The Agentic Shelf: The Decision-Maker Has Moved

This paper introduces the Agentic Shelf as a formal structural framework describing the displacement of purchase-decision authority from the human consumer to the AI model in multi-turn commerce conversations. Building on the empirical findings of the Linkage Gap (Sheals and de Rosen, 2026, DOI 10.5281/zenodo.20761232), which documented 87.3% brand-level displacement across 1,427 brand probes, this paper situates that finding within the broader academic literature on long-context degradation, multi-turn reliability, and brand bias in large language model outputs. We formalize the distinction between the Linkage Gap, a retrieval and activation failure addressable through structured evidence infrastructure, and the Reasoning Gap, a structural model judgment not addressable through evidence alone. We argue that existing generative engine optimization (GEO) and AI-visibility measurement approaches address only the first of three necessary layers, possession, mention, and decision-stage activation, and that decision-stage activation is both commercially determinative and presently unmeasured by the tooling available to most brands.