/**
 * Minimal, dependency-free magic-byte sniffer for the common upload types.
 * Content is the source of truth; the client-provided MIME is only a hint.
 *
 * This is intentionally self-contained (no `file-type` ESM dependency) so the core
 * builds as CommonJS and tests run offline. A richer detector can be plugged via
 * `FileValidatorService`'s `detector` option if a project needs exotic formats.
 */
export type MagicDetector = (buffer: Buffer) => string | null;
export declare const detectMime: MagicDetector;