[
  {
    "type": "alter_table",
    "description": "Add unique constraint on userId+deviceId for upsert support",
    "database": "kiosk_users",
    "check_query": "SELECT 1 FROM information_schema.TABLE_CONSTRAINTS WHERE TABLE_SCHEMA = 'kiosk_users' AND TABLE_NAME = 'userDeviceTokens' AND CONSTRAINT_NAME = 'uk_userId_deviceId'",
    "sql": "ALTER TABLE `userDeviceTokens` ADD UNIQUE KEY `uk_userId_deviceId` (`userId`, `deviceId`)"
  }
]