Terminal banner flickers on startup over SSH: two-phase rendering visible due to latency

Summary

Claude Code's startup banner flickers visibly when running over SSH. The banner renders in two phases (boxed → compact) with a ~50-150ms gap between them. Locally this is invisible, but over SSH the added latency makes both frames visible, causing 3 distinct flickers during a typical startup.

Steps to reproduce

1. SSH into any remote machine (no special config needed)
2. Run claude
3. Observe 3 visible flicker events during startup

Note: SSH alone is sufficient to reproduce — tmux, terminal emulator, TERM value, and COLORTERM are all irrelevant. The flicker occurs with xterm-256color, xterm-ghostty, with or without COLORTERM=truecolor, inside or outside tmux.

Root cause analysis

Claude Code performs two separate synchronized output updates during startup, each wrapped in its own \e[?2026h ... \e[?2026l pair:

1. First frame: Full boxed banner with version info
2. Second frame: Compact banner (replaces the boxed one)

Because these are separate sync-update blocks, the terminal flushes the first frame to the screen before receiving the second. Over SSH, the network latency (~50-150ms) makes the first frame visible before it gets replaced.

Timing analysis from asciinema recording

| Time (s) | Event | Description |
|-----------|-------|-------------|
| 0.082 | Startup | Claude process begins |
| 0.573 | Flicker 1 | Boxed banner appears (first sync update) |
| 0.623 | Replace | Compact banner replaces boxed (~50ms gap) |
| 1.049 | Flicker 2 | Boxed banner reappears |
| 1.100 | Replace | Compact banner again (~51ms gap) |
| 1.528 | Flicker 3 | Boxed banner reappears |
| 1.582 | Replace | Compact banner again (~54ms gap) |

What was ruled out

• Focus events / kitty keyboard protocol: Flicker occurs regardless of focus-events off in tmux
• TERM value: Happens with both xterm-ghostty and xterm-256color
• COLORTERM: Happens with and without COLORTERM=truecolor
• Missing terminfo: Happens even with correct terminfo installed
• tmux: Happens with direct SSH, tmux is irrelevant

Asciinema recording

https://asciinema.org/a/T9XuaIvScIBPtUwV

Environment

• Local: Ghostty terminal, TERM=xterm-ghostty, COLORTERM=truecolor
• Remote: NixOS, Linux 6.12.63
• Claude Code: Latest version at time of filing