It totally works with read-write enabled and in fact rancher uses it this way. Make this change:

    mounts:
    - location: "~/sandbox"
      writable: true 

Lima cautions against this:

      # Setting `writable` to true is possible, but untested and dangerous.

But I never hit any problems when I played around with it. Here are my notes: https://earthly.dev/blog/lima/