org cite "processor" example

org-cite-tone-down.el

(when-let ((basic (org-cite-get-processor 'basic))
           (activate (org-cite-processor-activate basic)))
    (org-cite-register-processor
        'activate-hide-@cite :activate
        (lambda (citation)
          "Activate CITATION, then make leadup to first ref invisible."
          (funcall activate citation)
          (when-let ((first-ref (car (org-cite-get-references citation)))
                     (beg (car (org-cite-boundaries citation))))
            (put-text-property (1+ beg) (car (org-cite-key-boundaries first-ref))
                               'invisible t)))))

Update: simplified to set only the activate slot of the new processor, since that is all that is used from the org-cite-activate-processor.