Machine-readable status of a generation that returned "pending". Returns status (queued, running, done, failed, not_found), progress (0 to 1, null when unknown), eta_seconds, and next_check_seconds while it runs; the asset links (viewer_url, glb_url, poster_png_url, embed_html) when done; and a plain error with a remedy when it failed. Safe to call on a schedule: it never starts work and is not counted against the generation quota. Use this to poll a pending job from code or a loop; call check_job with the same job_id when you want the finished model rendered in the inline viewer.