diff --git a/apps/web/src/app/data-tasks/__tests__/conversation-restore.test.ts b/apps/web/src/app/data-tasks/__tests__/conversation-restore.test.ts
index f0e1db07..bff348b6 100644
--- a/apps/web/src/app/data-tasks/__tests__/conversation-restore.test.ts
+++ b/apps/web/src/app/data-tasks/__tests__/conversation-restore.test.ts
@@ -1191,6 +1191,7 @@ describe("shouldRestoreConversationMessages", () => {
       shouldRestoreConversationMessages({
         conversationMemoryEnabled: true,
         isRunning: false,
+        replaceExistingMessages: true,
         agentMessages: [{ id: "msg-user-1", role: "user", content: "old question" }],
         dto,
       }),
@@ -1230,6 +1231,7 @@ describe("shouldRestoreConversationMessages", () => {
       shouldRestoreConversationMessages({
         conversationMemoryEnabled: true,
         isRunning: false,
+        replaceExistingMessages: false,
         agentMessages: [
           ...conversationToAgentMessages(dto),
           {
@@ -1276,6 +1278,7 @@ describe("shouldRestoreConversationMessages", () => {
       shouldRestoreConversationMessages({
         conversationMemoryEnabled: true,
         isRunning: false,
+        replaceExistingMessages: false,
         agentMessages: [
           ...conversationToAgentMessages(dto),
           {
@@ -1293,6 +1296,40 @@ describe("shouldRestoreConversationMessages", () => {
       }),
     ).toBe(false);
   });
+
+  it("does not replace an existing transcript during a same-thread background refresh", () => {
+    const dto: SessionConversationDto = {
+      sessionId: "thread-1",
+      messages: [
+        {
+          id: "persisted-user-1",
+          runId: "run-1",
+          role: "user",
+          source: "client",
+          messageId: "persisted-user-message-1",
+          contentText: "你好",
+          position: 1,
+          createdAt: "2026-06-25T10:00:01Z",
+        },
+      ],
+      runEventRefs: [],
+      toolCalls: [],
+    };
+
+    expect(
+      shouldRestoreConversationMessages({
+        conversationMemoryEnabled: true,
+        isRunning: false,
+        replaceExistingMessages: false,
+        agentMessages: [
+          { id: "live-user-1", role: "user", content: "你好" },
+          { id: "live-assistant-1", role: "assistant", content: "你好，有什么可以帮你？" },
+          { id: "live-user-2", role: "user", content: "继续" },
+        ],
+        dto,
+      }),
+    ).toBe(false);
+  });
 });
 
 describe("shouldHydrateLiveRunFromConversation", () => {
diff --git a/apps/web/src/app/data-tasks/components/chat/DataTaskChatInput.tsx b/apps/web/src/app/data-tasks/components/chat/DataTaskChatInput.tsx
index b633322f..9929055b 100644
--- a/apps/web/src/app/data-tasks/components/chat/DataTaskChatInput.tsx
+++ b/apps/web/src/app/data-tasks/components/chat/DataTaskChatInput.tsx
@@ -64,7 +64,7 @@ type DataTaskChatInputProps = CopilotChatInputProps & {
   onEditQueuedPrompt?: (id: string, text: string) => void;
   onDeleteQueuedPrompt?: (id: string) => void;
   onSendQueuedPromptNow?: (id: string) => void;
-  /** Client-side send/upload failure shown above the composer (never silent). */
+  /** Current run or client-side send/upload failure shown above the composer. */
   submitError?: string | null;
   /** Session lock / remote-busy prompt rendered above the composer. */
   sessionLockSlot?: ReactNode;
diff --git a/apps/web/src/app/data-tasks/components/chat/DataTaskChatInputBindingsContext.tsx b/apps/web/src/app/data-tasks/components/chat/DataTaskChatInputBindingsContext.tsx
index 2fadc11d..e7c1ac0e 100644
--- a/apps/web/src/app/data-tasks/components/chat/DataTaskChatInputBindingsContext.tsx
+++ b/apps/web/src/app/data-tasks/components/chat/DataTaskChatInputBindingsContext.tsx
@@ -52,6 +52,7 @@ export type DataTaskChatInputBindings = {
   onUserMessageSubmitted: (text: string) => void;
   liveRunStatus: LiveRunStatus;
   liveRunRunId: string | null;
+  liveRunErrorMessage: string | null;
   onCancelRun?: () => Promise<void> | void;
   stopActiveRun?: () => Promise<void>;
   stopActiveChatRunRef?: MutableRefObject<(() => void) | undefined>;
