diff --git a/src/feishu/__tests__/chat-history-fork.test.ts b/src/feishu/__tests__/chat-history-fork.test.ts
new file mode 100644
index 0000000..e87a8e2
--- /dev/null
+++ b/src/feishu/__tests__/chat-history-fork.test.ts
@@ -0,0 +1,294 @@
+/**
+ * Tests for buildChatHistoryContext fork semantics.
+ *
+ * buildChatHistoryContext now mirrors buildDirectTaskHistory's fork logic:
+ * - No threadId → fetch from parent chat only
+ * - Thread empty → fork from parent chat
+ * - Thread messages < max → supplement with parent chat messages
+ * - Thread messages ≥ max → first + latest (max - 1)
+ * - Structured sections (parentMsgCount) passed to formatHistoryMessages
+ */
+// @ts-nocheck — test file
+import { describe, it, expect, vi } from 'vitest';
+
+// ============================================================
+// Mocks
+// ============================================================
+
+const mockFetchRecentMessages = vi.fn();
+
+vi.mock('../client.js', () => ({
+  feishuClient: {
+    fetchRecentMessages: (...args: unknown[]) => mockFetchRecentMessages(...args),
+    getUserName: vi.fn().mockResolvedValue(null),
+    replyText: vi.fn(),
+    replyInThread: vi.fn(),
+    sendCard: vi.fn(),
+    updateCard: vi.fn(),
+    replyCardInThread: vi.fn(),
+    sendText: vi.fn(),
+  },
+}));
+
+vi.mock('../../utils/logger.js', () => ({
+  logger: {
+    info: vi.fn(),
+    warn: vi.fn(),
+    error: vi.fn(),
+    debug: vi.fn(),
+  },
+}));
+
+vi.mock('../../config.js', () => ({
+  config: {
+    feishu: { encryptKey: '', verifyToken: '' },
+    security: { allowedUserIds: [] },
+    claude: { defaultWorkDir: '/tmp/work' },
+    workspace: { baseDir: '/tmp/workspaces', branchPrefix: 'feat/test' },
+    db: { pipelineDbPath: ':memory:' },
+    agent: { bindings: [], groupConfigs: {} },
+    chat: { historyMaxCount: 10, historyMaxChars: 8000 },
+    memory: { enabled: false },
+  },
+  isMultiBotMode: vi.fn(() => false),
+}));
+
+// event-handler.ts dependency chain mocks
+vi.mock('../../claude/executor.js', () => ({
+  claudeExecutor: { execute: vi.fn(), killSession: vi.fn() },
+}));
+vi.mock('../../session/manager.js', () => ({
+  sessionManager: {
+    get: vi.fn(), getOrCreate: vi.fn(), setWorkingDir: vi.fn(),
+    setStatus: vi.fn(), setConversationId: vi.fn(), setThread: vi.fn(),
+    getThreadSession: vi.fn(), upsertThreadSession: vi.fn(),
+    setThreadConversationId: vi.fn(), setThreadWorkingDir: vi.fn(),
+    getRecentSummaries: vi.fn(() => []), saveSummary: vi.fn(), reset: vi.fn(),
+  },
+}));
+vi.mock('../../session/queue.js', () => ({
+  taskQueue: { enqueue: vi.fn(), dequeue: vi.fn(), complete: vi.fn(), pendingCount: vi.fn(() => 0), cancelPending: vi.fn(() => 0), isBusy: vi.fn(() => false) },
+}));
+vi.mock('../message-builder.js', () => ({
+  buildProgressCard: vi.fn(), buildResultCard: vi.fn(), buildStatusCard: vi.fn(),
+}));
+vi.mock('../../utils/security.js', () => ({
+  isUserAllowed: vi.fn(() => true), containsDangerousCommand: vi.fn(() => false),
+}));
+vi.mock('../../pipeline/store.js', () => ({
+  pipelineStore: { get: vi.fn(), findPendingByChat: vi.fn(), tryStart: vi.fn() },
+}));
+vi.mock('../../pipeline/runner.js', () => ({
+  createPendingPipeline: vi.fn(), startPipeline: vi.fn(),
+  abortPipeline: vi.fn(), cancelPipeline: vi.fn(), retryPipeline: vi.fn(),
+}));
+vi.mock('../../agent/router.js', () => ({
+  resolveAgent: vi.fn(() => 'dev'), shouldRespond: vi.fn(() => true),
+}));
+vi.mock('../../agent/registry.js', () => ({
+  agentRegistry: { get: vi.fn(), getOrThrow: vi.fn(), allIds: vi.fn(() => []) },
+}));
+vi.mock('../multi-account.js', () => ({
+  accountManager: { getAllBotOpenIds: vi.fn(() => new Set()), getBotOpenId: vi.fn() },
+}));
+vi.mock('../bot-registry.js', () => ({
+  chatBotRegistry: { getBots: vi.fn(() => []), addBot: vi.fn(), removeBot: vi.fn(), clearChat: vi.fn() },
+}));
+vi.mock('../approval.js', () => ({
