V75: Quantifying Σ-Cost via the Dynamic-Space Cutoff — From Interpretation to Testable Dictionary

V74 proposed that particle mass can be interpreted as Σ-maintenance cost. Here we show that this interpretation becomes testable when connected to the dynamic-space cutoff κ introduced in V64. The dimensionless invariant Ξ ≡ m · κΣ ≈ 0.0062, observed in the lepton sector, provides a consistency constraint linking mass to the dynamic-space cutoff. This connection transforms the qualitative "mass as cost" interpretation into a measurable dictionary. No parameter fitting or Standard Model modifications are introduced; Ξ is used as a consistency check, not a fit target. The invariant shows remarkable consistency across three orders of magnitude in mass (electron, muon, tau), suggesting that the κ–Σ-cost connection captures a genuine structural feature. This work establishes the first step toward answering "Why these masses?"