ocaml: wire dynamic-wind through CEK — WindFrame + winders stack

- sx_types.ml: CallccContinuation gains winders depth int field
- sx_runtime.ml: make_callcc_continuation(captured, winders_len),
  callcc_continuation_winders_len accessor; get_val maps after-thunk,
  winders-len, body-result to cf_f/cf_extra/cf_name
- sx_ref.ml: step_limit/step_count restored; make_wind_after_frame and
  make_wind_return_frame now store their args in the CekFrame fields
- transpiler.sx: after-thunk→cf_f, winders-len→cf_extra,
  body-result→cf_name for future bootstrap runs
- 8 new dynamic-wind tests pass (OCaml), 235/235 no regressions

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

hosts/ocaml/lib/sx_runtime.ml

@@ -46,7 +46,7 @@ let sx_call f args =
     !Sx_types._cek_eval_lambda_ref f args
   | Continuation (k, _) ->
     k (match args with x :: _ -> x | [] -> Nil)
-  | CallccContinuation _ ->
+  | CallccContinuation (_, _) ->
     raise (Eval_error "callcc continuations must be invoked through the CEK machine")
   | _ ->
     let nargs = List.length args in
@@ -156,6 +156,9 @@ let get_val container key =
      | "extra" -> f.cf_extra | "extra2" -> f.cf_extra2
      | "subscribers" -> f.cf_results
      | "prev-tracking" -> f.cf_extra
+     | "after-thunk" -> f.cf_f        (* wind-after frame *)
+     | "winders-len" -> f.cf_extra    (* wind-after frame *)
+     | "body-result" -> f.cf_name     (* wind-return frame *)
      | _ -> Nil)
   | VmFrame f, String k ->
     (match k with
@@ -381,15 +384,20 @@ let continuation_data v = match v with
   | _ -> raise (Eval_error "not a continuation")
 
 (* Callcc (undelimited) continuation support *)
-let callcc_continuation_p v = match v with CallccContinuation _ -> Bool true | _ -> Bool false
+let callcc_continuation_p v = match v with CallccContinuation (_, _) -> Bool true | _ -> Bool false
 
-let make_callcc_continuation captured =
-  CallccContinuation (sx_to_list captured)
+let make_callcc_continuation captured winders_len =
+  let n = match winders_len with Number f -> int_of_float f | Integer n -> n | _ -> 0 in
+  CallccContinuation (sx_to_list captured, n)
 
 let callcc_continuation_data v = match v with
-  | CallccContinuation frames -> List frames
+  | CallccContinuation (frames, _) -> List frames
   | _ -> raise (Eval_error "not a callcc continuation")
 
+let callcc_continuation_winders_len v = match v with
+  | CallccContinuation (_, n) -> Number (float_of_int n)
+  | _ -> Number 0.0
+
 (* Dynamic wind — simplified for OCaml (no async) *)
 let host_error msg =
   raise (Eval_error (value_to_str msg))