Beyond the Prompt: Building an LLM Harness

From ChatGPT text boxes to Claude Code and Codex, LLMs evolved from basic chat to tab completion to active digital workers. The secret isn't bigger models: it's the harness. We will build a complete harness live from scratch in Python, demonstrating how it bridges next-token prediction with managed state, action execution, and error handling. Plus, we'll peek at how these execution loops generate training data for future models.