Vs. Plague Rat, with undaunted on Fanatic and Lead from the front in play for Greatest Legacy it gave me the option to choose which would take place first, Undaunted preventing the damage or Lead from the front redirecting it.
As I understand Prevention should work like immunity in this case, and fall under the Damage that cannot be dealt cannot be redirected rule.
I let it be redirected and it did hit Legacy with 1 melee damage.
I can't get the same result when using Hypersonic or Throat Jab, so I assume it is a mistake.
I think the difference here is that Undaunted triggers only when Fanatic 'would be dealt' 1 damage. This is the same timing as redirection abilities, that trigger when a target would be dealt any amount of damage. Other methods of preventing damage, including the ones given here, prevent damage dealt by a target unconditionally, which is why they take precedence.
What did you use to test similar with Hypersonic Assault and Throat Jab? To me this is working as expected as similar should occur if cold damage was heading to Absolute Zero and he has Null Point Calibration Unit out.
When I throat Jabbed Plague Rat it did not ask if I wanted to redirect attacks, it simply said Rat couldn't deal damage.
That is as expected.
Undaunted/Lead from the front was allowing shots of 1 damage to be redirected away from fanatic, when they should be prevented by Undaunted. That should not be possible, because you cannot redirect damage unless the damage can be dealt.
I think it's working as expected on all ends. You don't get a prompt about Lead From the Front after preventing damage due to Throat Jab or Hypersonic Assault because the damage is being prevented before they would attempt to deal the damage. In of Undaunted you have to accept the damage before it is prevented for only being one damage and thus Lead From the Front can react at the same time. I would expect to see the same prompts if a Stealth Bot was out and Fanatic with Undaunted out was about to be dealt one damage. To me a better example to compare against is having AZ dealt cold damage from a villain target when he has Null Point Calibration Unit out instead of preventing villain damage through Throat Jab or Hypersonic Assault.
Prevention is at the same timing as Redirection. Thus it gives the choice. Prevention is in no way the same as damage Immunity or being unable to deal damage. How do we know this? Take Null Point Callibration Unit, if Meteor Storm is in play and he tries to deal hismelf Cold damage, it would not work. Same if Absolute Zero is suffering from the effects of Ensnaring Brambles. Null-Point Callibration Unit also takes place after damage type, say Imbued Fire is in play you will be unable to deal Absolute Zero Cold damage and thus not trigger it. Null-Point Callibration also factors in Damage Modifiers, so it can be reduced to 0 and actually be unable to trigger or it can be increased so it makes it a higher amount of healing. Effects like Meteor Storm and Ensnaring Brambles will not trigger any of these things because they are before them and stop them from working. This is exactly why Undaunted, Null-Point Callibration Unit, Flak Jacket, and any other cards that can prevent damage can occur at the same time as redirection cards.
Aside from "order of operations," there's another way to look at it. Redirected damage is always considered to come from the source to the end target and not be affected by effects that apply only to the target(s) not taking damagebecause of the redirection. This is most easily visible with Nightmist's amulet or Fixer's Mantis style.
For examplre, Baron Blade's Backlash Field. The Baron strikes Nightmist for 5 damage; she uses her amulet to redirect to the Baron. Legacy's +damage bonuses do not apply to the damage jujsyt because it "bounced off" Nightmist; the game considers Baron Blade to be attacker AND target. The Backlash field will attack Blade in retaliation.
The "middleman/woman/robot/alien" is not considered to be part of the damage sequence. It's always worked trhis way with "normal" damage reduction, too, like Haka's Ta Moko. If damage going to Haka is redirected to Legacy, it doesn't get to "keep" the -1 reduction from Ta Moko and apply it to the damage hitting Legacy.
If that principle is applied, when Lead from the Front redirects the damage from Fanatic, cards that affect damage to Fanatic (such as Undaunted) would not apply because Plague Rat is now directly damaging Legacy.
The argument in the video game I would make towards Phantaskippy's point is there are instances of DR where only one damage is incoming and Lead From the Front prompt does not come up.