diff --git a/web/hwlab-cloud-web/src/App.tsx b/web/hwlab-cloud-web/src/App.tsx
index 04be1e62..3a450f86 100644
--- a/web/hwlab-cloud-web/src/App.tsx
+++ b/web/hwlab-cloud-web/src/App.tsx
@@ -166,7 +166,7 @@ export function App(): ReactElement {
             />
           ) : null}
           <section className="center-workspace">
-            {route === "workspace" ? <ConversationPanel messages={store.state.messages} availability={store.state.codeAgentAvailability} live={store.state.live} chatPending={store.state.chatPending} codeAgentTimeoutMs={store.state.codeAgentTimeoutMs} onCopySession={() => copyTextToClipboard(firstNonEmptyString(store.composer.sessionId, store.state.workspace?.selectedAgentSessionId, store.state.workspace?.workspace?.selectedAgentSessionId, store.activeConversationId) ?? "")} onCancelMessage={(id) => void store.cancelAgentMessage(id)} onRetryMessage={(id) => void store.retryAgentMessage(id)} /> : null}
+            {route === "workspace" ? <ConversationPanel messages={store.state.messages} availability={store.state.codeAgentAvailability} live={store.state.live} chatPending={store.state.chatPending} codeAgentTimeoutMs={store.state.codeAgentTimeoutMs} onCopySession={() => copyTextToClipboard(firstNonEmptyString(store.composer.sessionId, store.state.workspace?.selectedAgentSessionId, store.state.workspace?.workspace?.selectedAgentSessionId, store.activeConversationId) ?? "")} onCancelMessage={(id) => void store.cancelAgentMessage(id)} onRetryMessage={(id) => void store.retryAgentMessage(id)} onReplayTrace={(id) => void store.replayAgentTrace(id)} /> : null}
             {route === "skills" ? <SkillsView /> : null}
             {route === "gate" ? <GateView /> : null}
             {route === "help" ? <HelpView help={help} /> : null}
diff --git a/web/hwlab-cloud-web/src/components/conversation/ConversationPanel.test.ts b/web/hwlab-cloud-web/src/components/conversation/ConversationPanel.test.ts
new file mode 100644
index 00000000..4500b386
--- /dev/null
+++ b/web/hwlab-cloud-web/src/components/conversation/ConversationPanel.test.ts
@@ -0,0 +1,34 @@
+import assert from "node:assert/strict";
+import { test } from "bun:test";
+
+import { shouldAutoReplayTrace } from "./ConversationPanel";
+import type { ChatMessage } from "../../types/domain";
+
+const baseAgentMessage: ChatMessage = {
+  id: "msg_agent",
+  role: "agent",
+  title: "Code Agent 回复",
+  text: "done",
+  status: "idle" as ChatMessage["status"],
+  createdAt: "2026-06-04T12:13:54.661Z",
+  traceId: "trc_issue849",
+  runnerTrace: {
+    traceId: "trc_issue849",
+    status: "completed",
+    eventCount: 49,
+    eventsCompacted: false,
+    fullTraceLoaded: false
+  }
+};
+
+test("conversation panel auto replays compact historical traces", () => {
+  assert.equal(shouldAutoReplayTrace(baseAgentMessage), true);
+});
+
+test("conversation panel does not auto replay loaded, empty, or running traces", () => {
+  assert.equal(shouldAutoReplayTrace({ ...baseAgentMessage, runnerTrace: { ...baseAgentMessage.runnerTrace, events: [{ seq: 1, label: "assistant:message" }] } }), false);
+  assert.equal(shouldAutoReplayTrace({ ...baseAgentMessage, runnerTrace: { ...baseAgentMessage.runnerTrace, eventCount: 0 } }), false);
+  assert.equal(shouldAutoReplayTrace({ ...baseAgentMessage, status: "running" }), false);
+  assert.equal(shouldAutoReplayTrace({ ...baseAgentMessage, traceReplayStatus: "完整 trace 已回放：49 个原始 event" }), false);
+  assert.equal(shouldAutoReplayTrace({ ...baseAgentMessage, runnerTrace: { ...baseAgentMessage.runnerTrace, fullTraceLoaded: true } }), false);
+});
diff --git a/web/hwlab-cloud-web/src/components/conversation/ConversationPanel.tsx b/web/hwlab-cloud-web/src/components/conversation/ConversationPanel.tsx
index 64a8d257..d57b5d64 100644
--- a/web/hwlab-cloud-web/src/components/conversation/ConversationPanel.tsx
+++ b/web/hwlab-cloud-web/src/components/conversation/ConversationPanel.tsx
@@ -1,5 +1,5 @@
 import type { ReactElement } from "react";
-import { useMemo } from "react";
+import { useEffect, useMemo, useRef } from "react";
 
