fix substruct contract blame setup

closes #2093

pkgs/racket-test/tests/racket/contract/contract-out.rkt

@@ -1212,6 +1212,24 @@
       (eval '(dynamic-require ''provide/contract65-m2 #f)))
    "provide/contract65-m2")
 
+  (test/spec-failed
+   'provide/contract66
+   '(let ()
+      (eval '(module provide/contract66-m1 racket/base
+               (require racket/contract)
+               (provide f
+                        (contract-out
+                         (struct base ([f (-> number? boolean?)])
+                           #:omit-constructor)))
+               (struct base (f) #:transparent)
+               (define (f x) ((base-f x) #f))))
+      (eval '(module provide/contract66-m2 racket/base
+               (require 'provide/contract66-m1)
+               (struct derived base () #:transparent)
+               (f (derived (λ (x) #f)))))
+      (eval '(dynamic-require ''provide/contract66-m2 #f)))
+   "provide/contract66-m1")
+
   (contract-error-test
    'contract-error-test8
    #'(begin

racket/collects/racket/contract/private/provide.rkt

@@ -1186,7 +1186,8 @@
                [field-name (in-list field-names)])
       ((get/build-late-neg-projection ctc)
        (blame-add-context blame
-                          (format "the ~a field of" field-name)))))
+                          (format "the ~a field of" field-name)
+                          #:swap? #t))))
   (chaperone-struct-type
    struct-type
    (λ (a b c d e f g h) (values a b c d e f g h))