Building a coding agent from scratch

I wanted to understand how coding agents work, so I built a minimal one from scratch, inspired by pi. I wrote a detailed breakdown of its architecture (link in the comments). The blog starts with a simple ReAct agent loop and then covers the concepts needed to build the plumbing around it, until it becomes a coding agent. In short: Agent loop: the loop publishes events at different checkpoints (turn start, message update, tool execution, etc.), and any consumer (TUI, CLI, RPC) can subscribe to them. It is async, so abort and steering messages are handled while the LLM is responding. Tools: read, write, edit and bash, with a sandbox (bubblewrap for bash). Tools use an operations interface, so they can run on a remote machine too. Sessions: stored as append-only JSONL, where each entry stores its parent id, so a single file holds multiple branches and rewind just moves a pointer. TUI: written in TypeScript, spawns Python as a subprocess, and the two talk over stdin/stdout with JSON lines.