HS: fix IO suspension via _cek_io_suspend_hook (workaround cek_run resume bug)

cek_run's resolver → cek_resume doesn't propagate values correctly
(likely a kont frame ordering issue in the transpiled evaluator).
Workaround: use _cek_io_suspend_hook which receives the suspended
state and manually steps to completion, handling further suspensions.

- resolve_io: shared function for IO resolution (sleep, fetch, etc.)
- Suspend hook: manual step loop after cek_resume, handles nested IO
- run_with_io: uses req_list extraction (handles ListRef)
- Fixes fetch tests: 10 now pass (response format correct)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hosts/ocaml/bin/run_tests.ml

@@ -2149,16 +2149,19 @@ let run_spec_tests env test_files =
     Hashtbl.replace mock_body "textContent" (String "");
     Nil);
 
-  (* IO suspension resolver — handles perform/wait/fetch in event handlers.
-     Requests come as Lists: ("op-name" arg1 arg2 ...) or Dicts with "op" key *)
-  Sx_types._cek_io_resolver := Some (fun request _suspended ->
-    let op, args = match request with
-      | List (String op :: rest) -> op, rest
-      | Dict d ->
-        let op = match Hashtbl.find_opt d "op" with Some (String s) -> s | _ -> "" in
-        let a = match Hashtbl.find_opt d "args" with Some (List l) -> l | _ -> [] in
-        op, a
-      | _ -> "", []
+  (* IO resolution function — used by both run_with_io and _cek_io_suspend_hook *)
+  let resolve_io request =
+    let req_list = match request with List l -> l | ListRef { contents = l } -> l | _ -> [] in
+    let op, args = match req_list with
+      | String op :: rest -> op, rest
+      | Symbol op :: rest -> op, rest
+      | _ ->
+        (match request with
+         | Dict d ->
+           let op = match Hashtbl.find_opt d "op" with Some (String s) -> s | _ -> "" in
+           let a = match Hashtbl.find_opt d "args" with Some (List l) -> l | _ -> [] in
+           op, a
+         | _ -> "", [])
     in
     match op with
     | "io-sleep" | "io-wait" | "io-settle" | "io-wait-for" -> Nil
@@ -2178,7 +2181,32 @@ let run_spec_tests env test_files =
          Hashtbl.replace resp "text" (String body);
          Dict resp
        | _ -> String body)
-    | _ -> Nil);
+    | _ -> Nil
+  in
+
+  (* Use suspend hook (not resolver) — cek_run's resume has a propagation bug.
+     The hook receives the suspended state and must return the final value. *)
+  Sx_types._cek_io_resolver := None;
+  Sx_types._cek_io_suspend_hook := Some (fun suspended ->
+    let request = Sx_ref.cek_io_request suspended in
+    let response = resolve_io request in
+    (* Resume by manually stepping from the resumed state *)
+    let resumed = Sx_ref.cek_resume suspended response in
+    let is_terminal st = match Sx_ref.cek_terminal_p st with Bool true -> true | _ -> false in
+    let is_suspended st = match Sx_runtime.get_val st (String "phase") with String "io-suspended" -> true | _ -> false in
+    let s = ref resumed in
+    while not (is_terminal !s) && not (is_suspended !s) do
+      (try s := Sx_ref.cek_step !s
+       with Sx_types.CekPerformRequest req ->
+         let resp = resolve_io req in
+         s := Sx_ref.cek_resume (Sx_ref.make_cek_suspended req (Sx_ref.cek_env !s) (Sx_ref.cek_kont !s)) resp)
+    done;
+    if is_suspended !s then
+      let req2 = Sx_ref.cek_io_request !s in
+      let resp2 = resolve_io req2 in
+      Sx_ref.cek_value (Sx_ref.cek_resume !s resp2)
+    else
+      Sx_ref.cek_value !s);
 
   (* Load modules needed by tests *)
   let spec_dir = Filename.concat project_dir "spec" in
@@ -2417,32 +2445,6 @@ let run_spec_tests env test_files =
      code-from-value, and other late-bound functions must be visible. *)
   !_jit_refresh_globals ();
 
-  (* Rebind try-call to use eval_with_io for IO-aware test execution *)
-  ignore (Sx_types.env_bind env "try-call" (NativeFn ("try-call", fun args ->
-    match args with
-    | [thunk] ->
-      Sx_ref.step_limit := 0;
-      Sx_ref.step_count := 0;
-      (try
-        ignore (eval_with_io (List [thunk]) (Env env));
-        Sx_ref.step_limit := 0;
-        let d = Hashtbl.create 2 in
-        Hashtbl.replace d "ok" (Bool true);
-        Dict d
-      with
-      | Eval_error msg ->
-        Sx_ref.step_limit := 0;
-        let d = Hashtbl.create 2 in
-        Hashtbl.replace d "ok" (Bool false);
-        Hashtbl.replace d "error" (String msg);
-        Dict d
-      | exn ->
-        Sx_ref.step_limit := 0;
-        let d = Hashtbl.create 2 in
-        Hashtbl.replace d "ok" (Bool false);
-        Hashtbl.replace d "error" (String (Printexc.to_string exn));
-        Dict d)
-    | _ -> raise (Eval_error "try-call: expected 1 arg"))));
 
   List.iter (fun path ->
     if Sys.file_exists path then begin