The electromagnetic spectrum is not a scale of energy, but a record of structural state.This paper proposes a structure-first framework for interpreting astrophysical emission, in which the electromagnetic spectrum encodes the state of structural constraint governing energy routing rather than energy scale alone. Three primary structural regimes are identified: collapse (over-constrained), threshold (marginal), and stable (persistent). These regimes correspond to distinct spectral signatures, with high-frequency emission tracing structural breakdown, low-frequency coherent radio emission tracing marginal structural formation near the registrability boundary, and multi-band emission tracing stable routing. The framework introduces registrability as a necessary condition for observable emission and embeds spectral behavior within a Structural Relaxation Ladder describing the progression from energy accumulation to radiative release. This interpretation decouples spectral form from magnetic field strength and object classification, providing a unified explanation for transient and persistent astrophysical phenomena. Testable predictions are outlined linking spectral characteristics to structural state across systems. This work is part of an ongoing series developing a structure-first framework for physical systems. It builds on prior work including: Structure Before Force: Geometric Conditions for Persistent Systems Heat as a Passenger: Structure, Entropy, and Why Earth Does Not Melt