feat(07-02): wire LoadResult into main.go and add --print-config flag

- Add printConfig bool var and --print-config flag registration
- runPrintConfig() early-exit before interface-required check (CFG-06)
- runLiveMode and runPcapMode accept config.LoadResult; user rules prepend via append(result.UserRules, classify.DefaultRules...)
- Remove unused synth import from main.go
- Add TestPrintConfigFlagRegistered, TestPrintConfigNoInterface, TestPrintConfigWithConfigFile
- newTestCmd() wires --print-config and --config flags through PersistentPreRunE

cmd/netsynth/main.go

@@ -18,17 +18,17 @@ import (
 	"github.com/netsynth/netsynth/classify"
 	"github.com/netsynth/netsynth/config"
 	"github.com/netsynth/netsynth/encode"
-	"github.com/netsynth/netsynth/synth"
 )
 
 var (
-	ifaceName  string
+	ifaceName   string
-	listIfaces bool
+	listIfaces  bool
-	verbose    bool
+	verbose     bool
-	outputPath string
+	outputPath  string
-	bpfFilter  string // NEW: --filter flag (CAPT-05)
+	bpfFilter   string // NEW: --filter flag (CAPT-05)
-	readPath   string // NEW: --read flag (CAPT-06)
+	readPath    string // NEW: --read flag (CAPT-06)
-	configPath string // NEW: --config flag (CFG-03)
+	configPath  string // NEW: --config flag (CFG-03)
+	printConfig bool   // NEW: --print-config flag (CFG-06)
 )
 
 func main() {
@@ -46,6 +46,7 @@ func main() {
 	rootCmd.Flags().StringVar(&bpfFilter, "filter", "", "BPF filter expression (tcpdump syntax, e.g. \"port 53\")")
 	rootCmd.Flags().StringVar(&readPath, "read", "", "Read packets from pcap file instead of live capture")
 	rootCmd.Flags().StringVar(&configPath, "config", "", "Path to TOML config file (default: auto-discover)")
+	rootCmd.Flags().BoolVar(&printConfig, "print-config", false, "Print effective config as commented TOML and exit")
 
 	if err := rootCmd.Execute(); err != nil {
 		os.Exit(1)
@@ -68,6 +69,11 @@ func run(cmd *cobra.Command, args []string) error {
 		return runListInterfaces()
 	}
 
+	// --print-config mode (CFG-06, D-09/D-10): must come before interface-required check
+	if printConfig {
+		return runPrintConfig()
+	}
+
 	// D-03: --read and -i are mutually exclusive
 	if readPath != "" && ifaceName != "" {
 		return fmt.Errorf("--read and -i are mutually exclusive; use one or the other")
@@ -84,11 +90,10 @@ func run(cmd *cobra.Command, args []string) error {
 	}
 
 	// Load config (CFG-01 through CFG-05, D-11: fail fast before capture)
-	loadResult, err := config.Load(configPath)
+	result, err := config.Load(configPath)
 	if err != nil {
 		return err
 	}
-	freqCfgs := loadResult.FreqCfgs
 
 	// Resolve output path
 	if outputPath == "" {
@@ -100,13 +105,24 @@ func run(cmd *cobra.Command, args []string) error {
 	}
 
 	if readPath != "" {
-		return runPcapMode(cmd, freqCfgs)
+		return runPcapMode(cmd, result)
 	}
-	return runLiveMode(cmd, freqCfgs)
+	return runLiveMode(cmd, result)
+}
+
+// runPrintConfig loads the config and prints the effective configuration as commented TOML.
+func runPrintConfig() error {
+	result, err := config.Load(configPath)
+	if err != nil {
+		return err
+	}
+	output := config.PrintConfig(result)
+	fmt.Print(output)
+	return nil
 }
 
 // runLiveMode runs the live packet capture pipeline.
-func runLiveMode(cmd *cobra.Command, freqCfgs map[classify.TrafficClass]synth.FreqConfig) error {
+func runLiveMode(cmd *cobra.Command, result config.LoadResult) error {
 	// Set up signal handling (Ctrl+C)
 	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
 	defer stop()
@@ -119,7 +135,9 @@ func runLiveMode(cmd *cobra.Command, freqCfgs map[classify.TrafficClass]synth.Fr
 	}
 
 	// Stage 2: Classify (CLAS-01)
-	classifier := classify.NewClassifier(classify.DefaultRules)
+	// D-04: user rules prepend before built-ins; first-match-wins (RULE-02)
+	allRules := append(result.UserRules, classify.DefaultRules...)
+	classifier := classify.NewClassifier(allRules)
 	classified := make(chan classify.ClassifiedPacket, 1024)
 	go func() {
 		defer close(classified)
@@ -155,7 +173,7 @@ func runLiveMode(cmd *cobra.Command, freqCfgs map[classify.TrafficClass]synth.Fr
 	// D-07: Encoding status line
 	fmt.Fprintf(os.Stderr, "Encoding %d windows to %s...\n", len(collectedSnapshots), outputPath)
 	encodeStart := time.Now()
-	if err := encode.RunSynthesis(collectedSnapshots, outputPath, freqCfgs); err != nil {
+	if err := encode.RunSynthesis(collectedSnapshots, outputPath, result.FreqCfgs); err != nil {
 		return fmt.Errorf("synthesis failed: %w", err)
 	}
 	encodeElapsed := time.Since(encodeStart)
@@ -172,7 +190,7 @@ func runLiveMode(cmd *cobra.Command, freqCfgs map[classify.TrafficClass]synth.Fr
 }
 
