AI が決めるとき誰が何を立証するのか：世界の穀物サプライチェーン意思決定における説明責任の空白

AI-assisted procurement, counterparty selection, pricing, and logistics raise a basic question for global grain supply chains: can an enterprise reconstruct who decided what, when, and on what information? This paper distinguishes product provenance from decision provenance and develops a four-layer accountability-void framework covering definition, regulation, enforcement, and precedent. The analysis examines the EU, the United States, China, Brazil, Singapore, Japan, and the WTO/FAO institutional setting, alongside five hypothetical risk scenarios. In the public records reviewed through February 2026, it identifies zero directly matching enforcement actions and judicial or arbitral decisions addressing the allocation of responsibility between AI recommendations and human approval in grain procurement and trading. Existing legal duties provide important points of entry, while the connection between those duties and decision-level evidence remains the central institutional problem. The paper explains how nominal human oversight and fragmented records complicate that connection, and sets out a research agenda for evidence that links data, model output, human review, compliance screening, and execution.