diff --git a/apps/web/src/app/data-tasks/components/chat/SessionConversationRestore.tsx b/apps/web/src/app/data-tasks/components/chat/SessionConversationRestore.tsx
index 29f9a0de..cb25dc6e 100644
--- a/apps/web/src/app/data-tasks/components/chat/SessionConversationRestore.tsx
+++ b/apps/web/src/app/data-tasks/components/chat/SessionConversationRestore.tsx
@@ -55,6 +55,7 @@ export function SessionConversationRestore({
   const { setThreadRestoring, markThreadRestored } = useConversationRestoreGate();
   const fetchGenerationRef = useRef(0);
   const prevThreadIdRef = useRef<string | undefined>(undefined);
+  const messageReplacementThreadRef = useRef<string | undefined>(undefined);
   const agentRef = useRef(agent);
   agentRef.current = agent;
   const restoreRunActive = isConversationRestoreRunActive({
@@ -88,6 +89,7 @@ export function SessionConversationRestore({
       return;
     }
     agentRef.current.setMessages([]);
+    messageReplacementThreadRef.current = threadId;
     clearRestoredInterrupts(threadId);
     clearPendingCollaborationInterrupt(threadId);
     clearConversationBranchSnapshot(threadId);
@@ -138,6 +140,9 @@ export function SessionConversationRestore({
           shouldRestoreConversationMessages({
             conversationMemoryEnabled,
             isRunning: restoreRunActive,
+            replaceExistingMessages:
+              messageReplacementThreadRef.current === threadId ||
+              (currentAgent.messages?.length ?? 0) === 0,
             agentMessages: currentAgent.messages,
             dto: conversation,
           })
@@ -186,6 +191,9 @@ export function SessionConversationRestore({
         }
       } finally {
         if (!cancelled && fetchGenerationRef.current === generation) {
+          if (messageReplacementThreadRef.current === threadId) {
+            messageReplacementThreadRef.current = undefined;
+          }
           markThreadRestored(threadId);
           setThreadRestoring(threadId, false);
         }
diff --git a/apps/web/src/app/data-tasks/conversation-restore.ts b/apps/web/src/app/data-tasks/conversation-restore.ts
index 259ea8f7..97b2751a 100644
--- a/apps/web/src/app/data-tasks/conversation-restore.ts
+++ b/apps/web/src/app/data-tasks/conversation-restore.ts
@@ -239,12 +239,20 @@ function hasLocalMessagesAfterRestoredPrefix(
 export function shouldRestoreConversationMessages(input: {
   conversationMemoryEnabled: boolean;
   isRunning: boolean;
+  replaceExistingMessages: boolean;
   agentMessages: unknown;
   dto: SessionConversationDto;
 }): boolean {
   if (!input.conversationMemoryEnabled || input.isRunning) {
     return false;
   }
+  if (
+    !input.replaceExistingMessages &&
+    Array.isArray(input.agentMessages) &&
+    input.agentMessages.length > 0
+  ) {
+    return false;
+  }
   const expected = conversationToAgentMessages(input.dto);
   if (expected.length === 0) {
     return false;
diff --git a/apps/web/src/app/data-tasks/data-tasks-app.tsx b/apps/web/src/app/data-tasks/data-tasks-app.tsx
index 331b417e..f1f6edf8 100755
--- a/apps/web/src/app/data-tasks/data-tasks-app.tsx
+++ b/apps/web/src/app/data-tasks/data-tasks-app.tsx
@@ -879,7 +879,7 @@ function StableDataTaskChatInput({
       onEditQueuedPrompt={handleEditQueuedPrompt}
       onDeleteQueuedPrompt={handleDeleteQueuedPrompt}
       onSendQueuedPromptNow={handleSendQueuedPromptNow}
-      submitError={submitError}
+      submitError={submitError ?? bindings.liveRunErrorMessage}
       showDisclaimer={false}
       sessionLockSlot={sessionLockSlot}
     />
@@ -1966,6 +1966,7 @@ function DataTaskWorkspace({
       onUserMessageSubmitted: handleUserMessageSubmitted,
       liveRunStatus: liveRun.runStatus,
       liveRunRunId: liveRun.runId ?? null,
+      liveRunErrorMessage: liveRun.errorMessage ?? null,
       onCancelRun: cancelCurrentRun,
       stopActiveRun,
       stopActiveChatRunRef,
@@ -2002,6 +2003,7 @@ function DataTaskWorkspace({
       toggleSessionResourceItem,
       sessionStartedHints,
       workspaceConfig,
+      liveRun.errorMessage,
       liveRun.runId,
       liveRun.runStatus,
       runCancelBusy,