fix(agent): preserve roster answer after completion

web/app/components/base/chat/chat/__tests__/hooks.spec.tsx

@@ -2010,7 +2010,7 @@ describe('useChat', () => {
       })
 
       const lastResponse = result.current.chatList[1]
-      expect(lastResponse!.content).toBe('')
+      expect(lastResponse!.content).toBe('history top-level answer')
       expect(lastResponse!.agent_response_parts).toBeUndefined()
       expect(lastResponse!.workflow_run_id).toBe('history-workflow-run')
       expect(lastResponse!.workflowProcess).toBeUndefined()
@@ -2028,6 +2028,71 @@ describe('useChat', () => {
       ])
     })
 
+    it('should keep new agent streaming response parts when completed history has no answer yet', async () => {
+      let callbacks: HookCallbacks
+      vi.mocked(ssePost).mockImplementation(async (_url, _params, options) => {
+        callbacks = options as HookCallbacks
+      })
+
+      const onGetConversationMessages = vi.fn().mockResolvedValue({
+        data: [{
+          id: 'm-new-agent-empty-history',
+          answer: '',
+          message: [{ role: 'user', text: 'hi' }],
+          agent_thoughts: [
+            {
+              id: 'history-thought',
+              thought: 'history thought',
+              answer: '',
+              tool: '',
+              tool_input: '',
+              observation: '',
+              position: 1,
+            },
+          ],
+          created_at: Date.now(),
+          inputs: {},
+          query: 'hi',
+        }],
+      })
+
+      const { result } = renderHook(() => useChat(
+        undefined,
+        undefined,
+        undefined,
+        undefined,
+        undefined,
+        undefined,
+        undefined,
+        { isNewAgent: true },
+      ))
+
+      act(() => {
+        result.current.handleSend('test-url', { query: 'new agent empty history' }, {
+          onGetConversationMessages,
+        })
+      })
+
+      await act(async () => {
+        callbacks.onThought({ id: 'stream-thought', thought: 'stream thought' })
+        callbacks.onData(' streamed answer', true, { event: 'agent_message', messageId: 'm-new-agent-empty-history', conversationId: 'c-new-agent-empty-history' })
+        await callbacks.onCompleted()
+      })
+
+      const lastResponse = result.current.chatList[1]
+      expect(lastResponse!.content).toBe('')
+      expect(lastResponse!.agent_response_parts).toEqual([
+        { type: 'thought', thought: expect.objectContaining({ id: 'stream-thought', thought: 'stream thought' }) },
+        { type: 'message', content: ' streamed answer' },
+      ])
+      expect(lastResponse!.agent_thoughts).toEqual([
+        expect.objectContaining({
+          id: 'history-thought',
+          thought: 'history thought',
+        }),
+      ])
+    })
+
     it('should handle onCompleted using agent thought when thought matches answer', async () => {
       let callbacks: HookCallbacks
       vi.mocked(ssePost).mockImplementation(async (_url, _params, options) => {

web/app/components/base/chat/chat/answer/__tests__/agent-roster-response-content.spec.tsx

@@ -38,7 +38,9 @@ describe('AgentRosterResponseContent', () => {
     render(<AgentRosterResponseContent item={item} />)
 
     expect(screen.getByRole('button', { name: /workFinished/i })).toBeInTheDocument()
-    expect(screen.queryByText('history answer')).not.toBeInTheDocument()
+    await waitFor(() => {
+      expect(screen.getByTestId('agent-roster-response-content')).toHaveTextContent('history answer')
+    })
 
     fireEvent.click(screen.getByRole('button', { name: /workFinished/i }))
 
@@ -47,6 +49,7 @@ describe('AgentRosterResponseContent', () => {
     })
 
     expect(screen.queryByText('internal thought should not render')).not.toBeInTheDocument()
+    expect(screen.getAllByTestId('agent-content-markdown')).toHaveLength(1)
   })
 
   it('should render new agent response parts in event order when thoughts and messages interleave', async () => {

web/app/components/base/chat/chat/answer/agent-roster-response-content.tsx

@@ -259,9 +259,11 @@ function ToolProcessCard({
 function AgentThoughtsProcessList({
   item,
   responding,
+  suppressAnswer,
 }: {
   item: ChatItem
   responding?: boolean
+  suppressAnswer?: boolean
 }) {
   return (
     <div className="mt-2 flex flex-col gap-1">
@@ -271,6 +273,7 @@ function AgentThoughtsProcessList({
           thought={thought}
           responding={responding}
           defaultOpen={index === 0}
+          suppressAnswer={suppressAnswer}
         />
       ))}
     </div>
@@ -281,17 +284,19 @@ function AgentThoughtProcessItem({
   thought,
   responding,
   defaultOpen,
+  suppressAnswer,
 }: {
   thought: ThoughtItem
   responding?: boolean
   defaultOpen?: boolean
+  suppressAnswer?: boolean
 }) {
   const tools = getToolProcesses(thought, responding)
   const answer = thought.answer?.trim()
 
