Best way for offline development

The copy pasting script is sometimes flaky (maybe there's a better more reliable way to inject the code?)

You can run the IDE and if you click the down-arrow next to the 'open file' button you can 'watch' a file - so when the file changes the IDE will automatically reload it and upload it.

running code on the watch over remote IDE only works online I guess?

Good question - it uses WebRTC which is peer to peer, but to establish that connection in the first place I think it needs a kind of broker server, so you have to be online for that :(