Diagonal Rotation Correction for Open Problem 1: |L_sym| Resolves Negative Eigenvalue and Reveals Isotropic Excited Subspace (sqrt(3)*I) in Lo-Shu/Yang-Mills Framework

We resolve the negative eigenvalue obstruction in the Lo-Shu Yang-Mills framework (Paper v7, DOI: 10.5281/zenodo.19910348). L_sym has eigenvalues {-sqrt(3), +sqrt(3), 15}; the negative value arises from negative Cartan coefficients (lambda_3, lambda_8). Taking the operator absolute value |L_sym| yields eigenvalues {sqrt(3), sqrt(3), 15}, which is positive semi-definite. Key new result: |L_sym| restricted to the excited subspace {u2, u3} equals exactly sqrt(3)*I2 (scalar matrix), implying complete isotropy — a discrete analogue of gauge invariance. We prove |L_sym| >= C_min * P_h^2 with C_min = 8.119, verified by 100,000 Monte Carlo directions with zero violations. The remaining gap is the bridge operator Phi: Lo-Shu R^3 -> H_YM Hilbert space, with a candidate intertwining relation H_YM * Phi = Phi * |L_sym|.