A 200-line POC that goes from 0/5 to 5/5 in four proposer steps Incredibuild · Islo · 2026-05-05 POC MIT licensed converges in 4 steps The optimization loop, on Islo primitives. Snapshot once, fork per task, harvest traces to runs/ , let the proposer read the full diagnostic context and write the next harness. Each step maps to one islo CLI primitive. 4 proposer steps to converge Abstract A harness is the prompt + tools + scaffolding around an LLM agent. A meta-harness is the loop that improves the harness automatically: a proposer agent reads the diagnostic logs of prior candidates, spots a failure mode, and writes a better harness. Yoonho Lee’s framing of the idea makes one sharp claim — the bottleneck is diagnostic context : most optimizers compress prior runs into summary statistics, while meta-harness gives the proposer up to 10M tokens of raw execution traces to grep through. That claim is only useful if the runtime can produce, store, and serve those traces cheaply.…