Learn to build a custom harness, folks! There is so much alpha in understanding how to optimize the harness. This work shows the benefits of a smart harness configuration and caching the decisions your agent harness has already made. (bookmark it) They propose HarnessMM, which cuts tokens per task on a DeepSeek harness from 96.28k to 11.62k while success rises from 71.43% to 85.71%. Harnesses often call the model again after tool feedback even when an earlier call already settled the next…