[Part 5/6] feat(telemetry): add activity monitor with event-driven snapshots

[eLyiN]

Summary

Introduces ActivityMonitor to track user events and trigger throttled memory snapshots when performance monitoring is active. This component bridges user activity detection with memory monitoring for intelligent telemetry collection.

Dependencies

✅ All dependencies merged to main:

• [Part 1/6] feat(telemetry): add rate limiter and high-water mark tracker with tests #8110 - Part 1: Telemetry Primitives (RateLimiter, HighWaterMarkTracker) - MERGED
• [Part 2/6] feat(telemetry): add activity detector with user interaction tracking #8111 - Part 2: Activity Detection (ActivityDetector, isUserActive) - MERGED
• [Part 3/6] feat(telemetry): enhance metrics with performance monitoring APIs #8113 - Part 3: Metrics Enhancement (performance metrics, recording functions) - MERGED
• [Part 4/6] feat(telemetry): add memory monitor with activity-aware recording and tests #8122 - Part 4: Memory Monitor (MemoryMonitor, memory tracking APIs) - MERGED

Branch Status: Rebased on latest main (all dependencies included).

Related PRs - Enhanced Performance Monitoring Split

This is Part 5 of 6 in the split implementation of #2127:

• ✅ Part 1/6: [Part 1/6] feat(telemetry): add rate limiter and high-water mark tracker with tests #8110 (telemetry-primitives) - MERGED
• ✅ Part 2/6: [Part 2/6] feat(telemetry): add activity detector with user interaction tracking #8111 (activity-detector) - MERGED
• ✅ Part 3/6: [Part 3/6] feat(telemetry): enhance metrics with performance monitoring APIs #8113 (metrics-enhancements) - MERGED
• ✅ Part 4/6: [Part 4/6] feat(telemetry): add memory monitor with activity-aware recording and tests #8122 (memory-monitor) - MERGED
• 🔄 Part 5/6: [Part 5/6] feat(telemetry): add activity monitor with event-driven snapshots #8124 (activity-monitor) - YOU ARE HERE
• ⏳ Part 6/6: TBD (cli-activity-hooks) - CLI integration
• 📋 Tracking Issue: [Split PRs] Enhanced Performance Monitoring Implementation - Split into 6 reviewable PRs #8120

Changes in This PR

🆕 Files Added:

• packages/core/src/telemetry/activity-monitor.ts - ActivityMonitor implementation
• packages/core/src/telemetry/activity-monitor.test.ts - Comprehensive unit tests
• packages/core/src/telemetry/index.ts - ActivityMonitor exports

ActivityMonitor (packages/core/src/telemetry/activity-monitor.ts)

Event-Driven Memory Snapshots:

• Smart triggering: Monitors user events and triggers memory snapshots when appropriate
• Performance-aware: Only active when isPerformanceMonitoringActive() returns true
• Throttled recording: Default config with minimal throttle to avoid telemetry noise
• Event integration: Hooks into key user interactions (input start, message added, tool calls, streams)

Key Features:

• Configurable triggers: Define which events should trigger memory snapshots
• Memory monitor integration: Uses getMemoryMonitor() from Part 4 for actual memory collection
• Activity detection integration: Leverages isUserActive() from Part 2 for smart timing
• Rate limiting: Uses primitives from Part 1 to prevent telemetry spam

Default Configuration:

// Triggers memory snapshots on key user interactions
const defaultTriggers = [
  'user_input_start',
  'message_added', 
  'tool_call_scheduled',
  'stream_start'
];

API Interface:

// Initialize activity monitor
initializeActivityMonitor(config);

// Get monitor instance
const monitor = getActivityMonitor();

// Lifecycle management
startGlobalActivityMonitoring();
stopGlobalActivityMonitoring();

// Manual event triggering
monitor.recordEvent('custom_event');

Testing

✅ ActivityMonitor unit tests:

• activity-monitor.test.ts - Event triggering, memory snapshot integration, throttling behavior
• Tests cover performance monitoring integration, event configuration, and memory monitor coordination
• Mock-based testing for external dependencies (memory monitor, activity detector)
• All 22 tests passing ✅

Technical Architecture

Component Integration Stack:

1. Listens for events → ActivityMonitor receives user interaction events
2. Checks performance config → Only proceeds if monitoring is active (Part 3)
3. Validates activity → Uses activity detection to ensure user is active (Part 2)
4. Triggers memory snapshot → Calls MemoryMonitor to capture current state (Part 4)
5. Applies rate limiting → Uses primitives to prevent spam (Part 1)

Rebase Status

✅ Successfully rebased on main (commit: 603ec2b)
✅ All preflight checks passing

• Build: ✅
• Tests: ✅ (5,237 tests passing)
• TypeCheck: ✅
• Lint: ✅
• Format: ✅

---

Next Steps: Part 6 will add CLI hooks to wire ActivityMonitor into the actual user interface event flows.

[jacob314]

It would be great to get this in! Please merge to reflect the changes already landed for memory monitor and then we can take a look.

[eLyiN]

/gemini review

[gemini-code-assist]

Code Review

Thank you for this contribution. The new ActivityMonitor is a great addition for event-driven telemetry. I've found a couple of high-severity issues that should be addressed to improve the robustness and maintainability of the new module. My main concerns are around the lifecycle management of listeners and a function name collision that could cause confusion. Please see my detailed comments below.

[eLyiN]

It would be great to get this in! Please merge to reflect the changes already landed for memory monitor and then we can take a look.

Hi @jacob314, ready for review!

[jacob314]

[eLyiN]

The test file-system-interactive.test.ts introduced in #11046 was failing due to a race condition. The test wasn't awaiting rig.waitForTelemetryReady() after the write operation, which meant it read the file before the file system had fully synced (especially problematic in sandboxed environments).

@jacob314 take a look for re-approval, so we can continue in #8125 , thanks

[eLyiN]

@jacob314 fixed conflict on rebase & format fix, ready for merge

[jacob314]