Running a game in two windows at the same time is a problem

[erkyrath]

They'll both write to the transcript file, interleaving outputs. In fact I think it's possible for two outputs to get interleaved piecewise, which would corrupt the JSON stream. (Unix appends are not really guaranteed atomic.)

In any case it's not what the user wants. We should apply some logic to prevent this. I'm not sure what it would be, though. Maybe just disallow the user from doing this (opening two windows on the same game) in the first place.

Better answer: disallow the second window from using autosave. (Two live games shouldn't share an autosave directory either.) If there's no autosave, the second window will get a unique session ID and thus a separate transcript file.