harness

Harness — Multi-Agent Build Orchestrator

Overview

Orchestrate long-running application development using three specialized agents: Planner, Generator, and Evaluator. Based on Anthropic's harness design pattern where separating the agent doing the work from the agent judging it produces dramatically better results than solo generation.

The harness runs a Plan-Build-Evaluate loop. Each agent gets a fresh context with only file-based handoff artifacts — context reset is structural, not manual.

Architecture

User brief → Planner → spec.md → Generator → app code → Evaluator → eval-report.md
                                       ↑                                    |
                                       └────── iterate/pivot ───────────────┘

Three agents, three distinct contexts, file-based communication:

• Planner (cyan): Expands brief into product spec. High-level only — no implementation details.
• Generator (magenta): Builds the application from spec. Runs in worktree isolation.
• Evaluator (yellow): Tests the running app like a real user. Skeptical by default.

Execution Flow

Phase 1: Initialize

Create the harness workspace in the current project:

.harness/
├── config.json          # Harness configuration
├── state.json           # Current phase, round, active components
├── spec.md              # Planner output (Phase 2)
├── build-summary-N.md   # Generator output per round
└── eval-report-N.md     # Evaluator output per round

Read .harness/config.json if it exists to check for disabled components (from /harness-simplify).

Initialize .harness/state.json:

{
  "phase": "planning",
  "round": 0,
  "maxRounds": 5,
  "components": {
    "planner": true,
    "evaluator": true
  },
  "brief": "<user's brief>"
}

Phase 2: Plan

Dispatch the harness-planner agent with the user's brief.

The planner writes .harness/spec.md. After it completes, present the spec summary to the user and ask for approval before proceeding. The user may request changes — re-dispatch the planner if needed.