fix: cascade channel_messages on packet delete

db/migrations/023_channel_messages_cascade.sql

@@ -0,0 +1,12 @@
+-- Copyright 2026 Beacon Contributors
+-- SPDX-License-Identifier: AGPL-3.0-or-later
+
+-- The packet_hash FK had no ON DELETE action, so packets carrying a channel
+-- message could never age out and DeleteOldPackets aborted. Match packet_observations.
+
+ALTER TABLE channel_messages
+  DROP CONSTRAINT IF EXISTS channel_messages_packet_hash_fkey;
+
+ALTER TABLE channel_messages
+  ADD CONSTRAINT channel_messages_packet_hash_fkey
+  FOREIGN KEY (packet_hash) REFERENCES packets(packet_hash) ON DELETE CASCADE;