A few resources on harness engineering I'm really enjoying learning from recently:
https://walkinglabs.github.io/learn-harness-engineering/en/ - excellent course that covers how to constrain agent behavior in a productive way, what the challenges are using LLMs especially maintaining context, and how to make the harness more agentic and work to the proper conclusion of a task
https://twotimespi.dev/ - build a simplified agent in Python (Tau). start with "uv tool install tau-ai"
https://www.humanlayer.dev/blog/skill-issue-harness-engineering-for-coding-agents - lessons and learnings from failing and succeeding to build harnesses for coding agents over 12+ months
https://www.langchain.com/blog/the-anatomy-of-an-agent-harness - higher-level overview of the many components that need to come together properly in a harness to make an agent work