spec: sets (make-set/set-add!/set-member?/union/intersection/etc)

Adds 13 set primitives to stdlib.sets. OCaml: SxSet as (string,value)
Hashtbl keyed by inspect(val); JS: SxSet wrapping Map keyed by
write-to-string. Structural equality — (make-set '(1 2)) contains 1.
Includes union, intersection, difference, for-each, map.
33 tests in test-sets.sx, all pass on both JS and OCaml.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

spec/primitives.sx

@@ -1116,3 +1116,83 @@
   :doc "Denominator of rational r (after reduction, always positive).")
 
 (define-module :stdlib.hash-table)
+
+(define-module :stdlib.sets)
+
+(define-primitive
+  "make-set"
+  :params (&rest (lst :as list))
+  :returns "set"
+  :doc "Create a fresh empty set. Optional list argument seeds the set: (make-set '(1 2 3)).")
+
+(define-primitive
+  "set?"
+  :params (v)
+  :returns "boolean"
+  :doc "True if v is a set.")
+
+(define-primitive
+  "set-add!"
+  :params (s val)
+  :returns "nil"
+  :doc "Add val to set s in place. No-op if already present.")
+
+(define-primitive
+  "set-member?"
+  :params (s val)
+  :returns "boolean"
+  :doc "True if val is in set s.")
+
+(define-primitive
+  "set-remove!"
+  :params (s val)
+  :returns "nil"
+  :doc "Remove val from set s in place. No-op if absent.")
+
+(define-primitive
+  "set-size"
+  :params (s)
+  :returns "integer"
+  :doc "Number of elements in set s.")
+
+(define-primitive
+  "set->list"
+  :params (s)
+  :returns "list"
+  :doc "All elements of set s as a list (unspecified order).")
+
+(define-primitive
+  "list->set"
+  :params (lst)
+  :returns "set"
+  :doc "Create a new set containing all elements of lst.")
+
+(define-primitive
+  "set-union"
+  :params (s1 s2)
+  :returns "set"
+  :doc "New set with all elements from s1 and s2.")
+
+(define-primitive
+  "set-intersection"
+  :params (s1 s2)
+  :returns "set"
+  :doc "New set with elements present in both s1 and s2.")
+
+(define-primitive
+  "set-difference"
+  :params (s1 s2)
+  :returns "set"
+  :doc "New set with elements in s1 that are not in s2.")
+
+(define-primitive
+  "set-for-each"
+  :params (s fn)
+  :returns "nil"
+  :doc "Call (fn val) for each element in set s. Order unspecified.")
+
+(define-primitive
+  "set-map"
+  :params (s fn)
+  :returns "set"
+  :doc "New set of results of (fn val) for each element in s.")