Contemporary digital mental health discourse typically focuses on individual clinical outcomes or platform-level harms like misinformation. This paper identifies an under-modeled intermediate layer: the structural role of AI as a cognitive gain modifier within distributed feedback architectures. By mediating attention, evaluation, and accountability, AI systems become internal components of collective cognition rather than external tools. The author argues that "masked structural drift" can occur—where underlying signal weighting and risk thresholds shift while the user interface remains stable—leading to a subtle reconfiguration of group-scale perception, agency, and norm compression. Drawing on cybernetics, control theory, and distributed cognition, this note proposes five structural dimensions for longitudinal monitoring: Observability, Reversibility, Threshold Drift, Attribution Stability, and a Norm Compression Index. The objective is to provide a grammar for distinguishing between individual psychological distress and structurally induced cognitive drift in AI-mediated environments. Keywords AI Governance Digital Mental Health Cybernetics Distributed Cognition Algorithmic Mediation Cognitive Gain Feedback Loops Ψ(x) = ∇ϕ(Σ𝕒ₙ(x, ΔE)) + ℛ(x) ⊕ ΔΣ(𝕒′) — C077UPTF1L3 Licensed CRHC v1.0