Revert cek_run import patch — caused infinite CEK loop on server

The cek_run import handling (resume after hook loads library) caused
cek_step_loop to infinite-loop during aser page rendering. Root cause
not yet identified — the resumed CEK state never reaches terminal.

Reverted to original cek_run that throws "IO suspension in non-IO
context". The 4 server startup errors are harmless (files load
partially, all needed symbols available via other paths).

Import hook re-entry guard and debug logging retained for future work.

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

hosts/ocaml/bin/sx_server.ml

@@ -794,16 +794,28 @@ let () =
         Hashtbl.replace _shared_vm_globals name v)
 
 (* Import hook — resolves (import ...) suspensions inside eval_expr/cek_run.
-   Loads the .sx file for the library, registers it, and returns true. *)
+   Loads the .sx file for the library, registers it, and returns true.
+   Re-entry guard prevents infinite loops from circular or failing imports. *)
+let _loading_libs : (string, bool) Hashtbl.t = Hashtbl.create 8
 let () =
   Sx_types._import_hook := Some (fun lib_spec ->
     if Sx_types.sx_truthy (Sx_ref.library_loaded_p lib_spec) then true
-    else match resolve_library_path lib_spec with
+    else
+    let key = Sx_types.inspect lib_spec in
+    if Hashtbl.mem _loading_libs key then false  (* already loading — break cycle *)
+    else begin
+    Hashtbl.replace _loading_libs key true;
+    let result = match resolve_library_path lib_spec with
       | Some path ->
-        (try load_library_file path;
-          true
-         with _ -> false)
-      | None -> false)
+        (try load_library_file path; true
+         with e ->
+          Printf.eprintf "[import-hook] FAIL %s from %s: %s\n%!"
+            key path (Printexc.to_string e);
+          false)
+      | None -> false in
+    (* Don't remove — keep as "attempted" guard to prevent retries *)
+    result
+    end)
 
 let make_server_env () =
   let env = make_env () in