/**
 * Multimodal image attachments on user messages (pearl th-25ce5c).
 *
 * All the logic lives here; the agent's body-assembly sites call {@link userContent}
 * once each, so this can land alongside the other workstreams on that same line.
 */
/**
 * An image attachment on a user message. `url` is a `data:` URL
 * (`data:image/png;base64,...`) or a remote `https` URL; `detail`
 * (`"low"`/`"high"`/`"auto"`) is an optional OpenAI vision hint, omitted when unset.
 */
export interface ImageContent {
    url: string;
    detail?: string;
}
/**
 * One part of an OpenAI multimodal `content` array.
 *
 * The `type` discriminator is REQUIRED on every part and is load-bearing beyond
 * this module: prompt caching (`cacheControl.ts`) decides whether it may wrap a
 * message's content by scanning parts for a `type` that isn't `"text"`. Drop it
 * and that guard fails open — cache_control flattens the parts into a text block
 * and the images vanish silently.
 */
export type ContentPart = {
    type: 'text';
    text: string;
} | {
    type: 'image_url';
    image_url: {
        url: string;
        detail?: string;
    };
};
/**
 * Build a user message's wire `content`: an OpenAI content-parts array when the
 * turn carries images (text part first — omitted when the text is empty, since
 * images may be sent alone — then one `image_url` part per image, in order),
 * otherwise the plain string every turn has always sent.
 *
 * No images ⇒ the exact input string, so every text-only turn stays
 * byte-identical to before this existed.
 */
export declare function userContent(text: string, images?: readonly ImageContent[]): string | ContentPart[];
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