   return (
     <div className="flex flex-col gap-1">
-      {answer && (
+      {answer && !suppressAnswer && (
         <div className="px-2 py-2 body-md-regular text-text-primary" data-testid="agent-content-markdown">
           <Markdown content={thought.answer || ''} />
         </div>
@@ -365,9 +370,11 @@ function AgentResponsePartList({
 function AgentThoughtsProcessGroup({
   item,
   responding,
+  suppressAnswer,
 }: {
   item: ChatItem
   responding?: boolean
+  suppressAnswer?: boolean
 }) {
   const { t } = useTranslation('agentV2')
   const [open, setOpen] = useState(false)
@@ -385,6 +392,7 @@ function AgentThoughtsProcessGroup({
         <AgentThoughtsProcessList
           item={item}
           responding={responding}
+          suppressAnswer={suppressAnswer}
         />
       </div>
     )
@@ -409,12 +417,26 @@ function AgentThoughtsProcessGroup({
         <AgentThoughtsProcessList
           item={item}
           responding={responding}
+          suppressAnswer={suppressAnswer}
         />
       )}
     </div>
   )
 }
 
+function getLastAgentThoughtAnswer(agentThoughts: ChatItem['agent_thoughts']) {
+  if (!agentThoughts?.length)
+    return ''
+
+  for (let index = agentThoughts.length - 1; index >= 0; index--) {
+    const answer = agentThoughts[index]?.answer?.trim()
+    if (answer)
+      return agentThoughts[index]?.answer || ''
+  }
+
+  return ''
+}
+
 export function AgentRosterResponseContent({
   item,
   responding,
@@ -434,6 +456,8 @@ export function AgentRosterResponseContent({
     )
   }
 
+  const visibleContent = content || getLastAgentThoughtAnswer(agent_thoughts)
+
   return (
     <div className="flex w-full flex-col gap-1" data-testid="agent-roster-response-content">
       {!!item.agent_response_parts?.length && (
@@ -448,11 +472,12 @@ export function AgentRosterResponseContent({
             <AgentThoughtsProcessGroup
               item={item}
               responding={responding}
+              suppressAnswer={!!visibleContent}
             />
           )}
-          {content && (
+          {visibleContent && (
             <div className="px-2 py-2 body-md-regular text-text-primary" data-testid="agent-content-markdown">
-              <Markdown content={content} />
+              <Markdown content={visibleContent} />
             </div>
           )}
         </>

web/app/components/base/chat/chat/hooks.ts

@@ -134,6 +134,20 @@ function upsertAgentResponseThoughtPart(responseItem: ChatItemInTree, thought: T
   })
 }
 
+function getLastAgentThoughtAnswer(agentThoughts: ThoughtItem[]) {
+  for (let index = agentThoughts.length - 1; index >= 0; index--) {
+    const answer = agentThoughts[index]?.answer?.trim()
+    if (answer)
+      return agentThoughts[index]?.answer || ''
+  }
+
+  return ''
+}
+
+function hasAgentResponseMessagePart(responseItem: ChatItem) {
+  return responseItem.agent_response_parts?.some(part => part.type === 'message' && !!part.content.trim()) ?? false
+}
+
 function getHistoryAgentThoughts(responseItem: HistoryConversationMessage) {
   if (!Array.isArray(responseItem.agent_thoughts))
     return []
@@ -984,19 +998,21 @@ export const useChat = (
               return onConversationComplete?.(conversationIdRef.current, completedWorkflowRunId)
 
             const historyAgentThoughts = getHistoryAgentThoughts(newResponseItem)
-            const hasHistoryAgentThoughtAnswer = historyAgentThoughts.some(thought => thought.answer?.trim())
             const lastHistoryAgentThought = historyAgentThoughts.at(-1)
             const historyAnswer = newResponseItem.answer || ''
-            const isUseAgentThought = (lastHistoryAgentThought?.thought === historyAnswer) || (options.isNewAgent && hasHistoryAgentThoughtAnswer)
+            const historyAgentThoughtAnswer = options.isNewAgent ? getLastAgentThoughtAnswer(historyAgentThoughts) : ''
+            const completedAnswer = historyAnswer || historyAgentThoughtAnswer
+            const isUseAgentThought = !options.isNewAgent && lastHistoryAgentThought?.thought === historyAnswer
+            const shouldKeepStreamingResponseParts = options.isNewAgent && !completedAnswer.trim() && hasAgentResponseMessagePart(responseItem)
             const messageLog = Array.isArray(newResponseItem.message) ? newResponseItem.message : []
             const answerTokens = newResponseItem.answer_tokens ?? 0
             const messageTokens = newResponseItem.message_tokens ?? 0
             const providerResponseLatency = newResponseItem.provider_response_latency ?? 0
             const historyAnswerFiles = getHistoryAnswerFiles(newResponseItem)
             updateChatTreeNode(responseItem.id, {
-              content: isUseAgentThought ? '' : historyAnswer,
+              content: shouldKeepStreamingResponseParts || isUseAgentThought ? '' : completedAnswer,
               agent_thoughts: historyAgentThoughts,
-              agent_response_parts: undefined,
+              agent_response_parts: shouldKeepStreamingResponseParts ? responseItem.agent_response_parts : undefined,
               citation: newResponseItem.retriever_resources,
               reasoningContent: newResponseItem.metadata?.reasoning,
               reasoningFinished: true,