Enable wait_for_changes on yet-to-be-present metadata.
On https://cloud.google.com/compute/docs/metadata, under "Waiting for updates", it is described that you may do a hanging wait for changes to the metadata server by appending the query parameter ?waitforchange=true. This works if the metadata is modified, but does not work to wait for the creation of metadata. Instead, you must resort to polling for changes on a loop.
Thanks, we’ll look into this.