visualize_chunk re-expanded chunks from scratch to recover their refs,
which could not faithfully reproduce the original merge, scores, and
clip — so a visualization could highlight different pages than the
citation covered. Carry the cited items on Citation.doc_item_refs and
resolve bounding boxes from them directly; re-expansion remains only as
the fallback for callers with no stored context (CLI, inspector). Chat,
inspector, the app endpoint, and the frontend pass the refs through.
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