Harness Engineering

Harness Engineering

Harness engineering turns repeated coding-agent mistakes into durable repository artifacts:

Harness = Instructions + Constraints + Feedback + Memory + Evaluation + Governance

Use this skill when the user asks to:

• make a repository more reliable for GitHub Copilot or other coding agents
• add durable agent instructions, repository rules, or guardrails
• prevent repeated AI coding-agent mistakes
• record known failure paths and the checks that prevent recurrence
• add lightweight drift checks for project rules
• review, refresh, or update an existing agent harness

Do not use this skill for ordinary feature implementation unless the user asks to improve the repository's agent operating environment.

Core Principles

• Treat the target repository as the source of truth.
• Inspect before editing. Preserve the existing stack, package manager, CI, docs, naming, and architecture.
• Add the smallest useful harness. Prefer updating existing files over adding duplicate guidance.
• Make important rules enforceable where practical through tests, linters, type checks, CI, pre-commit hooks, or drift scripts.
• Use manual review points only when automation would be brittle or misleading.
• Record high-risk failures that should not recur, and name the check or review point that catches recurrence.
• Do not copy generic templates blindly. Adapt every artifact to real evidence in the target repository.

Discovery

Before proposing or making harness changes, inspect the repository for existing rules and evidence.