NAK=69/~1060 lamp commands explains the observed stuck-bright/missed
lamps (fire-and-forget writes turn each corrupt 4-byte burst into a
visible state error) while 2-byte traffic is pristine (analog 88.1%,
counters flat, zero wedges, worst gap 0.14s). The HC11 RX ISR's worst
path sits right at ~320 E-cycles. Ladder: 9600 production, 31250v2
CLEAN (FastRIO), 62500 needs host NAK-retransmit, 125000 CPU-walled.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>