Fix streaming, add thread safety, settings UI, and request indicator

Fixes:
- Streaming was bypassed for all requests (system prompt auto-inject made
  messages.size always > 1). Stream=true now routes directly to generateStreaming
  before multi-turn check
- LiteRTModel: add Mutex to serialize Engine calls (not thread-safe)

New features:
- Settings card: temperature slider, max tokens, agent system prompt toggle
  (all saved to SharedPreferences, applied on server start)
- Active request indicator: "⚡ Processing request…" shown in status card
  while inference is running
- onActiveRequest callback from AIApiServer → ApiServerService → MainActivity

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/src/main/java/com/pixel10/ai/inference/LiteRTModel.kt

@@ -7,6 +7,8 @@ import com.google.ai.edge.litertlm.Engine
 import com.google.ai.edge.litertlm.EngineConfig
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.flow.catch
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
 import kotlinx.coroutines.withContext
 import java.io.File
 
@@ -29,42 +31,49 @@ class LiteRTModel private constructor(
     override var isReady: Boolean = true
         private set
 
+    // LiteRT Engine is not thread-safe — serialize all inference calls
+    private val mutex = Mutex()
+
     override suspend fun generate(
         prompt: String,
         maxTokens: Int,
         temperature: Float
-    ): String = withContext(Dispatchers.Default) {
-        val conversation = engine.createConversation()
-        try {
-            conversation.sendMessage(prompt).toString()
-        } catch (e: Exception) {
-            Log.e(TAG, "LiteRT inference error", e)
-            throw OnDeviceModel.InferenceException("Generation failed: ${e.message}", e)
-        } finally {
-            conversation.close()
+    ): String = mutex.withLock {
+        withContext(Dispatchers.Default) {
+            val conversation = engine.createConversation()
+            try {
+                conversation.sendMessage(prompt).toString()
+            } catch (e: Exception) {
+                Log.e(TAG, "LiteRT inference error", e)
+                throw OnDeviceModel.InferenceException("Generation failed: ${e.message}", e)
+            } finally {
+                conversation.close()
+            }
         }
     }
 
     override suspend fun generateStreaming(
         prompt: String,
         onToken: (String) -> Unit
-    ): String = withContext(Dispatchers.Default) {
-        val conversation = engine.createConversation()
-        val sb = StringBuilder()
-        try {
-            conversation.sendMessageAsync(prompt)
-                .catch { e ->
-                    throw OnDeviceModel.InferenceException("Streaming failed: ${e.message}", e)
-                }
-                .collect { message ->
-                    val token = message.toString()
-                    sb.append(token)
-                    onToken(token)
-                }
-        } finally {
-            conversation.close()
+    ): String = mutex.withLock {
+        withContext(Dispatchers.Default) {
+            val conversation = engine.createConversation()
+            val sb = StringBuilder()
+            try {
+                conversation.sendMessageAsync(prompt)
+                    .catch { e ->
+                        throw OnDeviceModel.InferenceException("Streaming failed: ${e.message}", e)
+                    }
+                    .collect { message ->
+                        val token = message.toString()
+                        sb.append(token)
+                        onToken(token)
+                    }
+            } finally {
+                conversation.close()
+            }
+            sb.toString()
         }
-        sb.toString()
     }
 
     override fun close() {

app/src/main/java/com/pixel10/ai/server/AIApiServer.kt

@@ -27,9 +27,16 @@ import java.util.concurrent.atomic.AtomicLong
  *     -H "Content-Type: application/json" \
  *     -d '{"messages":[{"role":"user","content":"Hello!"}]}'
  */
+data class ServerConfig(
+    val defaultTemperature: Float = 0.7f,
+    val defaultMaxTokens: Int = 1024,
+    val autoSystemPrompt: Boolean = true
+)
+
 class AIApiServer(
     port: Int,
-    private val model: OnDeviceModel
+    private val model: OnDeviceModel,
+    private val config: ServerConfig = ServerConfig()
 ) : NanoHTTPD(port) {
 
     private val gson = Gson()
@@ -37,6 +44,7 @@ class AIApiServer(
     val requestCount = AtomicLong(0)
 
     var onRequestLogged: ((String) -> Unit)? = null
+    var onActiveRequest: ((Boolean) -> Unit)? = null
 
     override fun serve(session: IHTTPSession): Response {
         val method = session.method
@@ -113,31 +121,48 @@ class AIApiServer(
             return errorResponse(400, "messages array is required and must not be empty")
         }
 
