Flatten multi-file arXiv LaTeX (\input/\include) in arxiv.fetch_source so the full body is assembled rather than just the primary file's include skeleton, and add section-aware chunking (tex.chunk_sections) so .tex chunks never span a \section boundary and are labelled by their real heading. The ingest .tex path now produces (section, chunk) pairs, quality-gated together so labels stay aligned; the stored 'section' column gains genuine signal instead of mostly 'body' (serves DQ-3 fidelity + audit R-12).
Adds scripts/rc_tex_reingest.py to re-ingest arXiv papers from .tex (dry-run by default; replaces chunks). Tests: flatten_inputs, chunk_sections, multi-file fetch_source, section-label ingest, is_arxiv_id. Full suite 365 passed; ruff + mypy clean.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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