/**
 * Merges two string arrays with priority-based ordering and duplicate removal.
 *
 * This function is used when merging object property keys in JSON schema,
 * preserving the order of important properties defined in the schema while including additional properties.
 *
 * @param preferredKeys - Array of keys to be placed first (order is preserved)
 * @param keys - Array of additional keys to merge
 * @returns Array of keys with duplicates removed and sorted by priority
 *
 * @example
 * ```ts
 * orderedMerge(['name', 'email'], ['id', 'name', 'phone'])
 * // Result: ['name', 'email', 'id', 'phone']
 * ```
 *
 * @performance
 * - Time complexity: O(n) for large arrays, O(n²) for small arrays (optimized)
 * - Space complexity: O(n)
 * - Hybrid approach: linear search for <20 elements, Set-based for >=20 elements
 * - Optimized for array sizes: 100~1000 elements
 */
export declare const orderedMerge: (preferred: readonly string[], source: readonly string[]) => string[];