diff --git a/integration-tests/file-system-interactive.test.ts b/integration-tests/file-system-interactive.test.ts
index 9099c89944..2dec6c593c 100644
--- a/integration-tests/file-system-interactive.test.ts
+++ b/integration-tests/file-system-interactive.test.ts
@@ -20,7 +20,7 @@ describe('Interactive file system', () => {
 
   it('should perform a read-then-write sequence', async () => {
     const fileName = 'version.txt';
-    rig.setup('interactive-read-then-write');
+    await rig.setup('interactive-read-then-write');
     rig.createFile(fileName, '1.0.0');
 
     const run = await rig.runInteractive();
@@ -44,5 +44,8 @@ describe('Interactive file system', () => {
       30000,
       (args) => args.includes('1.0.1') && args.includes(fileName),
     );
+
+    // Wait for telemetry to flush and file system to sync, especially in sandboxed environments
+    await rig.waitForTelemetryReady();
   });
 });
diff --git a/packages/core/src/telemetry/activity-monitor.test.ts b/packages/core/src/telemetry/activity-monitor.test.ts
new file mode 100644
index 0000000000..087b89fd0c
--- /dev/null
+++ b/packages/core/src/telemetry/activity-monitor.test.ts
@@ -0,0 +1,329 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import {
+  ActivityMonitor,
+  DEFAULT_ACTIVITY_CONFIG,
+  initializeActivityMonitor,
+  getActivityMonitor,
+  recordGlobalActivity,
+  startGlobalActivityMonitoring,
+  stopGlobalActivityMonitoring,
+} from './activity-monitor.js';
+import { ActivityType } from './activity-types.js';
+import type { ActivityEvent } from './activity-monitor.js';
+import type { Config } from '../config/config.js';
+
+// Mock the dependencies
+vi.mock('./metrics.js', () => ({
+  isPerformanceMonitoringActive: vi.fn(() => true),
+}));
+
+vi.mock('./memory-monitor.js', () => ({
+  getMemoryMonitor: vi.fn(() => ({
+    takeSnapshot: vi.fn(() => ({
+      timestamp: Date.now(),
+      heapUsed: 1000000,
+      heapTotal: 2000000,
+      external: 500000,
+      rss: 3000000,
+      arrayBuffers: 100000,
+      heapSizeLimit: 4000000,
+    })),
+  })),
+}));
+
+describe('ActivityMonitor', () => {
+  let activityMonitor: ActivityMonitor;
+  let mockConfig: Config;
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+    mockConfig = {
+      getSessionId: () => 'test-session-123',
+    } as Config;
+    activityMonitor = new ActivityMonitor();
+  });
+
+  afterEach(() => {
+    activityMonitor.stop();
+  });
+
+  describe('constructor', () => {
+    it('should initialize with default config', () => {
+      const monitor = new ActivityMonitor();
+      expect(monitor).toBeDefined();
+      expect(monitor.isMonitoringActive()).toBe(false);
+    });
+
+    it('should initialize with custom config', () => {
+      const customConfig = {
+        ...DEFAULT_ACTIVITY_CONFIG,
+        snapshotThrottleMs: 2000,
+      };
+      const monitor = new ActivityMonitor(customConfig);
+      expect(monitor).toBeDefined();
+    });
+  });
+
+  describe('start and stop', () => {
+    it('should start and stop monitoring', () => {
+      expect(activityMonitor.isMonitoringActive()).toBe(false);
+
+      activityMonitor.start(mockConfig);
+      expect(activityMonitor.isMonitoringActive()).toBe(true);
+
+      activityMonitor.stop();
+      expect(activityMonitor.isMonitoringActive()).toBe(false);
+    });
+
+    it('should not start monitoring when already active', () => {
+      activityMonitor.start(mockConfig);
+      expect(activityMonitor.isMonitoringActive()).toBe(true);
+
+      // Should not affect already active monitor
+      activityMonitor.start(mockConfig);
+      expect(activityMonitor.isMonitoringActive()).toBe(true);
+    });
+  });
+
+  describe('recordActivity', () => {
+    beforeEach(() => {
+      activityMonitor.start(mockConfig);
+    });
+
+    it('should record activity events', () => {
+      activityMonitor.recordActivity(
