A 3D job waiting for the picture model to give up the one card had an empty
progress; its client could not tell waiting from stuck. The control plane
says which model holds the cards and when it lets go, plus the waiting
model's last start; the 503 carries it as headers, and a job keeps it as
progress {state: waiting_gpu, held_by, eta_seconds}.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
