An Agent Control Loop Is More Useful When You Can Explain Every Turn

Most coding-agent demos leave out the part that determines whether the system will be maintainable: the control loop.

An answer may look simple—prompt, model call, tool call, result—but an implementation must also decide how streamed model events become stable messages, how a tool result is paired with the call that produced it, how a session resumes, and what survives context compaction.

pi-textbook is useful as a learning artifact because its public README organizes a Pi-style coding agent into 15 checkpoints. The stated path moves through a TypeScript protocol, streaming model events, a provider, tools, an agent loop, a session tree, context compaction, extensions, and evals.