My cat has claw cap glue stuck on his toe. How to remove it safely?

I'm glad to hear that the nail caps work well for your cat's front feet! Most cats are far more tolerant of having their front feet handled than their back feet. Since Your cat is unable to retract his toe, I do think it's worth trying to remove the glue. Walking in with his toe in an abnormal position could cause him to inadvertently injure himself. Most of these caps use some form of a super glue for attachment. If your cat will tolerate it without causing you any bodily harm, try to soak the affected area in either vegetable oil or mineral oil for a few minutes, then try to gently scrape away at the glue closest to his nail base. It's not a big deal if some of the glue remains on his nails - it will wear off eventually. You may want to try wrapping your cat's body tightly in a large towel with the foot in question left out of the wrapping. We all this a "kitty burrito" and it's often helpful for a bit of restraint. I hope this helps and that everything goes well!