GROBID extracts a cited DOI verbatim from PDF reference text, so it can be mixed-case, a https://doi.org/ URL, or doi:-prefixed. The PDF citation branch inserted it unchanged, while every other path (S2 supplement, OpenAlex, papers.id itself) uses the bare lower-cased DOI. Once R-A runs GROBID reference extraction over arXiv PDFs, those un-normalized cited-ids would never equal a bare-lowercase papers.id/cited_id — dangling the cross-citations and splitting one reference into case-/URL-variant graph nodes.
Extend _norm_cited_id to strip https://doi.org//http://doi.org//doi: prefixes and lower-case (mirroring openalex._normalize_doi), making it the single canonical cited-id normalizer, and route the GROBID branch through it. arXiv ids and S2 paperIds still pass through untouched.
Add test_ingest_pdf_grobid_citations_normalize_doi covering mixed-case, URL-form, and doi:-prefixed DOIs plus an arXiv-only ref.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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