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

ast.go

@@ -108,7 +108,7 @@ func (self *ast) Eval(ctx ExprContext) (result any, err error) {
 	self.Finish()
 
 	if self.root != nil {
-		initDefaultVars(ctx)
+		// initDefaultVars(ctx)
 		if self.forest != nil {
 			for _, root := range self.forest {
 				if result, err = root.compute(ctx); err == nil {