[racket] Unexpected procedure identity

I'm continuing with define/contract a bit. Let's say there are two
definitions like this

#lang racket

(define/contract (sum/c lon)
  ((listof number?) . -> . number?)
  (sum lon))

(define (sum lon)
  (if (empty? lon)
      0
      (+ (first lon)
         (sum (rest lon)))))

> (has-contract? sum/c)
#t
> (has-contract? sum)
#f

Is there a way to get to what is protected by the contract? I can figure out
that the procedure sum/c is protected by a contract with has-contract? but I
would like to get the wrapped procedure (unprotected sum/c) out in that
case. Perhaps that would be suitable for identity purposes? Or let's say the
blame object in case the procedure is to blame?

I couldn't find anything from the documentation about this.

-Markku
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