I quit BBEdit (9.3.1) and opened "~/Library/
com.barebones.bbedit.plist" in Property List Editor (which is part of
the XCode package) and scrolled down until I saw a meaningful line. I
found 4 lines that start with "Editor:WrapMode" one with the value
'WrPh' and 3 with the value 'WrCh' which I assume stands for wrap to
"page guide" and "character width", respectively. I took a guess (or
did I see this somewhere in there?) and changed all 4 of them to
'WrWn'. (save and quit)
Now when I open a document in BBEdit the window defaults to wrapping
to "window width" as I wanted. (Yippee! this has bugged me for some
time!)