Function countMessagesTokens

packages/node-runtime/src/ai/tokenizer.ts:79–97

(
  messages: Array<{ role: string; content: string }>,
  systemPrompt?: string,
)

 * 每条消息额外计 4 tokens 的格式开销（role + 分隔符）。
 */
export function countMessagesTokens(
  messages: Array<{ role: string; content: string }>,
  systemPrompt?: string,
): number {
  let total = 0

  if (systemPrompt) {
    total += countTokens(systemPrompt) + 4
  }

  for (const msg of messages) {
    total += countTokens(msg.content) + 4
  }

  // 回复引导 token
  total += 3

  return total
}