feat(service): add --discovery-enabled CLI flag and treat 0 interval as disabled (#229)

Why: Operators need to control device discovery from the command line
without touching the persisted settings file, and a zero discovery
interval should be unambiguously off rather than running an
immediate-fire scan loop.

- Add --discovery-enabled BoolFlag (default true, env DISCOVERY_ENABLED)
and thread it through serviceConfig, applyPersistedSettings, and
createDefaultSettings so CLI/env can seed initial state and persisted
settings still take precedence on subsequent runs.
- HandleUpdateSettings now forces discoveryEnabled=false whenever the
resulting discoveryInterval is zero.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

cmd/soundtouch-service/main.go

@@ -240,6 +240,12 @@ func main() {
 				Value:   true,
 				EnvVars: []string{"RECORD_INTERACTIONS"},
 			},
+			&cli.BoolFlag{
+				Name:    "discovery-enabled",
+				Usage:   "Enable periodic device discovery",
+				Value:   true,
+				EnvVars: []string{"DISCOVERY_ENABLED"},
+			},
 			&cli.StringFlag{
 				Name:    "discovery-interval",
 				Usage:   "Device discovery interval",
@@ -395,7 +401,7 @@ func main() {
 			sm.GetDNSRunning = server.GetDNSRunning
 			server.SetHTTPServerURL(config.httpsServerURL)
 			server.SetVersionInfo(version, commit, date, repoURL)
-			server.SetDiscoverySettings(config.discoveryInterval, persisted.DiscoveryEnabled)
+			server.SetDiscoverySettings(config.discoveryInterval, config.discoveryEnabled)
 			server.SetDNSSettings(persisted.DNSEnabled, strings.Join(persisted.DNSUpstream, ","), persisted.DNSBindAddr)
 			server.SetMirrorSettings(persisted.MirrorEnabled, persisted.MirrorEndpoints, persisted.SkipMirrorEndpoints, persisted.PreferredSource)
 			server.SetInternalPaths(persisted.InternalPaths)
@@ -526,6 +532,7 @@ type serviceConfig struct {
 	mirrorEndpoints     []string
 	skipMirrorEndpoints []string
 	internalPaths       []string
+	discoveryEnabled    bool
 	discoveryInterval   time.Duration
 	domains             []string
 	spotifyClientID     string
@@ -590,6 +597,7 @@ func loadConfig(c *cli.Context) serviceConfig {
 	dnsUpstream := c.String("dns-upstream")
 	dnsBind := c.String("dns-bind")
 
+	discoveryEnabled := c.Bool("discovery-enabled")
 	discoveryIntervalStr := c.String("discovery-interval")
 
 	discoveryInterval, err := time.ParseDuration(discoveryIntervalStr)
@@ -638,6 +646,7 @@ func loadConfig(c *cli.Context) serviceConfig {
 		mirrorEndpoints:     mirrorEndpoints,
 		skipMirrorEndpoints: skipMirrorEndpoints,
 		internalPaths:       internalPaths,
+		discoveryEnabled:    discoveryEnabled,
 		discoveryInterval:   discoveryInterval,
 		domains:             domains,
 		spotifyClientID:     spotifyClientID,
@@ -720,6 +729,7 @@ func applyPersistedSettings(ds *datastore.DataStore, config *serviceConfig) data
 		config.httpsServerURL = persisted.HTTPServerURL
 	}
 
+	config.discoveryEnabled = persisted.DiscoveryEnabled
 	if persisted.DiscoveryInterval != "" {
 		if d, durErr := time.ParseDuration(persisted.DiscoveryInterval); durErr == nil {
 			config.discoveryInterval = d
@@ -786,8 +796,8 @@ func createDefaultSettings(ds *datastore.DataStore, config serviceConfig) datast
 		RedactLogs:          config.redact,
 		LogBodies:           config.logBody,
 		RecordInteractions:  config.record,
+		DiscoveryEnabled:    config.discoveryEnabled,
 		DiscoveryInterval:   config.discoveryInterval.String(),
-		DiscoveryEnabled:    true,
 		DNSEnabled:          config.dnsEnabled,
 		DNSUpstream:         strings.Split(config.dnsUpstream, ","),
 		DNSBindAddr:         config.dnsBind,

pkg/service/handlers/handlers_setup.go

@@ -256,11 +256,15 @@ func (s *Server) HandleUpdateSettings(w http.ResponseWriter, r *http.Request) {
 	s.mu.Lock()
 	s.serverURL = settings.ServerURL
 
+	s.discoveryEnabled = settings.DiscoveryEnabled
 	if settings.DiscoveryInterval != "" {
 		s.discoveryInterval = interval
 	}
 
-	s.discoveryEnabled = settings.DiscoveryEnabled
+	if s.discoveryInterval == 0 {
+		s.discoveryEnabled = false
+	}
+
 	s.dnsEnabled = settings.DNSEnabled
 
 	// Handle comma-separated upstream DNS servers