React 18's root-level event delegation intercepts keydown events with
keyCode 229 (the "composition in progress" signal sent by the browser
during non-Latin IME input) and synthesises an onCompositionStart event.
That synthetic path sets internal composing state that interferes with
xterm.js's own IME handling on its hidden textarea, causing the first
keystroke of each composition chunk to be silently dropped.
The fix adds a capture-phase keydown listener on the terminal host div
that stops propagation of keyCode-229 events before they reach React's
delegation layer. xterm.js relies on native compositionstart/
compositionend on its internal textarea — not on keydown — so blocking
the propagation is safe.
Fixes#52111
liuhao1024
2af4da45ec