I tried to make this work today, but I don't understand how this could ever work - it seems to pass the pred into org-roam-node-read as the sort-fn? Maybe a merge changed those args up? I can't figure it out. Just wanted to call it out, as it was confusing and might be worth cleaning up.

I tried to make pred work as an additional org-roam-node-find arg (maybe those should switch to &key args at some point?), but I don't understand completing-read well enough... ultimately I found this vertico documentation. The very last code block in that section offers:

(setq read-file-name-completion-ignore-case t
      read-buffer-completion-ignore-case t
      completion-ignore-case t)

I was able to get case-insensitive completion by wrapping org-roam-node-find and org-roam-node-insert with a let, like:

;;;###autoload
(defun russ/org-roam-find-file ()
  ""
  (interactive)
  (let ((completion-ignore-case t))
    (org-roam-node-find
     nil nil (lambda (node)
               (= 0 (org-roam-node-level node))))))

;;;###autoload
(defun russ/org-roam-insert-file ()
  ""
  (interactive)
  (let ((completion-ignore-case t))
    (org-roam-node-insert
     (lambda (node)
       (= 0 (org-roam-node-level node))))))

Not sure if that applies to all completion frameworks though - it seems worth supporting a passed completion-predicate like this PR intended.