/**
 * Helpers for PromptPart handling.
 *
 * prompt_parts is an alternative to the prompt field on TextTextParams,
 * allowing structured parts with optional cache hints for providers that
 * support server-side prompt caching (e.g., Anthropic).
 */
import type { PromptPart } from './types.js';
/**
 * Concatenate prompt_parts into a single string.
 * Used as a fallback for providers that don't natively support prompt_parts.
 * Parts are joined with a newline separator.
 */
export declare function parts_to_prompt(parts: PromptPart[]): string;
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