 import { useScrollFollow } from "../../hooks/useScrollFollow";
 import type { ChatMessage, CodeAgentAvailability, LiveSurface } from "../../types/domain";
@@ -20,9 +20,10 @@ interface ConversationPanelProps {
   onCopySession(): void;
   onCancelMessage(messageId: string): void;
   onRetryMessage(messageId: string): void;
+  onReplayTrace(messageId: string): void;
 }
 
-export function ConversationPanel({ messages, availability, live, chatPending, codeAgentTimeoutMs, onCopySession, onCancelMessage, onRetryMessage }: ConversationPanelProps & { codeAgentTimeoutMs: number }): ReactElement {
+export function ConversationPanel({ messages, availability, live, chatPending, codeAgentTimeoutMs, onCopySession, onCancelMessage, onRetryMessage, onReplayTrace }: ConversationPanelProps & { codeAgentTimeoutMs: number }): ReactElement {
   const scrollFollow = useScrollFollow<HTMLElement>([messages]);
   return (
     <section className="view workbench-view" id="workspace" data-view="workspace" data-scroll-follow={scrollFollow.following ? "bottom" : "detached"} aria-labelledby="workspace-title" ref={scrollFollow.ref} onScroll={scrollFollow.onScroll}>
@@ -50,6 +51,7 @@ export function ConversationPanel({ messages, availability, live, chatPending, c
                 codeAgentTimeoutMs={codeAgentTimeoutMs}
                 onCancel={() => onCancelMessage(message.id)}
                 onRetry={() => onRetryMessage(message.id)}
+                onReplayTrace={() => onReplayTrace(message.id)}
               />
             ))}
           </div>
@@ -98,8 +100,28 @@ function CodeAgentSummary({ availability, live, latestMessage }: { availability:
   );
 }
 
-function MessageCard({ message, codeAgentTimeoutMs, onCancel, onRetry }: { message: ChatMessage; codeAgentTimeoutMs: number; onCancel(): void; onRetry(): void }): ReactElement {
+export function shouldAutoReplayTrace(message: ChatMessage): boolean {
+  if (message.role !== "agent") return false;
+  const trace = message.runnerTrace;
+  const traceId = message.traceId ?? trace?.traceId;
+  if (!traceId) return false;
+  if (message.status === "running" || trace?.status === "running") return false;
+  if (message.traceReplayStatus) return false;
+  if (trace?.fullTraceLoaded === true) return false;
+  const events = Array.isArray(trace?.events) ? trace.events : [];
+  const declaredCount = Number(trace?.eventCount ?? 0);
+  return events.length === 0 && declaredCount > 0;
+}
+
+function MessageCard({ message, codeAgentTimeoutMs, onCancel, onRetry, onReplayTrace }: { message: ChatMessage; codeAgentTimeoutMs: number; onCancel(): void; onRetry(): void; onReplayTrace(): void }): ReactElement {
   const traceKey = `hwlab.workbench.trace-open.${message.traceId ?? message.id}`;
+  const replayRequestedRef = useRef(false);
+  useEffect(() => {
+    if (replayRequestedRef.current) return;
+    if (!shouldAutoReplayTrace(message)) return;
+    replayRequestedRef.current = true;
+    onReplayTrace();
+  }, [message, onReplayTrace]);
   if (message.role === "agent") {
     const hasFinalResponse = message.status !== "running" && message.text.trim().length > 0;
     return (