setChannelOperator method
Makes agentId the fixed operator of channelId (mode: agent), or lets the channel
inherit the default of its space again for null.
Implementation
void setChannelOperator(String channelId, String? agentId) {
final c = channels[channelId]!;
c.json['operator'] = agentId == null
? _inheritOperator(c.spaceId!)
: {'mode': 'agent', 'agent_id': agentId, 'effective_agent_id': agentId};
}