Agree, and most of my harness isn't the model either. A pre-merge script fixes the boring failures deterministically, risk labels route security and tenant changes to me, and a lessons log gets read at the start of every task. 601 PRs merged in 30 days on that.
The more I study coding agent harnesses, the more I realize how much of the engineering happens OUTSIDE the LLM.
A complete harness brings together:
• LLM and tools
• Planning loop
• Context engineering
• Memory and sandboxing
• Orchestration and serving layers
Together, these components turn a simple model into a system that can execute complex tasks.
And now there’s been a shift toward headless architectures, where the same agent can operate through a terminal, web app, or messaging platform.
TL;DR: The LLM is just one piece of the puzzle.
The engineering is in the system surrounding it.