diff --git a/docs/BUG_HISTORY.md b/docs/BUG_HISTORY.md
index fd13a7b4..a2cba9c7 100644
--- a/docs/BUG_HISTORY.md
+++ b/docs/BUG_HISTORY.md
@@ -665,3 +665,19 @@
 - 相关记录：BUG-034、BUG-037、BUG-038
 - 复发自：无
 - 修复版本：本次流式修复提交
+
+## BUG-040 | Agent 活动状态与回答被错误渲染为互斥状态
+
+- 状态：resolved
+- 首次发现：2026-07-23
+- 最近更新：2026-07-23
+- 影响面：普通 session 与生时校正共用的 Agent 消息行、流式回答反馈、完成态识别
+- 用户现象：Agent 尚未产出正文时只显示 orb 活动状态；开始出现正文后状态与答案的关系不连续，完成后活动状态直接消失，用户无法从同一消息位置判断回答仍在生成还是已经结束。
+- 触发条件：任意 assistant 消息在 `thinking`、`streaming`、`settled` 三种视图状态之间切换。
+- 根因：共享 `ChatMessageRow` 使用条件分支把 `thinking` 渲染为仅有 `AgentActivityStatus`，又只在 `streaming` 时显示 composing 状态；`settled` 分支只保留正文，因此活动状态和正文被实现成了互斥内容，而不是同一消息的连续生命周期。
+- 修复：assistant 消息始终在同一气泡内先渲染活动状态，再渲染当前已有正文；thinking/streaming 继续使用 working/composing orb，settled 只把状态文案切换为“回答已完成”，并把 orb 替换为 Lucide 完成图标。普通 session 与生时校正共享该行为，React 消息 identity 与正文内容保持不变。
+- 验证：消息视图回归覆盖 working、composing、completed 三态、正文与状态同时存在、完成态 Lucide 图标；相关普通 session 与生时校正契约测试通过，并执行真实浏览器检查。
+- 防复发：Agent 活动状态只能描述消息生命周期，不得控制正文是否渲染；完成态必须保留稳定的视觉反馈，不能以卸载整个状态区域代替状态转换。
+- 相关记录：BUG-039
+- 复发自：无
+- 修复版本：待提交
diff --git a/frontend/src/app/globals.css b/frontend/src/app/globals.css
index 2cec35be..b1de26a1 100644
--- a/frontend/src/app/globals.css
+++ b/frontend/src/app/globals.css
@@ -165,7 +165,7 @@ button:disabled { cursor: default; opacity: .45; }
 .message-markdown ul, .message-markdown ol { margin: 10px 0 16px; padding-left: 24px; }
 .message-markdown li { margin: 6px 0; }
 .agent-activity-status { min-height: 24px; display: flex; align-items: center; gap: var(--space-2); color: var(--color-ink-secondary); font-size: var(--type-body-sm); line-height: 1.5; }
-.agent-activity-status canvas { flex: 0 0 auto; }
+.agent-activity-status canvas, .agent-activity-status svg { flex: 0 0 auto; }
 .agent-activity-status + .message-markdown { margin-top: var(--space-2); }
 .composer-suggestions::-webkit-scrollbar { display: none; }
 .composer textarea::placeholder { color: var(--color-ink-tertiary); }
diff --git a/frontend/src/components/agent-activity-status.tsx b/frontend/src/components/agent-activity-status.tsx
index 3b3d748e..0c1c422a 100644
--- a/frontend/src/components/agent-activity-status.tsx
+++ b/frontend/src/components/agent-activity-status.tsx
@@ -1,3 +1,4 @@
+import { CircleCheck } from "lucide-react";
 import { ThinkingOrb, type OrbState } from "thinking-orbs";
 
 const labels = {
@@ -7,18 +8,23 @@ const labels = {
   listening: "正在聆听…",
   composing: "正在组织回答…",
   shaping: "正在生成结果…",
-} as const satisfies Record<OrbState, string>;
+  completed: "回答已完成",
+} as const satisfies Record<OrbState | "completed", string>;
+
+export type AgentActivityState = OrbState | "completed";
 
 export function AgentActivityStatus({
   state,
   label = labels[state],
 }: Readonly<{
-  state: OrbState;
+  state: AgentActivityState;
   label?: string;
 }>) {
   return (
-    <div className="agent-activity-status" role="status">
-      <ThinkingOrb aria-hidden="true" state={state} size={20} />
+    <div className="agent-activity-status" role={state === "completed" ? undefined : "status"}>
+      {state === "completed"
+        ? <CircleCheck aria-hidden="true" size={20} strokeWidth={1.8} />
+        : <ThinkingOrb aria-hidden="true" state={state} size={20} />}
       <span>{label}</span>
     </div>
   );
diff --git a/frontend/src/components/chat-message-row.tsx b/frontend/src/components/chat-message-row.tsx
index 9d5dfa01..6103538d 100644
--- a/frontend/src/components/chat-message-row.tsx
+++ b/frontend/src/components/chat-message-row.tsx
@@ -50,12 +50,17 @@ export function ChatMessageRow({ message }: { readonly message: ChatMessageView
       <div className="message-content">
         <div className="message-bubble">
           {message.role === "assistant" ? (
-            message.state === "thinking"
-              ? <AgentActivityStatus state="working" label="正在核对星盘信息…" />
-              : <>
-                {message.state === "streaming" && <AgentActivityStatus state="composing" />}
-                <ChatMessageContent text={message.text} />
-              </>
+            <>
+              <AgentActivityStatus
+                state={message.state === "thinking"
+                  ? "working"
+                  : message.state === "streaming"
+                    ? "composing"
+                    : "completed"}
+                label={message.state === "thinking" ? "正在核对星盘信息…" : undefined}
+              />
+              {message.text && <ChatMessageContent text={message.text} />}
+            </>
           ) : <p>{message.text}</p>}
         </div>
       </div>
diff --git a/frontend/tests/chat-stream-layout.test.ts b/frontend/tests/chat-stream-layout.test.ts
index 8ce1b838..de13c7ed 100644
--- a/frontend/tests/chat-stream-layout.test.ts
+++ b/frontend/tests/chat-stream-layout.test.ts
@@ -45,10 +45,14 @@ test("does not duplicate a completed assistant answer while loading state settle
 });
 
 test("shows honest agent activity states before and during streamed text", () => {
-  assert.match(messageRowSource, /state="working" label="正在核对星盘信息…"/);
-  assert.match(messageRowSource, /message\.state === "streaming" && <AgentActivityStatus state="composing"/);
+  assert.match(messageRowSource, /message\.state === "thinking"[\s\S]*?\? "working"/);
+  assert.match(messageRowSource, /message\.state === "thinking" \? "正在核对星盘信息…"/);
+  assert.match(messageRowSource, /message\.state === "streaming"[\s\S]*?"composing"/);
+  assert.match(messageRowSource, /: "completed"/);
+  assert.match(messageRowSource, /message\.text && <ChatMessageContent text=\{message\.text\}/);
   assert.match(activitySource, /<ThinkingOrb aria-hidden="true" state=\{state\} size=\{20\}/);
-  assert.match(activitySource, /satisfies Record<OrbState, string>/);
+  assert.match(activitySource, /<CircleCheck aria-hidden="true" size=\{20\}/);
+  assert.match(activitySource, /satisfies Record<OrbState \| "completed", string>/);
   assert.doesNotMatch(globalStyles, /\.thinking\b/);
 });