scenario:
In recent commits this scenario had regressed and was throwing an error. Not serious but ugly. I've documented it in manual tests now.
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* run driver and then client app from a separate terminal. Driver window
populates with client app code.
* run client app and then driver from a separate terminal. Driver window
populates with client app code.
* run 2 client apps and then driver. Driver window populates with code from
one of the client apps at random. (NOT something to do in ernest; just
documenting expected behavior.)