[s30] step 1 — subscribe ai:bob on node-2 (ns_pattern=test/S30/20260503132246-4566/**)
[s30] step 2 — alice notifies bob from node-1
[s30]   bob notif_id=<none>
[s30] step 4 — HMAC-signed webhook delivery
[s30]   charlie sub_id=<none>
[s30]   charlie notif_id=<none>
[s30] step 5 — federation fanout (notify@node-1 → subscriber@node-3)