Set up Android project with Kotlin and Jetpack Compose

Initial project structure with manifest configured for foreground
audio service, AudioTrack-based playback, and background operation.
Includes Gradle wrapper, dependency catalog, placeholder icons,
and build instructions for Arch Linux.

app/build.gradle.kts

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+plugins {
+    alias(libs.plugins.android.application)
+    alias(libs.plugins.kotlin.android)
+    alias(libs.plugins.kotlin.compose)
+}
+
+android {
+    namespace = "net.jeena.pacer"
+    compileSdk = 36
+    buildToolsVersion = "36.1.0"
+
+    defaultConfig {
+        applicationId = "net.jeena.pacer"
+        minSdk = 24
+        targetSdk = 36
+        versionCode = 1
+        versionName = "1.0"
+
+        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
+    }
+
+    buildTypes {
+        release {
+            isMinifyEnabled = false
+            proguardFiles(
+                getDefaultProguardFile("proguard-android-optimize.txt"),
+                "proguard-rules.pro"
+            )
+        }
+    }
+
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_17
+        targetCompatibility = JavaVersion.VERSION_17
+    }
+
+    kotlinOptions {
+        jvmTarget = "17"
+    }
+
+    buildFeatures {
+        compose = true
+    }
+}
+
+dependencies {
+    implementation(libs.androidx.core.ktx)
+    implementation(libs.androidx.lifecycle.runtime.ktx)
+    implementation(libs.androidx.activity.compose)
+    implementation(platform(libs.androidx.compose.bom))
+    implementation(libs.androidx.ui)
+    implementation(libs.androidx.ui.graphics)
+    implementation(libs.androidx.ui.tooling.preview)
+    implementation(libs.androidx.material3)
+
+    testImplementation(libs.junit)
+    androidTestImplementation(libs.androidx.junit)
+    androidTestImplementation(libs.androidx.espresso.core)
+    androidTestImplementation(platform(libs.androidx.compose.bom))
+    androidTestImplementation(libs.androidx.ui.test.junit4)
+    debugImplementation(libs.androidx.ui.tooling)
+    debugImplementation(libs.androidx.ui.test.manifest)
+}

app/proguard-rules.pro

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+# Add project specific ProGuard rules here.
+# Keep AudioTrack-related classes unobfuscated for audio engine work
+-keep class android.media.AudioTrack { *; }
+-keep class android.media.AudioAttributes { *; }
+-keep class android.media.AudioFormat { *; }

app/src/main/AndroidManifest.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <!-- Required for foreground service (background audio) -->
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
+
+    <!-- Required on Android 14+ for media playback foreground service type -->
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE_MEDIA_PLAYBACK" />
+
+    <!-- Allows requesting battery optimization exemption for long walks (2+ hours) -->
+    <uses-permission android:name="android.permission.REQUEST_IGNORE_BATTERY_OPTIMIZATIONS" />
+
+    <!-- Keeps CPU awake during background audio playback -->
+    <uses-permission android:name="android.permission.WAKE_LOCK" />
+
+    <!-- Required on Android 13+ to show the foreground service notification -->
+    <uses-permission android:name="android.permission.POST_NOTIFICATIONS" />
+
+    <application
+        android:allowBackup="true"
+        android:icon="@mipmap/ic_launcher"
+        android:label="@string/app_name"
+        android:roundIcon="@mipmap/ic_launcher_round"
+        android:supportsRtl="true"
+        android:theme="@style/Theme.Pacer">
+
+        <activity
+            android:name=".MainActivity"
+            android:exported="true"
+            android:configChanges="orientation|keyboardHidden|screenSize"
+            android:windowSoftInputMode="adjustResize">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity>
+
+        <!--
+            PacerService will be implemented in Theme 4 (US-08).
+            foregroundServiceType="mediaPlayback" is required on Android 14+.
+        -->
+        <service
+            android:name=".PacerService"
+            android:exported="false"
+            android:foregroundServiceType="mediaPlayback" />
+
+    </application>
+
+</manifest>

app/src/main/kotlin/net/jeena/pacer/MainActivity.kt

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+package net.jeena.pacer
+
+import android.os.Bundle
+import androidx.activity.ComponentActivity
+import androidx.activity.compose.setContent
+import androidx.activity.enableEdgeToEdge
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material3.Scaffold
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.tooling.preview.Preview
+import net.jeena.pacer.ui.theme.PacerTheme
+
+class MainActivity : ComponentActivity() {
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        enableEdgeToEdge()
+        setContent {
+            PacerTheme {
+                Scaffold(modifier = Modifier.fillMaxSize()) { innerPadding ->
+                    Text(
+                        text = "Pacer",
+                        modifier = Modifier.padding(innerPadding)
+                    )
+                }
+            }
+        }
+    }
+}
+
+@Preview(showBackground = true)
+@Composable
+fun DefaultPreview() {
+    PacerTheme {
+        Text("Pacer")
+    }
+}

app/src/main/kotlin/net/jeena/pacer/PacerService.kt

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+package net.jeena.pacer
+
+import android.app.Service
+import android.content.Intent
+import android.os.IBinder
+
+// Stub — full implementation in Theme 4 (US-08)
+class PacerService : Service() {
+    override fun onBind(intent: Intent?): IBinder? = null
+}

app/src/main/kotlin/net/jeena/pacer/ui/theme/Color.kt

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+package net.jeena.pacer.ui.theme
+
+import androidx.compose.ui.graphics.Color
+
+val Green80 = Color(0xFF00FF41)   // retro terminal green (matches web version)
+val Green40 = Color(0xFF00A826)
+val DarkBackground = Color(0xFF0D0D0D)

app/src/main/kotlin/net/jeena/pacer/ui/theme/Theme.kt

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+package net.jeena.pacer.ui.theme
+
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.darkColorScheme
+import androidx.compose.runtime.Composable
+
+private val DarkColorScheme = darkColorScheme(
+    primary = Green80,
+    secondary = Green40,
+    tertiary = DarkBackground
+)
+
+@Composable
+fun PacerTheme(content: @Composable () -> Unit) {
+    MaterialTheme(
+        colorScheme = DarkColorScheme,
+        typography = Typography,
+        content = content
+    )
+}

app/src/main/kotlin/net/jeena/pacer/ui/theme/Type.kt

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+package net.jeena.pacer.ui.theme
+
+import androidx.compose.material3.Typography
+import androidx.compose.ui.text.TextStyle
+import androidx.compose.ui.unit.sp
+
+val Typography = Typography(
+    bodyLarge = TextStyle(fontSize = 16.sp)
+)

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

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+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <color name="green_primary">#FF00FF41</color>
+    <color name="dark_background">#FF0D0D0D</color>
+    <color name="black">#FF000000</color>
+    <color name="white">#FFFFFFFF</color>
+</resources>

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

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+<resources>
+    <string name="app_name">Pacer</string>
+    <string name="start">Start</string>
+    <string name="stop">Stop</string>
+    <string name="notification_channel_name">Pacer Audio</string>
+    <string name="notification_content_text">Pacing at %1$d BPM</string>
+</resources>

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

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+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <style name="Theme.Pacer" parent="android:Theme.DeviceDefault.NoActionBar">
+        <item name="android:statusBarColor">@color/dark_background</item>
+        <item name="android:windowBackground">@color/dark_background</item>
+    </style>
+</resources>