This is angling in the right direction, but I think it has two problems:

1) It's still assuming agents have CLIs. This is a very developer-centric concept of agents, and doesn't map well to either consumer or enterprise agents that aren't primarily working with files. Skills, plans, TODO lists, and memory are good, but don't have to be modeled as raw file access. Many harnesses have tools for them.

2) It's talking about a singular sandbox. That's not good enough for prompt injection prevention, secure credential management, and limiting the blast radius of attacks.