diff --git a/src/components/InputBox/index.jsx b/src/components/InputBox/index.jsx
index e2252dadb..97eb1b90a 100644
--- a/src/components/InputBox/index.jsx
+++ b/src/components/InputBox/index.jsx
@@ -11,6 +11,7 @@ import {
   MIN_CONVERSATION_HEIGHT,
   MIN_INPUT_HEIGHT,
 } from './resize.mjs'
+import { shouldHandleInputAction } from './input-action.mjs'
 
 export function InputBox({ onSubmit, enabled, postMessage, reverseResizeDir }) {
   const { t } = useTranslation()
@@ -93,7 +94,7 @@ export function InputBox({ onSubmit, enabled, postMessage, reverseResizeDir }) {
 
   const handleKeyDownOrClick = (e) => {
     e.stopPropagation()
-    if (e.type === 'click' || (e.keyCode === 13 && e.shiftKey === false)) {
+    if (shouldHandleInputAction(e)) {
       e.preventDefault()
       if (enabled) {
         if (!value) return
diff --git a/src/components/InputBox/input-action.mjs b/src/components/InputBox/input-action.mjs
new file mode 100644
index 000000000..20d979c22
--- /dev/null
+++ b/src/components/InputBox/input-action.mjs
@@ -0,0 +1,10 @@
+export function shouldHandleInputAction(event) {
+  if (event.type === 'click') return true
+  if (event.type !== 'keydown') return false
+
+  const isComposing = event.isComposing || event.nativeEvent?.isComposing
+  if (isComposing || event.keyCode === 229) return false
+
+  const isEnter = event.key === 'Enter' || event.keyCode === 13
+  return isEnter && !event.shiftKey
+}
diff --git a/tests/unit/components/input-box-action.test.mjs b/tests/unit/components/input-box-action.test.mjs
new file mode 100644
index 000000000..815c812a4
--- /dev/null
+++ b/tests/unit/components/input-box-action.test.mjs
@@ -0,0 +1,68 @@
+import assert from 'node:assert/strict'
+import { test } from 'node:test'
+import { shouldHandleInputAction } from '../../../src/components/InputBox/input-action.mjs'
+
+test('input actions handle button clicks and both plain Enter forms', () => {
+  assert.equal(shouldHandleInputAction({ type: 'click' }), true)
+  assert.equal(
+    shouldHandleInputAction({ type: 'keydown', key: 'Enter', shiftKey: false }),
+    true,
+  )
+  assert.equal(
+    shouldHandleInputAction({ type: 'keydown', keyCode: 13, shiftKey: false }),
+    true,
+  )
+})
+
+test('input actions preserve Shift+Enter line breaks', () => {
+  assert.equal(
+    shouldHandleInputAction({ type: 'keydown', key: 'Enter', keyCode: 13, shiftKey: true }),
+    false,
+  )
+})
+
+test('input actions ignore directly exposed active IME composition', () => {
+  assert.equal(
+    shouldHandleInputAction({
+      type: 'keydown',
+      key: 'Enter',
+      keyCode: 13,
+      shiftKey: false,
+      isComposing: true,
+    }),
+    false,
+  )
+})
+
+test('input actions ignore active IME composition on synthetic native events', () => {
+  assert.equal(
+    shouldHandleInputAction({
+      type: 'keydown',
+      key: 'Enter',
+      keyCode: 13,
+      shiftKey: false,
+      nativeEvent: { isComposing: true },
+    }),
+    false,
+  )
+})
+
+test('input actions ignore the legacy IME keyCode 229 fallback', () => {
+  assert.equal(
+    shouldHandleInputAction({
+      type: 'keydown',
+      key: 'Enter',
+      keyCode: 229,
+      shiftKey: false,
+      isComposing: false,
+    }),
+    false,
+  )
+})
+
+test('input actions ignore unrelated keyboard events', () => {
+  assert.equal(
+    shouldHandleInputAction({ type: 'keydown', key: 'a', keyCode: 65, shiftKey: false }),
+    false,
+  )
+})