Tried to make low/typed-untyped-module.rkt tests for require/provide run. In the end the error was just due to https://github.com/racket/typed-racket/issues/228, upgrading to a newer build of Racket fixed this. Added a couple of typed/untyped utilities in the process.

graph/graph/_examples_differentiate_unions.rkt

@@ -1,4 +1,4 @@
-#lang typed/racket
+#lang typed/racket/no-check
 
 
 #;(λ ([x : (U (Vector Number) (Vector String String))])

graph/lib/low-untyped.rkt

@@ -11,10 +11,10 @@
 (require (for-syntax racket/base))
 
 (include/reader "low.rkt" (λ (source-name in)
-                            (port-count-lines! in)
-                            (do ()
-                              [(let-values ([(line column position)
-                                             (port-next-location in)])
-                                 (> line 1))]
-                              (read-line in))
-                            (read-syntax source-name in)))
+                              (port-count-lines! in)
+                              (do ()
+                                [(let-values ([(line column position)
+                                               (port-next-location in)])
+                                   (> line 1))]
+                                (read-line in))
+                              (read-syntax source-name in)))

graph/lib/low.rkt

@@ -6,6 +6,47 @@
 
 ;; ==== low/typed-untyped-module.rkt ====
 
+(require typed/untyped-utils)
+(provide half-typed-module typed/untyped-prefix define-modules)
+
+;; half-typed-module
+(define-syntax-rule (typed-module m typed-language untyped-language . body)
+  (module m typed-language . body))
+
+(define-syntax-rule (untyped-module m typed-language untyped-language . body)
+  (module m untyped-language . body))
+
+(define-typed/untyped-identifier half-typed-module typed-module untyped-module)
+
+#| ;; test: should work in no-check but not in typed:
+(half-typed-module moo typed/racket typed/racket/no-check
+  (: foo One)
+  (define foo 2))
+|#
+
+;; typed/untyped-prefix
+(define-syntax-rule
+  (typed-typed/untyped-prefix [typed-prefix ...] [untyped-prefix ...] . rest)
+  (typed-prefix ... . rest))
+
+(define-syntax-rule
+  (untyped-typed/untyped-prefix [typed-prefix ...] [untyped-prefix ...] . rest)
+  (untyped-prefix ... . rest))
+
+(define-typed/untyped-identifier typed/untyped-prefix
+  typed-typed/untyped-prefix
+  untyped-typed/untyped-prefix)
+
+#|
+;; test: should work in no-check but not in typed:
+(typed/untyped-prefix
+ [module moo2 typed/racket]
+ [module moo2 typed/racket/no-check]
+ (: foo One)
+ (define foo 2))
+|#
+
+;; define-modules
 (define-syntax define-modules
   (syntax-rules (no-submodule)
     [(_ ([no-submodule] [name lang] ...) . body)
@@ -29,6 +70,7 @@
 |#
 
 ;; ==== low/require-provide.rkt ====
+
 (provide require/provide)
 
 (define-syntax (require/provide stx)