Loop Engineering: What Comes After the Loop
This article argues that naive agent loops relying on LLMs for autonomous decision-making have hit four fundamental walls: plans that rot in the context window, unbounded retries (no distinction between hard and impossible), self-written tests that pass wrong answers (maker-votes-checker), and actions that cannot be replayed. The author demonstrates with runnable code: the same model in a naive loop returns 747 (ground truth 615) with SUCCESS, while a graph harness with a verifier gate returns exactly 615, rejecting 12 corrupted outputs and absorbing 51 tool errors with fewer calls. Four properties fill these walls: explicit dependencies (plan as static graph, not remembered text), bounded recovery (fixed staircase: retry→patch→replan), immutable append-only log (hash-chained, replayable for audit), and a verifier gate (output must pass an independent check node, maker cannot talk past). The twist: frontier frameworks now have the model itself draw the graph of what to do (Anthropic dynamic workflows), while durable state, logging, and verification are infrastructure, not reasoning, and are used even by minimalists. The honest brake: most loops today don't need a graph yet—pick the one wall that cost you this week and close it with a single property.