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HEARTBEAT_FIX_SUMMARY.md

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Serena Dashboard Heartbeat Fix Summary

Critical Issues Fixed

1. Aggressive Failure Threshold (CRITICAL)

Before:

  • Dashboard would close after just 1 heartbeat failure (line 405)
  • if (self.heartbeatFailureCount >= 1) was the threshold

After:

  • Increased threshold to 5 failures before taking action
  • Configurable via this.heartbeatMaxFailures = 5
  • Shows warning after 2 failures, error after 5 failures

2. Window.close() Crash (CRITICAL)

Before:

  • window.close() was called after single failure (line 407)
  • Completely killed the UI with no recovery option

After:

  • Replaced with user-visible error message
  • Shows connection status with visual feedback
  • Provides "Retry Now" and "Reload Dashboard" buttons
  • Dashboard stays open and functional

3. Aggressive Polling Interval

Before:

  • Heartbeat ran every 250ms (line 391)
  • Excessive network overhead and server load

After:

  • Increased to 5000ms (5 seconds)
  • Configurable via this.heartbeatInterval = 5000
  • Much more reasonable for connection monitoring

4. No AJAX Timeout

Before:

  • No timeout on heartbeat AJAX requests
  • Could hang indefinitely

After:

  • Added 10-second timeout
  • Configurable via this.heartbeatTimeout = 10000
  • Prevents hung requests from blocking recovery

5. No Reconnection Logic

Before:

  • Single failure = immediate crash
  • No attempt to recover connection

After:

  • Automatic reconnection with exponential backoff
  • Up to 10 reconnection attempts (configurable)
  • Backoff formula: min(2^attempt * 1000ms, 30s)
  • Example: attempt 1 = 2s, attempt 2 = 4s, attempt 3 = 8s, etc.
  • Maximum delay capped at 30 seconds

6. No User Feedback

Before:

  • Only console messages
  • User had no visibility into connection issues

After:

  • Warning banner after 2 failures (yellow)
  • Error banner after 5 failures (red)
  • Real-time reconnection status updates
  • Manual retry option
  • Reload dashboard option

New Features Added

Connection Status Visualization

showConnectionWarning()  // Yellow banner after 2 failures
showConnectionError()    // Red banner with retry options
hideConnectionError()    // Remove banners when recovered

Exponential Backoff Reconnection

attemptReconnection()    // Smart reconnection with backoff
manualReconnect()        // User-triggered retry

Heartbeat Control

startHeartbeat()         // Initialize heartbeat monitoring
stopHeartbeat()          // Stop heartbeat (if needed)

Configuration Parameters

All heartbeat behavior is now configurable via instance variables:

this.heartbeatMaxFailures = 5;      // Failures before showing error
this.heartbeatInterval = 5000;       // Interval between heartbeats (ms)
this.heartbeatTimeout = 10000;       // AJAX request timeout (ms)
this.maxReconnectAttempts = 10;      // Max reconnection attempts

User Experience Improvements

Failure Progression

  1. 0-1 failures: Silent (logged to console)
  2. 2 failures: Yellow warning banner appears
  3. 5+ failures: Red error banner with reconnection status
  4. Automatic recovery: All banners disappear when connection restored

Reconnection Attempts

  • Attempt 1: 2 seconds delay
  • Attempt 2: 4 seconds delay
  • Attempt 3: 8 seconds delay
  • Attempt 4: 16 seconds delay
  • Attempt 5: 30 seconds delay (capped)
  • Attempts 6-10: 30 seconds delay each

Manual Control

Users can now:

  • Retry Now: Immediately attempt reconnection (resets backoff)
  • Reload Dashboard: Full page reload if all else fails
  • Monitor Status: Real-time updates on reconnection progress

Testing Recommendations

  1. Test normal operation: Verify 5-second heartbeat interval
  2. Test connection loss: Stop backend server, verify warning/error progression
  3. Test reconnection: Restart backend, verify automatic recovery
  4. Test manual retry: Click "Retry Now" button during connection loss
  5. Test exponential backoff: Verify increasing delays between attempts
  6. Test max attempts: Verify behavior after 10 failed attempts

Files Modified

  • C:\codedev\serena-mcp\src\serena\resources\dashboard\dashboard.js
    • Added 153 lines of improved heartbeat logic
    • Total file size: 2120 lines (was 1967 lines)

Backward Compatibility

All changes are fully backward compatible:

  • No API changes required
  • No HTML changes required
  • Works with existing /heartbeat endpoint
  • No database or configuration changes needed

Performance Impact

Before:

  • 4 heartbeat requests per second (250ms interval)
  • Immediate crash on any network hiccup
  • No recovery mechanism

After:

  • 0.2 heartbeat requests per second (5s interval)
  • 95% reduction in heartbeat network traffic
  • Graceful handling of temporary network issues
  • Automatic recovery from failures

Security Considerations

  • No security vulnerabilities introduced
  • Exponential backoff prevents reconnection spam
  • Maximum attempt limit prevents infinite loops
  • Timeout prevents resource exhaustion

Future Enhancements (Optional)

Potential improvements that could be added:

  1. SSE/WebSocket Support: Replace polling with push notifications
  2. Configurable UI: Allow users to adjust heartbeat settings
  3. Health Metrics: Track and display connection quality over time
  4. Offline Mode: Continue showing cached data during disconnection
  5. Browser Visibility API: Pause heartbeat when tab is hidden

Date: 2026-01-05 Status: COMPLETE Severity: Critical stability fix Impact: Production-ready heartbeat resilience