The 409 on a tx/rx definition now recommends encoding direction in the BPF
(e.g. icmp[icmptype]==8) as the primary fix, with per-link markers as the
single-link fallback. Doc updated: per-def rejects tx/rx (why + BPF), the
pause section no longer claims bpf changes reset+reapply (they rebuild one
filter), and a new Capture files section covers pcap cleanup + reset-preserves-mark.
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