so first, we treat context like a stack. Things are popped onto the stack; if we try to remove anything but the top of the stack, we'll break the cache.

So a good harness should be popping tool prompts, user hints after every return from the top so the context of tools and user hints never repeats and are allways prefixed to the current user prompt.

I've never inspected any harness, but opencode with the dynamic context compaction plugin appears to do this well.