* fix(chat): defer composer value writeback during IME composition
The controlled-writeback effect compared the value prop against the
CodeMirror document and, on mismatch, dispatched a wholesale replacement
with the caret forced to the end. While the browser composes (pinyin,
kana, hangul) the uncommitted text lives in the DOM, not in the document,
so the mismatch is expected and the dispatch interrupted the IME session
and jumped the cursor. Skip the writeback while the view is composing,
using CodeMirror's public compositionStarted getter; the composition
commits through its own pipeline and reports via onChange.
Fixes#2527
* fix(chat): preserve external composer writes during IME
* fix(chat): restore composition-wide writeback guard
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Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>
