The Impossibility of External Subjecthood - Why Complete External Constitution Cannot Generate Structural Self-Relevance

S001 identified the structural gap: Q1 and Q2 describe when a system can persist as itself but leave open the question of when that persistence becomes the system's own. Self-persistence — structurally relevant persistence — requires additional conditions. S002 identifies the first impossibility that forces the first of those conditions. The question is not: can a fully externally constituted system be complex? Yes. Can it process information? Yes. Can it satisfy Q1 and Q2? Yes. Can it model its environment, respond to perturbations, generate sophisticated adaptive behavior? All of these, yes. The question is: can a fully externally constituted system be a subject of its own persistence? The answer is no. Not because of complexity limits. Not because of information processing bounds. But because of a structural impossibility: complete external constitution is structurally indifferent to the system whose persistence is being constituted. And structural indifference cannot produce structural self-relevance — regardless of what else is true about the system.