Segment text into sentences — robust to the classic traps: abbreviations (Dr., e.g.), decimals ($3.14), URLs/emails (www.x.com), initials (J. R. R.) and ellipses. A period is a boundary only when followed by whitespace and a sentence-like start; !, ? and … are stronger; blank lines split paragraphs. Rule-based (EN/FR tuned), deterministic. A fine-grained chunking primitive, complements /v1/chunk. Over 1 MB truncated.