Don't start uncompressed history with a function response (#4141)

packages/core/src/core/client.test.ts

@@ -470,34 +470,31 @@ describe('Gemini Client (client.ts)', () => {
   describe('tryCompressChat', () => {
     const mockCountTokens = vi.fn();
     const mockSendMessage = vi.fn();
+    const mockGetHistory = vi.fn();
 
     beforeEach(() => {
       vi.mock('./tokenLimits', () => ({
         tokenLimit: vi.fn(),
       }));
 
-      const mockGenerator: Partial<ContentGenerator> = {
+      client['contentGenerator'] = {
         countTokens: mockCountTokens,
-      };
-      client['contentGenerator'] = mockGenerator as ContentGenerator;
+      } as unknown as ContentGenerator;
 
-      // Mock the chat's sendMessage method
-      const mockChat: Partial<GeminiChat> = {
-        getHistory: vi
-          .fn()
-          .mockReturnValue([
-            { role: 'user', parts: [{ text: '...history...' }] },
-          ]),
+      client['chat'] = {
+        getHistory: mockGetHistory,
         addHistory: vi.fn(),
         setHistory: vi.fn(),
         sendMessage: mockSendMessage,
-      };
-      client['chat'] = mockChat as GeminiChat;
+      } as unknown as GeminiChat;
     });
 
     it('should not trigger summarization if token count is below threshold', async () => {
       const MOCKED_TOKEN_LIMIT = 1000;
       vi.mocked(tokenLimit).mockReturnValue(MOCKED_TOKEN_LIMIT);
+      mockGetHistory.mockReturnValue([
+        { role: 'user', parts: [{ text: '...history...' }] },
+      ]);
 
       mockCountTokens.mockResolvedValue({
         totalTokens: MOCKED_TOKEN_LIMIT * 0.699, // TOKEN_THRESHOLD_FOR_SUMMARIZATION = 0.7
@@ -515,6 +512,9 @@ describe('Gemini Client (client.ts)', () => {
     it('should trigger summarization if token count is at threshold', async () => {
       const MOCKED_TOKEN_LIMIT = 1000;
       vi.mocked(tokenLimit).mockReturnValue(MOCKED_TOKEN_LIMIT);
+      mockGetHistory.mockReturnValue([
+        { role: 'user', parts: [{ text: '...history...' }] },
+      ]);
 
       const originalTokenCount = 1000 * 0.7;
       const newTokenCount = 100;
@@ -546,7 +546,69 @@ describe('Gemini Client (client.ts)', () => {
       expect(newChat).not.toBe(initialChat);
     });
 
+    it('should not compress across a function call response', async () => {
+      const MOCKED_TOKEN_LIMIT = 1000;
+      vi.mocked(tokenLimit).mockReturnValue(MOCKED_TOKEN_LIMIT);
+      mockGetHistory.mockReturnValue([
+        { role: 'user', parts: [{ text: '...history 1...' }] },
+        { role: 'model', parts: [{ text: '...history 2...' }] },
+        { role: 'user', parts: [{ text: '...history 3...' }] },
+        { role: 'model', parts: [{ text: '...history 4...' }] },
+        { role: 'user', parts: [{ text: '...history 5...' }] },
+        { role: 'model', parts: [{ text: '...history 6...' }] },
+        { role: 'user', parts: [{ text: '...history 7...' }] },
+        { role: 'model', parts: [{ text: '...history 8...' }] },
+        // Normally we would break here, but we have a function response.
+        {
+          role: 'user',
+          parts: [{ functionResponse: { name: '...history 8...' } }],
+        },
+        { role: 'model', parts: [{ text: '...history 10...' }] },
+        // Instead we will break here.
+        { role: 'user', parts: [{ text: '...history 10...' }] },
+      ]);
+
+      const originalTokenCount = 1000 * 0.7;
+      const newTokenCount = 100;
+
+      mockCountTokens
+        .mockResolvedValueOnce({ totalTokens: originalTokenCount }) // First call for the check
+        .mockResolvedValueOnce({ totalTokens: newTokenCount }); // Second call for the new history
+
+      // Mock the summary response from the chat
+      mockSendMessage.mockResolvedValue({
+        role: 'model',
+        parts: [{ text: 'This is a summary.' }],
+      });
+
+      const initialChat = client.getChat();
+      const result = await client.tryCompressChat('prompt-id-3');
+      const newChat = client.getChat();
+
+      expect(tokenLimit).toHaveBeenCalled();
+      expect(mockSendMessage).toHaveBeenCalled();
+
+      // Assert that summarization happened and returned the correct stats
+      expect(result).toEqual({
+        originalTokenCount,
+        newTokenCount,
+      });
+      // Assert that the chat was reset
+      expect(newChat).not.toBe(initialChat);
+
+      // 1. standard start context message
+      // 2. standard canned user start message
+      // 3. compressed summary message
+      // 4. standard canned user summary message
+      // 5. The last user message (not the last 3 because that would start with a function response)
+      expect(newChat.getHistory().length).toEqual(5);
+    });
+
     it('should always trigger summarization when force is true, regardless of token count', async () => {
+      mockGetHistory.mockReturnValue([
+        { role: 'user', parts: [{ text: '...history...' }] },
+      ]);
+
       const originalTokenCount = 10; // Well below threshold
       const newTokenCount = 5;
 

packages/core/src/core/client.ts

@@ -30,6 +30,7 @@ import { reportError } from '../utils/errorReporting.js';
 import { GeminiChat } from './geminiChat.js';
 import { retryWithBackoff } from '../utils/retry.js';
 import { getErrorMessage } from '../utils/errors.js';
+import { isFunctionResponse } from '../utils/messageInspectors.js';
 import { tokenLimit } from './tokenLimits.js';
 import {
   AuthType,
@@ -547,7 +548,8 @@ export class GeminiClient {
     // Find the first user message after the index. This is the start of the next turn.
     while (
       compressBeforeIndex < curatedHistory.length &&
-      curatedHistory[compressBeforeIndex]?.role !== 'user'
+      (curatedHistory[compressBeforeIndex]?.role === 'model' ||
+        isFunctionResponse(curatedHistory[compressBeforeIndex]))
     ) {
       compressBeforeIndex++;
     }