convert.py walks pdfs/ (recursing topic subfolders), mirrors a .md tree
into md/ via pymupdf4llm, idempotent on mtime. Detects no-text-layer PDFs
(needs-ocr.txt) and falls back to plain per-page text when pymupdf4llm's
layout pass returns near-empty despite a real text layer.
Pin pymupdf4llm==0.3.4 (lightweight line; 1.27.x bundles an ML/OCR
pipeline that fails on plain text PDFs). PDFs gitignored (copyrighted,
large) — only generated markdown is committed.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