-        // Auto-inject agent system prompt if the conversation has no system message.
-        // Auto-inject default tools if the request provides none.
-        // This makes the server zero-config as a coding agent for any OpenAI-compatible client.
-        val messages = if (raw.messages.none { it.role == "system" }) {
+        // Auto-inject agent system prompt if enabled and no system message present
+        val messages = if (config.autoSystemPrompt && raw.messages.none { it.role == "system" }) {
             listOf(Message(role = "system", content = AgentConfig.SYSTEM_PROMPT)) + raw.messages
         } else {
             raw.messages
         }
         val request = raw.copy(
             messages = messages,
-            tools = raw.tools.takeUnless { it.isNullOrEmpty() } ?: AgentConfig.DEFAULT_TOOLS
+            tools = raw.tools.takeUnless { it.isNullOrEmpty() }
+                ?: if (config.autoSystemPrompt) AgentConfig.DEFAULT_TOOLS else null,
+            temperature = if (raw.temperature == 0.7f) config.defaultTemperature else raw.temperature,
+            max_tokens = if (raw.max_tokens == 8192) config.defaultMaxTokens else raw.max_tokens
         )
 
         val id = "chatcmpl-${UUID.randomUUID().toString().take(8)}"
         val hasTools = !request.tools.isNullOrEmpty()
 
-        log("Chat: ${request.messages.size} messages, tools=${request.tools?.size ?: 0}, stream=${request.stream}")
+        log("Chat: ${request.messages.size} messages, tools=${request.tools?.size ?: 0}, stream=${request.stream}, temp=${request.temperature}")
+
+        // ── Streaming — always uses flat prompt + generateStreaming ────────────
+        if (request.stream) {
+            val prompt = buildFlatPrompt(request.messages)
+            onActiveRequest?.invoke(true)
+            return try {
+                handleStreamingResponse(id, prompt, request)
+            } finally {
+                onActiveRequest?.invoke(false)
+            }
+        }
 
         // ── Tool calling / multi-turn chat ─────────────────────────────────────
         if (hasTools || request.messages.size > 1 || request.messages.any { it.role == "system" }) {
             val convMessages = request.messages.map { it.toConvMessage() }
             val toolDefs = request.tools?.map { it.toToolDef() } ?: emptyList()
 
-            val result = runBlocking {
-                model.chat(convMessages, toolDefs, request.max_tokens, request.temperature)
+            onActiveRequest?.invoke(true)
+            val result = try {
+                runBlocking {
+                    model.chat(convMessages, toolDefs, request.max_tokens, request.temperature)
+                }
+            } finally {
+                onActiveRequest?.invoke(false)
             }
 
             if (result.toolCalls != null) {

app/src/main/java/com/pixel10/ai/server/ApiServerService.kt

@@ -34,6 +34,7 @@ class ApiServerService : Service() {
 
     var onStatusChanged: ((ServerState) -> Unit)? = null
     var onLog: ((String) -> Unit)? = null
+    var onActiveRequest: ((Boolean) -> Unit)? = null
 
     val isRunning: Boolean get() = server != null
     val requestCount: Long get() = server?.requestCount?.get() ?: 0
@@ -70,8 +71,15 @@ class ApiServerService : Service() {
 
                 // Start the HTTP server
                 notifyLog("Starting API server on port $port...")
-                val apiServer = AIApiServer(port, model!!)
+                val prefs = getSharedPreferences("pixel10_prefs", MODE_PRIVATE)
+                val serverConfig = ServerConfig(
+                    defaultTemperature = prefs.getFloat("temperature", 0.7f),
+                    defaultMaxTokens = prefs.getInt("max_tokens", 1024),
+                    autoSystemPrompt = prefs.getBoolean("auto_system_prompt", true)
+                )
+                val apiServer = AIApiServer(port, model!!, serverConfig)
                 apiServer.onRequestLogged = { msg -> notifyLog(msg) }
+                apiServer.onActiveRequest = { active -> onActiveRequest?.invoke(active) }
                 apiServer.start()
                 server = apiServer
 

app/src/main/java/com/pixel10/ai/ui/MainActivity.kt

@@ -13,6 +13,7 @@ import android.os.Build
 import android.os.Bundle
 import android.os.IBinder
 import android.view.View
+import android.widget.SeekBar
 import androidx.activity.result.contract.ActivityResultContracts
 import androidx.appcompat.app.AppCompatActivity
 import androidx.core.content.ContextCompat
@@ -53,6 +54,16 @@ class MainActivity : AppCompatActivity() {
             service?.onLog = { message ->
                 runOnUiThread { appendLog(message) }
             }
+            service?.onActiveRequest = { active ->
+                runOnUiThread {
+                    if (active) {
+                        binding.tvActiveRequest.text = "⚡ Processing request…"
+                        binding.tvActiveRequest.visibility = View.VISIBLE
+                    } else {
+                        binding.tvActiveRequest.visibility = View.GONE
+                    }
+                }
+            }
 
             if (service?.isRunning == true) {
                 updateStatus(ApiServerService.ServerState.RUNNING)
@@ -73,8 +84,21 @@ class MainActivity : AppCompatActivity() {
         prefs = getSharedPreferences("pixel10_prefs", MODE_PRIVATE)
         requestNotificationPermission()
 
