Agent debugging gets easier when you separate loops, graphs, and harnesses
Roger_M_Taylor · x · 2026-07-29
Loop, graph, and harness are three different layers in agent engineering
The post argues that most teams blur three distinct concepts into one, which makes agent debugging much harder:
- Loop engineering controls repetition: retries, budgets, exits, and no-progress conditions. Durable execution is recommended when a run must survive failure.
- Graph engineering controls topology: nodes, edges, state, branches, cycles, and checkpoints. Use a stateful graph when the agent decides its next step.
- Harness engineering controls reality: tools, permissions, memory, sandboxes, evals, traces, and humans. Keep code and tool execution isolated from the host, and add an eval gate before every model or prompt change.
The overall message is that a good agent system needs all three layers, not just a loop.
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