perf(app): lighter stress demo + profileable release build

- StressTestScreen: use MinMaxLTTB LOD (caps output <= pixelWidth,
  ~half the vertices vs MinMax's ~2x) and move the sample generator
  loop to Dispatchers.Default so it stops contending with the UI thread.
- SignalGenerator: run the shared producer loop off the main thread.
- Add a release buildType (R8 + resource shrink, debuggable=false,
  debug-signed for on-device profiling); proguard-rules.pro needs no
  keeps (no kotlinx.serialization; Compose/coroutines ship consumer rules).
- minSdk 26 -> 24.

Off-main producer un-starves the feed (280 -> ~1300 push/s); release
build (AOT+R8) vs debug at matched load: CPU -12%, fps +48%.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/build.gradle.kts

@@ -10,7 +10,7 @@ android {
 
     defaultConfig {
         applicationId = "dev.dtrentin.chart.demo"
-        minSdk = 26
+        minSdk = 24
         targetSdk = 35
         versionCode = 1
         versionName = "0.1.0"
@@ -23,6 +23,20 @@ android {
 
     buildFeatures { compose = true }
 
+    buildTypes {
+        release {
+            isMinifyEnabled = true          // R8 — the perf lever
+            isShrinkResources = true        // strip unused resources
+            isDebuggable = false            // let ART fully optimize (perf test)
+            // debug key so the release apk installs on a dev device (profiling build, not store build)
+            signingConfig = signingConfigs.getByName("debug")
+            proguardFiles(
+                getDefaultProguardFile("proguard-android-optimize.txt"),
+                "proguard-rules.pro"
+            )
+        }
+    }
+
     sourceSets["main"].kotlin.srcDirs("src/main/kotlin")
 }
 

app/proguard-rules.pro

@@ -0,0 +1,12 @@
+# Release R8 rules for :app (profiling build).
+#
+# Intentionally minimal. Consumer rules ship with the libraries:
+#   - Jetpack Compose (androidx.compose.*) — bundled consumer R8 rules
+#   - kotlinx-coroutines — bundled consumer R8 rules (keeps ServiceLoader/volatile)
+#   - AGP auto-keeps the manifest entry point (.MainActivity)
+#
+# No kotlinx.serialization in this app (chart-realtime does not apply the
+# serialization plugin), so no @Serializer keep rules are required.
+#
+# App-specific keeps are added below ONLY when a build/run failure proves them
+# necessary. Do NOT blanket-keep.

app/src/main/kotlin/dev/dtrentin/chart/demo/SignalGenerator.kt

@@ -1,9 +1,11 @@
 package dev.dtrentin.chart.demo
 
 import dev.dtrentin.chart.RealtimeChartState
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.isActive
-import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.withContext
 
 /**
  * Synthetic multi-signal producer. Single coroutine pushes one sample per active signal
@@ -34,9 +36,13 @@ suspend fun CoroutineScope.runSignalGenerator(
 
     val tickIntervalMs = (1_000L / sampleRateHz).coerceAtLeast(1L)
     val dt = 1f / sampleRateHz.toFloat()
+
+    // Push work off Main: sample generation + state.push run on Dispatchers.Default so they
+    // don't contend with Compose draw on the Main dispatcher. withContext inherits the caller's
+    // Job → cancelling the caller (e.g. leaving the composable) cancels this loop (no leak).
+    withContext(Dispatchers.Default) {
         val startMs = System.currentTimeMillis()
         var t = 0f
-
         while (isActive) {
             val ts = startMs + (t * 1000f).toLong()
             for (i in signalNames.indices) {
@@ -48,4 +54,5 @@ suspend fun CoroutineScope.runSignalGenerator(
             t += dt
             delay(tickIntervalMs)
         }
+    }
 }

app/src/main/kotlin/dev/dtrentin/chart/demo/StressTestScreen.kt

@@ -26,7 +26,7 @@ import dev.dtrentin.chart.RealtimeChart
 import dev.dtrentin.chart.RealtimeChartState
 import dev.dtrentin.chart.interaction.InteractionConfig
 import dev.dtrentin.chart.interaction.rememberChartInteractionState
-import dev.dtrentin.chart.lod.MinMaxLodStrategy
+import dev.dtrentin.chart.lod.MinMaxLttbLodStrategy
 import dev.dtrentin.chart.model.AxisConfig
 import dev.dtrentin.chart.model.AxisLabelMode
 import dev.dtrentin.chart.model.ChartConfig
@@ -39,8 +39,10 @@ import dev.dtrentin.chart.render.DecimalAxisFormatter
 import dev.dtrentin.chart.render.TimeAxisFormatter
 import kotlin.math.PI
 import kotlin.math.sin
+import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.isActive
+import kotlinx.coroutines.withContext
 
 private const val STRESS_SIGNAL_COUNT = 8
 private const val STRESS_SAMPLE_HZ = 200
@@ -58,8 +60,9 @@ private val STRESS_COLORS = listOf(
 
 /**
  * Stress test: 8 simultaneous signals @ 200 Hz each (1600 pushes/sec total). Uses
- * MinMax LoD (preserves peaks under heavy throughput). 10 s window — 16k samples
+ * MinMaxLTTB LoD (preserves min/max envelope, output capped at pixelWidth). 10 s window —
- * visible at once.
+ * 16k samples visible at once. Producer runs on [Dispatchers.Default] to keep sample
+ * generation off the Main dispatcher (away from Compose draw).
  */
 @Composable
 fun StressTestScreen() {
@@ -81,7 +84,7 @@ fun StressTestScreen() {
                 ),
                 render = RenderConfig(
                     theme = chartTheme,
-                    lodStrategy = MinMaxLodStrategy(),
+                    lodStrategy = MinMaxLttbLodStrategy(),
                 ),
             ),
         )
@@ -96,6 +99,10 @@ fun StressTestScreen() {
                 SignalConfig(color = STRESS_COLORS[i], strokeWidth = 1.5f),
             )
         }
+        // Push work off Main: generation + state.push run on Dispatchers.Default so they
+        // don't contend with Compose draw on the Main dispatcher. withContext inherits the
+        // effect's Job → leaving the composable cancels this loop (no leak).
+        withContext(Dispatchers.Default) {
             val tickIntervalMs = (1_000L / STRESS_SAMPLE_HZ).coerceAtLeast(1L)
             val startMs = System.currentTimeMillis()
             var n = 0L
@@ -115,6 +122,7 @@ fun StressTestScreen() {
                 delay(tickIntervalMs)
             }
         }
+    }
 
     var pushPerSec by remember { mutableIntStateOf(0) }
     var totalPushes by remember { mutableLongStateOf(0L) }