fix(car): address code review findings — lifecycle, security, thread safety

Critical fixes:
- EmergencyHandler: recreate scope on startCollecting() (singleton was permanently dead after first session)
- MeshtasticCarAppService: gate ALLOW_ALL_HOSTS_VALIDATOR behind BuildConfig.DEBUG, add hosts_allowlist.xml for production

High fixes:
- MeshtasticCarSession: wire destroy() via DefaultLifecycleObserver on ON_DESTROY
- MeshStatusPanel: remove unused CoroutineScope (no coroutines launched)
- CarStateCoordinator: use MutableStateFlow for channel index, ConcurrentHashMap for messagesCache
- CarTtsEngine: wire shutdown() call into coordinator destroy()

Medium fixes:
- NodeDetailScreen: replace all hardcoded strings with R.string resources
- DisconnectedScreen: replace hardcoded strings with resources
- Add comprehensive string resources for time formatting and status labels

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

feature/car/build.gradle.kts

@@ -24,6 +24,8 @@ plugins {
 android {
     namespace = "org.meshtastic.feature.car"
 
+    buildFeatures { buildConfig = true }
+
     defaultConfig {
         minSdk = 23
         consumerProguardFiles("proguard-rules.pro")

feature/car/src/main/kotlin/org/meshtastic/feature/car/alerts/EmergencyHandler.kt

@@ -37,23 +37,28 @@ import org.meshtastic.feature.car.model.EmergencyAlert
 @Single
 class EmergencyHandler {
 
-    private val scope = CoroutineScope(SupervisorJob() + Dispatchers.Main)
+    private var scope: CoroutineScope? = null
     private val _activeAlerts = MutableStateFlow<List<EmergencyAlert>>(emptyList())
     val activeAlerts: StateFlow<List<EmergencyAlert>> = _activeAlerts.asStateFlow()
 
     private var toneGenerator: ToneGenerator? = null
 
     fun startCollecting(emergencyFlow: Flow<EmergencyAlert>) {
-        scope.launch {
-            emergencyFlow.collect { alert ->
-                addAlert(alert)
-                playEmergencyTone()
+        scope?.cancel()
+        scope =
+            CoroutineScope(SupervisorJob() + Dispatchers.Main).also { newScope ->
+                newScope.launch {
+                    emergencyFlow.collect { alert ->
+                        addAlert(alert)
+                        playEmergencyTone()
+                    }
+                }
             }
-        }
     }
 
     fun stopCollecting() {
-        scope.cancel()
+        scope?.cancel()
+        scope = null
         toneGenerator?.release()
         toneGenerator = null
     }

feature/car/src/main/kotlin/org/meshtastic/feature/car/panels/MeshStatusPanel.kt

@@ -16,10 +16,6 @@
  */
 package org.meshtastic.feature.car.panels
 
-import kotlinx.coroutines.CoroutineScope
-import kotlinx.coroutines.Dispatchers
-import kotlinx.coroutines.SupervisorJob
-import kotlinx.coroutines.cancel
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
@@ -34,7 +30,6 @@ import org.meshtastic.feature.car.model.ConnectionStatus
 @Single
 class MeshStatusPanel {
 
-    private val scope = CoroutineScope(SupervisorJob() + Dispatchers.Main)
     private val _state =
         MutableStateFlow(
             CarSessionState(
@@ -86,10 +81,6 @@ class MeshStatusPanel {
         return "Last msg: $timeAgo"
     }
 
-    fun destroy() {
-        scope.cancel()
-    }
-
     companion object {
         private const val MILLIS_PER_MINUTE = 60_000L
         private const val MILLIS_PER_HOUR = 3_600_000L

feature/car/src/main/kotlin/org/meshtastic/feature/car/panels/MeshStatusSessionWiring.kt

@@ -45,6 +45,5 @@ class MeshStatusSessionWiring(private val panel: MeshStatusPanel) {
         connectionJob?.cancel()
         nodeCountJob?.cancel()
         messageTimeJob?.cancel()
-        panel.destroy()
     }
 }

feature/car/src/main/kotlin/org/meshtastic/feature/car/screens/DisconnectedScreen.kt

