game.

An "exchange" does not count as "combat" and that's where the line is.