feat: implement agent migration system

- Fix config version inflation bug in main.go
- Add dynamic subsystem checking to prevent false change detection
- Implement migration detection and execution system
- Add directory migration from /etc/aggregator to /etc/redflag
- Update all path references across codebase to use new directories
- Add configuration schema versioning and automatic migration
- Implement backup and rollback capabilities
- Add security feature detection and hardening
- Update installation scripts and sudoers for new paths
- Complete Phase 1 migration system

aggregator-agent/internal/config/config.go

@@ -47,6 +47,10 @@ type LoggingConfig struct {
 
 // Config holds agent configuration
 type Config struct {
+	// Version Information
+	Version     string `json:"version,omitempty"`     // Config schema version
+	AgentVersion string `json:"agent_version,omitempty"` // Agent binary version
+
 	// Server Configuration
 	ServerURL         string `json:"server_url"`
 	RegistrationToken string `json:"registration_token,omitempty"` // One-time registration token
@@ -133,8 +137,10 @@ type CLIFlags struct {
 // getDefaultConfig returns default configuration values
 func getDefaultConfig() *Config {
 	return &Config{
-		ServerURL:         "http://localhost:8080",
-		CheckInInterval:   300, // 5 minutes
+		Version:      "4", // Current config schema version
+		AgentVersion: "", // Will be set by the agent at startup
+		ServerURL:    "http://localhost:8080",
+		CheckInInterval: 300, // 5 minutes
 		Network: NetworkConfig{
 			Timeout:     30 * time.Second,
 			RetryCount:  3,
@@ -153,7 +159,7 @@ func getDefaultConfig() *Config {
 	}
 }
 
-// loadFromFile reads configuration from file
+// loadFromFile reads configuration from file with backward compatibility migration
 func loadFromFile(configPath string) (*Config, error) {
 	// Ensure directory exists
 	dir := filepath.Dir(configPath)
@@ -170,12 +176,57 @@ func loadFromFile(configPath string) (*Config, error) {
 		return nil, fmt.Errorf("failed to read config: %w", err)
 	}
 
-	var config Config
-	if err := json.Unmarshal(data, &config); err != nil {
+	// Start with latest default config
+	config := getDefaultConfig()
+
+	// Parse the existing config into a generic map to handle missing fields
+	var rawConfig map[string]interface{}
+	if err := json.Unmarshal(data, &rawConfig); err != nil {
 		return nil, fmt.Errorf("failed to parse config: %w", err)
 	}
 
-	return &config, nil
+	// Marshal back to JSON and unmarshal into our new structure
+	// This ensures missing fields get default values from getDefaultConfig()
+	configJSON, err := json.Marshal(rawConfig)
+	if err != nil {
+		return nil, fmt.Errorf("failed to re-marshal config: %w", err)
+	}
+
+	// Carefully merge into our config structure, preserving defaults for missing fields
+	if err := json.Unmarshal(configJSON, &config); err != nil {
+		return nil, fmt.Errorf("failed to merge config: %w", err)
+	}
+
+	// Handle specific migrations for known breaking changes
+	migrateConfig(config)
+
+	return config, nil
+}
+
+// migrateConfig handles specific known migrations between config versions
+func migrateConfig(cfg *Config) {
+	// Update config schema version to latest
+	if cfg.Version != "4" {
+		fmt.Printf("[CONFIG] Migrating config schema from version %s to 4\n", cfg.Version)
+		cfg.Version = "4"
+	}
+
+	// Migration 1: Ensure minimum check-in interval (30 seconds)
+	if cfg.CheckInInterval < 30 {
+		fmt.Printf("[CONFIG] Migrating check_in_interval from %d to minimum 30 seconds\n", cfg.CheckInInterval)
+		cfg.CheckInInterval = 300 // Default to 5 minutes for better performance
+	}
+
+	// Migration 2: Add missing subsystem fields with defaults
+	if cfg.Subsystems.System.Timeout == 0 && cfg.Subsystems.System.CircuitBreaker.FailureThreshold == 0 {
+		fmt.Printf("[CONFIG] Adding missing 'system' subsystem configuration\n")
+		cfg.Subsystems.System = GetDefaultSubsystemsConfig().System
+	}
+
+	if cfg.Subsystems.Updates.Timeout == 0 && cfg.Subsystems.Updates.CircuitBreaker.FailureThreshold == 0 {
+		fmt.Printf("[CONFIG] Adding missing 'updates' subsystem configuration\n")
+		cfg.Subsystems.Updates = GetDefaultSubsystemsConfig().Updates
+	}
 }
 
 // loadFromEnv loads configuration from environment variables