You can now use the
$app: metafield namespace prefix in Shopify Functions input queries to ensure your app's ownership of metafields used in your function.
We recommend use of reserved prefixes by default for all functions, so that you can control access to metafields used by your function. By default, they will be private to your app.
Learn more about metafield ownership and using metafields with input queries on Shopify.dev.