When the responses endpoint fails and execution falls back to
chat.completions, only the first image in a batch can be forwarded
(chat.completions accepts a single image_url per message in this
implementation). Previously extra frames were silently dropped.
Now we record batch_size before entering the fallback and append a plain-
language warning to fallback_reason when batch_size > 1, so the status
preview shown in ComfyUI makes the degradation explicit.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
