diff --git a/hosts/ocaml/lib/sx_primitives.ml b/hosts/ocaml/lib/sx_primitives.ml
index 15a64de7..6ebc6ed4 100644
--- a/hosts/ocaml/lib/sx_primitives.ml
+++ b/hosts/ocaml/lib/sx_primitives.ml
@@ -99,6 +99,8 @@ let rec to_string = function
   | RawHTML s -> s
   | v -> inspect v
 
+let gensym_counter = ref 0
+
 let () =
   (* === Arithmetic === *)
   register "+" (fun args ->
@@ -2118,6 +2120,7 @@ let () =
     match v with
     | Nil -> List []
     | List _ -> v
+    | ListRef { contents = items } -> List items
     | Vector arr -> List (Array.to_list arr)
     | String s ->
       let chars = ref [] in
@@ -2197,4 +2200,29 @@ let () =
         if (step > 0 && i >= hi) || (step < 0 && i <= hi) then acc
         else build (i + step) (Integer i :: acc) in
       List (List.rev (build lo []))
-    | _ -> raise (Eval_error "in-range: expected (end) or (start end) or (start end step)"))
+    | _ -> raise (Eval_error "in-range: expected (end) or (start end) or (start end step)"));
+  (* === gensym + symbol interning === *)
+  register "gensym" (fun args ->
+    let prefix = match args with
+      | [] -> "g"
+      | [String s] -> s
+      | [Symbol s] -> s
+      | _ -> raise (Eval_error "gensym: expected optional prefix string") in
+    incr gensym_counter;
+    Symbol (prefix ^ string_of_int !gensym_counter));
+  register "string->symbol" (fun args ->
+    match args with
+    | [String s] -> Symbol s
+    | _ -> raise (Eval_error "string->symbol: expected 1 string"));
+  register "symbol->string" (fun args ->
+    match args with
+    | [Symbol s] -> String s
+    | _ -> raise (Eval_error "symbol->string: expected 1 symbol"));
+  register "intern" (fun args ->
+    match args with
+    | [String s] -> Symbol s
+    | _ -> raise (Eval_error "intern: expected 1 string"));
+  register "symbol-interned?" (fun args ->
+    match args with
+    | [Symbol _] -> Bool true
+    | _ -> raise (Eval_error "symbol-interned?: expected 1 symbol"))
diff --git a/hosts/ocaml/lib/sx_ref.ml b/hosts/ocaml/lib/sx_ref.ml
index 6327d635..545ddea7 100644
--- a/hosts/ocaml/lib/sx_ref.ml
+++ b/hosts/ocaml/lib/sx_ref.ml
@@ -29,6 +29,7 @@ let seq_to_list v =
   match v with
   | Nil -> List []
   | List _ -> v
+  | ListRef { contents = items } -> List items
   | Vector arr -> List (Array.to_list arr)
   | String s ->
     let chars = ref [] in
diff --git a/plans/agent-briefings/primitives-loop.md b/plans/agent-briefings/primitives-loop.md
index 5ffe2568..226f5895 100644
--- a/plans/agent-briefings/primitives-loop.md
+++ b/plans/agent-briefings/primitives-loop.md
@@ -362,11 +362,18 @@ Primitives to add:
   the explicit interning operation for languages that distinguish interned vs uninterned)
 
 Steps:
-- [ ] Spec: add `gensym` counter to evaluator state; implement in `spec/evaluator.sx`.
+- [x] Spec: add `gensym` counter to evaluator state; implement in `spec/evaluator.sx`.
       `string->symbol` already exists — `gensym` is just a counter-suffixed variant.
-- [ ] OCaml: add global gensym counter; implement primitives.
-- [ ] JS bootstrapper: implement.
-- [ ] Tests: 15+ tests in `spec/tests/test-gensym.sx` — uniqueness, prefix, symbol?, string->symbol round-trip.
+      Added *gensym-counter*/gensym/string->symbol/symbol->string/intern/symbol-interned? to
+      evaluator.sx. Added string->symbol/symbol->string transpiler renames + platform.py aliases.
+      JS 2186/+1. OCaml builds. Committed edf4e525.
+- [x] OCaml: add global gensym counter; implement primitives.
+      gensym_counter ref + gensym/string->symbol/symbol->string/intern/symbol-interned? in sx_primitives.ml.
+      Also fixed ListRef case in seq_to_list (both sx_ref.ml + sx_primitives.ml). 4431/1080 (was 4385/1080).
+- [x] JS bootstrapper: implement.
+      Already done in Spec step. JS 2186/2497, all sequence tests pass.
+- [x] Tests: 15+ tests in `spec/tests/test-gensym.sx` — uniqueness, prefix, symbol?, string->symbol round-trip.
+      19 tests. OCaml 4450/1080, JS 2205/2497, zero regressions.
 - [ ] Commit: `spec: gensym + symbol interning`
 
