/**
 * Usage sink (ISP + DIP): the meter depends only on this one tiny method, so
 * swapping the JSONL file for a DB, HTTP endpoint, or UI stream later is a
 * one-class change with no meter or call-site edits.
 */
export interface UsageSink {
    /** Append one already-serialized record. Implementations must not throw. */
    write(line: string): void;
}
/**
 * Default sink: appends one JSONL line per event to
 * `<data>/logs/usage/usage-YYYYMMDD.jsonl` (one file per day). Best-effort —
 * any filesystem error is swallowed so telemetry never breaks a real call.
 */
export declare class JsonlUsageSink implements UsageSink {
    private readonly dir;
    /** Dirs already `mkdir`-ed this process, so we hit the FS once, not per write. */
    private readonly ensured;
    constructor(dir?: string);
    /** Create the target dir at most once per process; swallow any FS error. */
    private ensureDir;
    write(line: string): void;
}
//# sourceMappingURL=sink.d.ts.map