This article breaks down the “agent harness” as the orchestration layer—prompts, tool interfaces, loops, memory, guardrails—around foundation models. It argues that teams accumulate hidden technical debt when they treat harnesses as permanent and shows why training and production harnesses must differ to avoid failures as models evolve.

The author revisits Fred Brooks’s classic software lessons in the era of AI coding agents, arguing that while agents wipe out accidental complexity, they amplify essential design challenges and generate unprecedented technical debt. He warns of new “agentic” tar pits, scope creep, and coordination overhead as AI swarms bloat codebases and shift the real work back to human judgment and taste.