Fix last test: unify scope stacks between test runner and evaluator

run_tests.ml had a local _scope_stacks hash table, separate from
Sx_primitives._scope_stacks used by the CEK evaluator. SX-level
scope-push!/scope-peek used the local table, but step-sf-context's
scope_peek used the global one. Aser's provide handler pushed to
one table, context read from the other — always got nil.

Fix: alias run_tests.ml's _scope_stacks to Sx_primitives._scope_stacks.

2768/2768 OCaml tests pass. Zero failures.

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

hosts/ocaml/bin/run_tests.ml

@@ -332,9 +332,10 @@ let make_test_env () =
       let result = eval_expr (List [Symbol "aser"; expr; Env e]) (Env e) in
       (match result with SxExpr s -> String s | String s -> String s | _ -> String (Sx_runtime.value_to_str result))
     | _ -> String "");
-  (* Scope primitives — use a local scope stacks table.
-     Must match the same pattern as sx_server.ml's _scope_stacks. *)
-  let _scope_stacks : (string, Sx_types.value list) Hashtbl.t = Hashtbl.create 8 in
+  (* Scope primitives — share the same scope stacks as sx_primitives.ml
+     so that CEK evaluator's scope_push/scope_peek and SX-level scope-push!/scope-peek
+     operate on the same table. *)
+  let _scope_stacks = Sx_primitives._scope_stacks in
   bind "scope-push!" (fun args ->
     match args with
     | [String name; value] ->
@@ -1382,6 +1383,7 @@ let run_spec_tests env test_files =
       | Some (Lambda _ as fn) -> Sx_ref.cek_call fn (List args)
       | _ -> String "")));
 
+  
   let files = if test_files = [] then begin
     (* Spec tests (core language — always run) *)
     let spec_entries = Sys.readdir spec_tests_dir in