WIP: bytecode when/do/perform — host-callback _driveAsync fix + debugging

Root cause identified: nested cek_call_or_suspend calls on same VM
overwrite pending_cek. First call suspends (thunk's hs-wait), second
call from synchronous dom-listen callback overwrites before resume.

sandbox host-callback: removed _driveAsync call to prevent duplicate
resume chains. Still 3/6 in Node.js test — issue is in OCaml call
stack nesting, not JS async.

Next: prevent pending_cek overwrite in nested CEK→VM→CEK→VM chains.

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

hosts/ocaml/lib/sx_vm.ml

@@ -952,7 +952,14 @@ let () = _vm_suspension_to_dict := (fun exn ->
     Hashtbl.replace d "__vm_suspended" (Bool true);
     Hashtbl.replace d "request" request;
     Hashtbl.replace d "resume" (NativeFn ("vm-resume", fun args ->
-      match args with [result] -> resume_vm vm result | _ -> Nil));
+      match args with
+      | [result] ->
+        (try resume_vm vm result
+         with exn2 ->
+           match !_vm_suspension_to_dict exn2 with
+           | Some marker -> marker
+           | None -> raise exn2)
+      | _ -> Nil));
     Some (Dict d)
   | _ -> None)
 let () = _cek_eval_lambda_ref := (fun f args ->