Just about every harness is. This is common knowledge, no? Frontier lab TUI tend to steal from the OSS harnesses not the other way around.

It's not sus at all. You're looking at it from the perspective of a general purpose system that is not adapted to your use case. Basically you prompt the model and then let the agent do everything. That's the use case you have in mind when you think that it's about being "a tier above frontier labs' offerings".

It's missing the point. I mean think about the basics, why open the huge bash hole only then to have to close it? If you think about it logically, the only way you can sandbox bash is by writing your own bash implementation specifically for agentic use cases.