feat(web): expose continuable subagent interrupt

The composer's single primary action now stops a running continuable
child: Session.cancel() routes a continuable address through
subagent.interrupt (ordinary sessions keep session.cancel; one-shot
addresses stay uncancellable), and InputBar switches the same Send button
to Stop while a continuable child runs. A running parent-offline child
keeps the default composer with disabled input so that Stop stays
reachable; the read-only takeover returns once it stops.

Refs #1535

packages/client/ui-conversation/src/client/locales.ts

@@ -17,6 +17,7 @@ export const zh = {
   'placeholder.plan': PLAN_NEXT_ACTION_ZH,
   'placeholder.default': '给智能体发消息',
   'placeholder.unavailable': '会话不可用',
+  'placeholder.parentOffline': '父会话已离线，无法继续发送；仍可停止当前运行',
   'placeholder.hero': '描述你想要构建的内容',
   'placeholder.workspace': '选择一个工作区开始',
   'input.commands': '命令',
@@ -159,6 +160,7 @@ export const en = {
   'placeholder.plan': PLAN_NEXT_ACTION_EN,
   'placeholder.default': 'Message the agent',
   'placeholder.unavailable': 'Session unavailable',
+  'placeholder.parentOffline': 'Parent session offline; sending is unavailable but you can still stop the run',
   'placeholder.hero': 'Describe what you want to build',
   'placeholder.workspace': 'Choose a workspace to start',
   'input.commands': 'Commands',

packages/client/ui-conversation/src/client/skeleton/InputBar.tsx

@@ -83,11 +83,15 @@ export function InputBar({
   // (undefined = capability absent → the chip renders nothing).
   const permissions = useProjection('permissions')
 
+  // A continuable child without its live parent cannot accept human input,
+  // but its primary Stop below stays available while it runs.
+  const continuable = subagent?.address.mode === 'continuable'
+  const parentOffline = continuable && !subagent.parentAvailable
   // Queue cut 1: running input stays free; locked = session removed, the
-  // inert no-workspace state, or the machine faces absent (no session). The
-  // transient machine locks (adjudicating pending / submitting) render
-  // read-only — the draft stays visible and focused, keystrokes drop.
-  const disabled = removed || inert || !live || blocked !== undefined
+  // inert no-workspace state, the machine faces absent (no session), or a
+  // parent-offline continuable child. An owner block also disables input;
+  // adjudicating and submitting render read-only so the draft stays visible.
+  const disabled = removed || inert || !live || blocked !== undefined || parentOffline
   const locked = disabled
   // The model seat is the ONE control a block leaves live: every block this
   // contract has is cleared by choosing a model, so locking it too would leave
@@ -350,8 +354,9 @@ export function InputBar({
     if (el !== null) toggleCommandMenu?.(selectionOf(el))
   }
 
-  const ordinary = subagent === null
-  const stopping = running && ordinary
+  // Ordinary sessions and continuable children stop through the same primary
+  // action; one-shot children stay send-and-stop-free (read-only takeover).
+  const stopping = running && (subagent === null || continuable)
   const primaryLabel = stopping ? t('input.stop') : t('input.send')
   const onPrimary = (): void => {
     if (stopping) {
@@ -478,9 +483,11 @@ export function InputBar({
               disabled={locked}
               readOnly={machineBusy}
               data-phase={input?.phase ?? 'inert'}
-              placeholder={placeholder ?? (disabled
-                ? t('placeholder.unavailable')
-                : planActive ? t('placeholder.plan') : t('placeholder.default'))}
+              placeholder={placeholder ?? (parentOffline
+                ? t('placeholder.parentOffline')
+                : disabled
+                  ? t('placeholder.unavailable')
+                  : planActive ? t('placeholder.plan') : t('placeholder.default'))}
               rows={2}
               onChange={onChange}
               onKeyDown={onKeyDown}

packages/client/ui-conversation/tests/input-bar.spec.tsx

@@ -143,7 +143,8 @@ function bench(over?: BenchOptions) {
   }
   const view = render(<InputBar {...props} />)
   const textarea = view.container.querySelector('textarea')!
-  const stopping = over?.running === true && over.subagent === undefined
+  const stopping = over?.running === true
+    && (over.subagent === undefined || over.subagent.address.mode === 'continuable')
   const button = view.container.querySelector<HTMLButtonElement>(
     `button[aria-label="${stopping ? '停止生成' : '发送消息'}"]`,
   )!
@@ -250,8 +251,8 @@ describe('running and lock semantics (queue cut 1)', () => {
     expect(ctrl.sink).toHaveBeenCalledWith('also queue', 'queue')
   })
 
-  it('running subagent primary admits a follow-up instead of exposing Stop', () => {
-    const { button, sink, stop } = bench({
+  it('running continuable subagent turns the same primary into Stop while typing stays free', () => {
+    const { button, textarea, sink, stop } = bench({
       running: true,
       draft: '后续消息',
       subagent: {
@@ -263,23 +264,54 @@ describe('running and lock semantics (queue cut 1)', () => {
         parentAvailable: true,
       },
     })
-    expect(button.getAttribute('aria-label')).toBe('发送消息')
+    // One primary action only: Send switched to Stop, no side-by-side interrupt.
+    expect(button.getAttribute('aria-label')).toBe('停止生成')
+    expect(textarea.disabled).toBe(false)
     fireEvent.click(button)
+    expect(stop).toHaveBeenCalledTimes(1)
+    expect(sink).not.toHaveBeenCalled()
+    // Enter still queues the follow-up while the primary offers Stop.
+    fireEvent.keyDown(textarea, { key: 'Enter' })
     expect(sink).toHaveBeenCalledWith('后续消息', 'queue')
-    expect(stop).not.toHaveBeenCalled()
+  })
 
-    const empty = bench({
+  it('parent-offline running continuable locks the input but keeps the same primary Stop usable', () => {
+    const { button, textarea, stop, view } = bench({
       running: true,
+      draft: '',
       subagent: {
         address: {
           parentSessionId: 'parent' as SessionId,
           childSessionId: SID,
           mode: 'continuable',
         },
+        parentAvailable: false,
+      },
+    })
+    expect(textarea.disabled).toBe(true)
+    expect(textarea.placeholder).toBe('父会话已离线，无法继续发送；仍可停止当前运行')
+    expect((view.getByLabelText('命令') as HTMLButtonElement).disabled).toBe(true)
+    expect(button.getAttribute('aria-label')).toBe('停止生成')
+    expect(button.disabled).toBe(false)
+    fireEvent.click(button)
+    expect(stop).toHaveBeenCalledTimes(1)
+  })
+
+  it('running one-shot subagent never exposes Stop', () => {
+    const { button, stop } = bench({
+      running: true,
+      draft: '不可停止',
+      subagent: {
+        address: {
+          parentSessionId: 'parent' as SessionId,
+          childSessionId: SID,
+          mode: 'one-shot',
+        },
         parentAvailable: true,
       },
     })
-    expect(empty.button.disabled).toBe(true)
+    expect(button.getAttribute('aria-label')).toBe('发送消息')
+    expect(stop).not.toHaveBeenCalled()
   })
 
   it('keeps both running subagent Enter gestures on Queue transport', () => {