Function find 

pub async fn find(
    doi: &Doi,
    crossref_message: &Value,
    enabled: &MetadataAccess,
    ctx: &FetchContext,
) -> Result<Option<Found>, FetchError>

Look for a preprint of doi: Crossref’s relation, then OpenAlex (when openalex_enabled), then arXiv’s search. crossref_message is the record the fetch already holds.

Errors

A provenance-log failure only; a request that fails is a method that found nothing, and the next is tried.