Start

Build a coding harness that accepts a task in the terminal, inspects a working directory, edits files, and submits the result for one review. The finished program follows the same design as examples/coding_agent.py.

The harness has five participants:

• Client enters the task and receives the result.
• Planner lists and reads files, then sends an implementation plan.
• Coder writes files and reports the patch.
• Reviewer either ships the patch or requests one final correction.
• Workspace exposes filesystem operations as protocol messages.

The session protocol determines which messages each participant can send. During planning, the planner's endpoint contains List, Read, and Ready. The Write branch belongs to the coder's endpoint, and the planner cannot select it.

Prepare the script

Install uv and create an empty file named coding_agent.py. Add inline metadata so uv can select Python and install the OpenAI integration in an isolated environment:

# /// script
# requires-python = ">=3.10"
# dependencies = ["agentsparty[openai]"]
# ///

Append the imports. AsyncOpenAI provides the model client; agentsparty supplies roles, codecs, participants, and the runtime. The protocol combinators describe the conversation as a value.

from __future__ import annotations

import os
from pathlib import Path
from typing import Any

from openai import AsyncOpenAI

import agentsparty as ap
from agentsparty import debug
from agentsparty.protocol import alt, msg, project_all, rec, var

Follow the control flow

The program moves through three phases:

1. The planner repeatedly selects List or Read. Selecting Ready closes exploration and publishes the plan.
2. The coder may issue any number of Write requests. Selecting Done sends the patch to the reviewer.
3. The reviewer selects Ship or Fix. A fix permits one final write, after which the coder delivers the result.

Both repeating phases are finite at runtime because the allowance bounds recursive unfoldings. The protocol also makes the single-review policy visible in the topology: neither review branch returns to the reviewer.

The next page builds this control flow with roles, typed messages, alternatives, and recursion. Continue with declare the conversation.