We will want a registry in the BucketCatalog (most likely owned by a Stripe) to keep track of buckets we are fetching. When we add a bucket to the registry, it should be keyed by _id and store and a promise which other threads can wait on if they are interested in fetching the same bucket to avoid duplicate work. The initial thread should be able to either report an error and abort the fetch, or report success and provide the fetched bucket.