> Maybe we could add something to window-setup-hook when we have delayed
 > warnings to display after startup?

I'd leave 'window-setup-hook' alone and do something similar to the
attached patch.  We could also try "(reusable-frames . visible)" there
which should put any frame already showing *Warnings* on top of the
others (at least here it does that), but not all window managers out
there might comply.

Here I neither use desktop nor multiple frames.  So please test the
patch with the originally posted desktop saved multiple frames setup.

Thanks, martin