Horizon-Activated Möbius Geometry: Junction Structure and the First Physical Deviations Beyond General Relativity

This paper presents the first physically activated regime of Möbius Cosmology, identifying a compact, horizon-adjacent spacetime region in which General Relativity remains dynamically exact yet fails as a complete boundary description. Activation occurs exclusively through non-orientable junction geometry localized near compact-object horizons, with bounded deviations enforced by a geometric stability condition that forbids bulk propagation or global modification. Outside the activation region, Einstein gravity is recovered exactly with no residual corrections. A localized correction to relativistic time delay is derived, providing the first falsifiable observational handle on Möbius Cosmology without altering established gravitational dynamics.