A virtual NetMD device that runs the whole library in-process.

This is a NetMD.Transport backed by a GenServer that decodes the NetMD control and bulk protocol and keeps disc state, so you can drive the real library against a simulated recorder without any USB, VM or root access:

{:ok, device} = NetMD.open(transport: NetMD.Simulator)
{:ok, disc} = NetMD.list_content(device)
:ok = NetMD.play(device)

Pass disc: %NetMD.Simulator.Disc{...} to open/1 to start from a custom disc; the default is a small demo disc. State survives across calls and mutates in response to edits and downloads, so a listing after a rename or download reflects the change.

It implements the command subset the library actually uses: disc and track listing, status and playback, editing, the secure download session, and enough of factory mode to authenticate. Unknown commands answer not implemented, which surfaces as a clear error.