Harness Handbook: Making Evolving Agent Harnesses Readable, Navigable, and Editable

Beautiful paper on agent harness Agent harnesses fail to evolve cleanly because developers often know what must change, but not where the behavior lives. A behavior-based code handbook helped coding agents find more required edit sites while using fewer planning tokens. Agent harnesses control prompts, tools, memory, and execution, but one behavior often spans distant files, functions, and states. This makes code changes risky because a request describes what should change, while repositories reveal only where code lives. Harness Handbook reorganizes a repository around runtime behaviors, then links each behavior to verified source locations. It combines static analysis with LLM descriptions, 3 detail levels, shared-state maps, and automatic updates after edits. Its guided search starts broad, narrows to likely code, follows call and state links, then checks live source. Across Codex and Terminus-2 requests, it raised plan win rates by 10.0 and 18.9 points while cutting token use by 12.7% and 8.6%. – arxiv. org/abs/2607.13285 Title: "Harness Handbook: Making Evolving Agent Harnesses Readable,Navigable, and Editable"