No, it's a continuation of the same conflict with different weapons. Same battle, higher stakes.
Not really. That's only your extremely strict interpretation, not the only way to read the scene. Can you please accept that yours is not the only way to read a scene?
There is no discontinuity in physical location - the entire encounter takes place in the cavern chamber.
Please quote where the book says this is necessary to erase stress.
There is no discontinuity in temporality - the entire encounter is continuous, without pauses, breaks, or interruptions, and the entities involved have to stay on their toes the entire time.
Please quote where the book says this is necessary to erase stress.
And, come to think of it, this isn't true. After the Einherjar Squad's opening salvo, Harry outright says that they've created a quiet pocket, and he has at least a minute or two to talk to everyone, catch his breath, and strategize with Marcone about getting Lara's people out.
There is no discontinuity in the fundamental nature of the dangers and threats - I'd be willing to let a fistfight that turns into a car chase with gunfire count as two separate conflicts because the nature of the threats, and therefore the abstract 'stress', is so different between the two. But that's not what we have here.
Yes, there is. Read the passage again. Between the end of the duel and the mental attack, at no point is Harry or Ramirez in direct conflict with Vittorio. There is a whole chapter or two where Vitto is, from the perspective of the gameplay, a non-entity.
So we have one conflict -- Harry and Ramirez vs. Vittorio and Madrigal. That conflict ends, Madrigal is taken out, while Vittorio makes a Concession (he's out of the immediate conflict with a loss, but changes the terms).
Then we have a second conflict, which is Harry, Ramirez, Murphy, Marcone, Hendricks, and the Einherjar Dream Team vs. Uber Ghouls. Vittorio is a background detail in this conflict, and not a participant from the immediate perspective of Harry et al.
And, of course, the conflict that was initiated was a duel to the death between two Wardens and two WCVs. The stakes are raised, but the basic conflict does not end until both vampires are dead - which does not occur until the caverns are blown.
By your own personal reading of the scene, and by a definition of conflict that is not the game books' definition of conflict.
If there were a single real example of a break, I'd let it suffice for a rest. Say, something along the lines of that scene from The Phantom Menace where rotating force walls temporarily keep the combatants apart, and the bad guy paces while the good guy gets some meditation in. That would count. There was absolutely nothing like that. Everyone is constantly in danger until they escape the killing field.
The book does not have this requirement.
Which is precisely why Harry does that kiss with Lara to generate the force bubble that saves them both. He was on his very last legs at the very end of the battle and needed something, anything, that he could feed into the spell to power it. If he'd somehow cleared all his stress, mental and physical, he'd have been fresh as a daisy and wouldn't have needed to interact with a soul-sucking succubus to survive.
That's one possibility. The other possibility is that the GM set the difficulty of surviving it so high that Harry wasn't sure he could survive it on what he had left. He still has consequences, mental and physical. I've had players create declarations and bank aspects before they'd ever cast a single spell, as insurance.