Poll the status of a POST /open/v1/image-generations submission. Returns the same OpenImageGeneration shape — status is pending / processing / success / partial_success / failed, and image_ids populates once the request fans out into per-image tasks.

Polling cadence: poll every 2–5 seconds. The fan-out step typically completes in 5–15s; individual images then complete asynchronously over the next 15–60s each.

Terminal statuses: success (all images done), partial_success (some failed), failed (no images produced). Stop polling on any terminal state.

Use individual GET /open/v1/image-generations/{generation_id}/images/{image_id} calls to fetch each image's generated URL.

Returns: code=0 success; code=40001 invalid generation_id or workspace context missing; code=40401 when the generation does not belong to the caller's workspace; code=50001 when the upstream image-generation service is unavailable.