diff --git a/packages/client/ui-conversation/src/client/skeleton/InputBar.tsx b/packages/client/ui-conversation/src/client/skeleton/InputBar.tsx
index b4c04c67bb..43a0f3e1ec 100644
--- a/packages/client/ui-conversation/src/client/skeleton/InputBar.tsx
+++ b/packages/client/ui-conversation/src/client/skeleton/InputBar.tsx
@@ -285,13 +285,14 @@ export function InputBar({
   }
 
   const ordinary = subagent === null
-  const primaryLabel = running && ordinary ? t('input.stop') : t('input.send')
+  const stopping = running && ordinary
+  const primaryLabel = stopping ? t('input.stop') : t('input.send')
   const onPrimary = (): void => {
-    if (inputActions === undefined || stop === undefined) return // absent machine: the button is disabled
-    if (running && ordinary) {
-      stop()
+    if (stopping) {
+      stop?.()
       return
     }
+    if (inputActions === undefined) return // absent machine: the button is disabled
     /* v8 ignore next -- defensive: the primary button is disabled while empty||disabled, so a click cannot reach the false arm. */
     if (!empty && !disabled && !machineBusy) inputActions.submit()
   }
@@ -467,11 +468,11 @@ export function InputBar({
               className={css.primary}
               aria-label={primaryLabel}
               title={primaryLabel}
-              disabled={!running && (empty || disabled || machineBusy)}
+              disabled={stopping ? stop === undefined : empty || disabled || machineBusy}
               onMouseDown={keepFocus}
               onClick={onPrimary}
             >
-              {running ? (
+              {stopping ? (
                 <svg viewBox="0 0 16 16" width="16" height="16" aria-hidden>
                   <rect x="3" y="3" width="10" height="10" rx="3" fill="currentColor" />
                 </svg>
diff --git a/packages/client/ui-conversation/tests/input-bar.spec.tsx b/packages/client/ui-conversation/tests/input-bar.spec.tsx
index fb82f9a4e8..2072fd2c90 100644
--- a/packages/client/ui-conversation/tests/input-bar.spec.tsx
+++ b/packages/client/ui-conversation/tests/input-bar.spec.tsx
@@ -41,6 +41,7 @@ interface BenchOptions {
   permissions?: { options: { value: string; name: string; description?: string }[]; currentValue: string }
   draft?: string
   running?: boolean
+  subagent?: Exclude<ConversationSnapshot['subagent'], null>
   disabled?: boolean
   promptError?: ConversationSnapshot['promptError']
   variant?: 'hero' | 'composer'
@@ -76,6 +77,7 @@ function bench(over?: BenchOptions) {
   if (over?.draft !== undefined && over.draft !== '') shell.setDraft(over.draft)
   const session = createSnapshotStore<ConversationSnapshot>(snapshotOf({
     running: over?.running ?? false,
+    subagent: over?.subagent ?? null,
     removed: over?.disabled ?? false,
     promptError: over?.promptError ?? null,
   }))
@@ -124,8 +126,9 @@ function bench(over?: BenchOptions) {
   const view = render(<InputBar {...props} />)
   const textarea = view.container.querySelector('textarea')!
   // aria-label (not role name): title carries the same label and would double-match.
+  const stopping = over?.running === true && over.subagent === undefined
   const button = view.container.querySelector<HTMLButtonElement>(
-    `button[aria-label="${over?.running === true ? '停止生成' : '发送消息'}"]`,
+    `button[aria-label="${stopping ? '停止生成' : '发送消息'}"]`,
   )!
   return { view, textarea, button, props, sink, shell, wiring: shell, session, stop, slotCalls, menuLauncher }
 }
@@ -208,6 +211,38 @@ describe('running and lock semantics (queue cut 1)', () => {
     expect(stop).toHaveBeenCalledTimes(1)
   })
 
+  it('running subagent primary admits a follow-up instead of exposing Stop', () => {
+    const { button, sink, stop } = bench({
+      running: true,
+      draft: '后续消息',
+      subagent: {
+        address: {
+          parentSessionId: 'parent' as SessionId,
+          childSessionId: SID,
+          mode: 'continuable',
+        },
+        parentAvailable: true,
+      },
+    })
+    expect(button.getAttribute('aria-label')).toBe('发送消息')
+    fireEvent.click(button)
+    expect(sink).toHaveBeenCalledWith('后续消息')
+    expect(stop).not.toHaveBeenCalled()
+
+    const empty = bench({
+      running: true,
+      subagent: {
+        address: {
+          parentSessionId: 'parent' as SessionId,
+          childSessionId: SID,
+          mode: 'continuable',
+        },
+        parentAvailable: true,
+      },
+    })
+    expect(empty.button.disabled).toBe(true)
+  })
+
   it('disabled (session removed) locks the textarea and chrome', () => {
     const { textarea, view } = bench({ disabled: true })
     expect(textarea.disabled).toBe(true)