feat: speak through the vehicle's own voice service

The MG4 has no Android TTS engine and does not need one: it announces tyre faults and
navigation through a SAIC vendor service. Probing `android.speech.tts` and finding nothing
was the right answer to the wrong question — which is why the speak action reported "no
speech engine" on a car that talks.

  component  com.saicmotor.voicetts / .TtsService  (no intent filter, bound explicitly —
             the way the car's own voice app reaches it)
  descriptor com.saicmotor.voicetts.ITtsService
  tx 1       promptCommonWords(text, interrupt, tag)
  tx 3       stopPrompt()

Source: apks/saicvoiceservice_overseas_eh32 — VoiceAnnounceModel for the component name and
the call, ITtsService for the codes.

SaicService gains a by-component constructor for services that publish no action.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: malys

lib/src/main/java/com/mg4/hardware/saic/SaicIpc.kt

@@ -21,12 +21,19 @@ import com.mg4.hardware.AppLogger
  * service is up returns null rather than blocking: the rule engine has a cycle to finish, and
  * a vendor service that is slow to come up must not hold it.
  */
-class SaicService(
+class SaicService private constructor(
     private val packageName: String,
-    private val action: String,
+    private val action: String?,
+    private val className: String?,
     private val tag: String,
 ) {
 
+    /** Most vendor services publish an action; this is the usual way in. */
+    constructor(packageName: String, action: String, tag: String) :
+        this(packageName, action, null, tag)
+
+
+
     @Volatile
     private var binder: IBinder? = null
 
@@ -45,13 +52,17 @@ class SaicService(
     fun connect(context: Context) {
         if (isReady || connecting) return
         connecting = true
-        val intent = Intent(action).setPackage(packageName)
+        val intent = if (className != null) {
+            Intent().setComponent(ComponentName(packageName, className))
+        } else {
+            Intent(action).setPackage(packageName)
+        }
         val bound = runCatching {
             context.applicationContext.bindService(intent, connection, Context.BIND_AUTO_CREATE)
         }.getOrDefault(false)
         if (!bound) {
             connecting = false
-            AppLogger.w(TAG, "$tag: bindService($packageName/$action) refused")
+            AppLogger.w(TAG, "$tag: bindService($packageName/${className ?: action}) refused")
         }
     }
 
@@ -68,8 +79,15 @@ class SaicService(
         }
     }
 
-    private companion object {
-        const val TAG = "MG4_SAIC"
+    companion object {
+        private const val TAG = "MG4_SAIC"
+
+        /**
+         * For a service with no intent filter, reached by explicit component — how the car's
+         * own apps bind the TTS service, and the only way it answers.
+         */
+        fun byComponent(packageName: String, className: String, tag: String) =
+            SaicService(packageName, null, className, tag)
     }
 }
 

lib/src/main/java/com/mg4/hardware/saic/SaicMedia.kt

@@ -87,3 +87,45 @@ object SaicPhone {
         SaicAidl.callString(service.binder(), DESCRIPTOR, TX_GET_CONN_DEVICE_NAME)
             ?.takeIf { it.isNotBlank() }
 }
+
+/**
+ * The vehicle's own voice — the one that says "left front tyre abnormality".
+ *
+ * This is what makes the "speak" action work on a head unit with no Android TTS engine
+ * installed, which is the normal case: the car talks, but through a vendor service rather
+ * than through `android.speech.tts`. Probing for a platform engine and finding none was
+ * therefore the right answer to the wrong question.
+ *
+ * Bound by component name, not by action — the service declares no intent filter, and the
+ * car's own voice app reaches it exactly this way.
+ *
+ * Source: `apks/saicvoiceservice_overseas_eh32` — `VoiceAnnounceModel` (component name and
+ * the call it makes) and `ITtsService` (descriptor, transaction codes).
+ */
+object SaicTts {
+
+    private const val PACKAGE = "com.saicmotor.voicetts"
+    private const val CLASS = "com.saicmotor.voicetts.TtsService"
+    private const val DESCRIPTOR = "com.saicmotor.voicetts.ITtsService"
+
+    private const val TX_PROMPT = 1
+    private const val TX_STOP = 3
+
+    private val service = SaicService.byComponent(PACKAGE, CLASS, "voicetts")
+
+    val isAvailable: Boolean get() = service.isReady
+
+    fun connect(context: Context) = service.connect(context)
+
+    /**
+     * Speaks [text].
+     *
+     * [interrupt] true stops whatever the car is currently announcing — false queues behind
+     * it, which is what a rule message should do: a tyre warning outranks "profile applied".
+     * The tag is the caller's package, as the vendor apps pass their own.
+     */
+    fun speak(text: String, interrupt: Boolean = false, tag: String = "com.mg4.tasker"): Boolean =
+        SaicAidl.callVoid(service.binder(), DESCRIPTOR, TX_PROMPT, text, interrupt, tag)
+
+    fun stop(): Boolean = SaicAidl.callVoid(service.binder(), DESCRIPTOR, TX_STOP)
+}