Add graph.citing_coverage() (papers with >=1 out-edge / total) and a graph_min_citing_coverage setting (default 0.8). codex graph report now surfaces 'Citing coverage: N/M papers with out-edges (P%)' in text and JSON, and warns when the share is below threshold -- low citing coverage starves PageRank/coupling even when the paper count looks healthy (the DQ-1 sub-item). Separate from the existing total-count graph_min_corpus_size warning.
Tests: citing_coverage unit tests + CLI tests (line shown, warning fires/suppressed, JSON field). Full suite green; ruff + mypy clean. Live: graph report shows 29/29 (100%), no warning.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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