-        // Restore saved HF token
+        // Restore saved settings
         binding.etHfToken.setText(prefs.getString("hf_token", ""))
+        val savedTemp = (prefs.getFloat("temperature", 0.7f) * 100).toInt()
+        binding.seekTemperature.progress = savedTemp
+        binding.tvTemperatureValue.text = "%.1f".format(savedTemp / 100f)
+        binding.etMaxTokens.setText(prefs.getInt("max_tokens", 1024).toString())
+        binding.switchSystemPrompt.isChecked = prefs.getBoolean("auto_system_prompt", true)
+
+        binding.seekTemperature.setOnSeekBarChangeListener(object : SeekBar.OnSeekBarChangeListener {
+            override fun onProgressChanged(seekBar: SeekBar, progress: Int, fromUser: Boolean) {
+                binding.tvTemperatureValue.text = "%.1f".format(progress / 100f)
+            }
+            override fun onStartTrackingTouch(seekBar: SeekBar) {}
+            override fun onStopTrackingTouch(seekBar: SeekBar) {}
+        })
 
         binding.btnToggle.setOnClickListener {
             if (service?.isRunning == true) stopServer() else startServer()
@@ -201,7 +225,16 @@ class MainActivity : AppCompatActivity() {
         }
     }
 
+    private fun saveSettings() {
+        prefs.edit()
+            .putFloat("temperature", binding.seekTemperature.progress / 100f)
+            .putInt("max_tokens", binding.etMaxTokens.text.toString().toIntOrNull() ?: 1024)
+            .putBoolean("auto_system_prompt", binding.switchSystemPrompt.isChecked)
+            .apply()
+    }
+
     private fun startServer() {
+        saveSettings()
         val port = binding.etPort.text.toString().toIntOrNull() ?: 8080
         val intent = Intent(this, ApiServerService::class.java).apply {
             action = ApiServerService.ACTION_START
@@ -227,6 +260,9 @@ class MainActivity : AppCompatActivity() {
         val canEdit = state == ApiServerService.ServerState.STOPPED ||
                       state == ApiServerService.ServerState.ERROR
         binding.etPort.isEnabled = canEdit
+        binding.seekTemperature.isEnabled = canEdit
+        binding.etMaxTokens.isEnabled = canEdit
+        binding.switchSystemPrompt.isEnabled = canEdit
 
         when (state) {
             ApiServerService.ServerState.STOPPED -> {

app/src/main/res/layout/activity_main.xml

@@ -102,6 +102,16 @@
                 android:textColor="@color/log_text"
                 android:textSize="13sp"
                 android:layout_marginTop="2dp" />
+
+            <TextView
+                android:id="@+id/tvActiveRequest"
+                android:layout_width="wrap_content"
+                android:layout_height="wrap_content"
+                android:textColor="@color/primary"
+                android:textSize="13sp"
+                android:textStyle="bold"
+                android:layout_marginTop="2dp"
+                android:visibility="gone" />
         </LinearLayout>
     </com.google.android.material.card.MaterialCardView>
 
@@ -176,38 +186,143 @@
         </LinearLayout>
     </com.google.android.material.card.MaterialCardView>
 
-    <!-- Port Config -->
-    <LinearLayout
+    <!-- Settings Card -->
+    <com.google.android.material.card.MaterialCardView
         android:id="@+id/layoutPort"
         android:layout_width="0dp"
         android:layout_height="wrap_content"
-        android:orientation="horizontal"
-        android:gravity="center_vertical"
-        android:layout_marginTop="16dp"
+        android:layout_marginTop="12dp"
+        app:cardBackgroundColor="@color/surface_variant"
+        app:cardCornerRadius="16dp"
+        app:cardElevation="0dp"
+        app:strokeWidth="0dp"
         app:layout_constraintTop_toBottomOf="@id/cardModel"
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintEnd_toEndOf="parent">
 
-        <TextView
-            android:layout_width="wrap_content"
+        <LinearLayout
+            android:layout_width="match_parent"
             android:layout_height="wrap_content"
-            android:text="@string/port_label"
-            android:textColor="@color/on_surface"
-            android:textSize="16sp" />
+            android:orientation="vertical"
+            android:padding="16dp">
 
