Function joinTextAtSeam

src/utils/messages.ts:2505–2515

* Concatenate two content block arrays, appending `\n` to a's last text block * when the seam is text-text. The API concatenates adjacent text blocks in a * user message without a separator, so two queued prompts `"2 + 2"` + * `"3 + 3"` would otherwise reach the model as `"2 + 23 + 3"`. * * Blo

(
  a: ContentBlockParam[],
  b: ContentBlockParam[],
)

 * when b is an SR-wrapped attachment.
 */
function joinTextAtSeam(
  a: ContentBlockParam[],
  b: ContentBlockParam[],
): ContentBlockParam[] {
  const lastA = a.at(-1)
  const firstB = b[0]
  if (lastA?.type === 'text' && firstB?.type === 'text') {
    return [...a.slice(0, -1), { ...lastA, text: lastA.text + '\n' }, ...b]
  }
  return [...a, ...b]
}

type ToolResultContentItem = Extract<
  ToolResultBlockParam['content'],