Moar tests!
Doubting that Twist Fate gives 100% protection to the first damage a unit takes I tested it in a battle. I could have done it more simpler in hindsight but...
I took a Markata scout and equipped it with Shroud of the Saint conferring the Twist Fate effect. I equipped a Son of Niefel with a Rod of Death and set him to Attack Closest. I then sent them to battle each other. I tested 26 times and 5 times from watching the battles I saw this occur:
The Markata would be hit for 1 damage (with no floating number to indicate this but with a red "hit" splash) but the Twist Fate effect was still on the Markata. See the attached files for the 5 replays. Replay 5 in particular is good because the Markata loses one hp, gains an affliction and retains the Twist Fate effect. The replays require the
Dogfight map. The game name is simply "gh".
I know there is an effect with the battle replay being silly but I don't know enough about it to say if this is what I'm seeing. I think it happens in MP games and results in different results in the battle to whats reported.
If what I'm seeing is true then it seems Twist Fate works more like this:
Twist Fate gives roughly 75-80% immunity to ritual damage, but with no limit to damage taken if it fails. In battle 20-25% of the time 1 hp of damage will bypass the Twist Fate effect (and allow for afflictions) without removing the Twist Fate effect.
Poor test Markata fighting a Son of Niefel, however twice out of the 26 tests he the Markata took non-lethal damage, fled and survived to gain entry into the Hall of Fame! Totally worth it