The transition of artificial intelligence from a generative curiosity to an agentic workforce has precipitated a fundamental crisis in digital governance. This paper argues that the prevailing "Software Governance" paradigm—which relies on system prompts and application-layer logic—is insufficient for securing high-stakes autonomous agents. To this end, we analyze the "Hardware Renaissance" of 2026, a shift characterized by the rapid migration of agentic infrastructure toward Trusted Execution Environments (TEEs). While the underlying silicon—ranging from Intel SGX/TDX and NVIDIA H100 to IBM Z—is often shared across the industry, the architectural frameworks built atop these foundations are designed to solve radically different problems. Consequently, this taxonomic survey examines five distinct architectural archetypes: The Privacy Box (Oasis Network), The Pirate Ship (Phala Network), The Dark Pool (Flashbots SUAVE), The IP Vault (Super Protocol), and The Governance Anchor (The Citadel Protocol). We provide a detailed technical breakdown of their respective attestation flows, memory isolation mechanisms, and key management strategies. Ultimately, we conclude that while decentralized frameworks optimize for privacy or censorship resistance, the "Governance Anchor" model establishes the requisite standard for enterprise compliance (ISO 42001).