/** Accept an exact-key SWR payload from older consumers without weakening tagged chat isolation. */
export function canvasHistoryForChat<T>(
  payload: { chatId?: string; messages: T[] } | undefined,
  chatId: string,
): { messages: T[] } | undefined {
  if (!payload || !chatId || !Array.isArray(payload.messages)) return undefined;
  if (payload.chatId !== undefined && payload.chatId !== chatId) return undefined;
  return payload;
}