Harness
also: agent harness · harness engineering
The orchestration code around a model — the loop, tools, retries, budgets — that turns it into a product.
The harness is everything that runs the model: assembling context each turn, parsing outputs, executing tool calls safely, handling retries and errors, enforcing budgets and stop conditions, logging traces. Harness engineering is the emerging discipline of building this layer well — two systems with the same model can behave worlds apart because the harness, not the model, decides what actually happens.