feat(11-02): add [groups] TOML support and group-ordered PrintConfig

- Add Groups map[string]string field to rawConfig struct
- Add applyGroupOverrides function for [groups] reassignment with stderr warning on unknown class
- Add groupOrder canonical slice for section header ordering
- Refactor PrintConfig to emit group headers (Infrastructure, Web, Mail, Remote Access, File Transfer, Database, Discovery, VoIP, Unknown)
- Classes within each group sorted by ascending BaseHz
- User-defined classes emitted under '# User-defined' section
- Non-canonical group names (user-invented) emitted in sorted order after canonical groups

config/config.go

@@ -38,6 +38,7 @@ type RawRule struct {
 type rawConfig struct {
 	Sounds map[string]SoundOverride `toml:"sounds"`
 	Rules  []RawRule                `toml:"rules"`
+	Groups map[string]string        `toml:"groups"`
 }
 
 // LoadResult is the return type from Load(). It carries the merged FreqConfig map,
@@ -99,6 +100,7 @@ func Load(configPath string) (LoadResult, error) {
 	// Add auto-freq entries BEFORE merge so that [sounds.X] overrides for user classes apply.
 	addAutoFreqEntries(freqCfgs, userRules, autoClasses)
 	merge(freqCfgs, raw.Sounds)
+	applyGroupOverrides(freqCfgs, raw.Groups)
 
 	return LoadResult{
 		FreqCfgs:    freqCfgs,
@@ -262,6 +264,28 @@ func waveformString(wt synth.WaveformType) string {
 	}
 }
 
+// applyGroupOverrides overlays [groups] reassignments onto freqCfgs.Group in-place.
+// Unknown class names produce a warning to stderr (D-09).
+// Unknown group names are silently accepted -- users can invent custom groups (D-09).
+func applyGroupOverrides(cfgs map[classify.TrafficClass]synth.FreqConfig, groups map[string]string) {
+	for className, groupName := range groups {
+		cls := classify.TrafficClass(className)
+		cfg, known := cfgs[cls]
+		if !known {
+			fmt.Fprintf(os.Stderr, "Warning: config: [groups]: unknown class %q (ignored)\n", className)
+			continue
+		}
+		cfg.Group = groupName
+		cfgs[cls] = cfg
+	}
+}
+
+// groupOrder defines the canonical display order for --print-config section headers (D-04).
+var groupOrder = []string{
+	"Infrastructure", "Web", "Mail", "Remote Access",
+	"File Transfer", "Database", "Discovery", "VoIP", "Unknown",
+}
+
 // PrintConfig returns the effective configuration as commented TOML output.
 // The output includes a header with source path and generation date, an optional
 // [[rules]] section for user-defined rules, and a [sounds.*] section for all
@@ -294,23 +318,34 @@ func PrintConfig(result LoadResult) string {
 		}
 	}
 
-	// [sounds.*] section — built-in classes first, then user-defined sorted alphabetically
+	// [sounds.*] section — built-in classes grouped by family, then user-defined
+
+	// Build group -> []TrafficClass index from AllClasses()
+	builtinByGroup := map[string][]classify.TrafficClass{}
 	builtinSet := map[classify.TrafficClass]bool{}
 	for _, cls := range classify.AllClasses() {
 		builtinSet[cls] = true
+		cfg := result.FreqCfgs[cls]
+		grp := cfg.Group
+		builtinByGroup[grp] = append(builtinByGroup[grp], cls)
 	}
 
-	// Collect user-defined classes (in FreqCfgs but not in AllClasses)
-	var userClasses []string
-	for cls := range result.FreqCfgs {
-		if !builtinSet[cls] {
-			userClasses = append(userClasses, string(cls))
+	// Sort each group by ascending BaseHz (D-05) using result.FreqCfgs (effective Hz, not defaults)
+	for grp := range builtinByGroup {
+		classes := builtinByGroup[grp]
+		sort.Slice(classes, func(i, j int) bool {
+			return result.FreqCfgs[classes[i]].BaseHz < result.FreqCfgs[classes[j]].BaseHz
+		})
 	}
-	}
-	sort.Strings(userClasses)
 
