Atomic “Read + Mark Processed” with UPDATE … RETURNING

                  class OutboxClaimer
  SQL = <<~SQL
    UPDATE outbox_events
    SET status = 1, locked_at = NOW()
    WHERE id = (
      SELECT id
      FROM outbox_events
      WHERE status = 0
      ORDER BY id ASC
      FOR UPDATE SKIP LOCKED
      LIMIT 1
    )
    RETURNING *;
  SQL

  def claim
    row = ApplicationRecord.connection.exec_query(SQL).first
    row && OutboxEvent.instantiate(row)
  end
end