Stub VM uses real globals for CEK resume after IO suspension

The _cek_io_suspend_hook creates a stub VM to carry the suspended CEK
state. Previously used empty globals, which caused "Not callable: nil"
when the CEK resume needed platform functions. Now uses _default_vm_globals
(set to _vm_globals by sx_browser.ml) so all platform functions and
definitions are available during resume.

Remaining issue: still getting "resume: Not callable: nil" — the CEK
continuation env may not include letrec bindings from the island body.
The suspension point is inside reload-frame → hs-wait, and the resume
needs to call wait-boot (a letrec binding).

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

hosts/ocaml/browser/sx_browser.ml

@@ -237,6 +237,7 @@ let return_via_side_channel (v : Js.Unsafe.any) : Js.Unsafe.any =
    VmClosures from bytecode modules hold vm_env_ref pointing here.
    Must stay in sync so VmClosures see post-boot definitions. *)
 let _vm_globals : (string, value) Hashtbl.t = Hashtbl.create 512
+let () = Sx_types._default_vm_globals := _vm_globals
 let _in_batch = ref false
 
 (* Sync env→VM: copy all bindings from global_env.bindings to _vm_globals.

hosts/ocaml/lib/sx_types.ml

@@ -258,6 +258,10 @@ let _cek_io_resolver : (value -> value -> value) option ref = ref None
     to convert CEK suspensions to VmSuspended for _driveAsync handling. *)
 let _cek_io_suspend_hook : (value -> value) option ref = ref None
 
+(** Default VM globals for stub VMs created during IO suspension.
+    Set by sx_browser.ml to _vm_globals so CEK resume can access platform functions. *)
+let _default_vm_globals : (string, value) Hashtbl.t ref = ref (Hashtbl.create 0)
+
 (** Hook: convert VM suspension exceptions to CekPerformRequest.
     Set by sx_vm after it defines VmSuspended. Called by sx_runtime.sx_apply_cek. *)
 let _convert_vm_suspension : (exn -> unit) ref = ref (fun _ -> ())

hosts/ocaml/lib/sx_vm.ml

@@ -1027,7 +1027,7 @@ let () = _vm_suspension_to_dict := (fun exn ->
    gets swallowed as "IO suspension in non-IO context". *)
 let () = _cek_io_suspend_hook := Some (fun suspended_state ->
   let request = Sx_ref.cek_io_request suspended_state in
-  let vm = create (Hashtbl.create 0) in
+  let vm = create !_default_vm_globals in
   vm.pending_cek <- Some suspended_state;
   raise (VmSuspended (request, vm)))