revised: payment strategy

Signed-off-by: Kenneth Obsequio <k80308392@gmail.com>

database/migrations/20270101000075-add-user-tiers-active-per-tier-unique-index.js

@@ -0,0 +1,24 @@
+'use strict';
+
+// Backstop for the stacked-tier model: application code now enforces "at most
+// one active row per (user_id, tier)" (see controllers/client/tiers.controller.js
+// createOrder/captureOrder and controllers/admin/tiers.controller.js grantTier),
+// but a race or a future code path could still violate it. This partial unique
+// index makes the DB reject that case outright instead of silently allowing two
+// active rows for the same user+tier.
+//
+// NOT auto-run — this file only defines the migration. Do not execute it against
+// the shared dev/prod database without explicit confirmation.
+module.exports = {
+  async up(queryInterface) {
+    await queryInterface.addIndex('user_tiers', ['user_id', 'tier'], {
+      unique: true,
+      where: { status: 'active' },
+      name: 'user_tiers_one_active_per_user_tier',
+    });
+  },
+
+  async down(queryInterface) {
+    await queryInterface.removeIndex('user_tiers', 'user_tiers_one_active_per_user_tier');
+  },
+};