fix: stabilize ai design history switching

tests/unit/local-image-workspace.test.ts

@@ -286,6 +286,39 @@ describe('local AI design workspace', () => {
     })).resolves.toMatchObject({ turnRevision: 2 });
   });
 
+  it('pages local Conversation history in ten-message windows', async () => {
+    const service = createService(createTemporaryDirectory());
+    const created = await service.createWorkspace({
+      clientWorkspaceId: 'client-history-page',
+      title: '分页历史',
+    });
+    const conversationId = created.conversations[0].conversationId;
+
+    for (let revision = 0; revision < 6; revision += 1) {
+      await service.submitMessage({
+        workspaceId: created.workspaceId,
+        conversationId,
+        clientTurnId: `history-page-turn-${revision + 1}`,
+        expectedTurnRevision: revision,
+        message: `第 ${revision + 1} 条设计需求`,
+      });
+    }
+
+    const latest = await service.getConversation(created.workspaceId, conversationId);
+    expect(latest.messages).toHaveLength(10);
+    expect(latest.messages.map((message) => message.turnRevision))
+      .toEqual([2, 2, 3, 3, 4, 4, 5, 5, 6, 6]);
+    expect(latest.messagePage).toMatchObject({ hasOlder: true });
+
+    const older = await service.getConversation(
+      created.workspaceId,
+      conversationId,
+      latest.messagePage!.nextBefore!,
+    );
+    expect(older.messages.map((message) => message.turnRevision)).toEqual([1, 1]);
+    expect(older.messagePage).toEqual({ hasOlder: false, nextBefore: null });
+  });
+
   it('deletes a project while a task is queued and makes its task state inaccessible', async () => {
     const userDataDir = createTemporaryDirectory();
     const service = createService(userDataDir);