The title for your submission should be a Show HN:

Interesting point about the problem of HN's depth-first comment structure. It feels like perhaps HN should collapse sub-comments by default to encourage more breadth. Perhaps collapse by default at the 2nd level.

Your approach to solving that is an interesting UX idea but even with the basic understanding the comments are sorted by their levels, it wasn't very obvious how to navigate the app. I kinda expected to be able to easily scroll across all level 1 comments (whether scrolling vertically or horizontally).

I was also surprised that the first comment was already pre-selected, and that level 2 comments were only for the selected comment. You could require new users to click on a comment first before expanding to show the level 2 comments, gives them an opportunity to learn the relationship between the two.

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This is a great tool to avoid the constant de-railing of headline topics which is the biggest bane of HN. Too often serious news falls victim to misdirection ... which requires time spent poking endless hyphenated closures to work past. It'd be great to see this solution embedded at the end of each headline.

I've been noodling on this for a few years now but have procrastinated on trying to build something similar. Surprised there aren't more platforms that use breadth-first navigation or provide it as an option.