RunResult.Lines

Lines is what the terminal showed when the command finished, its history included, without the blank lines tmux pads a screen with. A line the window's width wrapped is joined back into one, and each line ends at its last character that is not a space: a screen cannot tell spaces a program wrote from the blank cells after them. tmux keeps at most the session's history-limit lines above the screen, 2000 by default, so the start of a longer output is gone.