/**
 * Surrogate-pair-aware UTF-16 boundary snaps. Port of transponder's
 * text-boundary.mjs. Never cut between a high surrogate (U+D800–U+DBFF) and
 * its low pair (U+DC00–U+DFFF). Sufficient to keep well-formed UTF-16; not a
 * full grapheme-cluster segmenter (Intl.Segmenter would be heavier for these
 * hot tail paths).
 */
/**
 * Snap an inclusive start index left so `s.slice(start)` never begins on a
 * lone low surrogate. Prefer including the full pair over dropping a fragment.
 */
export declare function snapStartInclusive(s: string, start: number): number;
/**
 * Tail slice of at most `cap` UTF-16 units, never starting mid-pair.
 * May keep `cap+1` when the cut would split a surrogate pair (include the high).
 */
export declare function sliceTailSafe(s: string, cap: number): string;