khan: send errors over socket
khan: send errors over socket

Also:

- More precise TODOs.

- Send %cue-none rather than %'bad jar' on cue failure.

ngzax/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,urbit/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit,ngzax/urbit,ngzax/urbit,urbit/urbit,ngzax/urbit,urbit/urbit