@@ -37,13 +37,13 @@ class DisconnectedScreen(carContext: CarContext) : Screen(carContext) {
             .addRow(
                 Row.Builder()
                     .setTitle(carContext.getString(R.string.car_disconnected))
-                    .addText("Radio connection lost. Showing cached data.")
+                    .addText(carContext.getString(R.string.car_disconnected_body))
                     .build(),
             )
             .addRow(
                 Row.Builder()
-                    .setTitle("Reconnecting...")
-                    .addText("The app will automatically reconnect when the radio is available.")
+                    .setTitle(carContext.getString(R.string.car_reconnecting_title))
+                    .addText(carContext.getString(R.string.car_reconnecting_body))
                     .build(),
             )
             .build(),

feature/car/src/main/kotlin/org/meshtastic/feature/car/screens/NodeDetailScreen.kt

@@ -39,15 +39,38 @@ class NodeDetailScreen(
 
         val paneBuilder = Pane.Builder()
 
-        paneBuilder.addRow(Row.Builder().setTitle("Signal").addText(formatSignal(node.signalQuality)).build())
+        paneBuilder.addRow(
+            Row.Builder()
+                .setTitle(carContext.getString(R.string.car_status_signal))
+                .addText(formatSignal(node.signalQuality))
+                .build(),
+        )
 
         node.batteryPercent?.let { battery ->
-            paneBuilder.addRow(Row.Builder().setTitle("Battery").addText("$battery%").build())
+            paneBuilder.addRow(
+                Row.Builder().setTitle(carContext.getString(R.string.car_status_battery)).addText("$battery%").build(),
+            )
         }
 
-        paneBuilder.addRow(Row.Builder().setTitle("Last Heard").addText(formatLastHeard(node.lastHeard)).build())
+        paneBuilder.addRow(
+            Row.Builder()
+                .setTitle(carContext.getString(R.string.car_status_last_heard))
+                .addText(formatLastHeard(node.lastHeard))
+                .build(),
+        )
 
-        paneBuilder.addRow(Row.Builder().setTitle("Status").addText(if (node.isOnline) "Online" else "Offline").build())
+        paneBuilder.addRow(
+            Row.Builder()
+                .setTitle(carContext.getString(R.string.car_status_status))
+                .addText(
+                    if (node.isOnline) {
+                        carContext.getString(R.string.car_status_online)
+                    } else {
+                        carContext.getString(R.string.car_status_offline)
+                    },
+                )
+                .build(),
+        )
 
         paneBuilder.addAction(
             Action.Builder()
@@ -61,10 +84,18 @@ class NodeDetailScreen(
             .build()
     }
 
-    private fun buildErrorTemplate(): Template =
-        PaneTemplate.Builder(Pane.Builder().addRow(Row.Builder().setTitle("Node not found").build()).build())
-            .setHeader(Header.Builder().setTitle("Error").setStartHeaderAction(Action.BACK).build())
-            .build()
+    private fun buildErrorTemplate(): Template = PaneTemplate.Builder(
+        Pane.Builder()
+            .addRow(Row.Builder().setTitle(carContext.getString(R.string.car_node_not_found)).build())
+            .build(),
+    )
+        .setHeader(
+            Header.Builder()
+                .setTitle(carContext.getString(R.string.car_error))
+                .setStartHeaderAction(Action.BACK)
+                .build(),
+        )
+        .build()
 
     private fun formatSignal(quality: SignalQuality): String = when (quality) {
         SignalQuality.EXCELLENT -> carContext.getString(R.string.car_signal_excellent)
@@ -75,13 +106,18 @@ class NodeDetailScreen(
     }
 
     private fun formatLastHeard(epochMillis: Long): String {
-        if (epochMillis == 0L) return "Never"
+        if (epochMillis == 0L) return carContext.getString(R.string.car_time_never)
         val elapsed = System.currentTimeMillis() - epochMillis
         return when {
-            elapsed < MILLIS_PER_MINUTE -> "Just now"
-            elapsed < MILLIS_PER_HOUR -> "${elapsed / MILLIS_PER_MINUTE}m ago"
-            elapsed < MILLIS_PER_DAY -> "${elapsed / MILLIS_PER_HOUR}h ago"
-            else -> "${elapsed / MILLIS_PER_DAY}d ago"
+            elapsed < MILLIS_PER_MINUTE -> carContext.getString(R.string.car_time_just_now)
+
+            elapsed < MILLIS_PER_HOUR ->
+                carContext.getString(R.string.car_time_minutes_ago, (elapsed / MILLIS_PER_MINUTE).toInt())
+
+            elapsed < MILLIS_PER_DAY ->
+                carContext.getString(R.string.car_time_hours_ago, (elapsed / MILLIS_PER_HOUR).toInt())
+
+            else -> carContext.getString(R.string.car_time_days_ago, (elapsed / MILLIS_PER_DAY).toInt())
         }
     }
 

feature/car/src/main/kotlin/org/meshtastic/feature/car/service/CarStateCoordinator.kt

