I get what you're saying. I'm just not a fan of the Magic-style "target" keyword thing - not because it doesn't say anything about it in the rules, but because it is a contradictory principle to the structured chart principle I have been working with so far. Searching for target keywords is the same as going "in this example, the structure doesn't work, so let's find a different principle instead" - but I want the structure to work for all examples, otherwise it clearly isn't valid for future examples we haven't come across yet, which would make me sad. A principle that doesn't apply to all relevant situations is a worthless principle.
I guess I can crowbar Ambush into the four-phase structure and have it not trigger Aegis like this:
1. Pay 1 Favor to trigger Ambush.
2. Select Ambush target.
3. Roll Ambush combat (which is always a net 1 success for the aggressor).
4. Resolve combat damage.
It would work by saying that in phase 2, the Ambush isn't actually an attack yet, just like opportunity attack - it only becomes an attack when it is succesful. It just requires us to interpret "immediately resolve an attack" to mean "this event only counts as an attack when it turns from a combat into a successful attack". As opposed to Spite which counts as an attack as soon as it has triggered.
That actually works pretty well. Hmm.
Now I'm happy again. I'm so glad we keep discussing this! Keeps my brain working.