Harness Build-vs-Buy

The measured price of owning a coding agent: 12 months of public GitHub activity across four harnesses (OpenHands, Codex, OpenCode, Hermes) shows 5,679–7,736 merged PRs/year and 1.05M–1.75M lines each, so a fork frozen a year ago sits ~4,600 PRs (≈13/day) behind upstream — an OpenHands (vendor, commercially interested) argument for customizing at the highest layer that works: prompts/config → MCP → skills/plugins → SDK