perf: sync protocol and core hardening updates

deploy/migrations/0063_channel_update_retention.down.sql

@@ -0,0 +1,19 @@
+-- Once a retained floor advances, channel_update_events below it are physically gone.  Dropping
+-- the checkpoint would make an old client pts look like an ordinary empty difference and silently
+-- lose the required channelDifferenceTooLong recovery boundary.  Refuse that irreversible down.
+DO $$
+BEGIN
+    IF EXISTS (
+        SELECT 1
+        FROM public.channel_update_checkpoints
+        WHERE retained_through_pts > 0
+    ) THEN
+        RAISE EXCEPTION
+            'cannot roll back channel update retention: retained floor has advanced'
+            USING ERRCODE = '55000';
+    END IF;
+END
+$$;
+
+DROP INDEX IF EXISTS public.channel_update_events_retention_seek_idx;
+DROP TABLE IF EXISTS public.channel_update_checkpoints;