Looks good but try this:

tmux new
tmux set menu-border-lines none
tmux neww
tmux display-menu -t%0 a b c
tmux selectw -t%0

The menu has lines even though that window is configured with none.

Thanks, I reproduced the exact sequence. The issue was that display-menu read menu-border-lines from the current window after neww instead of the explicitly targeted window (%0), so it saw the default border setting. I updated it to use the target window options, added a regression case for this sequence, and verified the rebuilt binary renders the borderless menu. Commit 2776e2e is pushed for recheck.

Rebased and resolved the conflicts.

I think this looks good now, thanks. This will be for after 3.8 and I will look at it again after that is released.