Not… really?
I’m kind of unclear what it is you are proposing?
It is obvious that replies are to the overall topic by default because the replies exist in the topic. So the only callout needed is in the case where a reply is specific to a particular post:
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the in-reply-to indicator (with the caveats around “one reply directly under” which is what the site setting is for, if you want that) which indicates the target post
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quotes of the target post
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@usernamementions which can imply a reply is to a person in general across the topic, e.g. “I want to address the points raised in the 5 posts@usernamemade in this topic..”