/**
 * GUID helpers for OOXML.
 *
 * Office parts that need stable cross-reference ids (threaded comments,
 * chart uniqueIds, slicer caches, …) use the canonical Microsoft
 * `{XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX}` format — 32 uppercase hex
 * characters split into 8-4-4-4-12 groups, surrounded by braces.
 *
 * `synthGuid()` returns an RFC-4122 version-4-compatible value suitable
 * for those callers. We don't use `crypto.randomUUID()` directly because
 * it isn't available in every supported runtime (older Node without
 * `node:crypto` globals); `Math.random` is good enough for uniqueness
 * within a single workbook, which is the only thing Office cares about.
 */
export declare function synthGuid(): string;