Control vars are now stored in the globalCtx only.

However, it is still allowed to store control var in a local context in special situation

operator-context.go

@@ -34,7 +34,8 @@ func evalContextValue(ctx ExprContext, self *term) (v any, err error) {
 		if formatter, ok := sourceCtx.(Formatter); ok {
 			v = formatter.ToString(0)
 		} else {
-			keys := sourceCtx.EnumVars(func(name string) bool { return name[0] != '_' })
+			// keys := sourceCtx.EnumVars(func(name string) bool { return name[0] != '_' })
+			keys := sourceCtx.EnumVars(nil)
 			d := make(map[string]any)
 			for _, key := range keys {
 				d[key], _ = sourceCtx.GetVar(key)