This chapter integrates governance and security into the infrastructure core. It formalizes policy enforcement as structured, executable metadata applied across the data lifecycle. The chapter adopts a zero-trust perspective and demonstrates how access control, masking, and compliance policies can be modeled as deterministic contracts. A case study illustrates how relational policy representation enables continuous auditability and measurable enforcement. By embedding governance within system architecture, the chapter completes the trust foundation required for scalable and regulated AI systems.