[BUG] Terminal blinks/flickers when pasting long messages in tmux

Description

When running Claude Code inside a tmux session and pasting long messages (multi-line, typically >10 lines), the terminal blinks or flickers repeatedly until the paste completes. This does not occur with short pastes.

Steps to Reproduce

1. Start Claude Code inside a tmux session
2. Paste a long multi-line message (>10 lines) into the input
3. Observe terminal flickering/blinking during paste

Expected Behaviour

No visual artifacts when pasting text of any length.

Environment

• Platform: macOS Darwin 25.2.0
• Shell: zsh
• tmux (homebrew)
• Claude Code CLI

Notes

This has been reproduced consistently across multiple sessions and is the most frequently reported friction point in user session logs (~12 separate mentions). Does not occur outside of tmux.