What data is embedded in chat_data parameter passed to chats and risk of removing it

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I'm trying to use some functionality I've developed that is being impeded by the fact that conditional chat link is passing a chat_data parameter to chat, and the existence of this parameter seems to override the Rule I use in my functionality. When it's present, the rule doesn't work.

In the bevy of documentation I can't find anything to tell me what the embedded chat_data contents drives or what impact it has upon the chat if I change the code to make the ignore_preroute default value to TRUE. We currently Product ID passed separately, and it should drive a rule that gets the chat to the right queue, so I'm just puzzled as to the purpose of this field.