It was a calibration ghost from an earlier firmware iteration. The SR1 update had improved much, but it had introduced a scheduler jitter on rare sequences. Marta wrote a corrective patch, tested it against a simulated workload, and queued the update. She felt the familiar blend of fatigue and satisfaction as she initiated the upload and watched Bart accept the change. The machine rebooted, and when it came back online, its diagnostics read cleaner than they'd ever been.