OP seems to be reading HN on the Kindle with a pay for subscription kindle app, that he sells. Via a free kindle to obsidian plug-in for obsidian, these are transferred into obsidian, which is a freemium knowledge management app.
Edit: I have added a sentence about the subscription details now.
Replicating the obsidian plug-in functionality to suit your own note/knowledge management app would be probably even easier.
What I don't like is the tagging part - kindles are terrible to type in. And if you want to avoid it by using your phone/tablet, you'd be better to avoid kindle app altogether and do the note taking using browser extension or something.
Did you get a chance to try the recent Kindle SW update(> v.5.13.7)? Performance has improved a lot, Tagging (Notes) is smooth due to a surprisingly responsive keyboard.
The browser is out of experminetal too.
I wrote this comment from a Kindle Oasis 9th gen.