diff --git a/internal/cloud/access-control.test.ts b/internal/cloud/access-control.test.ts
index 43d63077..eef9686e 100644
--- a/internal/cloud/access-control.test.ts
+++ b/internal/cloud/access-control.test.ts
@@ -1756,6 +1756,79 @@ test("cloud api terminal workspace sync rebuilds missing user message from saved
   }
 });
 
+test("access controller preserves user message when owner evidence updates with agent-only result", async () => {
+  const projectId = "prj_device_pod_workbench";
+  const ownerUserId = "usr_issue853_owner_merge";
+  const conversationId = "cnv_issue853_owner_merge";
+  const sessionId = "ses_issue853_owner_merge";
+  const traceId = "trc_issue853_owner_merge";
+  const threadId = "thread-issue-853-owner-merge";
+  const nowValue = "2026-06-04T10:45:00.000Z";
+  const userText = "请执行 hwpod profile list，并在最终回复里原样包含 HWLAB-853-FINAL-owner-merge";
+  const accessController = createAccessController({ now: () => nowValue });
+
+  await accessController.recordAgentSessionOwner({
+    ownerUserId,
+    sessionId,
+    projectId,
+    agentId: "hwlab-code-agent",
+    status: "active",
+    conversationId,
+    threadId,
+    traceId,
+    session: {
+      source: "workbench-status-sync",
+      sessionStatus: "running",
+      lastTraceId: traceId,
+      messages: [
+        { id: "msg_issue853_owner_user", role: "user", title: "用户", text: userText, status: "sent", traceId, conversationId, sessionId, threadId, createdAt: nowValue },
+        { id: "msg_issue853_owner_agent_pending", role: "agent", title: "Code Agent 处理中", text: "Code Agent 仍在处理，可以继续 steer 或等待 trace 完成。", status: "running", traceId, conversationId, sessionId, threadId, createdAt: nowValue }
+      ],
+      messageCount: 2,
+      firstUserMessagePreview: userText,
+      valuesRedacted: true,
+      secretMaterialStored: false
+    }
+  });
+
+  await accessController.recordAgentSessionOwner({
+    ownerUserId,
+    sessionId,
+    projectId,
+    agentId: "hwlab-code-agent",
+    status: "failed",
+    conversationId,
+    threadId,
+    traceId,
+    session: {
+      source: "code-agent-result",
+      status: "failed",
+      sessionStatus: "failed",
+      messages: [
+        { id: "msg_issue853_owner_agent_result", role: "agent", title: "Code Agent result", text: "HyueAPI 403 INSUFFICIENT_BALANCE", status: "failed", traceId, conversationId, sessionId, threadId, createdAt: nowValue }
+      ],
+      messageCount: 1,
+      firstUserMessagePreview: userText,
+      valuesRedacted: true,
+      secretMaterialStored: false
+    }
+  });
+
+  const session = await accessController.getAgentSession(sessionId);
+  const conversation = await accessController.visibleConversationForActor({ id: ownerUserId, role: "user" }, conversationId, projectId, { includeArchived: true });
+  assert.deepEqual(session.session.messages.map((message) => message.role), ["user", "agent"]);
+  assert.deepEqual(conversation.messages.map((message) => message.role), ["user", "agent"]);
+  assert.equal(session.session.messages[0].text, userText);
+  assert.equal(conversation.messages[0].text, userText);
+  assert.equal(session.session.messages[0].traceId, traceId);
+  assert.equal(conversation.messages[0].traceId, traceId);
+  assert.equal(session.session.messages[1].text, "HyueAPI 403 INSUFFICIENT_BALANCE");
+  assert.equal(conversation.messages[1].status, "failed");
+  assert.equal(session.session.messageCount, 2);
+  assert.equal(conversation.messageCount, 2);
+  assert.equal(conversation.firstUserMessagePreview, userText);
+});
+
 test("access controller restores AgentRun mapping by Code Agent traceId", async () => {
   const accessController = createAccessController({ now: () => "2026-06-01T00:00:00.000Z" });
   await accessController.recordAgentSessionOwner({
diff --git a/internal/cloud/access-control.ts b/internal/cloud/access-control.ts
index e588c1ce..657d80fe 100644
--- a/internal/cloud/access-control.ts
+++ b/internal/cloud/access-control.ts
@@ -2350,7 +2350,18 @@ function mergeAgentSessionOwnerEvidence(nextValue, existingValue) {
   const merged = { ...existing, ...next };
   const existingMessages = Array.isArray(existing.messages) ? existing.messages : null;
   const nextMessages = Array.isArray(next.messages) ? next.messages : null;
-  if (existingMessages?.length && (!nextMessages || nextMessages.length === 0)) merged.messages = existingMessages;
+  if (nextMessages?.length) {
+    merged.messages = mergeAgentSessionOwnerMessages(nextMessages, existingMessages, {
+      traceId: next.lastTraceId ?? next.traceId ?? existing.lastTraceId ?? existing.traceId ?? firstMessageTraceId(nextMessages) ?? firstMessageTraceId(existingMessages),
