import { MessageObject } from '../types/memory.js';

/**
 * Flattens a stored message's content into prompt text.
 *
 * `MessageContentObject.parts` is `unknown[]` and its shape depends on
 * `content.type` — `"text"` holds plain strings, while `"rich"`/`"document"`
 * hold {@link MessagePart} OBJECTS. Model providers must never hand one of
 * those objects to a chat API as `content`: OpenAI-compatible endpoints reject
 * the whole request with `400 Invalid type for 'messages[N].content'`, which
 * breaks every later turn in the thread because the message is persisted.
 *
 * Document parts render as a short label only. The body is not inlined here —
 * `injectAttachedDocuments` resolves it to fresh text once per turn, so
 * embedding a (possibly stale) copy per history entry would duplicate it.
 *
 * Total function: returns `""` for empty, unknown or malformed content rather
 * than leaking a non-string value.
 */
declare function messageToPromptText(message: MessageObject): string;

export { messageToPromptText };