+        ActivityType.USER_INPUT_START,
+        'test-context',
+      );
+
+      const stats = activityMonitor.getActivityStats();
+      expect(stats.totalEvents).toBe(2); // includes the start event
+      expect(stats.eventTypes[ActivityType.USER_INPUT_START]).toBe(1);
+    });
+
+    it('should include metadata in activity events', () => {
+      const metadata = { key: 'value', count: 42 };
+      activityMonitor.recordActivity(
+        ActivityType.MESSAGE_ADDED,
+        'test-context',
+        metadata,
+      );
+
+      const recentActivity = activityMonitor.getRecentActivity(1);
+      expect(recentActivity[0].metadata).toEqual(metadata);
+    });
+
+    it('should not record activity when monitoring is disabled', () => {
+      activityMonitor.updateConfig({ enabled: false });
+
+      activityMonitor.recordActivity(ActivityType.USER_INPUT_START);
+
+      const stats = activityMonitor.getActivityStats();
+      expect(stats.totalEvents).toBe(1); // only the start event
+    });
+
+    it('should limit event buffer size', () => {
+      activityMonitor.updateConfig({ maxEventBuffer: 3 });
+
+      // Record more events than buffer size
+      for (let i = 0; i < 5; i++) {
+        activityMonitor.recordActivity(
+          ActivityType.USER_INPUT_START,
+          `event-${i}`,
+        );
+      }
+
+      const stats = activityMonitor.getActivityStats();
+      expect(stats.totalEvents).toBe(3); // buffer limit
+    });
+  });
+
+  describe('listeners', () => {
+    let listenerCallCount: number;
+    let lastEvent: ActivityEvent | null;
+
+    beforeEach(() => {
+      listenerCallCount = 0;
+      lastEvent = null;
+      activityMonitor.start(mockConfig);
+    });
+
+    it('should notify listeners of activity events', () => {
+      const listener = (event: ActivityEvent) => {
+        listenerCallCount++;
+        lastEvent = event;
+      };
+
+      activityMonitor.addListener(listener);
+      activityMonitor.recordActivity(ActivityType.MESSAGE_ADDED, 'test');
+
+      expect(listenerCallCount).toBe(1);
+      expect(lastEvent?.type).toBe(ActivityType.MESSAGE_ADDED);
+      expect(lastEvent?.context).toBe('test');
+    });
+
+    it('should remove listeners correctly', () => {
+      const listener = () => {
+        listenerCallCount++;
+      };
+
+      activityMonitor.addListener(listener);
+      activityMonitor.recordActivity(ActivityType.USER_INPUT_START);
+      expect(listenerCallCount).toBe(1);
+
+      activityMonitor.removeListener(listener);
+      activityMonitor.recordActivity(ActivityType.USER_INPUT_START);
+      expect(listenerCallCount).toBe(1); // Should not increase
+    });
+
+    it('should handle listener errors gracefully', () => {
+      const faultyListener = () => {
+        throw new Error('Listener error');
+      };
+      const goodListener = () => {
+        listenerCallCount++;
+      };
+
+      // Spy on console.debug to check error handling
+      const debugSpy = vi.spyOn(console, 'debug').mockImplementation(() => {});
+
+      activityMonitor.addListener(faultyListener);
+      activityMonitor.addListener(goodListener);
+
+      activityMonitor.recordActivity(ActivityType.USER_INPUT_START);
+
+      expect(listenerCallCount).toBe(1); // Good listener should still work
+      expect(debugSpy).toHaveBeenCalled();
+
+      debugSpy.mockRestore();
+    });
+  });
+
+  describe('getActivityStats', () => {
+    beforeEach(() => {
+      activityMonitor.start(mockConfig);
+    });
+
+    it('should return correct activity statistics', () => {
+      activityMonitor.recordActivity(ActivityType.USER_INPUT_START);
+      activityMonitor.recordActivity(ActivityType.MESSAGE_ADDED);
+      activityMonitor.recordActivity(ActivityType.USER_INPUT_START);
+
+      const stats = activityMonitor.getActivityStats();
+      expect(stats.totalEvents).toBe(4); // includes start event
