fix(core): Prepend user message to loop detection history if it starts with a function call (#11860)

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

@@ -5,6 +5,7 @@
  */
 
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import type { Content } from '@google/genai';
 import type { Config } from '../config/config.js';
 import type { GeminiClient } from '../core/client.js';
 import type { BaseLlmClient } from '../core/baseLlmClient.js';
@@ -754,4 +755,34 @@ describe('LoopDetectionService LLM Checks', () => {
     expect(result).toBe(false);
     expect(mockBaseLlmClient.generateJson).not.toHaveBeenCalled();
   });
+
+  it('should prepend user message if history starts with a function call', async () => {
+    const functionCallHistory: Content[] = [
+      {
+        role: 'model',
+        parts: [{ functionCall: { name: 'someTool', args: {} } }],
+      },
+      {
+        role: 'model',
+        parts: [{ text: 'Some follow up text' }],
+      },
+    ];
+    vi.mocked(mockGeminiClient.getHistory).mockReturnValue(functionCallHistory);
+
+    mockBaseLlmClient.generateJson = vi
+      .fn()
+      .mockResolvedValue({ confidence: 0.1 });
+
+    await advanceTurns(30);
+
+    expect(mockBaseLlmClient.generateJson).toHaveBeenCalledTimes(1);
+    const calledArg = vi.mocked(mockBaseLlmClient.generateJson).mock
+      .calls[0][0];
+    expect(calledArg.contents[0]).toEqual({
+      role: 'user',
+      parts: [{ text: 'Recent conversation history:' }],
+    });
+    // Verify the original history follows
+    expect(calledArg.contents[1]).toEqual(functionCallHistory[0]);
+  });
 });

packages/core/src/services/loopDetectionService.ts

@@ -404,6 +404,12 @@ export class LoopDetectionService {
       ...trimmedHistory,
       { role: 'user', parts: [{ text: taskPrompt }] },
     ];
+    if (contents.length > 0 && isFunctionCall(contents[0])) {
+      contents.unshift({
+        role: 'user',
+        parts: [{ text: 'Recent conversation history:' }],
+      });
+    }
     const schema: Record<string, unknown> = {
       type: 'object',
       properties: {