+      conversationId: next.conversationId ?? existing.conversationId ?? firstMessageField(nextMessages, "conversationId") ?? firstMessageField(existingMessages, "conversationId"),
+      sessionId: next.sessionId ?? existing.sessionId ?? firstMessageField(nextMessages, "sessionId") ?? firstMessageField(existingMessages, "sessionId"),
+      threadId: next.threadId ?? existing.threadId ?? firstMessageField(nextMessages, "threadId") ?? firstMessageField(existingMessages, "threadId"),
+      now: next.updatedAt ?? existing.updatedAt ?? firstMessageField(nextMessages, "updatedAt") ?? firstMessageField(nextMessages, "createdAt") ?? firstMessageField(existingMessages, "updatedAt") ?? firstMessageField(existingMessages, "createdAt"),
+      firstUserPreview: firstUserPreviewFromMessages(nextMessages) ?? next.firstUserMessagePreview ?? firstUserPreviewFromMessages(existingMessages) ?? existing.firstUserMessagePreview
+    });
+  } else if (existingMessages?.length) {
+    merged.messages = existingMessages;
+  }
   const existingChatMessages = Array.isArray(existing.chatMessages) ? existing.chatMessages : null;
   const nextChatMessages = Array.isArray(next.chatMessages) ? next.chatMessages : null;
   if (existingChatMessages?.length && (!nextChatMessages || nextChatMessages.length === 0)) merged.chatMessages = existingChatMessages;
@@ -2367,6 +2378,37 @@ function mergeAgentSessionOwnerEvidence(nextValue, existingValue) {
   }
   return merged;
 }
+function mergeAgentSessionOwnerMessages(nextMessages = [], existingMessages = [], context = {}) {
+  const next = Array.isArray(nextMessages) ? nextMessages.map(redactConversationMessage).filter(Boolean) : [];
+  if (next.some((message) => message.role === "user")) return next;
+  const existing = Array.isArray(existingMessages) ? existingMessages.map(redactConversationMessage).filter(Boolean) : [];
+  const merged = [...existing];
+  for (const message of next) {
+    const index = merged.findIndex((item) => sameConversationMessage(item, message));
+    if (index >= 0) merged[index] = message;
+    else merged.push(message);
+  }
+  return ensureTerminalUserMessage(merged, context).slice(-50);
+}
+function sameConversationMessage(left = {}, right = {}) {
+  const leftId = textOr(left.id, "");
+  const rightId = textOr(right.id, "");
+  if (leftId && rightId && leftId === rightId) return true;
+  const leftTrace = safeTraceIdLocal(left.traceId);
+  const rightTrace = safeTraceIdLocal(right.traceId);
+  return Boolean(leftTrace && rightTrace && leftTrace === rightTrace && textOr(left.role, "") === textOr(right.role, ""));
+}
+function firstMessageTraceId(messagesSource) {
+  return safeTraceIdLocal(firstMessageField(messagesSource, "traceId")) || null;
+}
+function firstMessageField(messagesSource, key) {
+  if (!Array.isArray(messagesSource)) return null;
+  for (const message of messagesSource) {
+    const value = textOr(message?.[key], "");
+    if (value) return boundedText(value, 240);
+  }
+  return null;
+}
 function agentSessionIdForRecord(sessionId, traceId) { const sessionText = textOr(sessionId, ""); if (/^ses_[A-Za-z0-9_.:-]+$/u.test(sessionText)) return sessionText; const traceText = textOr(traceId, ""); return /^trc_[A-Za-z0-9_.:-]+$/u.test(traceText) ? `ses_pending_${traceText.slice(4)}` : null; }
 function safeConversationIdLocal(value) { return /^cnv_[A-Za-z0-9_.:-]+$/u.test(textOr(value, "")); }
 function boundedListLimit(value) { const parsed = Number.parseInt(String(value ?? ""), 10); return Math.min(Math.max(Number.isInteger(parsed) && parsed > 0 ? parsed : 20, 1), 100); }
@@ -2719,7 +2761,15 @@ function conversationsFromAgentSessions(sessions = []) {
 }
 function publicAgentConversation(session) {
   const snapshot = normalizeObject(session.session);
-  const messages = Array.isArray(snapshot.messages) ? snapshot.messages : Array.isArray(snapshot.chatMessages) ? snapshot.chatMessages : [];
+  const rawMessages = Array.isArray(snapshot.messages) ? snapshot.messages : Array.isArray(snapshot.chatMessages) ? snapshot.chatMessages : [];
+  const messages = ensureTerminalUserMessage(rawMessages, {
+    traceId: session.lastTraceId ?? snapshot.lastTraceId,
+    conversationId: session.conversationId,
+    sessionId: session.id,
+    threadId: session.threadId,
+    now: session.updatedAt,
+    firstUserPreview: snapshot.firstUserMessagePreview
+  });
   const status = resolvedConversationStatus(session.status, snapshot, messages);
   const lastTraceId = resolvedConversationLastTraceId(session.lastTraceId, status, messages, snapshot);
   return {