Developer Builds Custom AI Coding Agent 'Dasan' Using OpenAI Codex OAuth

A developer has created a personal AI agent called Dasan, named after the pen name of Joseon-era scholar Jeong Yak-yong, rather than relying on existing tools like Claude Code. The agent runs on an LLM powered by Codex OAuth, a choice driven by the cost constraints of using paid API access freely. Dasan operates on a ReAct loop, enabling it to explore, read, modify, and execute commands on local files within a single persistent session stored via SQLite. The system uses a two-layer prompt architecture separating a fixed core role from a learnable user-alignment layer. The project is open source on GitHub and can be installed globally on macOS, Linux, or Windows with a single command.