/**
 * The MCP usage fold (DES-MCP-TOOLS-001 §7 Usage, §8 `GET /mcp/usage`; slice S7).
 *
 * A pure function over call records (`calls.ndjson`, written by the broker, S3): counts, the
 * decision split (allow / ask / deny / guard_error), the error rate and nearest-rank p50/p95/p99
 * over the calls that ran, a per-tool table, per-server totals, the tool × seat × run drill-down,
 * the common tool chains and one row per UTC day. Nothing is cached and no poller runs: every
 * `GET /mcp/usage` folds the records as they are on disk.
 */
import type { McpCallDecision, McpCallRecord, McpUsageChain, McpUsageResponse } from '../core/types.js';
export declare const MCP_USAGE_MAX_DAYS = 30;
export declare const MCP_USAGE_DEFAULT_DAYS = 7;
export declare const MCP_USAGE_DECISIONS: readonly McpCallDecision[];
export declare const MCP_USAGE_MAX_RUNS = 200;
export declare const MCP_USAGE_MAX_CHAINS = 20;
export interface McpUsageQuery {
    days?: number;
    subject?: string;
    seat?: string;
    decision?: McpCallDecision;
}
/** Nearest-rank percentile of ascending `sorted`: the value at position `ceil(q * n)`. */
export declare function nearestRank(sorted: readonly number[], q: number): number | null;
/** The tool chains of `records`: consecutive calls of one unit attempt, with different subjects. */
export declare function foldChains(records: readonly McpCallRecord[], subject?: string): McpUsageChain[];
/**
 * Fold `records` into the usage view for the last `days` × 24 h before `now`. `skipped` passes
 * through the count of lines the reader could not parse.
 */
export declare function foldMcpUsage(records: readonly McpCallRecord[], query: McpUsageQuery, now: number, skipped?: number): McpUsageResponse;
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