Phase-1 Closure of Protected Reduced Spinor Geometry: Born Law, Boundary Measurement, Light Without Trajectory, and Electron 𝒈−2

This work closes the microphysical phase-1 sector of protected reduced spinor geometry. Starting from the regular reduced phase plane with one isotropic complex mode, a protected admissible sector, and a detector boundary projector, the paper derives detector-resolved realization channels and shows that the Born rule appears as the normalized quadratic weight of those channels. Measurement is formulated as boundary selection of one admissible continuation, and light-channel realization is described without requiring an underlying microscopic trajectory. The same reduced phase mode is then lifted to a closure spinor by an exact half-angle construction. From this, the paper derives the physical spin-1/2 operator and the exact bare electron gyromagnetic law g = 2. The dressed electron is described through the action excess of its closure cycle. The first reduced geometric share is alpha/(4pi), and quarter-sector self-screening yields the renormalized cycle law Xi_cyc = alpha/(4pi) * (1 - alpha/4), leading to the dressed electron law. In this way, probability, measurement, light-channel realization, spin, exact bare g = 2, and the first dressed electron anomaly are treated as parts of one closed reduced geometric structure. The paper is positioned as the completion of phase 1 of the theory. Its natural continuation is phase 2: the atomic sector, including the minimal electron closure cycle, the principal spectrum, fine structure, and the Lamb-like shift.