/**
 * @name observability/metrics
 * @description Process-local Prometheus metrics for SAP MCP Server.
 *
 * The exporter is opt-in and VPS-only: it starts only when `enableMetrics` is
 * true in the server config (default false). On local user deployments metrics
 * stay disabled, preserving the current optional behavior. Tool-call counters
 * are incremented from the central `tools/call` handler in `sdk-compat.ts`
 * regardless of whether the HTTP exporter is running, but the recording is a
 * no-op until `initMetrics` is called, so there is zero overhead when disabled.
 *
 * Metrics exposed on the `/metrics` endpoint (Prometheus text format):
 *   - sap_mcp_tool_calls_total{tool,status}        counter
 *   - sap_mcp_tool_call_duration_seconds{tool}     histogram (bucketed)
 *   - sap_mcp_tool_calls_in_flight                 gauge
 *   - sap_mcp_requests_total{endpoint,status}      counter
 *   - sap_mcp_uptime_seconds                       gauge
 *
 * @module observability/metrics
 */
/**
 * @name initMetrics
 * @description Enables metric collection. Safe to call multiple times; the first
 *   call records the baseline start time.
 */
export declare function initMetrics(): void;
/**
 * @name isMetricsEnabled
 * @description Reports whether metric collection is active.
 */
export declare function isMetricsEnabled(): boolean;
/**
 * @name recordToolCall
 * @description Records a completed tool invocation. No-op when metrics are disabled.
 *
 * @param tool      — Canonical tool name.
 * @param durationMs — Call duration in milliseconds.
 * @param ok        — Whether the call returned without throwing.
 */
export declare function recordToolCall(tool: string, durationMs: number, ok: boolean): void;
/**
 * @name recordRequest
 * @description Records an inbound HTTP request (MCP endpoint, landing, well-known).
 *
 * @param endpoint — Logical endpoint label.
 * @param status   — HTTP status class (`ok` | `error`).
 */
export declare function recordRequest(endpoint: string, status: 'ok' | 'error'): void;
/**
 * @name trackInFlight
 * @description Increments the in-flight gauge on call start and decrements on finish.
 */
export declare function trackInFlight(delta: number): void;
/**
 * @name renderMetrics
 * @description Serializes the current metric state in Prometheus text exposition format.
 */
export declare function renderMetrics(): string;
/**
 * @name startMetricsExporter
 * @description Starts the Prometheus `/metrics` HTTP exporter on the given port.
 *
 * The exporter is independent of the MCP HTTP server so it can bind a dedicated
 * scrape port (default 9090) without affecting the MCP endpoint. Returns the
 * created HTTP server, or `null` when metrics are disabled.
 *
 * @param port — TCP port for the `/metrics` endpoint.
 */
export declare function startMetricsExporter(port: number): import('http').Server | null;
/**
 * @name stopMetricsExporter
 * @description Stops a previously started metrics exporter server.
 */
export declare function stopMetricsExporter(server: import('http').Server | null): void;
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