Harness, Loop, Graph: Which Layer Actually Broke Your Agent
The author splits agent failures into three layers: the harness (everything around the model — tools, memory, permissions, traces), the loop (a check that can genuinely fail, plus feedback and exits), and the graph (dependencies and state handoff between loops). The claim is that each layer fixes a different class of failure, and that most engineers burn weeks editing prompts or swapping models when the real defect lives elsewhere. Concrete patterns include a task contract with an explicit done_when field, an AGENTS.md file that acts as a map instead of a manual, retry loops that exit when the same evidence appears twice, and an early-start test that removes fake arrows between steps. The author concedes most tasks should collapse back to a single loop, and that drawing a twelve-node graph first is a common mistake. Suited to engineers building agent workflows. Second-hand synthesis, no original measurements.