I too, like the idea of “TW Desktop Agent” to overcome the sandbox limitation of browsers, and think it’s worth discussing. The term “Desktop Agent” is so apt, I am going to steal it !
“I then asked an AI about how to replicate this functionality with a NodeJs TW, and It recommended to install a TW desktop agent in my computer so it acts as a bridge between the browsed TW and the OS.”
I’m not a TW node.js user, but I believe if node.js is your desktop, then node.js is capable of the Desktop Agent role i.e. receive commands from frontend TW instance to launch desktop file or interface with backend storage solution etc. But if it’s anything like my other experiences with TW, this was probably already done a decade back, became a norm, people move on and you can’t find any trace of it on a new forum like talk.tiddlywiki.org 
I did test a proof-of-concept of TW Desktop Agent and shared at https://talk.tiddlywiki.org/t/exploring-tw-desktop-integration-using-tm-http-request. This is meant to be just a small tool to allow TW’s TM-HTTP-REQUEST to inform the desktop agent to perform (via user scripts) those desktop tasks that the TW frontend cannot.
I didn’t work on it since. I think the utility will be more obvious if I have made the demo a TW desktop file browser that can launch files at where the desktop agent is planted. However, that will need more time. For now, I’m just collecting info. Today, I read that Android’s Tasker app is not an Android TV app, but it can be sideloaded on Android TV and use, with some difficulties. Tasker supports the XML-HTTP-REQUEST protocol used in TM-HTTP-REQUEST so there is that slim, slim possibility of controlling your Android TV from TW using TW desktop agent