Most AI demos look impressive. Most AI agents in production quietly fail. The difference is rarely the model — it's everything built around it. Agentic AI refers to systems where a model takes autonomous, multi-step actions to complete a goal — browsing the web, writing and running code, calling APIs — acting, observing the result, and acting again, often over hours. Harness engineering is the discipline of building the system that makes those actions reliable. As LangCha