Word assignment: Replace nearest-center-distance with containment-first
strategy. Words whose center falls within a column's bounds (+ 15% pad)
are assigned to that column before falling back to nearest-center. This
fixes long example sentences losing their rightmost words to adjacent
columns.
LLM review: Strengthen prompt to explicitly forbid changing proper nouns,
place names, and correctly-spelled words. Add _is_spurious_change()
post-filter that rejects case-only changes and hallucinated word
replacements (< 50% character overlap).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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