import type { IncomingHttpHeaders } from 'node:http';
/**
 * HTTP status codes that warrant retrying with the API key.
 *
 * 402 — Payment Required ("out of extra usage", subscription credits gone).
 * 403 — Forbidden (sometimes used for quota exhaustion).
 * 429 — Rate Limited (5h window cap).
 *
 * Intentionally excludes 5xx/529. Retrying a POST after an ambiguous server
 * failure can duplicate work/cost if the upstream already started processing.
 */
export declare function isRetryableStatus(code: number | undefined): boolean;
/**
 * Peek the first chunk of an SSE/JSON body to detect an Anthropic error
 * envelope (`{"type":"error", ...}` or `event: error\ndata: ...`).
 *
 * Anthropic sometimes returns HTTP 200 with an SSE stream whose first event
 * is an error (notably for `out of extra usage`). The proxy must look at
 * the body to know it's an error, not the status code.
 */
export declare function looksLikeErrorBody(head: string): boolean;
/** Strip `oauth-2025-04-20` from a comma-separated `anthropic-beta` value. */
export declare function stripOauthBeta(value: string): string;
/** Headers for a pass-through attempt: forwarded as-is, only `host` dropped. */
export declare function buildPassthroughHeaders(incoming: IncomingHttpHeaders): IncomingHttpHeaders;
/**
 * Headers for an API-key request: replaces OAuth auth with `x-api-key` and
 * strips `oauth-2025-04-20` from `anthropic-beta` so Anthropic bills credits.
 */
export declare function buildApiKeyHeaders(incoming: IncomingHttpHeaders, apiKey: string): IncomingHttpHeaders;