+      expect(stats.eventTypes[ActivityType.USER_INPUT_START]).toBe(2);
+      expect(stats.eventTypes[ActivityType.MESSAGE_ADDED]).toBe(1);
+      expect(stats.timeRange).toBeDefined();
+    });
+
+    it('should return null time range for empty buffer', () => {
+      const emptyMonitor = new ActivityMonitor();
+      const stats = emptyMonitor.getActivityStats();
+      expect(stats.totalEvents).toBe(0);
+      expect(stats.timeRange).toBeNull();
+    });
+  });
+
+  describe('updateConfig', () => {
+    it('should update configuration correctly', () => {
+      const newConfig = { snapshotThrottleMs: 2000 };
+      activityMonitor.updateConfig(newConfig);
+
+      // Config should be updated (tested indirectly through behavior)
+      expect(activityMonitor).toBeDefined();
+    });
+  });
+});
+
+describe('Global activity monitoring functions', () => {
+  let mockConfig: Config;
+
+  beforeEach(() => {
+    mockConfig = {
+      getSessionId: () => 'test-session-456',
+    } as Config;
+    vi.clearAllMocks();
+  });
+
+  afterEach(() => {
+    stopGlobalActivityMonitoring();
+  });
+
+  describe('initializeActivityMonitor', () => {
+    it('should create global monitor instance', () => {
+      const monitor = initializeActivityMonitor();
+      expect(monitor).toBeDefined();
+      expect(getActivityMonitor()).toBe(monitor);
+    });
+
+    it('should return same instance on subsequent calls', () => {
+      const monitor1 = initializeActivityMonitor();
+      const monitor2 = initializeActivityMonitor();
+      expect(monitor1).toBe(monitor2);
+    });
+  });
+
+  describe('recordGlobalActivity', () => {
+    it('should record activity through global monitor', () => {
+      startGlobalActivityMonitoring(mockConfig);
+
+      recordGlobalActivity(ActivityType.TOOL_CALL_SCHEDULED, 'global-test');
+
+      const monitor = getActivityMonitor();
+      const stats = monitor?.getActivityStats();
+      expect(stats?.totalEvents).toBeGreaterThan(0);
+    });
+
+    it('should handle missing global monitor gracefully', () => {
+      stopGlobalActivityMonitoring();
+
+      // Should not throw error
+      expect(() => {
+        recordGlobalActivity(ActivityType.USER_INPUT_START);
+      }).not.toThrow();
+    });
+  });
+
+  describe('startGlobalActivityMonitoring', () => {
+    it('should start global monitoring with default config', () => {
+      startGlobalActivityMonitoring(mockConfig);
+
+      const monitor = getActivityMonitor();
+      expect(monitor?.isMonitoringActive()).toBe(true);
+    });
+
+    it('should start global monitoring with custom config', () => {
+      const customConfig = {
+        ...DEFAULT_ACTIVITY_CONFIG,
+        snapshotThrottleMs: 3000,
+      };
+
+      startGlobalActivityMonitoring(mockConfig, customConfig);
+
+      const monitor = getActivityMonitor();
+      expect(monitor?.isMonitoringActive()).toBe(true);
+    });
+  });
+
+  describe('stopGlobalActivityMonitoring', () => {
+    it('should stop global monitoring', () => {
+      startGlobalActivityMonitoring(mockConfig);
+      expect(getActivityMonitor()?.isMonitoringActive()).toBe(true);
+
+      stopGlobalActivityMonitoring();
+      expect(getActivityMonitor()?.isMonitoringActive()).toBe(false);
+    });
+
+    it('should handle missing global monitor gracefully', () => {
+      expect(() => {
+        stopGlobalActivityMonitoring();
+      }).not.toThrow();
+    });
+  });
+});
diff --git a/packages/core/src/telemetry/activity-monitor.ts b/packages/core/src/telemetry/activity-monitor.ts
new file mode 100644
index 0000000000..85db30a416
--- /dev/null
+++ b/packages/core/src/telemetry/activity-monitor.ts
@@ -0,0 +1,292 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import type { Config } from '../config/config.js';
+import { isPerformanceMonitoringActive } from './metrics.js';
