That's interesting - I just fixed my terminals rendering by having Claude build a test harness that used tmux as an oracle, and one of the programs it fixed the rendering of by reading out the tmux pane was Claude Code itself...
Turn off vim mode if you use it. There is some kind of bug with it I found it basically unusable. With vim mode off it sort of works ok. Only breaks occasionally.
Is this a new regression for others? I feel like I used it in a tmux setup without issues for 6+ months and only recently am I forced to Ctrl+L or resize the window constantly.