What does this equation mean?

Collect what has actually been shown, and what has only been proposed. That a Bogoliubov transformation mixes particle content between mode decompositions, and that a uniformly accelerated detector reports a thermal spectrum at the Unruh temperature, are OBSERVED-baseline, DERIVED results inherited whole from the existing literature [ 1 , 2 , 3 , 7 ] . That a click’s meaning, but not its occurrence, depends on the observer describing it is likewise inherited [ 4 ] . What is PROPOSED, by this article and nowhere else, is $D_{\rm det}$ itself: the specific normalization of the response functional into a probability density over gap, the total-variation distance built on top of it, the four-clause treaty that has to hold before that distance is attributed to a worldline rather than to an instrument, and the demonstration, both in the eternal-acceleration limit and in the eternal-inertial limit, of where that distance succeeds and where it fails outright. The single worked numerical evaluation — the 0.394\,$\delta$ a/a leading-order coefficient — is an exact analytic result under the stated small-parameter assumption, illustrative only, and not a simulation of anything.