Coherence First: A Relational Principle for the Emergence of Quantum Subsystems and Spacetime

Coherence First develops a relational reformulation of Radial Coherential Dynamics (RCD) centered on a prior question: what physically selects the factorization of a quantum system into subsystems? Because entanglement is defined only relative to a tensor-product structure or a partition of observable algebras, programs that derive classicality, locality, or geometry from entanglement already presuppose a cut. The paper proposes the Coherential Selection Principle (CSP): the physical factorization is the one that maximizes the persistence of coherent information within its parts while minimizing coherent persistence across their boundaries. In this framework, subsystems are dynamically persistent regions of a relational quantum structure, and the coherential field C(x,t)C(x,t) is reinterpreted as a possible continuous, effective description of a deeper network of selected relations. A numerical proof of concept is presented for an open three-qubit system. Keeping the Hamiltonian fixed while rotating the environmentally monitored algebra shifts the factorization favored by a provisional functional. The effect survives a generic non-commuting control, remains stable under sampling, and follows a continuous five-point rotation of the monitored algebra. The result establishes that open dynamics can transport and recover a recognizable structure of parts that is not fixed by the Hamiltonian alone. The full CSP, the emergence of geometric locality, and the proposed connection to cosmological relaxation remain the next stages of the program. Version 0.2. Preprint; not peer reviewed. This record contains the PDF, LaTeX source, numerical scripts, and reproducibility materials used in the closed- and open-system studies.