/**
 * Single-line JSON logger to stderr.
 *
 * Both transports use stderr for diagnostics:
 *   - stdio: stdout is the protocol channel — anything else corrupts framing.
 *   - http : stderr keeps logs out of HTTP responses and lines them up with
 *            `fly logs` (Fly captures both streams; stderr is the convention).
 *
 * Every line is redacted with `redactApiKeys` before write — bearers must
 * never reach disk. Keep the schema additive: consumers parse line-by-line
 * and tolerate extra fields, so adding new keys is non-breaking.
 */
/** Fields the caller fills in on every log line. */
export interface LogInput {
    /** Logical event name — `http_request`, `stdio_start`, `tool_error`, … */
    event: string;
    /** Optional caller-supplied timestamp; otherwise we set it. */
    ts?: string;
    /** HTTP status code, when applicable. */
    status?: number;
    /** Wall-clock duration in milliseconds. */
    duration_ms?: number;
    /** JSON-RPC method extracted from the request body, if any. */
    mcp_method?: string;
    /** Tool name when `mcp_method === "tools/call"`. */
    tool?: string;
    /** `MCP-Protocol-Version` header from the request. */
    mcp_protocol_version?: string;
    /** Inbound `User-Agent` header. */
    client_user_agent?: string;
    /** Upstream `X-Request-Id`, captured from the Meertrack client when available. */
    meertrack_request_id?: string;
    /** Free-form message for human readers (still redacted). */
    message?: string;
    /** Anything else worth tagging — kept open-ended on purpose. */
    [extra: string]: unknown;
}
export type LogSink = (line: string) => void;
/** Default sink: stderr, newline-terminated. */
export declare const defaultSink: LogSink;
export declare class Logger {
    private readonly sink;
    constructor(sink?: LogSink);
    log(record: LogInput): void;
}
/** Process-wide default. Tests can construct their own with a custom sink. */
export declare const logger: Logger;
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