Expose local HTTP/Unix socket API for real-time monitoring stats

[Copilot]

This PR implements a comprehensive local API system that exposes real-time monitoring statistics via both HTTP and Unix socket endpoints. The implementation enables building Terminal UI (TUI) applications and web interfaces while maintaining Fluxa's lightweight architecture.

Key Features

Real-time Monitoring API:

• /api/services - List all monitored services with comprehensive stats
• /api/services/{id} - Get individual service details (by index or URL)
• Available via both HTTP and Unix socket for flexible access patterns

Comprehensive Service Statistics:

• Health status (Healthy/Unhealthy)
• Latest response time in milliseconds
• Timestamps for last check and next scheduled check
• Detailed error messages from failed requests
• Current retry attempt count for unhealthy services

Enhanced Configuration:

[fluxa]
listen = "127.0.0.1:8080"        # HTTP server (existing)
api_socket = "/tmp/fluxa.sock"   # Unix socket API (new, optional)

Implementation Details

The solution follows SOLID principles and uses idiomatic Rust patterns:

• Shared State Management: Thread-safe Arc<RwLock<MonitoringState>> enables real-time data sharing between monitoring tasks and API server
• Extended Model: Enhanced MonitoredService with ServiceInfo and MonitoringStats structs that serialize cleanly to JSON
• Axum Integration: Lightweight HTTP handlers with proper error handling and status codes
• Unix Socket Support: Platform-specific Unix domain socket server for enhanced security and local access

API Usage Examples

HTTP API:

curl http://127.0.0.1:8080/api/services
curl http://127.0.0.1:8080/api/services/0

Unix Socket API:

curl --unix-socket /tmp/fluxa.sock http://localhost/api/services
curl --unix-socket /tmp/fluxa.sock http://localhost/api/services/0

Response Format:

{
  "services": [{
    "url": "https://example.com",
    "interval_seconds": 300,
    "max_retries": 3,
    "retry_interval_seconds": 5,
    "stats": {
      "status": "Healthy",
      "last_response_time_ms": 150,
      "last_check_timestamp": 1672531200,
      "next_check_timestamp": 1672531500,
      "last_error": null,
      "current_retry_count": 0
    }
  }],
  "total_count": 1
}

Testing

Added comprehensive test coverage including:

• Shared state management operations
• JSON serialization/deserialization of monitoring data
• Configuration parsing with Unix socket options
• Service information conversion and retrieval

All existing functionality remains unchanged and backward compatible.

Fixes #51.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• api.pushover.net
  • Triggering command: target/debug/fluxa --config config.test.toml (dns block)
  • Triggering command: target/debug/fluxa --config demo-config.toml (dns block)
• httpbin.org
  • Triggering command: target/debug/fluxa --config config.test.toml (dns block)
  • Triggering command: target/debug/fluxa --config demo-config.toml (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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