chunk() reconstructs Chunk objects before _split_oversized/_as_dicts and
was dropping page_number on the floor, so every chunk came out NULL
regardless of what chunk_statute computed. Also flip _as_dicts to prefer
the caller-supplied c.page_number (derived from the chunk's starting
offset) over any marker that survived inside c.content — the latter can
resolve to a later page when a section spans pages.
Verified: ספר הליקויים chunks now carry page_number matching the PDF
page where each section actually begins.
Refs Task Master #2
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
chaim
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