-        <com.google.android.material.textfield.TextInputEditText
-            android:id="@+id/etPort"
-            android:layout_width="100dp"
-            android:layout_height="48dp"
-            android:layout_marginStart="12dp"
-            android:text="@string/port_default"
-            android:inputType="number"
-            android:textColor="@color/on_surface"
-            android:backgroundTint="@color/primary"
-            android:fontFamily="monospace"
-            android:textSize="16sp"
-            android:gravity="center" />
-    </LinearLayout>
+            <!-- Port row -->
+            <LinearLayout
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:orientation="horizontal"
+                android:gravity="center_vertical">
+
+                <TextView
+                    android:layout_width="0dp"
+                    android:layout_height="wrap_content"
+                    android:layout_weight="1"
+                    android:text="@string/port_label"
+                    android:textColor="@color/on_surface"
+                    android:textSize="14sp" />
+
+                <com.google.android.material.textfield.TextInputEditText
+                    android:id="@+id/etPort"
+                    android:layout_width="80dp"
+                    android:layout_height="40dp"
+                    android:text="@string/port_default"
+                    android:inputType="number"
+                    android:textColor="@color/on_surface"
+                    android:backgroundTint="@color/primary"
+                    android:fontFamily="monospace"
+                    android:textSize="14sp"
+                    android:gravity="center" />
+            </LinearLayout>
+
+            <!-- Temperature row -->
+            <LinearLayout
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:orientation="horizontal"
+                android:gravity="center_vertical"
+                android:layout_marginTop="12dp">
+
+                <TextView
+                    android:layout_width="0dp"
+                    android:layout_height="wrap_content"
+                    android:layout_weight="1"
+                    android:text="@string/setting_temperature"
+                    android:textColor="@color/on_surface"
+                    android:textSize="14sp" />
+
+                <TextView
+                    android:id="@+id/tvTemperatureValue"
+                    android:layout_width="36dp"
+                    android:layout_height="wrap_content"
+                    android:text="0.7"
+                    android:textColor="@color/log_text"
+                    android:textSize="13sp"
+                    android:fontFamily="monospace"
+                    android:gravity="end" />
+
+                <SeekBar
+                    android:id="@+id/seekTemperature"
+                    android:layout_width="120dp"
+                    android:layout_height="wrap_content"
+                    android:layout_marginStart="8dp"
+                    android:max="100"
+                    android:progress="70" />
+            </LinearLayout>
+
+            <!-- Max tokens row -->
+            <LinearLayout
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:orientation="horizontal"
+                android:gravity="center_vertical"
+                android:layout_marginTop="8dp">
+
+                <TextView
+                    android:layout_width="0dp"
+                    android:layout_height="wrap_content"
+                    android:layout_weight="1"
+                    android:text="@string/setting_max_tokens"
+                    android:textColor="@color/on_surface"
+                    android:textSize="14sp" />
+
+                <com.google.android.material.textfield.TextInputEditText
+                    android:id="@+id/etMaxTokens"
+                    android:layout_width="80dp"
+                    android:layout_height="40dp"
+                    android:text="1024"
+                    android:inputType="number"
+                    android:textColor="@color/on_surface"
+                    android:backgroundTint="@color/primary"
+                    android:fontFamily="monospace"
+                    android:textSize="14sp"
+                    android:gravity="center" />
+            </LinearLayout>
+
+            <!-- System prompt toggle -->
+            <LinearLayout
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:orientation="horizontal"
+                android:gravity="center_vertical"
+                android:layout_marginTop="8dp">
+
+                <TextView
+                    android:layout_width="0dp"
+                    android:layout_height="wrap_content"
+                    android:layout_weight="1"
+                    android:text="@string/setting_auto_system_prompt"
+                    android:textColor="@color/on_surface"
+                    android:textSize="14sp" />
+
+                <com.google.android.material.switchmaterial.SwitchMaterial
+                    android:id="@+id/switchSystemPrompt"
+                    android:layout_width="wrap_content"
+                    android:layout_height="wrap_content"
+                    android:checked="true" />
+            </LinearLayout>
+
+        </LinearLayout>
+    </com.google.android.material.card.MaterialCardView>
 
     <!-- Start/Stop Button -->
     <com.google.android.material.button.MaterialButton

app/src/main/res/values/strings.xml

@@ -25,7 +25,10 @@
     <string name="model_not_downloaded">No local model. Enter HuggingFace token and download.</string>
     <string name="btn_start">Start Server</string>
     <string name="btn_stop">Stop Server</string>
-    <string name="port_label">Port:</string>
+    <string name="port_label">Port</string>
+    <string name="setting_temperature">Temperature</string>
+    <string name="setting_max_tokens">Max tokens</string>
+    <string name="setting_auto_system_prompt">Agent system prompt</string>
     <string name="port_default">8080</string>
     <string name="requests_served">Requests served: %d</string>
     <string name="request_log_label">Request Log</string>