Stanford/Meta/UIUC Publish 102-Page 'Code as Agent Harness' Survey: Code Is No Longer Output — It's the Operational Substrate for Agent Reasoning, Action, and Self-Evolution

arXiv·high signal

arXiv 2605.18747 (May 18) argues that code has shifted from being what agents produce to the medium through which they reason, act, and model environments. The survey covers harness mechanisms (planning, memory, tool use), feedback-driven control, and introduces 'evolution agents' that treat the harness itself as the optimization target — collecting telemetry, diagnosing failures, and promoting only mutations that pass regression. Essential reading for anyone building agent infrastructure.