Add support for specifying maxSessionTurns via the settings configuration (#3507)

4 files changed, 141 insertions, 13 deletions

diff --git a/packages/core/src/config/config.ts b/packages/core/src/config/config.ts
index 15e9e73b..12767133 100644
--- a/packages/core/src/config/config.ts
+++ b/packages/core/src/config/config.ts
@@ -139,6 +139,7 @@ export interface ConfigParameters {
   bugCommand?: BugCommandSettings;
   model: string;
   extensionContextFilePaths?: string[];
+  maxSessionTurns?: number;
   listExtensions?: boolean;
   activeExtensions?: ActiveExtension[];
   noBrowser?: boolean;
@@ -182,6 +183,7 @@ export class Config {
   private readonly extensionContextFilePaths: string[];
   private readonly noBrowser: boolean;
   private modelSwitchedDuringSession: boolean = false;
+  private readonly maxSessionTurns: number;
   private readonly listExtensions: boolean;
   private readonly _activeExtensions: ActiveExtension[];
   flashFallbackHandler?: FlashFallbackHandler;
@@ -227,6 +229,7 @@ export class Config {
     this.bugCommand = params.bugCommand;
     this.model = params.model;
     this.extensionContextFilePaths = params.extensionContextFilePaths ?? [];
+    this.maxSessionTurns = params.maxSessionTurns ?? -1;
     this.listExtensions = params.listExtensions ?? false;
     this._activeExtensions = params.activeExtensions ?? [];
     this.noBrowser = params.noBrowser ?? false;
@@ -308,6 +311,10 @@ export class Config {
     this.flashFallbackHandler = handler;
   }
 
+  getMaxSessionTurns(): number {
+    return this.maxSessionTurns;
+  }
+
   setQuotaErrorOccurred(value: boolean): void {
     this.quotaErrorOccurred = value;
   }
diff --git a/packages/core/src/core/client.test.ts b/packages/core/src/core/client.test.ts
index 2769e1b0..bbcb549b 100644
--- a/packages/core/src/core/client.test.ts
+++ b/packages/core/src/core/client.test.ts
@@ -17,7 +17,7 @@ import { findIndexAfterFraction, GeminiClient } from './client.js';
 import { AuthType, ContentGenerator } from './contentGenerator.js';
 import { GeminiChat } from './geminiChat.js';
 import { Config } from '../config/config.js';
-import { Turn } from './turn.js';
+import { GeminiEventType, Turn } from './turn.js';
 import { getCoreSystemPrompt } from './prompts.js';
 import { DEFAULT_GEMINI_FLASH_MODEL } from '../config/models.js';
 import { FileDiscoveryService } from '../services/fileDiscoveryService.js';
@@ -43,7 +43,13 @@ vi.mock('./turn', () => {
     }
   }
   // Export the mock class as 'Turn'
-  return { Turn: MockTurn };
+  return {
+    Turn: MockTurn,
+    GeminiEventType: {
+      MaxSessionTurns: 'MaxSessionTurns',
+      ChatCompressed: 'ChatCompressed',
+    },
+  };
 });
 
 vi.mock('../config/config.js');
@@ -68,12 +74,13 @@ vi.mock('../telemetry/index.js', () => ({
 
 describe('findIndexAfterFraction', () => {
   const history: Content[] = [
-    { role: 'user', parts: [{ text: 'This is the first message.' }] },
-    { role: 'model', parts: [{ text: 'This is the second message.' }] },
-    { role: 'user', parts: [{ text: 'This is the third message.' }] },
-    { role: 'model', parts: [{ text: 'This is the fourth message.' }] },
-    { role: 'user', parts: [{ text: 'This is the fifth message.' }] },
+    { role: 'user', parts: [{ text: 'This is the first message.' }] }, // JSON length: 66
+    { role: 'model', parts: [{ text: 'This is the second message.' }] }, // JSON length: 68
+    { role: 'user', parts: [{ text: 'This is the third message.' }] }, // JSON length: 66
+    { role: 'model', parts: [{ text: 'This is the fourth message.' }] }, // JSON length: 68
+    { role: 'user', parts: [{ text: 'This is the fifth message.' }] }, // JSON length: 65
   ];
+  // Total length: 333
 
