Local Rigidity of the Spine-Normal Defect

This paper proves a local rigidity principle: transverse defects in the spine-normal derivative cannot occur in isolation. Any pointwise instability forces either a neighborhood of elevated defect or a near-zero event, producing a detectable geometric signature. The argument is purely local and geometric, independent of global averaging assumptions and independent of the Riemann Hypothesis. Its role is to convert rare instability into impossible instability once mean control is available. This paper supplies the local bridge between averaged admissibility (Paper I) and fixed-threshold closure (Paper III).