fix case-> to not abuse procedure-chaperone

closes PR 13697

collects/racket/contract/private/arrow.rkt

@@ -1561,7 +1561,12 @@ v4 todo:
            (this-parameter ... dom-formals ... . #,(if rst #'rst-formal '()))
            #,(cond
                [rng
-                (let ([rng-checkers (list #'(λ (rng-id ...) (values/drop (rng-proj-x rng-id) ...)))]
+                (let ([rng-checkers (list #`(case-lambda
+                                              [(rng-id ...) (values/drop (rng-proj-x rng-id) ...)]
+                                              [args 
+                                               (bad-number-of-results blame f 
+                                                                      #,(length (syntax->list #'(rng-id ...)))
+                                                                      args)]))]
                       [rng-length (length (syntax->list rng))])
                   (if rst
                       (check-tail-contract #'(rng-proj-x ...) rng-checkers

collects/tests/racket/contract-test.rktl

@@ -3578,6 +3578,16 @@
             (f 'x (open-input-string (format "~s" "string")))))
    (list #\a #f "xstring"))
   
+  (test/pos-blame
+   'contract-case->15
+   '((contract (case-> (-> real? real? real?)
+                       (-> real? (values real? real?)))
+               (case-lambda
+                 [(x y) 1]
+                 [(x) 1])
+               'pos 'neg)
+     1))
+
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   ;;                                                        ;;
   ;;   case-> arity checking tests                          ;;