This work develops a structural framework explaining how identical underlying combinatorial structures can yield different observed values of physical quantities without modifying the structure itself. Building on the projection–exclusion grammar established in v1.0–v1.1, we introduce a strict two-tier separation between structure constants and effective observables. Structure constants are fixed upstream by a unique combinatorial grammar, while effective quantities arise downstream through observer-dependent embeddings, measures, and boundary re-routing. Observers are defined purely as mathematical objects (embedding, measure), avoiding subjective assumptions. Within this framework, bulk and boundary are defined as structural roles rather than spatial locations, leading to an intrinsic asymmetry in update structure. We prove that first-order variations cancel identically and that observable deviations necessarily arise only at second order, yielding explicit rigidity bounds for quantities such as the fine-structure constant. Running couplings are reinterpreted as boundary scale-dependence, and cosmological phenomena—including dark components, inflationary features, and Hubble tension—are recovered as boundary-dominated effective regimes of the same fixed structure. The framework is closed at the level of effective observables and delineates the precise boundary where a theory of time and irreversibility must be introduced.