Smart Borders exists in main repro

[openpaul]

Just so the next person does not start looking for it:

The patch 'smart borders' for i3 is actually somewhat already in the main i3 package included.

you can use it via the option

hide_edge_borders none|vertical|horizontal|both|smart

As described here: https://i3wm.org/docs/userguide.html

So need to compile it your self.

Cheers