/**
 * Minimal leveled logger that writes to **stderr only**.
 *
 * On the stdio transport, stdout is reserved for the MCP JSON-RPC stream —
 * anything written there corrupts the protocol. Every diagnostic in this
 * server therefore goes through here, which is hard-wired to stderr.
 *
 * The sink is injectable so the bootstrap and tests can capture output without
 * touching the real `process.stderr`.
 */
import { LOG_LEVELS, type TwinklyMcpConfig } from './config.js';
export type LogLevel = (typeof LOG_LEVELS)[number];
/** Where a logger writes a finished line. Defaults to `process.stderr`. */
export type LogSink = (line: string) => void;
export interface Logger {
    error(message: string, ...rest: unknown[]): void;
    warn(message: string, ...rest: unknown[]): void;
    info(message: string, ...rest: unknown[]): void;
    debug(message: string, ...rest: unknown[]): void;
}
/**
 * Create a logger that emits at or below `level`. `sink` is injectable for
 * tests; production passes the default stderr sink.
 */
export declare function createLogger(level: TwinklyMcpConfig['logLevel'], sink?: LogSink): Logger;