feat: implement isolated model worker with auto-restart and hot-reload

Introduce a supervised child process for capture, VAD, and recognition,
enabling automatic restart on crash/hang and hot-reload via SIGHUP.
Add `--model-auto-restart`, `--model-timeout`, and
`--model-shutdown-timeout` options. Refactor `Run()` with lifecycle
hooks for proper process group cleanup. Update README with new
behavior and CLI flags.

src/config/config.go

@@ -12,6 +12,8 @@ const (
 	DefaultModelsDir            = "models"
 	DefaultOverlayFontFamily    = "Sans"
 	MinimumOverlayFinalLifetime = 3 * time.Second
+	DefaultModelTimeout         = 30 * time.Second
+	DefaultModelShutdownTimeout = 2 * time.Second
 )
 
 type Mode string
@@ -22,11 +24,14 @@ const (
 )
 
 type Settings struct {
-	Mode               Mode
-	ChunkDuration      time.Duration
-	ModelsDir          string
-	Threads            int
-	PreviewThresholdDB float64
+	Mode                 Mode
+	ChunkDuration        time.Duration
+	ModelsDir            string
+	Threads              int
+	PreviewThresholdDB   float64
+	ModelAutoRestart     bool
+	ModelTimeout         time.Duration
+	ModelShutdownTimeout time.Duration
 }
 
 func Parse() Settings {
@@ -37,6 +42,9 @@ func Parse() Settings {
 	flag.StringVar(&settings.ModelsDir, "models-dir", DefaultModelsDir, "directory containing downloaded Sherpa models")
 	flag.IntVar(&settings.Threads, "threads", 2, "CPU threads used by recognition and VAD")
 	flag.Float64Var(&settings.PreviewThresholdDB, "preview-threshold-dbfs", -45, "RMS dBFS threshold used to begin VAD previews")
+	flag.BoolVar(&settings.ModelAutoRestart, "model-auto-restart", true, "restart the isolated model worker after a crash or timeout")
+	flag.DurationVar(&settings.ModelTimeout, "model-timeout", DefaultModelTimeout, "maximum model startup or processing time; zero disables hang detection")
+	flag.DurationVar(&settings.ModelShutdownTimeout, "model-shutdown-timeout", DefaultModelShutdownTimeout, "time allowed for model flush and cleanup before force-killing the worker")
 	flag.Parse()
 	settings.Mode = Mode(mode)
 	return settings
@@ -87,6 +95,9 @@ func ParseDesktop() DesktopSettings {
 	flags.StringVar(&desktop.ModelsDir, "models-dir", DefaultModelsDir, "directory containing downloaded Sherpa models")
 	flags.IntVar(&desktop.Threads, "threads", 2, "CPU threads used by recognition and VAD")
 	flags.Float64Var(&desktop.PreviewThresholdDB, "preview-threshold-dbfs", -45, "RMS dBFS threshold used to begin VAD previews")
+	flags.BoolVar(&desktop.ModelAutoRestart, "model-auto-restart", true, "restart the isolated model worker after a crash or timeout")
+	flags.DurationVar(&desktop.ModelTimeout, "model-timeout", DefaultModelTimeout, "maximum model startup or processing time; zero disables hang detection")
+	flags.DurationVar(&desktop.ModelShutdownTimeout, "model-shutdown-timeout", DefaultModelShutdownTimeout, "time allowed for model flush and cleanup before force-killing the worker")
 	flags.StringVar(&output, "output", "", "caption output: terminal, overlay, or both (required)")
 	flags.StringVar(&backend, "overlay-backend", "auto", "display backend: auto, wayland, or x11")
 	flags.Float64Var(&desktop.Overlay.Opacity, "overlay-opacity", 0.90, "caption background opacity from 0 to 1")
@@ -114,6 +125,12 @@ func (s Settings) Validate() error {
 	if s.Threads <= 0 {
 		return errors.New("--threads must be positive")
 	}
+	if s.ModelTimeout < 0 {
+		return errors.New("--model-timeout cannot be negative")
+	}
+	if s.ModelShutdownTimeout <= 0 {
+		return errors.New("--model-shutdown-timeout must be positive")
+	}
 	return nil
 }
 

src/config/config_test.go

@@ -6,7 +6,12 @@ import (
 )
 
 func TestSettingsValidate(t *testing.T) {
-	valid := Settings{Mode: ModeFixed, ChunkDuration: time.Second, Threads: 1}
+	valid := Settings{
+		Mode:                 ModeFixed,
+		ChunkDuration:        time.Second,
+		Threads:              1,
+		ModelShutdownTimeout: DefaultModelShutdownTimeout,
+	}
 	if err := valid.Validate(); err != nil {
 		t.Fatalf("valid settings failed: %v", err)
 	}
@@ -17,8 +22,14 @@ func TestSettingsValidate(t *testing.T) {
 
 func validDesktopSettings() DesktopSettings {
 	return DesktopSettings{
-		Settings: Settings{Mode: ModeVAD, ChunkDuration: time.Second, Threads: 2},
-		Output:   OutputOverlay,
+		Settings: Settings{
+			Mode:                 ModeVAD,
+			ChunkDuration:        time.Second,
+			Threads:              2,
+			ModelTimeout:         DefaultModelTimeout,
+			ModelShutdownTimeout: DefaultModelShutdownTimeout,
+		},
+		Output: OutputOverlay,
 		Overlay: OverlaySettings{
 			Backend: BackendAuto, Opacity: 0.9, FontSize: 28, FontFamily: DefaultOverlayFontFamily, BottomMargin: 100,
 			MaxWidth: 1200, Monitor: "auto", FinalTimeout: 4 * time.Second, ClickThrough: true,
@@ -46,6 +57,8 @@ func TestDesktopSettingsValidate(t *testing.T) {
 		{"empty monitor", func(s *DesktopSettings) { s.Overlay.Monitor = "" }},
 		{"negative timeout", func(s *DesktopSettings) { s.Overlay.FinalTimeout = -time.Second }},
 		{"short timeout", func(s *DesktopSettings) { s.Overlay.FinalTimeout = time.Second }},
+		{"negative model timeout", func(s *DesktopSettings) { s.ModelTimeout = -time.Second }},
+		{"zero model shutdown timeout", func(s *DesktopSettings) { s.ModelShutdownTimeout = 0 }},
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {