Agent Harness
The runtime around a model that supplies tools, state, prompts, permissions, logs, and execution loops.
Plain English
The model is the brain, but the harness is the workbench, clipboard, tool belt, and supervisor.
Example
A coding harness gives an agent shell access, file editing, browser QA, progress logs, and rules for ending each session cleanly.
Why it matters
Many agent improvements now come from better harness design rather than only stronger models.