ELI5 what is a harness?

EDIT from https://arcprize.org/media/ARC_AGI_3_Technical_Report.pdf:

> We seek to fight two forms of overfitting that would muddy public sensefinding:

> Task-specific overfitting. This includes any agent that is created with knowledge of public ARC-AGI-3 environments, subsequently being evaluated on the same environments. It could be either directly trained on these environments, or using a harness that is handcrafted or specifically configured by someone with knowledge of the public environments.

The point of this test is to check if an AI system can figure out the game. This isn't what happened here. A human figured out the game, wrote in their prompts exactly how the game works and THEN put the AI on the problem. This is 100% cheating and imo quite stupid.

I think generally people regard a harness as the system instructions + tools made available to the LLM (and probably the thing that runs the LLM conversation in a loop.) An agent is collectively, the LLM plus the harness.