Build Your Own AI Coding Agent Harness

This course walks through building TeensyCode, a TypeScript AI coding agent harness with a tool loop (read, grep, write, edit, bash, task, askUser), execute-level safety gates, structured system prompts, and a swappable Sandbox interface with local and in-memory backends. It also covers context management via pruneMessages and bounded tool output, subagent delegation, human-in-the-loop questions, sandbox lifecycle, and extensibility, across 11 modules plus a capstone. Prerequisites include TypeScript, an AI_GATEWAY_API_KEY, and Node.js 22+ or Bun.