arXiv detection for library papers, whose source_id keeps the "arxiv:" namespace (unlike search results' stripped ids — those use isArxivId). Prefix only: PROVIDER defaults to "arxiv" on legacy rows, so paper.source can't answer this.
arXiv detection for library papers, whose source_id keeps the "arxiv:" namespace (unlike search results' stripped ids — those use isArxivId). Prefix only: PROVIDER defaults to "arxiv" on legacy rows, so paper.source can't answer this.