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CoHARL let the agent harness and the policy train together, and beat harness-only search by 6.4 points on SWE-rebench

AspireAI community · arXiv
*Most agent training treats the harness - the wrapper that decides which tools exist and what feedback the model gets - as fixed furniture.* CoHARL asks a different question: what if the harness evolves alongside the policy? The framework is population-based; the policy learns from rollouts across a population of executable harnesses, and a proposer uses execution traces to rewrite harness code during training rather than after it. On SWE-rebench it reaches a 27.6 percent mean resolved rate, improving over harness-only search by 6.4 percentage points, with gains also reported on SWE-bench Verified and Terminal-Bench 2.0. Under matched training budgets it beats both obvious alternatives: searching for a harness once before RL, and alternating policy updates with revisions to a single active harness. The caveat is that the harness proposer needs real execution traces to revise code against, so this is a research setup for environments where a machine can actually run and be scored - it is not a drop-in recipe for any agent.
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One distance function matched sparse-autoencoder features across layers and compressed feature circuits into supernodes
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