+import { getMemoryMonitor } from './memory-monitor.js';
+import { ActivityType } from './activity-types.js';
+
+/**
+ * Activity event data structure
+ */
+export interface ActivityEvent {
+  type: ActivityType;
+  timestamp: number;
+  context?: string;
+  metadata?: Record<string, unknown>;
+}
+
+/**
+ * Configuration for activity monitoring
+ */
+export interface ActivityMonitorConfig {
+  /** Enable/disable activity monitoring */
+  enabled: boolean;
+  /** Minimum interval between memory snapshots (ms) */
+  snapshotThrottleMs: number;
+  /** Maximum number of events to buffer */
+  maxEventBuffer: number;
+  /** Activity types that should trigger immediate memory snapshots */
+  triggerActivities: ActivityType[];
+}
+
+/**
+ * Activity listener callback function
+ */
+export type ActivityListener = (event: ActivityEvent) => void;
+
+/**
+ * Default configuration for activity monitoring
+ */
+export const DEFAULT_ACTIVITY_CONFIG: ActivityMonitorConfig = {
+  enabled: true,
+  snapshotThrottleMs: 1000, // 1 second minimum between snapshots
+  maxEventBuffer: 100,
+  triggerActivities: [
+    ActivityType.USER_INPUT_START,
+    ActivityType.MESSAGE_ADDED,
+    ActivityType.TOOL_CALL_SCHEDULED,
+    ActivityType.STREAM_START,
+  ],
+};
+
+/**
+ * Activity monitor class that tracks user activity and triggers memory monitoring
+ */
+export class ActivityMonitor {
+  private listeners = new Set<ActivityListener>();
+  private eventBuffer: ActivityEvent[] = [];
+  private lastSnapshotTime = 0;
+  private config: ActivityMonitorConfig;
+  private isActive = false;
+  private memoryMonitoringListener: ActivityListener | null = null;
+
+  constructor(config: ActivityMonitorConfig = DEFAULT_ACTIVITY_CONFIG) {
+    this.config = { ...config };
+  }
+
+  /**
+   * Start activity monitoring
+   */
+  start(coreConfig: Config): void {
+    if (!isPerformanceMonitoringActive() || this.isActive) {
+      return;
+    }
+
+    this.isActive = true;
+
+    // Register default memory monitoring listener
+    this.memoryMonitoringListener = (event) => {
+      this.handleMemoryMonitoringActivity(event, coreConfig);
+    };
+    this.addListener(this.memoryMonitoringListener);
+
+    // Record activity monitoring start
+    this.recordActivity(
+      ActivityType.MANUAL_TRIGGER,
+      'activity_monitoring_start',
+    );
+  }
+
+  /**
+   * Stop activity monitoring
+   */
+  stop(): void {
+    if (!this.isActive) {
+      return;
+    }
+
+    this.isActive = false;
+    if (this.memoryMonitoringListener) {
+      this.removeListener(this.memoryMonitoringListener);
+      this.memoryMonitoringListener = null;
+    }
+    this.eventBuffer = [];
+  }
+
+  /**
+   * Add an activity listener
+   */
+  addListener(listener: ActivityListener): void {
+    this.listeners.add(listener);
+  }
+
+  /**
+   * Remove an activity listener
+   */
+  removeListener(listener: ActivityListener): void {
+    this.listeners.delete(listener);
+  }
+
+  /**
+   * Record a user activity event
+   */
+  recordActivity(
+    type: ActivityType,
+    context?: string,
+    metadata?: Record<string, unknown>,
+  ): void {
+    if (!this.isActive || !this.config.enabled) {
+      return;
+    }
+
+    const event: ActivityEvent = {
+      type,
+      timestamp: Date.now(),
+      context,
+      metadata,
+    };
+
+    // Add to buffer
+    this.eventBuffer.push(event);
+    if (this.eventBuffer.length > this.config.maxEventBuffer) {
+      this.eventBuffer.shift(); // Remove oldest event
+    }
+
+    // Notify listeners
+    this.listeners.forEach((listener) => {
+      try {
+        listener(event);
+      } catch (error) {
+        // Silently catch listener errors to avoid disrupting the application
+        console.debug('ActivityMonitor listener error:', error);
+      }
+    });
+  }
+
+  /**
+   * Get recent activity events
+   */
