/**
 * Checks if a value is a plain object.
 *
 * @param value - The value to check
 * @returns True if the value is a plain object
 */
export declare function isPlainObject(value: unknown): value is Record<string, unknown>;
/**
 * Deep merge utility for configuration objects.
 * Recursively merges nested objects while preserving function references.
 *
 * This implementation includes protections against:
 * - Circular references (using path-based WeakSet tracking)
 * - Prototype pollution (skipping dangerous keys)
 * - Non-plain object corruption (only merging plain objects)
 * - Stack overflow from deep nesting (depth limit)
 * - Array reference sharing (shallow copying arrays)
 *
 * Note on Arrays:
 * Arrays are shallow copied. Objects inside arrays are shared by reference.
 * If you need deep cloning of array elements, this utility does not support it.
 *
 * Note on null/undefined:
 * - `undefined` values in source are skipped (target value preserved).
 * - `null` values in source overwrite target values.
 *
 * Note on Special Objects:
 * - `Object.create(null)` objects are treated as plain objects and merged.
 * - Symbol properties are ignored (as Object.keys is used).
 *
 * @param target - Target object
 * @param source - Source object to merge from
 * @param seen - Set of objects in the current recursion path to detect cycles
 * @param depth - Current recursion depth
 * @returns Merged object
 */
export declare function deepMerge<T extends Record<string, unknown>>(target: T, source: Partial<T>, seen?: WeakSet<object>, depth?: number): T;
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