Char Jackson wrote:

With some newsreaders, such as my old copy of Agent 2.0, brackets
aren't a workaround for a deficient client. They are simply markers
to let the composition window know that the configured line length
value should be ignored for text between the brackets.

Ah, it's a sender's client trick to prevent line breaks. Understood.
In my NNTP client, I don't need to do that for URLs as they kept intact
in one physical line; however, it does have a Word Wrap toggle that I
can click to insert a composition marker (not in the sent copy) to keep a long string from line wrapping. I use it occasionally, like for a wide data table where line wrapping makea it unintelligible. (I used it on this line as an example.)
It keeps the long string as one long physical line. The reader's client
might enforce line splitting at their configured line length. Nothing I
can do about that. My tricks sounds similar to your bracketing trick.

However, I've seen those long strings in a long line include the angle
brackets. They might be a hint in the composition window in the
sender's client, but they were also included in the sent copy. As a
test, could you reply with a long string, like 200 characters, enclosed
in your non-wrap markers, so I could see if the submitted copy has the
non-wrap markers or not?