[BUG] Characters swallowed when typing immediately after launching claude

Bug Description

When launching claude and immediately starting to type before the TUI has fully initialized, the first several characters are lost/swallowed. They never appear in the input field.

OS: macOS
Terminal: iTerm2 v3.6.6
Shell: zsh 5.9 (configuration)

Steps to Reproduce

1. Run claude in a terminal
2. Immediately start typing a prompt before the UI finishes loading
3. Observe that the first characters typed are missing from the input

Expected Behavior

Characters typed during startup should be buffered and appear in the input field once the TUI is ready.

Actual Behavior

Characters typed before the TUI finishes initializing are silently dropped.

Related Issues

• #21059 — requests that Claude Code buffer keystrokes instead of dropping them
• #5303 — describes swallowed keystrokes when the event loop is busy
• #8308 — lost input during UI freezes