OpenAI shipped the Agents API this week and called it "a hosted version of the Codex harness"
the word is in the product copy now, written by the company that sells you the model
DHH spent 5 hours with Lex Fridman on that same layer. the chapter is literally called "best AI coding harnesses"
1.5M people watched it and quote the model comparison, not this part
watch it, then read what a harness is made of in the article below