Arrest of Spontaneous Splitting and Emergence of New Orthogonal Rotation Planes in N-Body Relational-Wave Closed Systems

From the two axioms sum x_n^2 = 0 and U^n = I, a single wave localized in one rotation plane amplifies from a tiny seed and splits spontaneously, then moves into a metastable state. This paper measures the arrest process directly and finds that, at the moment splitting stops, several new mutually orthogonal rotation planes and a new conserved direction arise spontaneously: the splitting quantity f equals the fraction of conserved norm that flows out of the dominant plane into the other rotation subspaces and the generator kernel (identity f = 1 - E_P1, verified to machine precision). The N=4/5 boundary of sustained splitting coincides with the appearance of a second nonzero rotation plane. The metastable per-relation amplitude follows A_rel = 1/sqrt(M) with M = N(N-1)/2. Plane inflow is measured by an exact dense-matrix method (N=5,40) and a low-rank method with an explicitly stated threshold (N=300), the two agreeing to 2e-15 at N=40. The physical identification of the new directions (time, charge) is left as future work.