1) The PG17 gating seems inconsistent between the dump and the check now. dumpReplicationOrigins() is called unconditionally:
if (binary_upgrade && archDumpFormat == archNull) dumpReplicationOrigins(conn);
but get_subscription_info(), which sets nrepl_origins, is still only called for old clusters >= 17 in check_new_cluster():
if (GET_MAJOR_VERSION(old_cluster.major_version) >= 1700) ... get_subscription_info(&old_cluster);
and check_new_cluster_replication_origins() returns early on it:
if (old_cluster.nrepl_origins == 0) return;
For a < 17 old cluster get_subscription_info() is never called, so nrepl_origins stays 0 and this returns early. So when such a cluster has a (user-created) origin, the origin still gets dumped and recreated, while the "new cluster must have no origins" and max_active_replication_origins checks are skipped, and the upgrade fails during restore instead of at the check step. nrepl_origins is just a count(*) on pg_replication_origin, so moving its collection out of the >= 1700 block should be enough.
2) 004_subscription.pl only checks subscription origins (pg_<oid>). Since the patch migrates all origins, should we also create a user origin (pg_replication_origin_create()) and verify its roident/remote_lsn after the upgrade? That would also cover the case in (1).
