Add optional "log_file" configuration option.

config.go

@@ -17,6 +17,9 @@ type Config struct {
 	// DataDir is the base directory for all database files.
 	DataDir string `json:"data_dir"`
 
+	// LogFile is the optional path to a file where logs will be written.
+	LogFile string `json:"log_file"`
+
 	// HotRetentionHours is how many hours of raw ticks to keep in the hot DB.
 	HotRetentionHours int `json:"hot_retention_hours"`
 
@@ -42,6 +45,7 @@ func DefaultConfig() Config {
 		WebSocketURL:               "wss://stream.bybit.com/v5/public/linear",
 		Symbol:                     "BTCUSDT",
 		DataDir:                    "data",
+		LogFile:                    "engine.log",
 		HotRetentionHours:          12,
 		FeatureRetentionDays:       30,
 		WriterFlushIntervalMs:      500,
@@ -52,14 +56,12 @@ func DefaultConfig() Config {
 }
 
 // LoadConfig reads a JSON config file and merges with defaults.
-// If the file does not exist, defaults are returned and a config file is written.
 func LoadConfig(path string) (Config, error) {
 	cfg := DefaultConfig()
 
 	data, err := os.ReadFile(path)
 	if err != nil {
 		if os.IsNotExist(err) {
-			// Write default config for user reference
 			if writeErr := writeDefaultConfig(path, cfg); writeErr != nil {
 				return cfg, fmt.Errorf("failed to write default config: %w", writeErr)
 			}

config.json

@@ -2,6 +2,7 @@
   "websocket_url": "wss://stream.bybit.com/v5/public/linear",
   "symbol": "BTCUSDT",
   "data_dir": "data",
+  "log_file": "engine.log",
   "hot_retention_hours": 12,
   "feature_retention_days": 30,
   "writer_flush_interval_ms": 500,

main.go

@@ -40,7 +40,7 @@ func main() {
 		}
 
 		if isDaemon {
-			startDaemon()
+			startDaemon(cfg.LogFile)
 			return
 		}
 		runEngine(cfg)
@@ -78,13 +78,17 @@ func printUsage() {
 	fmt.Println("Usage: engine [command] [--daemon]")
 	fmt.Println("\nCommands:")
 	fmt.Println("  run       Start the WebSocket ingestor and processing engine")
-	fmt.Println("            Use --daemon to run in background and log to engine.log")
+	fmt.Println("            Use --daemon to run in background and log to the file defined in config")
 	fmt.Println("  recover   Run startup recovery to migrate stale ticks")
 	fmt.Println("  maintain  Run a single maintenance cycle (cleanup/retention)")
 	fmt.Println("  help      Show this help message")
 }
 
-func startDaemon() {
+func startDaemon(logPath string) {
+	if logPath == "" {
+		logPath = "engine.log"
+	}
+
 	// Prepare arguments for the child process (remove --daemon)
 	args := []string{}
 	for _, arg := range os.Args[1:] {
@@ -93,24 +97,24 @@ func startDaemon() {
 		}
 	}
 
-	// Prepare the command
+	// Prepare the command to re-run the current binary
 	cmd := exec.Command(os.Args[0], args...)
 	
-	// Open log file for output redirection
-	logFile, err := os.OpenFile("engine.log", os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
+	// Open the configured log file for output redirection
+	logFile, err := os.OpenFile(logPath, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
 	if err != nil {
-		log.Fatalf("Failed to open log file: %v", err)
+		log.Fatalf("Failed to open log file %s: %v", logPath, err)
 	}
 
 	cmd.Stdout = logFile
 	cmd.Stderr = logFile
 
-	// Start the process
+	// Start the process in the background
 	if err := cmd.Start(); err != nil {
 		log.Fatalf("Failed to start daemon: %v", err)
 	}
 
-	fmt.Printf("Engine started in background (PID: %d). Logs: engine.log\n", cmd.Process.Pid)
+	fmt.Printf("Engine started in background (PID: %d). Logs: %s\n", cmd.Process.Pid, logPath)
 	os.Exit(0)
 }