+  getRecentActivity(limit?: number): ActivityEvent[] {
+    const events = [...this.eventBuffer];
+    return limit ? events.slice(-limit) : events;
+  }
+
+  /**
+   * Get activity statistics
+   */
+  getActivityStats(): {
+    totalEvents: number;
+    eventTypes: Record<ActivityType, number>;
+    timeRange: { start: number; end: number } | null;
+  } {
+    const eventTypes = {} as Record<ActivityType, number>;
+    let start = Number.MAX_SAFE_INTEGER;
+    let end = 0;
+
+    for (const event of this.eventBuffer) {
+      eventTypes[event.type] = (eventTypes[event.type] || 0) + 1;
+      start = Math.min(start, event.timestamp);
+      end = Math.max(end, event.timestamp);
+    }
+
+    return {
+      totalEvents: this.eventBuffer.length,
+      eventTypes,
+      timeRange: this.eventBuffer.length > 0 ? { start, end } : null,
+    };
+  }
+
+  /**
+   * Update configuration
+   */
+  updateConfig(newConfig: Partial<ActivityMonitorConfig>): void {
+    this.config = { ...this.config, ...newConfig };
+  }
+
+  /**
+   * Handle memory monitoring for activity events
+   */
+  private handleMemoryMonitoringActivity(
+    event: ActivityEvent,
+    config: Config,
+  ): void {
+    // Check if this activity type should trigger memory monitoring
+    if (!this.config.triggerActivities.includes(event.type)) {
+      return;
+    }
+
+    // Throttle memory snapshots
+    const now = Date.now();
+    if (now - this.lastSnapshotTime < this.config.snapshotThrottleMs) {
+      return;
+    }
+
+    this.lastSnapshotTime = now;
+
+    // Take memory snapshot
+    const memoryMonitor = getMemoryMonitor();
+    if (memoryMonitor) {
+      const context = event.context
+        ? `activity_${event.type}_${event.context}`
+        : `activity_${event.type}`;
+
+      memoryMonitor.takeSnapshot(context, config);
+    }
+  }
+
+  /**
+   * Check if monitoring is active
+   */
+  isMonitoringActive(): boolean {
+    return this.isActive && this.config.enabled;
+  }
+}
+
+// Singleton instance for global activity monitoring
+let globalActivityMonitor: ActivityMonitor | null = null;
+
+/**
+ * Initialize global activity monitor
+ */
+export function initializeActivityMonitor(
+  config?: ActivityMonitorConfig,
+): ActivityMonitor {
+  if (!globalActivityMonitor) {
+    globalActivityMonitor = new ActivityMonitor(config);
+  }
+  return globalActivityMonitor;
+}
+
+/**
+ * Get global activity monitor instance
+ */
+export function getActivityMonitor(): ActivityMonitor | null {
+  return globalActivityMonitor;
+}
+
+/**
+ * Record a user activity on the global monitor (convenience function)
+ */
+export function recordGlobalActivity(
+  type: ActivityType,
+  context?: string,
+  metadata?: Record<string, unknown>,
+): void {
+  if (globalActivityMonitor) {
+    globalActivityMonitor.recordActivity(type, context, metadata);
+  }
+}
+
+/**
+ * Start global activity monitoring
+ */
+export function startGlobalActivityMonitoring(
+  coreConfig: Config,
+  activityConfig?: ActivityMonitorConfig,
+): void {
+  const monitor = initializeActivityMonitor(activityConfig);
+  monitor.start(coreConfig);
+}
+
+/**
+ * Stop global activity monitoring
+ */
+export function stopGlobalActivityMonitoring(): void {
+  if (globalActivityMonitor) {
+    globalActivityMonitor.stop();
+  }
+}
diff --git a/packages/core/src/telemetry/index.ts b/packages/core/src/telemetry/index.ts
index 2b5ff5c1f3..77af50fe06 100644
--- a/packages/core/src/telemetry/index.ts
+++ b/packages/core/src/telemetry/index.ts
@@ -87,6 +87,13 @@ export {
   recordUserActivity,
   isUserActive,
 } from './activity-detector.js';
+export {
+  ActivityMonitor,
+  initializeActivityMonitor,
+  getActivityMonitor,
+  startGlobalActivityMonitoring,
+  stopGlobalActivityMonitoring,
+} from './activity-monitor.js';
 export {
   // Core metrics functions
   recordToolCallMetrics,