$candidate_agent_ids Agents offering this start. * @param array $busy_counts Agent id => booking count in range. * @param array $round_robin_state Mutable state bag for strategies. */ public function choose( array $candidate_agent_ids, array $busy_counts, array &$round_robin_state ): int { unset( $busy_counts ); sort( $candidate_agent_ids ); $idx = $round_robin_state['idx'] ?? 0; $choice = $candidate_agent_ids[ $idx % count( $candidate_agent_ids ) ]; $round_robin_state['idx'] = $idx + 1; return $choice; } }