This article models agentic AI as the emerging integrative layer of cyberspace's pre-existing sensing-and-control infrastructure, grounded in betweenness centrality and the attack–defense speed asymmetry. Situated against cybernetics, autonomic computing, and artificial immune systems, it argues that cybersecurity is reflexive because agent, medium, and protected object share one level of abstraction. The centrality hypothesis is made operationally explicit through a graph-theoretic illustration — a hybrid pre-agentic/agentic security-operations graph in which betweenness centrality is tracked as a function of increasing delegation to the agentic layer — and the operational boundary between agentic AI and earlier autonomic-computing systems is made explicit.