How about adding a config option? 
Ideally, it might be nice to have this option "per record" or "per logbook", but "per instance" should be good enough.

I'm sorry for being annoying... 
but I have tried to wrap the <pre> tag in a <div> and it seems to do the trick
(the text is a single line with repeating aaa-b-cc sequence)

In the READ mode, the width is limited by the div's width 
(see the first attachment)

In the EDIT mode, the width is only limited by the textarea width
(see the second attachment)

All this is with "wrap=hard" removed. 

That's great! Thank you very much. 

see https://elog.psi.ch/elogs/Forum/69594

I added a reply to my previous post about this issue (a few months ago) to point to the solution, but ELOG moved it to the top of the forum. 
And I cannot delete this now, because I change my user name from "Andrey" to "Andrey Pashnin" :)

"Only user Andrey can delete this entry"

Sorry, I forgot to mention that I also added some styles to the <pre> tag:
style="white-space: normal"
(see the screenshot on my previous post)

> I guess we want "white-space: pre-wrap" which keeps the old line breaks.

Yep. You're right. Thanks!