Skip JIT for lambdas with closure bindings

The closure merging in jit_compile_lambda (copying globals + injecting
closure bindings into vm_env_ref) produces incorrect variable resolution
for inner functions. Symptoms: sx-parse's read-list-loop mishandles
closing parens (siblings become children), parser produces wrong ASTs.

Fix: vm_call skips JIT compilation for lambdas with non-empty closures.
These run on CEK which handles closures correctly. Top-level defines
(empty closure) are still JIT-compiled.

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

hosts/ocaml/lib/sx_vm.ml

@@ -327,7 +327,13 @@ and vm_call vm f args =
        (* Compile failed — CEK *)
        push vm (Sx_ref.cek_call f (List args))
      | None ->
-       if l.l_name <> None then begin
+       if l.l_name <> None
+          (* Skip JIT for lambdas with closure bindings — the closure
+             merging into vm_env_ref produces incorrect variable resolution
+             for inner functions (e.g. parser's read-list-loop). *)
+          && Hashtbl.length l.l_closure.bindings = 0
+          && l.l_closure.parent = None
+       then begin
          (* Pre-mark before compile attempt to prevent re-entrancy *)
          l.l_compiled <- Some jit_failed_sentinel;
          match !jit_compile_ref l vm.globals with