Bulk-creates cards on one board. Use for new cards, not updates. Returns created[] with clientKey + the real id for a later connect pass; failed[] carries clientKey + title + reason. Pass type as a label ("Epic"); the tool resolves it. header is cosmetic and is not used to connect cards. One board per call. Max 40 cards per call — chunk larger sets and concatenate created[] before connecting. Partial success is normal: isError: false with some cards in failed[]. Cards in created[] already exist — NEVER resubmit those clientKeys. To complete a partial batch, resubmit only the failed[] (and any never-sent) cards. This applies to every partial result, not just retryAfter rate-limit cases. If retryAfter is set, wait that many seconds, then resubmit only the never-sent cards (not created[]). Never invent board, type, or lane ids. Attach to an existing parent with parentCards; otherwise create all cards first, then connect using the returned ids.