/**
 * Is a provider's response envelope structurally usable by the response mappers?
 *
 * Moved out of `backend.ts` unchanged (HOTSPOT-10). The bodies below are byte-identical to the
 * ones that lived there; only the two names `backend.ts` still calls became exports.
 *
 * ⚠ It answers about FORM, never about content: whether the discriminator the mapper switches on
 * is present and carries the field that discriminator promises. That is the same side of the
 * repair boundary as the tool-call validator — the relay never judges what a model said, only
 * whether the shape it arrived in can be read.
 *
 * ⚠ This module imports `isRecord` and nothing else. Keep it that way: it sits beneath the
 * transport it validates for, and a dependency pointing back at `backend.js` would be a cycle.
 */
export type ResponseProtocol = "openai-chat" | "anthropic-messages" | "openai-responses";
/**
 * Validate only the protocol structure the response mappers rely on. Optional identifiers,
 * model names and usage remain optional because several compatible providers legitimately omit
 * them; the required response discriminator must not be optional, or `{}` becomes a successful
 * empty assistant message.
 */
export declare function invalidEnvelopeReason(value: unknown, protocol: ResponseProtocol, streamed: boolean): string | null;