Harness or Model? Isolating the Harness Effect in Agentic Coding with a Contamination-Controlled Private Suite
An agentic coding system couples a language model to a harness: the tools, prompts and control flow that turn a chat model into an autonomous software engineer. Vendors ship harnesses tuned to their own models, and practitioners assume the vendor-native pairing solves more tasks. We measure that assumption with paired...