/**
 * backend-fetch — shared retry+timeout primitive for every PromQL-compatible
 * backend the MCP talks to.
 *
 * The single retry+timeout contract for metrics-backend.ts and
 * customer-metrics.ts, in place of per-backend bespoke `fetch(...)` blocks:
 *
 *   - Default 3 attempts (`LOG10X_RETRY_ATTEMPTS` override).
 *   - 250ms base backoff, exponential with jitter (`LOG10X_RETRY_BASE_MS`).
 *   - 30s per-attempt timeout via AbortController (`LOG10X_REQUEST_TIMEOUT_MS`).
 *   - Retry classes: network exception, HTTP 5xx, HTTP 429.
 *   - Timeout (AbortError) is NOT retried by default: re-issuing an identical
 *     query with an identical budget almost always times out again, so
 *     retrying a single slow read costs up to attempts×timeout (~90s) of
 *     wall-clock before failing. Set `LOG10X_RETRY_TIMEOUTS=true` (or
 *     opts.retryTimeouts) for retry-on-timeout — an escape hatch for
 *     cold-warmup self-hosted stores (e.g. Mimir/Cortex store-gateway lazy load).
 *   - Non-retryable: any other 4xx — surfaced immediately with kind-labelled body.
 *   - AMP path: `reSignPerAttempt` callback rebuilds the signed init each
 *     attempt so SigV4 timestamps stay fresh.
 *
 * Error envelope:
 *   `${kindLabel} HTTP <status> <statusText>: <body.slice(0,400)>`
 *   `${kindLabel}: request timed out after ${timeoutMs}ms`
 *   `${kindLabel}: fetch failed after ${attempts} attempts`
 *
 * Consumed by promJsonFetch (metrics-backend.ts) and all six customer-metrics
 * backends. tool-errors.ts widens its transient-failure regex to match these
 * error tails.
 */
export interface BackendFetchOpts {
    /** Short identifier for error envelopes + console.warn lines. */
    kindLabel: string;
    /** Per-attempt timeout. Defaults to LOG10X_REQUEST_TIMEOUT_MS or 30000. */
    timeoutMs?: number;
    /** Max attempts (1 = no retry). Defaults to LOG10X_RETRY_ATTEMPTS or 3. */
    attempts?: number;
    /** Exponential backoff base. Defaults to LOG10X_RETRY_BASE_MS or 250. */
    baseMs?: number;
    /**
     * Retry on timeout (AbortError). Defaults to false (fail fast on the first
     * timeout). Falls back to the LOG10X_RETRY_TIMEOUTS env flag when unset.
     * Network / 5xx / 429 retries are unaffected by this.
     */
    retryTimeouts?: boolean;
    /**
     * AMP-style: rebuild a freshly-signed init each attempt. When provided,
     * the caller-supplied `init` is ignored and replaced per attempt with
     * the return value of `reSignPerAttempt()`. The `signal` from the
     * per-attempt AbortController is merged in.
     */
    reSignPerAttempt?: () => Promise<RequestInit>;
}
/**
 * Core fetch primitive. Returns the Response on success (2xx). Throws on:
 *   - retryable exhaustion (5xx / 429 / network / timeout × attempts)
 *   - non-retryable 4xx (status < 500, status !== 429) — immediately.
 */
export declare function backendFetch(url: string, init: RequestInit, opts: BackendFetchOpts): Promise<Response>;
/**
 * JSON wrapper. Parses .json() on success. Error envelope on non-ok was
 * already thrown by backendFetch. Network/timeout failures bubble up
 * unchanged.
 */
export declare function backendJsonFetch<T>(url: string, init: RequestInit, opts: BackendFetchOpts): Promise<T>;