If you turn off your water right before it’s boiling and cook your pasta, then Barilla is an energy generator*.
By the same logic, yes, your hypothetical statement can be rephrased as "if you already have boiling water, cooking pasta doesn't require any energy".
> The only definition that really makes sense is how much energy did it take to get the pasta from the box to my plate
Including the energy required (and the carbon footprint) to manufacture the pasta in the first place, yes? Or no?
Back in reality, the purpose of a heat pump is to heat/cool an enclosed space. Its efficiency is rated by comparing it to a direct conversion from electricity to heat. So long as what occurs outside doesn't affect what occurs inside, it isn't relevant to the question of efficiency.
I haven’t tried this technique yet, but one of the aims is to still cook the pasta effectively. I know from experience that your hypothetical won’t cook most dried pasta.
https://www.seriouseats.com/tips-for-better-easier-pasta
Getting the water to a boil is probably just a way for Barilla to make the instructions foolproof- after adding the pasta, the water will still be hot enough to rehydrate said pasta.
and allows a leeway for a different pots, stoves, fried off power cables...
I use this technique when I don't want to bother running a second stove top and making a sauce or something for the pasta.
It takes more time, though.