@@ -49,6 +49,7 @@ import org.meshtastic.feature.car.model.NodeUi
 import org.meshtastic.feature.car.model.SignalQuality
 import org.meshtastic.feature.car.model.TopologyHeader
 import org.meshtastic.feature.car.util.CarTtsEngine
+import java.util.concurrent.ConcurrentHashMap
 
 /** Snapshot of a message for car display (avoids leaking domain models to UI). */
 data class MessageSnapshot(
@@ -106,7 +107,7 @@ class CarStateCoordinator(
     private val _quickChatActions = MutableStateFlow<List<String>>(emptyList())
     val quickChatActions: StateFlow<List<String>> = _quickChatActions.asStateFlow()
 
-    private var selectedChannelIndex = 0
+    private val selectedChannel = MutableStateFlow(0)
 
     fun start() {
         collectConnectionState()
@@ -116,7 +117,7 @@ class CarStateCoordinator(
     }
 
     fun selectChannel(index: Int) {
-        selectedChannelIndex = index
+        selectedChannel.value = index
         _messagingState.value = _messagingState.value.copy(selectedChannelIndex = index)
     }
 
@@ -145,7 +146,7 @@ class CarStateCoordinator(
                 to = contactKey,
                 bytes = text.encodeToByteArray().toByteString(),
                 dataType = DATA_TYPE_TEXT,
-                channel = selectedChannelIndex,
+                channel = selectedChannel.value,
             )
         commandSender.sendData(packet)
     }
@@ -159,7 +160,7 @@ class CarStateCoordinator(
         }
     }
 
-    private val messagesCache = mutableMapOf<String, List<MessageSnapshot>>()
+    private val messagesCache = ConcurrentHashMap<String, List<MessageSnapshot>>()
 
     fun cacheMessages(contactKey: String, messages: List<MessageSnapshot>) {
         messagesCache[contactKey] = messages
@@ -172,6 +173,7 @@ class CarStateCoordinator(
 
     fun destroy() {
         scope.cancel()
+        ttsEngine.shutdown()
     }
 
     private fun collectConnectionState() {
@@ -243,7 +245,7 @@ class CarStateCoordinator(
                 _messagingState.value =
                     MessagingUiState(
                         channels = channels,
-                        selectedChannelIndex = selectedChannelIndex,
+                        selectedChannelIndex = selectedChannel.value,
                         conversations = conversations,
                         emergencySpotlight = null,
                     )

feature/car/src/main/kotlin/org/meshtastic/feature/car/service/MeshtasticCarAppService.kt

@@ -20,10 +20,16 @@ import androidx.car.app.CarAppService
 import androidx.car.app.Session
 import androidx.car.app.SessionInfo
 import androidx.car.app.validation.HostValidator
+import org.meshtastic.feature.car.BuildConfig
+import org.meshtastic.feature.car.R
 
 class MeshtasticCarAppService : CarAppService() {
 
-    override fun createHostValidator(): HostValidator = HostValidator.ALLOW_ALL_HOSTS_VALIDATOR
+    override fun createHostValidator(): HostValidator = if (BuildConfig.DEBUG) {
+        HostValidator.ALLOW_ALL_HOSTS_VALIDATOR
+    } else {
+        HostValidator.Builder(applicationContext).addAllowedHosts(R.array.car_hosts_allowlist).build()
+    }
 
     override fun onCreateSession(sessionInfo: SessionInfo): Session = MeshtasticCarSession()
 }

feature/car/src/main/kotlin/org/meshtastic/feature/car/service/MeshtasticCarSession.kt

@@ -20,6 +20,8 @@ import android.content.Intent
 import android.content.res.Configuration
 import androidx.car.app.Screen
 import androidx.car.app.Session
+import androidx.lifecycle.DefaultLifecycleObserver
+import androidx.lifecycle.LifecycleOwner
 import kotlinx.coroutines.flow.emptyFlow
 import org.koin.core.component.KoinComponent
 import org.koin.core.component.inject
@@ -42,6 +44,15 @@ class MeshtasticCarSession :
         stateCoordinator.start()
         // Emergency flow wired to emptyFlow() until emergency packet detection is implemented
         emergencyWiring.attach(emptyFlow())
+
+        lifecycle.addObserver(
+            object : DefaultLifecycleObserver {
+                override fun onDestroy(owner: LifecycleOwner) {
+                    destroy()
+                }
+            },
+        )
+
         return HomeScreen(carContext, stateCoordinator)
     }
 