 ---
diff --git a/spec/tests/test-gensym.sx b/spec/tests/test-gensym.sx
new file mode 100644
index 00000000..4b85995f
--- /dev/null
+++ b/spec/tests/test-gensym.sx
@@ -0,0 +1,78 @@
+(defsuite
+  "gensym"
+  (deftest "gensym returns a symbol" (assert= true (symbol? (gensym))))
+  (deftest
+    "gensym default prefix is g"
+    (let
+      ((s (symbol-name (gensym))))
+      (assert= true (string-contains? s "g"))))
+  (deftest
+    "gensym with prefix uses that prefix"
+    (let
+      ((s (symbol-name (gensym "var"))))
+      (assert= "var" (substring s 0 3))))
+  (deftest
+    "gensym produces unique symbols"
+    (let
+      ((a (gensym)) (b (gensym)))
+      (assert= false (= (symbol-name a) (symbol-name b)))))
+  (deftest
+    "gensym same prefix produces unique symbols"
+    (let
+      ((a (gensym "x")) (b (gensym "x")) (c (gensym "x")))
+      (assert= false (= (symbol-name a) (symbol-name b)))
+      (assert= false (= (symbol-name b) (symbol-name c)))))
+  (deftest
+    "gensym counter increases: names differ"
+    (let
+      ((a (gensym "k")) (b (gensym "k")))
+      (assert= false (= (symbol-name a) (symbol-name b)))))
+  (deftest
+    "gensym no-arg and prefix-arg both unique"
+    (let
+      ((a (gensym)) (b (gensym "g")))
+      (assert= false (= (symbol-name a) (symbol-name b)))))
+  (deftest
+    "string->symbol returns a symbol"
+    (assert= true (symbol? (string->symbol "hello"))))
+  (deftest
+    "string->symbol symbol has correct name"
+    (assert= "hello" (symbol-name (string->symbol "hello"))))
+  (deftest
+    "string->symbol empty string"
+    (assert= true (symbol? (string->symbol ""))))
+  (deftest
+    "symbol->string returns a string"
+    (assert= true (string? (symbol->string (quote foo)))))
+  (deftest
+    "symbol->string round-trips with string->symbol"
+    (assert= "hello" (symbol->string (string->symbol "hello"))))
+  (deftest
+    "string->symbol/symbol->string round-trip"
+    (let
+      ((sym (string->symbol "my-var")))
+      (assert= "my-var" (symbol->string sym))))
+  (deftest
+    "intern returns a symbol"
+    (assert= true (symbol? (intern "foo"))))
+  (deftest
+    "intern same as string->symbol"
+    (assert= "bar" (symbol-name (intern "bar"))))
+  (deftest
+    "symbol-interned? true for literal symbols"
+    (assert= true (symbol-interned? (quote hello))))
+  (deftest
+    "symbol-interned? true for gensym'd symbol"
+    (assert= true (symbol-interned? (gensym "g"))))
+  (deftest
+    "symbol-interned? true for string->symbol"
+    (assert= true (symbol-interned? (string->symbol "test"))))
+  (deftest
+    "multiple gensym calls all unique"
+    (let
+      ((syms (map (fn (i) (gensym "t")) (in-range 5))))
+      (let
+        ((names (map symbol-name syms)))
+        (let
+          ((unique-names (reduce (fn (acc n) (if (some (fn (x) (= x n)) acc) acc (cons n acc))) (list) names)))
+          (assert-equal 5 (len unique-names)))))))