M9: add a `TODO(P2/P3)` comment near the NULL persistence at
documents.rs (put_chunks). The `section_label` column exists in the §5.5
DDL but neither the in-memory Chunk struct nor the §2.6 wire schema
carries the field, so NULL is the correct canonical value today —
flag the future-bump intent in-line rather than leaving it implicit.
M10: add a one-line invariant comment near the i64 -> u32 narrowing for
`doc_version` in `get_document`. The invariant is documented at the
write site (UPSERT bumps by 1 per re-ingest) — restate it at the read
site so the cast is not silently load-bearing.
No behaviour change. No tests touched.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>