[Part 2/6] feat(telemetry): add activity detector with user interaction tracking (#8111)

packages/core/src/telemetry/activity-detector.ts

@@ -0,0 +1,70 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * Tracks user activity state to determine when memory monitoring should be active
+ */
+export class ActivityDetector {
+  private lastActivityTime: number = Date.now();
+  private readonly idleThresholdMs: number;
+
+  constructor(idleThresholdMs: number = 30000) {
+    this.idleThresholdMs = idleThresholdMs;
+  }
+
+  /**
+   * Record user activity (called by CLI when user types, adds messages, etc.)
+   */
+  recordActivity(): void {
+    this.lastActivityTime = Date.now();
+  }
+
+  /**
+   * Check if user is currently active (activity within idle threshold)
+   */
+  isUserActive(): boolean {
+    const timeSinceActivity = Date.now() - this.lastActivityTime;
+    return timeSinceActivity < this.idleThresholdMs;
+  }
+
+  /**
+   * Get time since last activity in milliseconds
+   */
+  getTimeSinceLastActivity(): number {
+    return Date.now() - this.lastActivityTime;
+  }
+
+  /**
+   * Get last activity timestamp
+   */
+  getLastActivityTime(): number {
+    return this.lastActivityTime;
+  }
+}
+
+// Global activity detector instance (eagerly created with default threshold)
+const globalActivityDetector: ActivityDetector = new ActivityDetector();
+
+/**
+ * Get global activity detector instance
+ */
+export function getActivityDetector(): ActivityDetector {
+  return globalActivityDetector;
+}
+
+/**
+ * Record user activity (convenience function for CLI to call)
+ */
+export function recordUserActivity(): void {
+  globalActivityDetector.recordActivity();
+}
+
+/**
+ * Check if user is currently active (convenience function)
+ */
+export function isUserActive(): boolean {
+  return globalActivityDetector.isUserActive();
+}