   it('should throw an error for non-positive numbers', () => {
     expect(() => findIndexAfterFraction(history, 0)).toThrow(
@@ -88,14 +95,23 @@ describe('findIndexAfterFraction', () => {
   });
 
   it('should handle a fraction in the middle', () => {
-    // Total length is 257. 257 * 0.5 = 128.5
-    // 0: 53
-    // 1: 53 + 54 = 107
-    // 2: 107 + 53 = 160
-    // 160 >= 128.5, so index is 2
+    // 333 * 0.5 = 166.5
+    // 0: 66
+    // 1: 66 + 68 = 134
+    // 2: 134 + 66 = 200
+    // 200 >= 166.5, so index is 2
     expect(findIndexAfterFraction(history, 0.5)).toBe(2);
   });
 
+  it('should handle a fraction that results in the last index', () => {
+    // 333 * 0.9 = 299.7
+    // ...
+    // 3: 200 + 68 = 268
+    // 4: 268 + 65 = 333
+    // 333 >= 299.7, so index is 4
+    expect(findIndexAfterFraction(history, 0.9)).toBe(4);
+  });
+
   it('should handle an empty history', () => {
     expect(findIndexAfterFraction([], 0.5)).toBe(0);
   });
@@ -178,6 +194,7 @@ describe('Gemini Client (client.ts)', () => {
         getProxy: vi.fn().mockReturnValue(undefined),
         getWorkingDir: vi.fn().mockReturnValue('/test/dir'),
         getFileService: vi.fn().mockReturnValue(fileService),
+        getMaxSessionTurns: vi.fn().mockReturnValue(0),
         getQuotaErrorOccurred: vi.fn().mockReturnValue(false),
         setQuotaErrorOccurred: vi.fn(),
         getNoBrowser: vi.fn().mockReturnValue(false),
@@ -366,6 +383,42 @@ describe('Gemini Client (client.ts)', () => {
         contents,
       });
     });
+
+    it('should allow overriding model and config', async () => {
+      const contents = [{ role: 'user', parts: [{ text: 'hello' }] }];
+      const schema = { type: 'string' };
+      const abortSignal = new AbortController().signal;
+      const customModel = 'custom-json-model';
+      const customConfig = { temperature: 0.9, topK: 20 };
+
+      const mockGenerator: Partial<ContentGenerator> = {
+        countTokens: vi.fn().mockResolvedValue({ totalTokens: 1 }),
+        generateContent: mockGenerateContentFn,
+      };
+      client['contentGenerator'] = mockGenerator as ContentGenerator;
+
+      await client.generateJson(
+        contents,
+        schema,
+        abortSignal,
+        customModel,
+        customConfig,
+      );
+
+      expect(mockGenerateContentFn).toHaveBeenCalledWith({
+        model: customModel,
+        config: {
+          abortSignal,
+          systemInstruction: getCoreSystemPrompt(''),
+          temperature: 0.9,
+          topP: 1, // from default
+          topK: 20,
+          responseSchema: schema,
+          responseMimeType: 'application/json',
+        },
+        contents,
+      });
+    });
   });
 
   describe('addHistory', () => {
@@ -660,6 +713,59 @@ describe('Gemini Client (client.ts)', () => {
       expect(eventCount).toBeLessThan(200); // Should not exceed our safety limit
     });
 
