AI Agent Engineering in Practice: Prompt / Context / Harness Engineering

Appendices

Appendix D

Glossary

This book intentionally separates concepts that are often collapsed into one another in AI-agent discussions. Prompt Engineering, Context Engineering, and Harness Engineering are related, but they solve different problem

Purpose

This book intentionally separates concepts that are often collapsed into one another in AI-agent discussions. Prompt Engineering, Context Engineering, and Harness Engineering are related, but they solve different problems. task brief, Progress Note, and context pack are also different artifacts with different jobs. If the terminology drifts, the artifact boundaries drift with it.

For the English manuscript, docs/en/glossary.md is the English counterpart used by the English chapters and appendices. It must stay aligned with the repo-wide glossary in docs/glossary.md, which remains the single source of truth for terminology. This appendix is the reader-facing guide: it groups the terms that are easiest to confuse and explains why the distinctions matter in practice.

Included Artifacts

  • docs/glossary.md
  • docs/en/glossary.md

1. Terms for the maturity model

The book moves through three stages.

  • Prompt Engineering: define the input and output contract for one task
  • Context Engineering: select and maintain the repo, task, session, and tool context needed for that task
  • Harness Engineering: design execution boundaries, verification, restart rules, and approval gates

The order is deliberate. If the prompt contract is weak, adding more context only wraps a weak task definition in a larger pile of text. If the context is weak, adding a harness only verifies work built on the wrong assumptions.

2. Terms for actors and tools

AI agent, coding agent, ChatGPT, and Codex CLI are not interchangeable.

  • AI agent: an actor that advances work through multi-step decisions and tool use
  • coding agent: an AI agent that reads a repo, changes code or docs or tests or artifacts, and runs verify steps
  • ChatGPT: a conversational environment for shaping requirements, comparing options, and surfacing review angles
  • Codex CLI: an execution environment for making repo changes, running commands, and collecting verification evidence

This distinction protects the book's core claim. Explaining a solution well in a chat is not the same as finishing the work inside a repository.

3. Terms for work artifacts

The most reused artifacts in the book are these.

  • Prompt Contract: a prompt artifact that fixes objective, constraints, completion criteria, and output format for one task
  • task brief: a task specification that restructures an issue for coding-agent execution
  • Progress Note: a short progress record for interruption, handoff, and restart
  • context pack: the smallest bundle of reference material required for one task
  • verification harness: the verification system that bundles tests, lint, typecheck, evidence, CI, and approval rules

These are not just explanatory documents. They are operational inputs. A good artifact must be readable by humans and difficult for an agent to misuse.

4. Terms for harness operations

The later chapters depend on a second layer of terminology.

  • acceptance criteria: the conditions a feature or change must satisfy from the specification side
  • done criteria: the conditions that make the work complete from the operational side
  • evidence bundle: the logs, commands, screenshots, and summaries that let a reviewer verify the result
  • restart packet: the minimum input needed to resume work after interruption
  • permission policy: the rule set that separates autonomous execution from human approval
  • work package: the smallest unit of work that can be completed safely in one session or by one owner

The near-miss pairs matter. acceptance criteria and done criteria are close, but not identical. Meeting the spec without running verify is not done. Running verify without meeting the spec is also not done.

5. Spelling and naming rules

To reduce drift, the English manuscript uses these rules.

  • Use repo and artifact names exactly as they appear in code and files
  • Keep sample-repo hyphenated
  • Preserve product and artifact spellings such as ChatGPT, Codex CLI, Prompt Contract, and Progress Note
  • Prefer the English glossary terms in the English manuscript, even when the Japanese text allows a Japanese equivalent such as AIエージェント

When a new chapter or artifact is added, normalize the wording against docs/en/glossary.md first. Early naming discipline is cheaper than retroactive terminology cleanup.

Parity Notes

  • Japanese source: manuscript/appendices/app-d-用語集.md
  • Publication target: preserve the Japanese appendix's terminology groups, maturity-model ordering, and naming-discipline guidance while making the English glossary usable on its own.

Referenced Artifacts

  • docs/glossary.md
  • docs/en/glossary.md