rig observations (buggy arm): payload bytes 1..31 remain 0xA5 after delivery of 1 byte; verbatim sbp_recv1 runs the
stale-driven debug prints and sbp_dequeue_ocb walk; kernel fault follows - but the SAME fault occurs with a zeroed
payload, so the fault is a rig artifact (fake firewire graph NULL), not the defect.
firewire module build with M_ZERO fix: BUILD OK.