feat(core): introduce decoupled ContextManager and Sidecar architecture (#24752)

packages/core/src/context/contextManager.barrier.test.ts

@@ -0,0 +1,82 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { testTruncateProfile } from './testing/testProfile.js';
+import {
+  createSyntheticHistory,
+  createMockContextConfig,
+  setupContextComponentTest,
+} from './testing/contextTestUtils.js';
+
+describe('ContextManager Sync Pressure Barrier Tests', () => {
+  beforeEach(() => {
+    vi.useFakeTimers();
+  });
+
+  afterEach(() => {
+    vi.useRealTimers();
+    vi.restoreAllMocks();
+  });
+
+  it('should instantly truncate history when maxTokens is exceeded using truncate strategy', async () => {
+    // 1. Setup
+    const config = createMockContextConfig();
+    const { chatHistory, contextManager } = setupContextComponentTest(
+      config,
+      testTruncateProfile,
+    );
+
+    // 2. Add System Prompt (Episode 0 - Protected)
+    chatHistory.set([
+      { role: 'user', parts: [{ text: 'System prompt' }] },
+      { role: 'model', parts: [{ text: 'Understood.' }] },
+    ]);
+
+    // 3. Add massive history that blows past the 150k maxTokens limit
+    // 20 turns * 10,000 tokens/turn = ~200,000 tokens
+    const massiveHistory = createSyntheticHistory(20, 35000);
+    chatHistory.set([...chatHistory.get(), ...massiveHistory]);
+
+    // 4. Add the Latest Turn (Protected)
+    chatHistory.set([
+      ...chatHistory.get(),
+      { role: 'user', parts: [{ text: 'Final question.' }] },
+      { role: 'model', parts: [{ text: 'Final answer.' }] },
+    ]);
+
+    const rawHistoryLength = chatHistory.get().length;
+
+    // 5. Project History (Triggers Sync Barrier)
+    const projection = await contextManager.renderHistory();
+
+    // 6. Assertions
+    // The barrier should have dropped several older episodes to get under 150k.
+
+    expect(projection.length).toBeLessThan(rawHistoryLength);
+
+    // Verify Episode 0 (System) is perfectly preserved at the front
+
+    expect(projection[0].role).toBe('user');
+    expect(projection[0].parts![0].text).toBe('System prompt');
+
+    // Filter out synthetic Yield nodes (they are model responses without actual tool/text bodies)
+    const contentNodes = projection.filter(
+      (p) =>
+        p.parts && p.parts.some((part) => part.text && part.text !== 'Yield'),
+    );
+
+    // Verify the latest turn is perfectly preserved at the back
+    const lastUser = contentNodes[contentNodes.length - 2];
+    const lastModel = contentNodes[contentNodes.length - 1];
+
+    expect(lastUser.role).toBe('user');
+    expect(lastUser.parts![0].text).toBe('Final question.');
+
+    expect(lastModel.role).toBe('model');
+    expect(lastModel.parts![0].text).toBe('Final answer.');
+  });
+});