🚀 go-pugleaf

 > At the end of vm.el (VM 5.21), you do:
 > 
 > (if (not (memq 'vm-write-file-hook write-file-hooks))
 >     (setq write-file-hooks
 > 	  (cons 'vm-write-file-hook write-file-hooks)))
 > 
 > which means that your write-file-hook will be a permanent feature of the
 > global emacs environment after VM has been invoked once:

The hook has no effect in any other buffers, because other buffer
won't be in vm-mode.  So it is harmless.

 > I think it might be a little cleaner to include a
 > 
 >   (make-local-variable 'write-file-hooks)
 > 
 > in vm-mode-internal () to avoid altering the global value of
 > write-file-hooks after entering VM.

Perhaps.  But Emacs will trash the local copy of write-file-hooks
if you C-x C-w and save to a different filename.  I could restore
it afterwards, but it seemed simpler to just set it globally and
forget about it.