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harness-kit Wiki

The knowledge base for harness-kit: a set of Claude Code agents that carry a raw idea to a merged PR through one gated pipeline, plus a system-architect agent that turns a problem into a rigorous System Design Doc.

The repo holds the condensed, agent-facing form (guides, sensors, evals as terse markdown). This wiki is the human-facing depth: the theory behind the harness, how each control works, and full study material with references for each system design.

The harness

How and why harness-kit is built the way it is.

Page	What it covers
Harness Engineering	Agent = Model + Harness, feedforward vs feedback, computational vs inferential controls, humans on the loop (Böckeler/Fowler)
Guides	feedforward controls: templates, examples, writing style, conventions
Sensors	deterministic feedback: structure checks, the sensor runner, hard gates
Evals	inferential feedback: LLM-judge rubrics, threshold 8.0, retry, spec-satisfied
Pipeline and Stages	the six gated stages, anatomy of a stage, markers, tokens, status bar, SDD loop
Golden Path	the paved road, the five properties, detours, per-discipline paving
Agents	product-manager, staff-software-engineer, system-architect

Start here: Harness Engineering explains the whole mental model; everything else is a detailed view of one part.

System design

The system-architect agent and its topic playbooks. Each episode of the System Design series becomes a skill plus a detailed page here: theory, reference architecture, trade-offs, and citations.

Page	Design problem
System Design Method	the 13-stage method, the three pillars, back-of-envelope numbers, the canon
URL Shortener (#1)	read-heavy key lookup, short-code generation, cache, abuse
Rate Limiter (#2)	distributed throttling, token bucket, fail-open, multi-region budgets
Search Engine (#3)	web crawler, indexing, ranking, query serving at scale

More episodes land as new playbooks and new pages. Candidates: API gateway, distributed queue, news feed, distributed cache, notification system.

How the two halves connect

A System Design Doc is an optional front stage before the main pipeline: a strong design feeds a sharper PRP and a grounded plan. The same harness shape, guides, sensors, evals, gated approval, runs under both halves.

Global references

• Birgitta Böckeler, Harness engineering for coding agent users & Maintainability sensors for coding agents, martinfowler.com, 2026.
• Martin Kleppmann, Designing Data-Intensive Applications, O'Reilly, 2017.
• Jeff Dean, Designs, Lessons and Advice from Building Large Distributed Systems, LADIS, 2009.
• Werner Vogels (design for failure), Pat Helland (immutability, distributed transactions), Michael Nygard (Release It!), John Ousterhout (A Philosophy of Software Design).