In the coderunner read me it talks about reading files without sending them to the cloud. Does that mean there is something agentic going on? That’s more than I expect from something called a sandbox.

Also if it is agentic, why is it less cloud based than eg Claude code? Are there LLMs running locally?

Regarding files, they are volume mapped (local <--> sandbox) as with docker.

It's not agentic - agents can use it to execute code. Those agents can be powered by any LLM including local.