fix(desktop): commit IME-composed text on compositionend

[chajinheon]

Problem

Korean/CJK input in the desktop chat composer is broken: while typing, the last syllable is dropped on send ("글자가 짤려나감"), and input can stall after a few words. This is widely reported across CJK languages but had no merged fix.

Root cause

In Chromium (Electron), the final input event of an IME commit carries isComposing=true. handleEditorInput correctly skips state writes during composition — but no input event follows compositionend. The existing onCompositionEnd handler only flipped composingRef.current = false and never committed the finalized DOM text into draft state.

Result: the committed cluster lives in the contentEditable DOM but never reaches draftRef/the composer store. On submit, submitDraft() reads the stale draft → the trailing syllable is lost. The same stale-draft divergence is why the send button can stay as the voice button (it derives from hasComposerPayload, i.e. draft). ASCII typing is unaffected because isComposing is always false there — which is likely why this survived: contributors typing ASCII never see it.

The existing guards covered "don't submit on Enter mid-composition" but missed "commit the text when composition ends" — the fix completes the other half.

Fix

Extract the input-commit logic into a shared commitEditorState(editor) and invoke it from onCompositionEnd after clearing the composing flag, so IME-finalized text is written to draft state exactly once. No behavior change for non-IME input.

Surgical: two handlers in apps/desktop/src/app/chat/composer/index.tsx, plus a regression test driving the real Chromium IME event order (compositionstart → input{isComposing:true} → compositionend).

Related issues

Desktop composer CJK truncation / stale-draft cluster this addresses:

• Windows desktop: Enter does not submit Chinese IME text because rich composer draft state can stay stale #39025 — Windows desktop: rich composer draft state stays stale (same mechanism, named exactly)
• CJK IME input truncation on macOS: Chinese text after English is dropped #39457 — CJK IME truncation on macOS
• [Bug]: Desktop composer drops or fails to send CJK IME text on Enter #39538 — Desktop composer drops/fails to send CJK text on Enter
• [Bug]: IME composition causes send button to show as voice button + text truncation on submit #39651 — IME composition: text truncation on submit
• Hermes Desktop App: Chinese IME input broken — pressing Enter submits empty/incomplete text, requires Shift+Enter #38826 — Chinese IME: Enter submits empty/incomplete text

Likely resolved as a side effect (send button stuck on voice/hidden stems from the same empty draft): #39231, #38883, #40146.

Not covered here (different code path): #38117 is the TUI/CLI (prompt_toolkit) analog, not the desktop composer.

Verification

• npm run type-check — clean
• eslint on changed files — clean
• vitest composer suite — 12 passed (10 existing + 2 new)

The regression test reproduces the exact Chromium IME event order. Runtime verification in a packaged build is in progress.

🤖 Generated with Claude Code

[chajinheon]

Verified in a packaged build on macOS (arm64, ad-hoc signed --dir pack of this branch).

Typed long Korean sentences with rapid input, e.g. 한글을 사용하면 마지막 문자가 남아있는 버그가 있어:

• Trailing syllable is no longer dropped on submit — the full message sends intact.
• No mid-composition input stalls / freezes.
• No added latency while composing.

For contrast, the current released desktop build (without this change) still drops the trailing syllable on the same input — which is the originally reported symptom.

[tonydwb]

Approved. Fixes IME composition commit on compositionend in desktop composer. Shared commitEditorState helper, regression test included. Clean.

[chajinheon]

Closing as superseded — #40210 landed the same compositionend-commit fix on main first, so this is now redundant and conflicting. Glad the IME truncation is resolved either way. Thanks @tonydwb for the review.