As AI agents take on critical business workflows, enterprise technology is shifting toward a stack comprised not of applications, but of cognitive skills. This creates three architectural concerns around building agents, orchestrating them in business processes, and governing them across the enterprise. The first two concerns have established platform categories: the build and orchestrate planes. The third, the agent control plane, remains an emerging architectural layer and represents a growing gap in enterprise readiness. This report introduces the three-plane model and makes the case for a distinct, independent control plane.