 // runPcapMode runs the pcap file processing pipeline (CAPT-06).
-func runPcapMode(cmd *cobra.Command, freqCfgs map[classify.TrafficClass]synth.FreqConfig) error {
+func runPcapMode(cmd *cobra.Command, result config.LoadResult) error {
 	// D-06: bookend start message
 	fmt.Fprintf(os.Stderr, "Reading %s...\n", readPath)
 
@@ -183,7 +201,9 @@ func runPcapMode(cmd *cobra.Command, freqCfgs map[classify.TrafficClass]synth.Fr
 	}
 
 	// Classify packets (reuse same classifier)
-	classifier := classify.NewClassifier(classify.DefaultRules)
+	// D-04: user rules prepend before built-ins; first-match-wins (RULE-02)
+	allRules := append(result.UserRules, classify.DefaultRules...)
+	classifier := classify.NewClassifier(allRules)
 	classified := make(chan classify.ClassifiedPacket, 1024)
 	go func() {
 		defer close(classified)
@@ -223,7 +243,7 @@ func runPcapMode(cmd *cobra.Command, freqCfgs map[classify.TrafficClass]synth.Fr
 	// Encode
 	fmt.Fprintf(os.Stderr, "Encoding %d windows to %s...\n", len(collectedSnapshots), outputPath)
 	encodeStart := time.Now()
-	if err := encode.RunSynthesis(collectedSnapshots, outputPath, freqCfgs); err != nil {
+	if err := encode.RunSynthesis(collectedSnapshots, outputPath, result.FreqCfgs); err != nil {
 		return fmt.Errorf("synthesis failed: %w", err)
 	}
 	encodeElapsed := time.Since(encodeStart)

cmd/netsynth/main_test.go

@@ -2,6 +2,8 @@ package main
 
 import (
 	"bytes"
+	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 
@@ -16,6 +18,8 @@ func newTestCmd() *cobra.Command {
 	var testFilter string
 	var testRead string
 	var testOutput string
+	var testPrintConfig bool
+	var testConfigPath string
 
 	rootCmd := &cobra.Command{
 		Use:          "netsynth",
@@ -29,6 +33,8 @@ func newTestCmd() *cobra.Command {
 	rootCmd.Flags().StringVarP(&testOutput, "output", "o", "", "Output MP3 file path")
 	rootCmd.Flags().StringVar(&testFilter, "filter", "", "BPF filter expression")
 	rootCmd.Flags().StringVar(&testRead, "read", "", "Read packets from pcap file instead of live capture")
+	rootCmd.Flags().BoolVar(&testPrintConfig, "print-config", false, "Print effective config")
+	rootCmd.Flags().StringVar(&testConfigPath, "config", "", "Path to TOML config file")
 
 	// Wire test variables to package-level vars used by run()
 	rootCmd.PersistentPreRunE = func(cmd *cobra.Command, args []string) error {
@@ -38,6 +44,8 @@ func newTestCmd() *cobra.Command {
 		outputPath = testOutput
 		bpfFilter = testFilter
 		readPath = testRead
+		printConfig = testPrintConfig
+		configPath = testConfigPath
 		return nil
 	}
 
@@ -320,3 +328,72 @@ func TestHelpOutputNewFlags(t *testing.T) {
 		t.Errorf("expected help/usage output to contain '--read', usage: %s", usageStr)
 	}
 }
+
+// TestPrintConfigFlagRegistered verifies --print-config flag is registered.
+func TestPrintConfigFlagRegistered(t *testing.T) {
+	rootCmd := newTestCmd()
+	f := rootCmd.Flags().Lookup("print-config")
+	if f == nil {
+		t.Fatal("expected --print-config flag to be registered")
+	}
+}
+
+// TestPrintConfigNoInterface verifies --print-config works without -i flag.
+func TestPrintConfigNoInterface(t *testing.T) {
+	// Reset globals
+	ifaceName = ""
+	listIfaces = false
+	verbose = false
+	bpfFilter = ""
+	readPath = ""
+	outputPath = ""
+	printConfig = false
+	configPath = ""
+
+	// Use a temp dir with no netsynth.toml so no config is auto-discovered
+	t.Chdir(t.TempDir())
+
+	rootCmd := newTestCmd()
+	rootCmd.SetArgs([]string{"--print-config"})
+
+	var outBuf, errBuf bytes.Buffer
+	rootCmd.SetOut(&outBuf)
+	rootCmd.SetErr(&errBuf)
+
+	err := rootCmd.Execute()
+	if err != nil {
+		t.Fatalf("--print-config should not require -i, got error: %v", err)
+	}
+}
+
+// TestPrintConfigWithConfigFile verifies --print-config loads and displays a user config.
+func TestPrintConfigWithConfigFile(t *testing.T) {
+	// Create temp TOML with an override
+	dir := t.TempDir()
+	tomlPath := filepath.Join(dir, "test.toml")
+	if err := os.WriteFile(tomlPath, []byte("[sounds.ICMP]\nfrequency = 100.0\n"), 0644); err != nil {
+		t.Fatalf("WriteFile: %v", err)
+	}
+
+	// Reset globals
+	ifaceName = ""
+	listIfaces = false
+	verbose = false
+	bpfFilter = ""
+	readPath = ""
+	outputPath = ""
+	printConfig = false
+	configPath = ""
+
+	rootCmd := newTestCmd()
+	rootCmd.SetArgs([]string{"--print-config", "--config", tomlPath})
+
+	var outBuf, errBuf bytes.Buffer
+	rootCmd.SetOut(&outBuf)
+	rootCmd.SetErr(&errBuf)
+
+	err := rootCmd.Execute()
+	if err != nil {
+		t.Fatalf("--print-config with --config should succeed, got: %v", err)
+	}
+}