Keep late background progress out of a newer conversation turn

Why: Completion or progress from an earlier task could appear in the process of an unrelated newer answer.

Evidence: The new ownership regression fails before the guard and passes afterward; the frontend suite, TypeScript and unchanged export gate pass.

Impact: Project child progress only into its originating live turn while still reconciling background results.

Refs: feature/workbench-flow-completion chronological display requirement

test/work-state.test.ts

@@ -64,6 +64,21 @@ it('preserves rejected referenced input without retrying it or blocking later qu
 })
 
 describe('work projection ordering and context', () => {
+  it('keeps an earlier background task out of a newer foreground process', async () => {
+    const current: Run = { id: 'new-topic', conversationId: 'a', projectId: 'p', kind: 'conversation', status: 'running', createdAt: '' }
+    const child: Run = { ...current, id: 'old-child', kind: 'subagent', parentRunId: 'old-topic' }
+    vi.mocked(api.conversationDetail).mockResolvedValue(detail('a', [current, child]))
+    await store.openConversation('a')
+    store.applyEvent(event(1, 'message.delta', { index: 0, text: '正在回答新的问题' }, current.id))
+    store.applyEvent(event(2, 'agent.progress', { agentRun: child.id, note: '旧材料仍在整理' }, child.id))
+    expect(store.getState().live?.agentNotes[child.id]).toBeUndefined()
+    store.applyEvent(event(3, 'agent.spawn', { agentRun: 'new-child', name: '新任务', task: '核对新问题' }, current.id))
+    store.applyEvent(event(4, 'agent.progress', { agentRun: 'new-child', note: '核对当前问题' }, 'new-child'))
+    expect(store.getState().live?.agentNotes['new-child']).toBe('核对当前问题')
+    store.applyEvent(event(5, 'agent.result', { agentRun: child.id, summary: '旧材料已整理' }, child.id))
+    expect(store.getState().live?.runId).toBe(current.id)
+    expect(store.getState().live?.agentNotes[child.id]).toBeUndefined()
+  })
   it('settles foreground completion and queued input when background events overtake its detail response', async () => {
     vi.useFakeTimers()
     const run: Run = { id: 'front', conversationId: 'a', projectId: 'p', kind: 'conversation', status: 'running', createdAt: '' }