Chern-Simons Boundary Completion of Degenerate Disformal Scalar-Tensor Theories

In degenerate disformal scalar-tensor theories, the degeneracy surface D: epsilon = 0 constitutes a hard boundary for classical metric evolution: hyperbolicity, finiteness of stress-energy, perturbative control, and curvature regularity all fail simultaneously (the No-Go Theorem of the companion paper, DOI 10.5281/zenodo.18866200). We propose a boundary Chern-Simons completion of the transition at D. In the epsilon -> 0+ limit, scalar freezing and destruction of the bulk metric leave a unique finite variational sector: the induced three-dimensional Einstein-Hilbert action on the transition hypersurface Sigma_K with positive cosmological constant. By the Achucarro-Townsend-Witten correspondence, this is…