[Fix] Stability

migrations/003_registration_lease_request_id.sql

@@ -0,0 +1,8 @@
+-- A relay retry uses the original MTP request ID.  Make allocation idempotent
+-- for that authenticated Iota/request pair, so a lost response returns the
+-- same user ID and lease rather than allocating another one.
+ALTER TABLE registration_leases
+    -- Existing leases predate retry correlation; leave their request ID NULL
+    -- rather than assigning a shared sentinel that could violate uniqueness.
+    ADD COLUMN request_id INT UNSIGNED NULL,
+    ADD CONSTRAINT uk_registration_leases_iota_request UNIQUE (iota_id, request_id);