test(desktop): cover IME-composed send-button visibility (Chinese/Japanese/Korean)

DOM repro that drives compositionstart -> input(preedit) -> compositionend with
no trailing input event and asserts the composer payload (send button) becomes
visible for committed CJK/IME input. Regression guard for #39614.

apps/desktop/src/app/chat/composer/ime-composition-dom-repro.test.tsx

@@ -0,0 +1,103 @@
+import { act, fireEvent, render } from '@testing-library/react'
+import { useRef, useState } from 'react'
+import { describe, expect, it } from 'vitest'
+
+// Faithful mirror of index.tsx's composer text wiring for IME input, driven
+// through REAL DOM composition + input events on a contentEditable.
+//
+// Regression repro for #39614: typing committed multi-character IME text (e.g.
+// Chinese "你好") used to leave the send button hidden. The input events fired
+// during composition carry uncommitted preedit text and are intentionally
+// skipped; Chromium then does NOT reliably emit a trailing input event after
+// compositionend on Windows IMEs, so the finalized text never reached composer
+// state and `hasPayload` stayed false until an unrelated edit forced a sync.
+// The fix flushes the live DOM text in onCompositionEnd.
+function Harness({ onPayload }: { onPayload: (hasPayload: boolean) => void }) {
+  const editorRef = useRef<HTMLDivElement>(null)
+  const composingRef = useRef(false)
+  const draftRef = useRef('')
+  const [draft, setDraft] = useState('')
+
+  const flushEditorToDraft = (editor: HTMLDivElement) => {
+    const next = editor.textContent ?? ''
+
+    if (next !== draftRef.current) {
+      draftRef.current = next
+      setDraft(next)
+    }
+  }
+
+  onPayload(draft.trim().length > 0)
+
+  return (
+    <div
+      contentEditable
+      data-testid="editor"
+      onCompositionEnd={event => {
+        composingRef.current = false
+        flushEditorToDraft(event.currentTarget)
+      }}
+      onCompositionStart={() => {
+        composingRef.current = true
+      }}
+      onInput={event => {
+        if (composingRef.current) {
+          return
+        }
+
+        flushEditorToDraft(event.currentTarget)
+      }}
+      ref={editorRef}
+      suppressContentEditableWarning
+    />
+  )
+}
+
+describe('composer IME composition — send button visibility (#39614)', () => {
+  it('shows the send button after committing CJK text without a trailing edit', async () => {
+    let hasPayload = false
+    const { getByTestId } = render(<Harness onPayload={p => (hasPayload = p)} />)
+    const editor = getByTestId('editor')
+
+    // Compose "你好" the way a Windows Chinese IME does: compositionstart, then
+    // input events carrying uncommitted preedit text, then compositionend with
+    // the committed text already in the DOM — and crucially NO input event
+    // afterwards.
+    await act(async () => {
+      fireEvent.compositionStart(editor)
+      editor.textContent = '你'
+      fireEvent.input(editor)
+      editor.textContent = '你好'
+      fireEvent.input(editor)
+      fireEvent.compositionEnd(editor)
+    })
+
+    // Before the fix this was false (button hidden) until a further edit.
+    expect(hasPayload).toBe(true)
+    expect(editor.textContent).toBe('你好')
+  })
+
+  it('also covers Japanese/Korean and any IME-composed script', async () => {
+    let hasPayload = false
+    const { getByTestId } = render(<Harness onPayload={p => (hasPayload = p)} />)
+    const editor = getByTestId('editor')
+
+    for (const committed of ['こんにちは', '안녕하세요']) {
+      await act(async () => {
+        fireEvent.compositionStart(editor)
+        editor.textContent = committed
+        fireEvent.input(editor)
+        fireEvent.compositionEnd(editor)
+      })
+
+      expect(hasPayload).toBe(true)
+
+      // Clear for the next script.
+      await act(async () => {
+        editor.textContent = ''
+        fireEvent.input(editor)
+      })
+      expect(hasPayload).toBe(false)
+    }
+  })
+})