feat(cli): add multi-instance mode via subprocess spawning

cli/cmd/start.go

@@ -37,6 +37,7 @@ var (
 	bandwidthMbps     float64
 	psiphonConfigPath string
 	statsFilePath     string
+	numInstances      int
 )
 
 var startCmd = &cobra.Command{
@@ -61,8 +62,10 @@ func init() {
 
 	startCmd.Flags().IntVarP(&maxClients, "max-clients", "m", config.DefaultMaxClients, "maximum number of proxy clients (1-1000)")
 	startCmd.Flags().Float64VarP(&bandwidthMbps, "bandwidth", "b", config.DefaultBandwidthMbps, "total bandwidth limit in Mbps (-1 for unlimited)")
-	startCmd.Flags().StringVarP(&statsFilePath, "stats-file", "s", "", "persist stats to JSON file (default: stats.json in data dir if flag used without value)")
+	startCmd.Flags().StringVarP(&statsFilePath, "stats-file", "s", "", "persist stats to JSON file (-s for default, -s=path or --stats-file=path for custom)")
 	startCmd.Flags().Lookup("stats-file").NoOptDefVal = "stats.json"
+	startCmd.Flags().IntVar(&numInstances, "multi-instance", 0, "run multiple instances: 0=single (default), N=N instances, or no value=auto (1 per 50 clients, max 32)")
+	startCmd.Flags().Lookup("multi-instance").NoOptDefVal = "-1" // -1 means auto-calculate
 
 	// Only show --psiphon-config flag if no config is embedded
 	if !config.HasEmbeddedConfig() {
@@ -108,12 +111,6 @@ func runStart(cmd *cobra.Command, args []string) error {
 		return fmt.Errorf("failed to load configuration: %w", err)
 	}
 
-	// Create conduit service
-	service, err := conduit.New(cfg)
-	if err != nil {
-		return fmt.Errorf("failed to create conduit service: %w", err)
-	}
-
 	// Setup context with cancellation
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
@@ -128,6 +125,34 @@ func runStart(cmd *cobra.Command, args []string) error {
 		cancel()
 	}()
 
+	// Multi-instance mode: spawn subprocesses
+	if numInstances != 0 {
+		instances := numInstances
+		if instances < 0 {
+			instances = conduit.CalculateInstances(maxClients)
+		}
+		if instances > conduit.MaxInstances {
+			return fmt.Errorf("too many instances: %d (maximum: %d)", instances, conduit.MaxInstances)
+		}
+
+		multiService, err := conduit.NewMultiService(cfg, instances)
+		if err != nil {
+			return fmt.Errorf("failed to create multi-instance service: %w", err)
+		}
+
+		if err := multiService.Run(ctx); err != nil && ctx.Err() == nil {
+			return fmt.Errorf("multi-instance service error: %w", err)
+		}
+
+		return nil
+	}
+
+	// Single instance mode (default)
+	service, err := conduit.New(cfg)
+	if err != nil {
+		return fmt.Errorf("failed to create conduit service: %w", err)
+	}
+
 	// Print startup message
 	bandwidthStr := "unlimited"
 	if bandwidthMbps != config.UnlimitedBandwidth {