[Fix] Stability

migrations/002_registration_leases.sql

@@ -0,0 +1,13 @@
+-- Registration IDs are allocated before the user row is created.  Keep the
+-- allocation durable and bound to the Iota that requested it so a completed
+-- registration can safely be retried after any response is lost.
+CREATE TABLE registration_leases (
+    token CHAR(36) CHARACTER SET ascii COLLATE ascii_bin NOT NULL PRIMARY KEY,
+    user_id BIGINT NOT NULL UNIQUE,
+    iota_id BIGINT NOT NULL,
+    expires_at DATETIME NOT NULL,
+    completed_at DATETIME NULL,
+    CONSTRAINT fk_registration_leases_iota
+        FOREIGN KEY (iota_id) REFERENCES iotas (id),
+    INDEX idx_registration_leases_expiry (expires_at)
+);