Sorry for the long delay.

I guess I better start with a short summary to spare you the trouble of
reading through the previous messages relating to this bug.

When "cvs commit [file...]" is invoked from the command line, cvs prepares
a temp file with a template of a commit message and invokes an editor on
it. The template commit message, by default, is like this:

CVS: ----------------------------------------------------------------------
CVS: Enter Log.  Lines beginning with `CVS:' are removed automatically
CVS: 
CVS: Committing in .
CVS: 
CVS: Modified Files:
CVS: 	test.txt 
CVS: ----------------------------------------------------------------------

After saving the edited commit message and exiting the editor, cvs strips
lines beginning with 'CVS:' from the temp file.  NB. this is the only
documentation for this feature.  The CVS manual doesn't mention this.

When committing with "cvs commit -m 'Commit message.' [files...]" this
stripping is *not* performed.

The commit message template in the temp file is augmented with the
contents of the file 'CVS/Template', if it exists or a template received
from the CVS server..

I work on NetBSD where we make use of such a template.

'vc-cvs-checkin' emulates the first part of this (inserting the template
from the server/'CVS/Template file.  However, it does not strip the lines
beginning with "CVS:" and uses the "cvs commit -m 'Commit message.'" method
to do the actual commit.  That causes the "CVS:"-lines to end up in the
actual commit.

I have drafted a change that adds a function to the 'log-edit-done-hook'
that strips lines beginning with "CVS:" from the commit message if the
'log-edit-vc-backend' is "'CVS".

Because this hook function does its work only when the
'log-edit-vc-backend' is CVS and since this just makes 'vc-cvs-checkin'
behave like invking "cvs commit [files...]" from the command line I
consider this a change low risk and don't think that it would surprise
existing users.  Therefore I think it is appropriate to enable this hook
by default.

It would be nice if this would end up in emacs-30.1.

I'd appreciate any review and guidance what is missing to make this
committable.

I guess I need to add an entry to the NEWS file.

--chris