A by-digest pull leaves the image carrying every digest it was pulled under, so reading RepoDigests[0] reported a healthy pinned image as wrong and refused a window that was ready to run. Membership, not position. Also records the measured step optimum: 106 tok/s at an 8,192-token step against 76 at 16,384 on a 32,768 calibration window, so the wide step has a ceiling, not a plateau.