The traction side is on the exhaust (outer) side of the head for the front cassette. There is very little curve to it as shown in the photo below.
Since it is fairly straight, as the guide chain contact material wears the relative timing between the jackshaft and the camshaft does not change.
The slack side is the side where the hydraulic tensioner contacts the guide and keeps the slack side of the chain from slapping.
My front guide assembly was in excellent condition until I broke off the small, curved bottom piece of the traction side trying to remove it from the head. The main reason I decided to replace it was my fear that the all plastic assembly would structurally fail into fragments like the rear assembly did. As you can see in the photo, the new one is a metal structure with attached chain contact material. Unfortunately, the plastic is not bonded to the metal. It is attached with plastic friction latches. I will possibly separate (very carefully) the plastic from the metal and reassemble the pieces with epoxy glue. My only concern is the different coefficients of expansion for metal vs plastic.