My play is generally not as aggressive in scene-framing as you describe - there is occasional "downtime", for instance, in which the players take stock and the PCs, as narrated by their players, do things like check their inventories and look around their physical environment.
Ha! Maybe I'm getting old, but I've found I have less and less patience for planning, shopping, arguing, all that stuff that players will do. I'm running Diaspora (FATE) at the moment and if that starts I give the players, I dunno, five minutes while I drink beer and smoke a cig and then say 'Either something happens here or we're moving on...' If they're genuinely arguing about a course of action, they say their piece and get to roll, using all the mechanics available to them - Skills, FATE points, aspects, the works. Then (hopefully) I have an idea of where the winner is going with their thinking and I'm into that scene.
I take downtime as a GM, sometimes mid-scene. Experience has taught me to give scenes thought, when setting them, when talking with my players about stakes and outcomes or even just having to think for a bit about an NPCs goals and motivations. If that means spending a few minutes I take the time.
FATE is also interesting because of the interplay of Aspects and Compels. The player gets a chance to reject the compel. If they accept they know I can go in no holds barred, but I think the fact that there is that negotiation before gives it a lighter touch than, say, Apocalypse World - where you just dump a PC right into a horrible dilemma with no apologies.
But yeah, overall, I think I described the technique on the aggressive end because that's how I roll
And when closing scenes, I have a bit more give-and-take than you describe. For instance, if the player insisted that they were going to buy a new gun, I would probably back up to that - but my preference would be for the ruleset itself to minimise the mechanical significance of buying new guns, and hence to minimise the incentive for players to do that sort of more exploratory play in pursuit of mechanical advantages.
I agree about the rules preferences. I'm the same. Personally, I won't back up. I just say "Yeah, you bought a gun. So, what about this rattlesnake?"
Your "scouting for the rattlesnake" example is interesting.
My intention was to show one (common) type of resistance to scene-framing. That is, you get a counter-offer from the player of a different scene. I've met (and played with) plenty whose motive for doing so is to re-frame themselves into a 'better' position - that is better from the point of view of succeeding in overcoming the problem or not encountering it at all.
That's where I was trying to go with the stuff about a scene-framing style not being a vehicle for showboating competency. It's a vehicle for showcasing characterisation, I think.