fix(core): preserve rewind parents after resume

packages/cli/src/acp-integration/acpAgent.test.ts

@@ -6256,9 +6256,11 @@ describe('QwenAgent loadSession / unstable_resumeSession', () => {
   let lastSessionMock:
     | {
         getId: ReturnType<typeof vi.fn>;
+        getConfig: ReturnType<typeof vi.fn>;
         sendAvailableCommandsUpdate: ReturnType<typeof vi.fn>;
         replayHistory: ReturnType<typeof vi.fn>;
         installRewriter: ReturnType<typeof vi.fn>;
+        startCronScheduler: ReturnType<typeof vi.fn>;
         dispose: ReturnType<typeof vi.fn>;
       }
     | undefined;
@@ -6320,6 +6322,9 @@ describe('QwenAgent loadSession / unstable_resumeSession', () => {
       resumedConversation?: { messages: unknown[] };
     } = {},
   ) {
+    const recording = {
+      rebuildTurnBoundaries: vi.fn(),
+    };
     return {
       initialize: vi.fn().mockResolvedValue(undefined),
       waitForMcpReady: vi.fn().mockResolvedValue(undefined),
@@ -6345,6 +6350,7 @@ describe('QwenAgent loadSession / unstable_resumeSession', () => {
       getHookSystem: vi.fn().mockReturnValue(undefined),
       getDisableAllHooks: vi.fn().mockReturnValue(true),
       hasHooksForEvent: vi.fn().mockReturnValue(false),
+      getChatRecordingService: vi.fn().mockReturnValue(recording),
       // load path reads back the persisted conversation here and feeds
       // it to `session.replayHistory`. resume path doesn't read this.
       getResumedSessionData: vi
@@ -6433,10 +6439,11 @@ describe('QwenAgent loadSession / unstable_resumeSession', () => {
   });
 
   it('loadSession returns LoadSessionResponse and replays history on the session', async () => {
+    const messages = [{ role: 'user', parts: [{ text: 'hi' }] }];
     bindRestoreMocks({
       sessionExists: true,
       resumedConversation: {
-        messages: [{ role: 'user', parts: [{ text: 'hi' }] }],
+        messages,
       },
     });
     const { agent, agentPromise } = await spawnAgent();
@@ -6454,9 +6461,10 @@ describe('QwenAgent loadSession / unstable_resumeSession', () => {
     });
     // load semantic: history MUST be replayed so SSE subscribers see
     // the persisted turns.
-    expect(lastSessionMock?.replayHistory).toHaveBeenCalledWith([
-      { role: 'user', parts: [{ text: 'hi' }] },
-    ]);
+    expect(lastSessionMock?.replayHistory).toHaveBeenCalledWith(messages);
+
+    const recording = lastSessionMock?.getConfig().getChatRecordingService();
+    expect(recording?.rebuildTurnBoundaries).toHaveBeenCalledWith(messages);
 
     mockConnectionState.resolve();
     await agentPromise;
@@ -6539,10 +6547,11 @@ describe('QwenAgent loadSession / unstable_resumeSession', () => {
   });
 
   it('unstable_resumeSession returns the response without replaying history', async () => {
+    const messages = [{ role: 'user', parts: [{ text: 'hi' }] }];
     bindRestoreMocks({
       sessionExists: true,
       resumedConversation: {
-        messages: [{ role: 'user', parts: [{ text: 'hi' }] }],
+        messages,
       },
     });
     const { agent, agentPromise } = await spawnAgent();
@@ -6562,6 +6571,8 @@ describe('QwenAgent loadSession / unstable_resumeSession', () => {
     // the SSE stream stays clean for clients that already have the
     // history rendered.
     expect(lastSessionMock?.replayHistory).not.toHaveBeenCalled();
+    const recording = lastSessionMock?.getConfig().getChatRecordingService();
+    expect(recording?.rebuildTurnBoundaries).toHaveBeenCalledWith(messages);
 
     mockConnectionState.resolve();
     await agentPromise;

packages/cli/src/acp-integration/acpAgent.ts

@@ -7318,6 +7318,12 @@ class QwenAgent implements Agent {
         .restoreFromSnapshots(sessionData.fileHistorySnapshots);
     }
 
+    if (sessionData?.conversation.messages) {
+      config
+        .getChatRecordingService()
+        ?.rebuildTurnBoundaries(sessionData.conversation.messages);
+    }
+
     if (options.replayHistory !== false && sessionData?.conversation.messages) {
       await session.replayHistory(sessionData.conversation.messages);
     }

packages/core/src/services/chatRecordingService.test.ts

@@ -169,6 +169,47 @@ describe('ChatRecordingService', () => {
     });
   });
 
+  describe('rewindRecording', () => {
+    it('preserves a resumed user turn parent when rebuilding rewind boundaries', async () => {
+      vi.mocked(mockConfig.getResumedSessionData).mockReturnValue({
+        lastCompletedUuid: 'assistant-1',
+      } as unknown as ReturnType<Config['getResumedSessionData']>);
+      chatRecordingService = new ChatRecordingService(mockConfig);
+
+      chatRecordingService.rebuildTurnBoundaries([
+        {
+          uuid: 'user-1',
+          parentUuid: 'pre-resume-parent',
+          sessionId: 'test-session-id',
+          timestamp: '2026-06-27T00:00:00.000Z',
+          type: 'user',
+          cwd: '/test/project/root',
+          version: '1.0.0',
+          message: { role: 'user', parts: [{ text: 'first resumed turn' }] },
+        },
+        {
+          uuid: 'assistant-1',
+          parentUuid: 'user-1',
+          sessionId: 'test-session-id',
+          timestamp: '2026-06-27T00:00:01.000Z',
+          type: 'assistant',
+          cwd: '/test/project/root',
+          version: '1.0.0',
+          message: { role: 'model', parts: [{ text: 'response' }] },
+          model: 'gemini-pro',
+        },
+      ]);
+
+      chatRecordingService.rewindRecording(0, { truncatedCount: 2 });
+      await chatRecordingService.flush();
+
+      expect(jsonl.writeLine).toHaveBeenCalledTimes(1);
+      const rewind = vi.mocked(jsonl.writeLine).mock.calls[0][1] as ChatRecord;
+      expect(rewind.subtype).toBe('rewind');
+      expect(rewind.parentUuid).toBe('pre-resume-parent');
+    });
+  });
+
   describe('recordAtCommand', () => {
     it('should record @-command metadata as a system payload', async () => {
       const userParts: Part[] = [{ text: 'Hello, world!' }];

packages/core/src/services/chatRecordingService.ts

@@ -1230,10 +1230,6 @@ export class ChatRecordingService {
    */
   rebuildTurnBoundaries(messages: ChatRecord[]): void {
     this.turnParentUuids = [];
-    let prevUuid: string | null =
-      this.config.getResumedSessionData()?.lastCompletedUuid !== undefined
-        ? null
-        : this.lastRecordUuid;
 
     for (let i = 0; i < messages.length; i++) {
       const record = messages[i];
@@ -1243,9 +1239,10 @@ export class ChatRecordingService {
         record.subtype !== 'cron' &&
         record.subtype !== 'mid_turn_user_message'
       ) {
-        this.turnParentUuids.push(prevUuid);
+        // Reconstructed histories can start mid-chain; the persisted edge is
+        // the source of truth, not the previous item in this sliced list.
+        this.turnParentUuids.push(record.parentUuid ?? null);
       }
-      prevUuid = record.uuid;
     }
     // Ensure lastRecordUuid points to the end of the reconstructed chain.
     if (messages.length > 0) {