Agentic AI security is not application security with extra steps — it is a fundamentally different problem. This episode dismantles the perimeter myth, walks through the Lethal Trifecta of indirect prompt injection, memory poisoning, MCP supply chain attacks, and east-west LangGraph pipeline cascades, then closes with concrete architectural defenses: per-action authorization, zero-trust agent boundaries, and mandatory human-in-the-loop circuit breakers.