[Bug] TUI rendering corruption in tmux on macOS Terminal.app: input box duplicated at top of screen, text overlapping

Bug Description
Running Claude Code inside tmux: the TUI screen state gets out of sync with what's actually drawn. Likely related to / same root cause as #66538 (reported there with Ghostty) — reproduces on the stock macOS Terminal.app too, so the common factor appears to be tmux, not the terminal emulator.

Symptoms

• The input box gets rendered a second time near the top of the screen while the real one stays at the bottom; typed text appears in the wrong (upper) copy, so new input shows up "somewhere above" instead of at the prompt.
• Multiple stale -- INSERT -- vim-mode status lines remain on screen at different vertical positions.
• Previous output and new output get interleaved character-by-character on the same lines (text overlapping/overwriting each other).
• Possibly relevant: a lot of the corrupted text is Cyrillic, in case wide/multibyte character width calculation contributes to the screen-state mismatch.
• No pane resize needed to trigger; happens during normal streaming output and agent status updates.

Environment Info

• Platform: darwin (macOS 26.5.1, Darwin 25.5.0, Apple Silicon)
• Terminal: tmux 3.6a (TERM=tmux-256color), outer terminal: macOS Terminal.app (xterm-256color)
• Claude Code version: 2.1.173
• vim mode: enabled
• auto mode (shift+tab) active

Related

• #66538 (macOS + tmux + Ghostty, same symptoms)
• #29937 (Linux + tmux, same class)