/**
 * Parse an ISO timestamp string. Returns null for null/undefined input or
 * an unparseable value rather than throwing — callers can fall back.
 */
export declare function parseIsoDateOrNull(value?: string | null): Date | null;
/**
 * Compare two ISO timestamp strings descending. Null/undefined values sort
 * last regardless of order. Used for ProjectChat list ordering and latest
 * conversation selection.
 */
export declare function compareIsoDesc(a?: string | null, b?: string | null): number;
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