/**
 * Load a prompt from a file path. Supports .md and .txt files.
 * Paths are sandboxed to basePath (or cwd) — traversal outside is rejected.
 *
 * @param promptFilePath - Path to the prompt file (relative to basePath; absolute paths are rejected)
 * @param basePath - Base directory for resolving relative paths (defaults to cwd)
 * @returns The file contents as a string, or null if the file doesn't exist or path escapes the sandbox
 */
export declare function loadPromptFile(promptFilePath: string, basePath?: string): string | null;