+  checkAndRequestApproval: vi.fn(() => true), handleApprovalTextCommand: vi.fn(() => false), handleApprovalCardAction: vi.fn(), setOnApproved: vi.fn(),
+}));
+vi.mock('../thread-context.js', () => ({ resolveThreadContext: vi.fn() }));
+vi.mock('../../agent/config-loader.js', () => ({ readPersonaFile: vi.fn(), loadKnowledgeContent: vi.fn() }));
+vi.mock('../../agent/tools/discussion.js', () => ({ createDiscussionMcpServer: vi.fn() }));
+vi.mock('../oauth.js', () => ({ generateAuthUrl: vi.fn(), hasCallbackUrl: vi.fn(), handleManualCode: vi.fn() }));
+vi.mock('../../memory/injector.js', () => ({ injectMemories: vi.fn(() => '') }));
+vi.mock('../../memory/extractor.js', () => ({ extractMemories: vi.fn() }));
+vi.mock('../../memory/commands.js', () => ({ handleMemoryCommand: vi.fn(), handleMemoryCardAction: vi.fn() }));
+vi.mock('../../workspace/identity.js', () => ({ getRepoIdentity: vi.fn((p: string) => p) }));
+vi.mock('../../utils/quick-ack.js', () => ({ generateQuickAck: vi.fn() }));
+vi.mock('../../utils/thread-relevance.js', () => ({ checkThreadRelevance: vi.fn() }));
+vi.mock('../../workspace/manager.js', () => ({ setupWorkspace: vi.fn() }));
+
+// ============================================================
+// Replicate buildChatHistoryContext fork logic for testing
+// (function is private, same approach as direct-thread.test.ts)
+// ============================================================
+
+const HISTORY_MAX_COUNT = 10;
+
+type SimpleMessage = {
+  messageId: string;
+  senderId: string;
+  senderType: 'user' | 'app';
+  content: string;
+  msgType: string;
+  createTime?: string;
+};
+
+interface ForkResult {
+  messages: SimpleMessage[];
+  parentMsgCount: number;
+}
+
+/**
+ * Extracted fork logic from the updated buildChatHistoryContext.
+ */
+function forkMessages(
+  threadId: string | undefined,
+  threadMsgs: SimpleMessage[],
+  parentMsgs: SimpleMessage[],
+  currentMessageId?: string,
+): ForkResult {
+  let messages: SimpleMessage[];
+  let parentMsgCount = 0;
+
+  if (!threadId) {
+    messages = currentMessageId
+      ? parentMsgs.filter(m => m.messageId !== currentMessageId)
+      : parentMsgs;
+    return { messages, parentMsgCount: 0 };
+  }
+
+  // Thread mode: fork semantics
+  const filtered = currentMessageId
+    ? threadMsgs.filter(m => m.messageId !== currentMessageId)
+    : threadMsgs;
+
+  if (filtered.length === 0) {
+    // Thread empty → fork from parent
+    messages = parentMsgs;
+  } else if (filtered.length <= HISTORY_MAX_COUNT) {
+    // Thread < max → supplement with parent
+    const remaining = HISTORY_MAX_COUNT - filtered.length;
+    if (remaining > 0 && parentMsgs.length > 0) {
+      parentMsgCount = parentMsgs.length;
+      messages = [...parentMsgs, ...filtered];
+    } else {
+      messages = filtered;
+    }
+  } else {
+    // Thread > max → first + latest (max - 1)
+    const first = filtered[0];
+    const latest = filtered.slice(-(HISTORY_MAX_COUNT - 1));
+    messages = [first, ...latest];
+  }
+
+  return { messages, parentMsgCount };
+}
+
+function makeMsg(id: string, content: string, senderType: 'user' | 'app' = 'user'): SimpleMessage {
+  return { messageId: id, senderId: `sender_${id}`, senderType, content, msgType: 'text' };
+}
+
+// ============================================================
+// Tests
+// ============================================================
+
+describe('buildChatHistoryContext fork semantics', () => {
+  describe('fork logic (unit)', () => {
+    it('no threadId → returns parent chat messages only', () => {
+      const parentMsgs = [makeMsg('p1', 'hello'), makeMsg('p2', 'world')];
+      const { messages, parentMsgCount } = forkMessages(undefined, [], parentMsgs);
+      expect(messages).toHaveLength(2);
+      expect(parentMsgCount).toBe(0);
+    });
+
+    it('no threadId → filters current message', () => {
+      const parentMsgs = [makeMsg('p1', 'hello'), makeMsg('current', 'me')];
