Code as Agent Harness
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A 100+ page survey treating the agent harness as a first-class research object rather than glue around an LLM. The authors argue that code-as-harness is the most promising path to general-purpose agency, and that future agent systems should satisfy four properties: executable, inspectable, stateful, and governed. The report consolidates methods, applications, and open problems across the harness layer.
Harness engineering as a discipline: The paper frames harness design as a science distinct from model training, with its own primitives, failure modes, and evaluation criteria. The taxonomy gives a vocabulary for comparing systems that has been missing in prior agent literature.
Four-property test for production agents: Executable, inspectable, stateful, and governed. Each property maps to a class of operational concerns. The authors use it to audit current open-source agent frameworks and identify where defaults fall short.
Code as the unifying substrate: Across browsing, tool use, and multi-step reasoning, harnesses that compile decisions into code consistently outperform JSON-call orchestration on the surveyed benchmarks. The paper traces this back to determinism, composability, and inspectability of the resulting traces.
Why it matters: If code-as-harness is the right substrate, then the next round of agent-system progress will come from harness-level innovation rather than from new base models. The survey gives builders a structured reference for that work.
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