QEM-Closure is a self-consistent geometric-dynamical framework for quantum bipartite nonlocality, constructed based on globally shared hidden phase, π-reflection symmetry, and second-harmonic phase-locking dynamics. Without invoking quantum states, Hilbert spaces, or unitary evolution, the model rigorously derives three core features of quantum entanglement: no-signaling condition, nonlocal correlation structure, and Tsirelson bound, from classical diffusion dynamics and planar geometry. A unified observable invariant Λ is introduced as the sole free parameter, and three experimentally falsifiable predictions (universal scaling law, symmetric two-peak phase distribution, even-order harmonic corrections only) are provided. The framework is mathematically rigorous, closed, and testable, offering an underlying structural origin of quantum entanglement while being compatible with standard quantum mechanics.