+      const { messages } = forkMessages(undefined, parentMsgs, parentMsgs, 'current');
+      expect(messages).toHaveLength(1);
+      expect(messages[0].messageId).toBe('p1');
+    });
+
+    it('empty thread → fork from parent chat', () => {
+      const parentMsgs = [makeMsg('p1', 'parent msg 1'), makeMsg('p2', 'parent msg 2')];
+      const threadMsgs = [makeMsg('current', 'hi')]; // only current message
+      const { messages, parentMsgCount } = forkMessages('thread1', threadMsgs, parentMsgs, 'current');
+      expect(messages).toEqual(parentMsgs);
+      expect(parentMsgCount).toBe(0); // fork mode, not supplement
+    });
+
+    it('thread with 3 messages (< max) → supplement with parent', () => {
+      const threadMsgs = [
+        makeMsg('t1', 'thread first'),
+        makeMsg('t2', 'thread second'),
+        makeMsg('t3', 'thread third'),
+      ];
+      const parentMsgs = Array.from({ length: 7 }, (_, i) => makeMsg(`p${i}`, `parent ${i}`));
+      const { messages, parentMsgCount } = forkMessages('thread1', threadMsgs, parentMsgs);
+
+      // Parent messages first, then thread messages
+      expect(messages).toHaveLength(10);
+      expect(messages[0].content).toBe('parent 0');
+      expect(messages[7].content).toBe('thread first');
+      expect(parentMsgCount).toBe(7);
+    });
+
+    it('thread with exactly 10 messages → no supplementing', () => {
+      const threadMsgs = Array.from({ length: 10 }, (_, i) => makeMsg(`t${i}`, `msg ${i}`));
+      const { messages, parentMsgCount } = forkMessages('thread1', threadMsgs, []);
+      expect(messages).toHaveLength(10);
+      expect(parentMsgCount).toBe(0);
+    });
+
+    it('thread with 15 messages (> max) → first + last 9', () => {
+      const threadMsgs = Array.from({ length: 15 }, (_, i) => makeMsg(`t${i}`, `thread msg ${i}`));
+      const { messages, parentMsgCount } = forkMessages('thread1', threadMsgs, []);
+
+      expect(messages).toHaveLength(10);
+      expect(messages[0].content).toBe('thread msg 0'); // first
+      expect(messages[1].content).toBe('thread msg 6'); // latest[0]
+      expect(messages[9].content).toBe('thread msg 14'); // latest[8]
+      expect(parentMsgCount).toBe(0);
+    });
+
+    it('filters current message from thread before fork calculation', () => {
+      const threadMsgs = [
+        makeMsg('t1', 'old msg'),
+        makeMsg('current', 'current msg'),
+      ];
+      const parentMsgs = Array.from({ length: 9 }, (_, i) => makeMsg(`p${i}`, `parent ${i}`));
+      const { messages, parentMsgCount } = forkMessages('thread1', threadMsgs, parentMsgs, 'current');
+
+      // After filtering: 1 thread msg, supplement with 9 parent
+      expect(messages).toHaveLength(10);
+      expect(messages.find(m => m.content === 'current msg')).toBeUndefined();
+      expect(parentMsgCount).toBe(9);
+    });
+  });
+
+  describe('structured sections via formatHistoryMessages', () => {
+    it('renders structured sections when parentMsgCount > 0', async () => {
+      const { _testFormatHistoryMessages: formatHistoryMessages } = await import('../event-handler.js');
+      const parentMsgs = [
+        makeMsg('p1', 'parent context 1'),
+        makeMsg('p2', 'parent context 2'),
+      ];
+      const threadMsgs = [
+        makeMsg('t1', 'thread question'),
+      ];
+      const combined = [...parentMsgs, ...threadMsgs];
+
+      const result = await formatHistoryMessages(combined, 'chat1', undefined, { parentMsgCount: 2 });
+
+      expect(result).toContain('### 群主聊天');
+      expect(result).toContain('### 当前话题');
+      expect(result).toContain('parent context 1');
+      expect(result).toContain('thread question');
+    });
+
+    it('renders flat list when no parent supplement (parentMsgCount = 0)', async () => {
+      const { _testFormatHistoryMessages: formatHistoryMessages } = await import('../event-handler.js');
