/**
 * Codex (OpenAI Responses) SSE usage tap.
 *
 * The Codex proxy engine relays `upstream.body` to the client untouched and
 * logs before a single byte is read, so no Codex request has ever carried token
 * counts. This module adds a pass-through tap that scrapes `usage` out of the
 * stream without holding back or altering any bytes.
 *
 * ## Safety contract
 *
 * This sits in the hot path of a live proxy, so it is built to be incapable of
 * breaking a stream:
 *
 * - every chunk is enqueued **before** it is inspected;
 * - all parsing runs inside try/catch, and a throw is swallowed;
 * - a stream whose shape is unrecognised resolves `usage` to `null`, which is
 *   exactly today's behaviour (a log with no token fields).
 *
 * The worst case is therefore "no tokens recorded", never a truncated or
 * corrupted response.
 *
 * ## Wire shape
 *
 * **Verified against real traffic.** Captured from a live `codex exec` run
 * through the proxy on 2026-08-21; the trimmed sample is at
 * `test/fixtures/codex-response-usage.sse` and is asserted against in the
 * codex suite. The real shape is
 *
 *   event: response.completed
 *   data: {"type":"response.completed","response":{"usage":{
 *     "input_tokens":N,"output_tokens":M,
 *     "input_tokens_details":{"cached_tokens":K,"cache_write_tokens":W},
 *     "output_tokens_details":{"reasoning_tokens":R}}}}
 *
 * Note that `response.created` arrives first carrying `usage: null`, which is
 * why the scanner keeps the last non-null result rather than the first.
 *
 * It also accepts a `usage` object at the top level of any event and the
 * `prompt_tokens`/`completion_tokens` spellings. A `null` result means "not
 * observed", never "zero tokens".
 */
import type { CodexStreamUsage, CodexStreamEvidence } from "../types/index.js";
/**
 * Pull usage out of one parsed SSE `data:` payload.
 *
 * Returns null when the payload carries no recognisable usage object, so the
 * caller can keep the last non-null result rather than overwriting it with a
 * later event that happens not to carry usage.
 */
export declare function extractCodexUsage(payload: unknown): CodexStreamUsage | null;
/**
 * Scan a slice of SSE text for usage, returning the last one found.
 *
 * Exported for tests: it is the whole parsing decision, and driving it through
 * a real Codex stream would need a live ChatGPT subscription.
 */
export declare function scanCodexSSEForUsage(text: string): CodexStreamUsage | null;
/**
 * A pass-through TransformStream that reports the usage seen on a Codex SSE
 * stream.
 *
 * `usage` resolves when the stream ends: to the last usage observed, or null if
 * none was. It never rejects.
 */
export declare function createCodexUsageTap(): {
    stream: TransformStream<Uint8Array, Uint8Array>;
    usage: Promise<CodexStreamUsage | null>;
    evidence: () => CodexStreamEvidence;
};