Put assertion-struct and message-struct back.

syndicate-examples/box-and-client.rkt

@@ -1,8 +1,8 @@
 #lang syndicate
 ;; Simple mutable box and count-to-infinity box client.
 
-(struct set-box (new-value) #:prefab)
-(struct box-state (value) #:prefab)
+(message-struct set-box (new-value))
+(assertion-struct box-state (value))
 
 (module+ main
   (actor-system/dataspace (ds)

syndicate/main.rkt

@@ -3,12 +3,21 @@
 (provide (all-from-out "actor.rkt")
          (all-from-out "syntax.rkt")
          (all-from-out preserves)
+
+         assertion-struct
+         message-struct
+
          :pattern
          :template)
 
 (require (except-in "actor.rkt" actor-system))
 (require "syntax.rkt")
 (require preserves)
+
+;; Thin veneers over `struct` for declaring intent.
+(define-syntax-rule (assertion-struct item ...) (struct item ... #:prefab))
+(define-syntax-rule (message-struct item ...) (struct item ... #:prefab))
+
 (require (only-in "pattern.rkt" :pattern :template))
 
 (module reader syntax/module-reader syndicate/lang)