Old arXiv submissions (e.g. legacy math/* papers) are served as a bare gzipped .tex rather than a .tar.gz, which tarfile.open rejected with 'invalid header'. Fall back to gunzipping the body directly when the tar parse fails, so R-C covers those papers too (recovers math/0001176 + math/0306167). Adds a regression test. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>