Function addCacheControlToLastContentPart

src/common/utils/ai/cacheStrategy.ts:52–83

* Add providerOptions to the last content part of a message. * The SDK requires providerOptions on content parts, not on the message itself. * * For system messages with string content, we use message-level providerOptions * (which the SDK handles correctly). For user/assistant messages with arr

(
  msg: ModelMessage,
  cacheTtl?: AnthropicCacheTtl | null
)

 * content, we add providerOptions to the last content part.
 */
function addCacheControlToLastContentPart(
  msg: ModelMessage,
  cacheTtl?: AnthropicCacheTtl | null
): ModelMessage {
  const cacheOpts = cacheTtl ? anthropicCacheControl(cacheTtl) : ANTHROPIC_CACHE_CONTROL;
  const content = msg.content;

  // String content (typically system messages): use message-level providerOptions
  // The SDK correctly translates this for system messages
  if (typeof content === "string") {
    return {
      ...msg,
      providerOptions: cacheOpts,
    };
  }

  // Array content: add providerOptions to the last part
  // Use type assertion since we're adding providerOptions which is valid but not in base types
  if (Array.isArray(content) && content.length > 0) {
    const lastIndex = content.length - 1;
    const newContent = content.map((part, i) =>
      i === lastIndex ? { ...part, providerOptions: cacheOpts } : part
    );
    // Type assertion needed: ModelMessage types are strict unions but providerOptions
    // on content parts is valid per SDK docs
    const result = { ...msg, content: newContent };
    return result as ModelMessage;
  }

  // Empty or unexpected content: return as-is
  return msg;
}

/**
 * Apply cache control to messages for Anthropic models.