Harness Engineering: A Composable Architecture
Three engineers at OpenAI produced a million lines of code last year. None of it was written by hand. What made that work was the structure around the model, not the model itself: a pipeline where quality gates check every transition and failures loop back as structural fixes rather than prompt patches.
Tatsunori Hashimoto named the discipline: when an agent makes a mistake, engineer a structural fix so it can never make that mistake again. Birgitta Böckeler, writing on martinfowler.com, distinguished what steers agents before they act from what corrects them after, mapping a taxonomy of guides and sensors. Anthropic's multi-agent research showed the shape at a different scale: separate generation from evaluation, make the evaluator skeptical, loop until everything passes. Four groups, different problems, the same skeleton.
That skeleton is a pipe. A signal enters, gets transformed through stages, and produces an artifact, with quality checked at every seam. The scientific method follows this shape; so does OODA. The structure is older than software, the basic form of structured inquiry.
But if harness engineering names only the pipe, then what has been named is not new. The field needed explicit terminology for the age of agents, and the terminology is valuable. The question is whether an architecture exists underneath: something an engineer can compose and configure, something that explains how the system that produces runs gets better over time. The pipe comes first, because you need the skeleton before you can see what has grown around it.