/**
 * Friendly-error sentinel for CLI UX.
 *
 * `UserError` marks errors that are caused by user configuration / input
 * problems (missing env var, malformed flag value, etc.). The CLI catch
 * handler at the bottom of `src/cli/index.ts` checks `instanceof UserError`
 * and prints `obsidian-brain: <message>` without a stack trace, instead of
 * the noisy "CLI error: Error: …" + full stack the default path produces.
 *
 * Internal / programmer errors (anything NOT a UserError) keep printing
 * the full stack so bugs remain debuggable.
 *
 * Optional `hint` is an additional one-line tip appended to the message —
 * useful for "did you mean X?" or "see `--help` for valid values".
 */
export declare class UserError extends Error {
    readonly hint?: string;
    constructor(message: string, options?: {
        hint?: string;
    });
}
/**
 * Format a UserError for stderr output. Used by the CLI catch handler so
 * the exact wording stays consistent across entry-points (the bin shim,
 * `npm run cli`, direct `tsx src/cli/index.ts`).
 */
export declare function formatUserError(err: UserError): string;