This work proposes a structural foundation for physical law based on a single requirement: an embedded observer must remain distinguishable from the system it inhabits. This constraint is formalized by a Distinction Functional built from four structural variables—systemic complexity, observer capacity, curvature, and boundary area—whose logarithms form a coherence manifold with metric signature (+,+,−,−). A coherence action on this manifold yields emergent spacetime geometry, GR-like curvature dynamics, and the complete mathematical structure of quantum mechanics as distinct projections of coherence flow. Classical limits—including incompleteness, undecidability, uncertainty, entropy increase, holographic bounds, and curvature regularization—arise as boundary phenomena in coherence space. The result is a unified, non-arbitrary substrate from which spacetime, quantum behavior, and physical constraints emerge as structural necessities rather than postulates.