+    it('should yield MaxSessionTurns and stop when session turn limit is reached', async () => {
+      // Arrange
+      const MAX_SESSION_TURNS = 5;
+      vi.spyOn(client['config'], 'getMaxSessionTurns').mockReturnValue(
+        MAX_SESSION_TURNS,
+      );
+
+      const mockStream = (async function* () {
+        yield { type: 'content', value: 'Hello' };
+      })();
+      mockTurnRunFn.mockReturnValue(mockStream);
+
+      const mockChat: Partial<GeminiChat> = {
+        addHistory: vi.fn(),
+        getHistory: vi.fn().mockReturnValue([]),
+      };
+      client['chat'] = mockChat as GeminiChat;
+
+      const mockGenerator: Partial<ContentGenerator> = {
+        countTokens: vi.fn().mockResolvedValue({ totalTokens: 0 }),
+      };
+      client['contentGenerator'] = mockGenerator as ContentGenerator;
+
+      // Act & Assert
+      // Run up to the limit
+      for (let i = 0; i < MAX_SESSION_TURNS; i++) {
+        const stream = client.sendMessageStream(
+          [{ text: 'Hi' }],
+          new AbortController().signal,
+          'prompt-id-4',
+        );
+        // consume stream
+        for await (const _event of stream) {
+          // do nothing
+        }
+      }
+
+      // This call should exceed the limit
+      const stream = client.sendMessageStream(
+        [{ text: 'Hi' }],
+        new AbortController().signal,
+        'prompt-id-5',
+      );
+
+      const events = [];
+      for await (const event of stream) {
+        events.push(event);
+      }
+
+      expect(events).toEqual([{ type: GeminiEventType.MaxSessionTurns }]);
+      expect(mockTurnRunFn).toHaveBeenCalledTimes(MAX_SESSION_TURNS);
+    });
+
     it('should respect MAX_TURNS limit even when turns parameter is set to a large value', async () => {
       // This test verifies that the infinite loop protection works even when
       // someone tries to bypass it by calling with a very large turns value
diff --git a/packages/core/src/core/client.ts b/packages/core/src/core/client.ts
index 5d9ac0cb..0ff8026b 100644
--- a/packages/core/src/core/client.ts
+++ b/packages/core/src/core/client.ts
@@ -86,6 +86,7 @@ export class GeminiClient {
     temperature: 0,
     topP: 1,
   };
+  private sessionTurnCount = 0;
   private readonly MAX_TURNS = 100;
   /**
    * Threshold for compression token count as a fraction of the model's token limit.
@@ -266,6 +267,14 @@ export class GeminiClient {
     turns: number = this.MAX_TURNS,
     originalModel?: string,
   ): AsyncGenerator<ServerGeminiStreamEvent, Turn> {
+    this.sessionTurnCount++;
+    if (
+      this.config.getMaxSessionTurns() > 0 &&
+      this.sessionTurnCount > this.config.getMaxSessionTurns()
+    ) {
+      yield { type: GeminiEventType.MaxSessionTurns };
+      return new Turn(this.getChat(), prompt_id);
+    }
     // Ensure turns never exceeds MAX_TURNS to prevent infinite loops
     const boundedTurns = Math.min(turns, this.MAX_TURNS);
     if (!boundedTurns) {
diff --git a/packages/core/src/core/turn.ts b/packages/core/src/core/turn.ts
index aeeaa889..6135b1f6 100644
--- a/packages/core/src/core/turn.ts
+++ b/packages/core/src/core/turn.ts
@@ -48,6 +48,7 @@ export enum GeminiEventType {
   Error = 'error',
   ChatCompressed = 'chat_compressed',
   Thought = 'thought',
+  MaxSessionTurns = 'max_session_turns',
 }
 
 export interface StructuredError {
@@ -128,6 +129,10 @@ export type ServerGeminiChatCompressedEvent = {
   value: ChatCompressionInfo | null;
 };
 
+export type ServerGeminiMaxSessionTurnsEvent = {
+  type: GeminiEventType.MaxSessionTurns;
+};
+
 // The original union type, now composed of the individual types
 export type ServerGeminiStreamEvent =
   | ServerGeminiContentEvent
@@ -137,7 +142,8 @@ export type ServerGeminiStreamEvent =
   | ServerGeminiUserCancelledEvent
   | ServerGeminiErrorEvent
   | ServerGeminiChatCompressedEvent
-  | ServerGeminiThoughtEvent;
+  | ServerGeminiThoughtEvent
+  | ServerGeminiMaxSessionTurnsEvent;
 
 // A turn manages the agentic loop turn within the server context.
 export class Turn {