+      const threadMsgs = [
+        makeMsg('t1', 'msg one'),
+        makeMsg('t2', 'msg two'),
+      ];
+
+      const result = await formatHistoryMessages(threadMsgs, 'chat1');
+
+      expect(result).toContain('以下是用户 @bot 之前的聊天记录');
+      expect(result).not.toContain('### 群主聊天');
+      expect(result).not.toContain('### 当前话题');
+    });
+  });
+});
diff --git a/src/feishu/event-handler.ts b/src/feishu/event-handler.ts
index 58abf6c..47fcb4e 100644
--- a/src/feishu/event-handler.ts
+++ b/src/feishu/event-handler.ts
@@ -1444,31 +1444,62 @@ async function buildChatHistoryContext(
   selfBotOpenIds?: Set<string>,
 ): Promise<HistoryResult> {
   try {
-    const containerId = threadId ?? chatId;
-    const containerType = threadId ? 'thread' as const : 'chat' as const;
-    const messages = await feishuClient.fetchRecentMessages(containerId, containerType, config.chat.historyMaxCount, threadId ? chatId : undefined);
+    type HistoryMsg = { messageId: string; senderId: string; senderType: 'user' | 'app'; content: string; msgType: string; createTime?: string; imageRefs?: Array<{ imageKey: string }> };
+    let messages: HistoryMsg[];
+    let parentMsgCount = 0;
 
-    // 过滤掉当前消息
-    let filtered = currentMessageId
-      ? messages.filter(m => m.messageId !== currentMessageId)
-      : messages;
+    if (!threadId) {
+      // 主聊天区：直接取父群最近消息
+      messages = await feishuClient.fetchRecentMessages(chatId, 'chat', config.chat.historyMaxCount);
+    } else {
+      // 话题模式：fork 语义（与 buildDirectTaskHistory 一致）
+      const threadMsgs = await feishuClient.fetchRecentMessages(threadId, 'thread', 50, chatId);
+      const filtered = currentMessageId
+        ? threadMsgs.filter(m => m.messageId !== currentMessageId)
+        : threadMsgs;
+
+      if (filtered.length === 0) {
+        // 话题为空，从父群 fork
+        messages = await feishuClient.fetchRecentMessages(chatId, 'chat', config.chat.historyMaxCount);
+      } else if (filtered.length <= config.chat.historyMaxCount) {
+        // 话题消息不足 max，补充父群消息
+        const remaining = config.chat.historyMaxCount - filtered.length;
+        if (remaining > 0) {
+          const parentMsgs = await feishuClient.fetchRecentMessages(chatId, 'chat', remaining);
+          parentMsgCount = parentMsgs.length;
+          messages = [...parentMsgs, ...filtered];
+        } else {
+          messages = filtered;
+        }
+      } else {
+        // 话题消息 > max：首条 + 最近 (max - 1) 条
+        const first = filtered[0];
+        const latest = filtered.slice(-(config.chat.historyMaxCount - 1));
+        messages = [first, ...latest];
+      }
+    }
+
+    // 过滤当前消息（主聊天区路径，话题路径已在上面过滤）
+    if (!threadId && currentMessageId) {
+      messages = messages.filter(m => m.messageId !== currentMessageId);
+    }
 
     // 记录最新 messageId（去重锚点，在过滤 afterMsgId 之前取）
-    const newestMsgId = filtered.length > 0 ? filtered[filtered.length - 1].messageId : undefined;
+    const newestMsgId = messages.length > 0 ? messages[messages.length - 1].messageId : undefined;
 
     // 增量去重：只保留 afterMsgId 之后的新消息
-    if (afterMsgId && filtered.length > 0) {
-      const idx = filtered.findIndex(m => m.messageId === afterMsgId);
+    if (afterMsgId && messages.length > 0) {
+      const idx = messages.findIndex(m => m.messageId === afterMsgId);
       if (idx >= 0) {
-        filtered = filtered.slice(idx + 1);
+        messages = messages.slice(idx + 1);
       }
       // afterMsgId 不在列表中 → 可能消息已过期滚动，注入全部
     }
 
     const [text, images, historyFiles] = await Promise.all([
-      formatHistoryMessages(filtered, chatId, selfBotOpenIds),
-      downloadHistoryImages(filtered),
-      downloadHistoryFiles(filtered),
+      formatHistoryMessages(messages, chatId, selfBotOpenIds, parentMsgCount > 0 ? { parentMsgCount } : undefined),
+      downloadHistoryImages(messages),
+      downloadHistoryFiles(messages),
     ]);
     return {
       text: text ?? undefined,