Afaik many harnesses ship the "default" which is grep+read (like Claude Code). But I agree, IMO it's a weird gap. To be fair I don't think providers are that incentivised to reduce token burn at the moment, but my guess is that that will change and tools like this will become at least an natively supported option in some harnesses.

I'm playing with PI as a custom harness ( for Claude code because that what is provided to me )

I will try that ! It make sense and I'm curious to see results, for this or any similar projects mentioned in the thread