[Bug]: Hangul/CJK composition is overwritten in the Native Chat composer while a turn streams #16911

What happens

Typing Hangul in the Native Chat composer while an agent turn is streaming loses and mangles syllables. A composed character is written into the textarea and then overwritten by the next streaming render before it can paint.

Plain (non-CJK) typing is unaffected because there is no composition window to overwrite.

Why

The transcript watcher emits one frame per 40ms debounce (src/main/native-chat/transcript-watch-scheduler.ts). Each frame lands as an urgent setAppended(...) in src/renderer/src/components/native-chat/use-native-chat-live-session.ts, so React cannot interrupt it. That render redraws NativeChatView, whose pass contains both the (non-virtualized) message list and the composer. The composer's textarea is controlled (value={draft}), so every one of those renders rewrites the DOM value — including while an IME composition is in flight.

Measured

14s window, 16 composed syllables, 105 transcript frames appended, ~1200 DOM nodes in the chat:

What this is not

Terminal panes are not affected. Flooding a visible terminal pane with high-volume output measures 0 long tasks / 0% blocked, and the per-syllable cost there is the agent TUI's own redraw — 58 bytes/syllable in a Claude Code pane vs 6 bytes in a plain PowerShell pane (paint p50 35.5ms vs 18.5ms). That is not Orca's render path.

Reproduction (no agent, no tokens)

1. Write a synthetic Claude transcript JSONL to ~/.claude/projects/<encoded-cwd>/<uuid>.jsonl with one user + one assistant turn.
2. Repoint the pane: window.__store.setState so the pane's agentStatusByPaneKey[key].providerSession.transcriptPath points at that file.
3. Enable the experimental Chat UI and switch the tab to chat.
4. Append an assistant turn to the file every 40ms.
5. Type with a CJK IME in the composer and watch the committed characters get rewritten.

window.__orcaTypingDiagnostic.start() / report() / stop() in the renderer console reports mainThreadBlocking and per-source echo latencies for the terminal side.

Environment

• Orca dev build from main, Windows 11
• Root cause is platform-independent React render scheduling, so macOS/Linux should reproduce identically.

Related

• Refs [Bug]: Chinese IME input lags/stutters in text fields (not present in Ghostty) #12829 — same class (CJK IME lag in text fields) but broader scope; search fields and the macOS candidate window are not addressed by this report.
• Refs Chinese IME: single character not displayed during composition #16260 — proposes the same composition-guard approach app-wide.
• Not related: [Bug]: Persistent Korean character doubling (duplicate rendering) in Orca terminal #15550 / [Bug]: Issues with duplicate Korean text and content disappearing in the terminal #15192 are terminal output rendering bugs, not input.