Update: I think I found a decent way to do it. Please tell me if and where I'm being senseless:
<div class="custom-start-conversation-button">
<a class="lia-button lia-button-primary" href="/t5/forums/postpage/board-id/${coreNode.id}forum-board">Start a Discussion</a>
</div>I'd call that "hacky" but also "good enough". It's a bit fragile, but for what you're trying to do, it will work.
The "right" way, would be to make a LiQL call to get the list of child boards, constrained to forum, and then get the id of the forum.
You could add some logic around the button too to show it as disabled or hidden if the user isn't logged in or not a member of the grouphub, or also hide the button if the component is placed outside of a grouphub.
