The Sentinel Phenotype: A Structural Criticality Framework for Intestinal Permeability and Glucose Signaling in Autism Spectrum Disorder

Abstract The rising prevalence of Autism Spectrum Disorder (ASD) and its high comorbidity with gastrointestinal dysfunction (~70%) challenge static genetic models. This paper proposes the Sentinel Phenotype Hypothesis, a structural framework based on the Constructive Fractal Framework (CFF) v3.6. We posit that the ASD neurotype is not a pathological error, but an adaptive calibration to high-entropy maternal-fetal signals (elevated glucose/cortisol). Under this model, "Leaky Gut" functions as a high-bandwidth sensory interface, and "Sugar Cravings" act as a temporal buffer ($\tau$) to maintain cognitive agency in a hyper-sensitive system. By analyzing the Integration Efficiency ($\eta$) between the microbiome (Layer 0) and neuro-cognition (Layer 2), we identify current dietary guidelines (high-carbohydrate based) as a source of "metabolic noise" that destabilizes neurodivergent homeostasis. We propose a Signal Substitution Protocol to recalibrate the axis without suppressing the adaptive intent of the phenotype. Keywords: Sentinel Phenotype, H.E.A.R.T. Model, Leaky Gut, Sugar Scream, Microbiota-Gut-Brain Axis, Structural Criticality.