@@ -53,7 +64,7 @@ class MeshtasticCarSession :
         // Handle theme/density changes — templates auto-update
     }
 
-    fun destroy() {
+    private fun destroy() {
         emergencyWiring.detach()
         stateCoordinator.destroy()
         crashlyticsCarTagger.setCarSession(false)

feature/car/src/main/res/values/hosts_allowlist.xml

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <string-array name="car_hosts_allowlist">
+        <!-- Android Auto host (Google) -->
+        <item>com.google.android.projection.gearhead</item>
+        <!-- Android Automotive OS system host -->
+        <item>com.android.car.carlauncher</item>
+        <!-- Android Auto for Phone Screens (testing) -->
+        <item>com.google.android.apps.auto</item>
+    </string-array>
+</resources>

feature/car/src/main/res/values/strings.xml

@@ -1,30 +1,46 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
     <string name="car_app_name">Meshtastic</string>
-    <string name="car_tab_messages">Messages</string>
-    <string name="car_tab_nodes">Nodes</string>
-    <string name="car_disconnected">Disconnected</string>
-    <string name="car_reconnecting">Radio connection lost. Will reconnect automatically.</string>
+    <string name="car_battery_level">Battery: %d%%</string>
     <string name="car_connecting">Connecting…</string>
-    <string name="car_no_channels">No channels configured</string>
-    <string name="car_no_nodes">No nodes heard</string>
-    <string name="car_no_messages">No messages yet</string>
-    <string name="car_nodes_online">%d nodes online</string>
-    <string name="car_last_message">Last msg: %s</string>
+    <string name="car_disconnected">Disconnected</string>
+    <string name="car_disconnected_body">Radio connection lost. Showing cached data.</string>
     <string name="car_emergency_alert">Emergency Alert</string>
-    <string name="car_voice_reply">Reply</string>
+    <string name="car_error">Error</string>
+    <string name="car_last_heard">Last heard: %s</string>
+    <string name="car_last_message">Last msg: %s</string>
+    <string name="car_message_node">Message</string>
+    <string name="car_message_too_long">Message exceeds 237 bytes</string>
+    <string name="car_no_channels">No channels configured</string>
+    <string name="car_no_messages">No messages yet</string>
+    <string name="car_no_nodes">No nodes heard</string>
+    <string name="car_node_not_found">Node not found</string>
+    <string name="car_nodes_online">%d nodes online</string>
+    <string name="car_onboarding_text">Open Meshtastic on your phone to configure channels and connect to a radio.</string>
+    <string name="car_onboarding_title">Setup Required</string>
     <string name="car_quick_reply">Quick Reply</string>
     <string name="car_read_aloud">Read Aloud</string>
-    <string name="car_message_node">Message</string>
+    <string name="car_reconnecting">Radio connection lost. Will reconnect automatically.</string>
+    <string name="car_reconnecting_title">Reconnecting…</string>
+    <string name="car_reconnecting_body">The app will automatically reconnect when the radio is available.</string>
     <string name="car_signal_excellent">Excellent</string>
-    <string name="car_signal_good">Good</string>
     <string name="car_signal_fair">Fair</string>
+    <string name="car_signal_good">Good</string>
     <string name="car_signal_poor">Poor</string>
     <string name="car_signal_unknown">Unknown</string>
-    <string name="car_battery_level">Battery: %d%%</string>
-    <string name="car_last_heard">Last heard: %s</string>
-    <string name="car_onboarding_title">Setup Required</string>
-    <string name="car_onboarding_text">Open Meshtastic on your phone to configure channels and connect to a radio.</string>
-    <string name="car_message_too_long">Message exceeds 237 bytes</string>
+    <string name="car_status_battery">Battery</string>
+    <string name="car_status_last_heard">Last Heard</string>
+    <string name="car_status_offline">Offline</string>
+    <string name="car_status_online">Online</string>
+    <string name="car_status_signal">Signal</string>
+    <string name="car_status_status">Status</string>
+    <string name="car_tab_messages">Messages</string>
+    <string name="car_tab_nodes">Nodes</string>
+    <string name="car_time_days_ago">%dd ago</string>
+    <string name="car_time_hours_ago">%dh ago</string>
+    <string name="car_time_just_now">Just now</string>
+    <string name="car_time_minutes_ago">%dm ago</string>
+    <string name="car_time_never">Never</string>
     <string name="car_unread_badge">%d unread</string>
+    <string name="car_voice_reply">Reply</string>
 </resources>