it lists 'Garbage Collection' as one of the 3 components of a harness

I don't know any harness that solves 'Garbage Collection' in the way described here

(most harnesses accelerate context pollution and code base drift via instructions they embed into system prompts, tool descriptions and skills)

I think most people that use LLM coding tools enough independently derive most of the stuff in the article. For example my approach to garbage collection is to sample paths within the project and chunks of file content, then assemble context (similarity search results, git blame) for the agent to use to assess cruftiness and if found schedule cleanup.