-	// Emit built-in classes first
-	for _, cls := range classify.AllClasses() {
+	// Emit built-in classes grouped with headers (D-04)
+	for _, grp := range groupOrder {
+		classes, ok := builtinByGroup[grp]
+		if !ok || len(classes) == 0 {
+			continue
+		}
+		fmt.Fprintf(&sb, "# %s\n\n", grp)
+		for _, cls := range classes {
 			cfg := result.FreqCfgs[cls]
 			annotation := classAnnotation(cls, cfg, result.AutoClasses)
 			fmt.Fprintf(&sb, "# %s -- %.1f Hz (%s)\n", string(cls), cfg.BaseHz, annotation)
@@ -319,8 +354,58 @@ func PrintConfig(result LoadResult) string {
 			fmt.Fprintf(&sb, "waveform = %q\n", waveformString(cfg.WaveformType))
 			fmt.Fprintf(&sb, "\n")
 		}
+	}
 
-	// Emit user-defined classes sorted alphabetically
+	// Check for custom groups (from [groups] reassignment) that are not in groupOrder.
+	// For non-canonical group names (user-invented), collect and emit separately.
+	customGroups := map[string][]classify.TrafficClass{}
+	for _, cls := range classify.AllClasses() {
+		cfg := result.FreqCfgs[cls]
+		grp := cfg.Group
+		isCanonical := false
+		for _, cg := range groupOrder {
+			if grp == cg {
+				isCanonical = true
+				break
+			}
+		}
+		if !isCanonical {
+			customGroups[grp] = append(customGroups[grp], cls)
+		}
+	}
+	// Sort and emit custom group sections
+	var customGroupNames []string
+	for grp := range customGroups {
+		customGroupNames = append(customGroupNames, grp)
+	}
+	sort.Strings(customGroupNames)
+	for _, grp := range customGroupNames {
+		classes := customGroups[grp]
+		sort.Slice(classes, func(i, j int) bool {
+			return result.FreqCfgs[classes[i]].BaseHz < result.FreqCfgs[classes[j]].BaseHz
+		})
+		fmt.Fprintf(&sb, "# %s\n\n", grp)
+		for _, cls := range classes {
+			cfg := result.FreqCfgs[cls]
+			annotation := classAnnotation(cls, cfg, result.AutoClasses)
+			fmt.Fprintf(&sb, "# %s -- %.1f Hz (%s)\n", string(cls), cfg.BaseHz, annotation)
+			fmt.Fprintf(&sb, "[sounds.%s]\n", string(cls))
+			fmt.Fprintf(&sb, "frequency = %.1f\n", cfg.BaseHz)
+			fmt.Fprintf(&sb, "waveform = %q\n", waveformString(cfg.WaveformType))
+			fmt.Fprintf(&sb, "\n")
+		}
+	}
+
+	// Emit user-defined classes (in FreqCfgs but not in AllClasses) under "# User-defined" (D-06)
+	var userClasses []string
+	for cls := range result.FreqCfgs {
+		if !builtinSet[cls] {
+			userClasses = append(userClasses, string(cls))
+		}
+	}
+	sort.Strings(userClasses)
+	if len(userClasses) > 0 {
+		fmt.Fprintf(&sb, "# User-defined\n\n")
 		for _, clsStr := range userClasses {
 			cls := classify.TrafficClass(clsStr)
 			cfg := result.FreqCfgs[cls]
@@ -331,6 +416,7 @@ func PrintConfig(result LoadResult) string {
 			fmt.Fprintf(&sb, "waveform = %q\n", waveformString(cfg.WaveformType))
 			fmt.Fprintf(&sb, "\n")
 		}
+	}
 
 	return sb.String()
 }