fix: restore iOS controls and background artwork

ControllerApp/src/main/java/com/example/controllerapp/ui/ControllerAppUi.kt

@@ -825,14 +825,15 @@ private fun VolumeControl(
     enabled: Boolean,
     onVolume: (Int) -> Unit
 ) {
-    var value by remember(playback.volumeCurrent, playback.volumeMax) {
-        mutableFloatStateOf(playback.volumeCurrent.toFloat())
+    val sliderState = remember { VolumeSliderState() }
+    val value = sliderState.displayedValue(playback.volumeCurrent, playback.volumeMax)
+    LaunchedEffect(enabled, playback.volumeMax) {
+        if (!enabled || playback.volumeMax <= 0) sliderState.cancel()
     }
-    var dragging by remember { mutableStateOf(false) }
-    LaunchedEffect(value, dragging) {
-        if (dragging) {
+    LaunchedEffect(sliderState.draggedValue, enabled, playback.volumeMax) {
+        if (sliderState.draggedValue != null && enabled && playback.volumeMax > 0) {
             delay(90L)
-            onVolume(value.toInt())
+            onVolume(sliderState.displayedValue(playback.volumeCurrent, playback.volumeMax).toInt())
         }
     }
     Row(
@@ -845,12 +846,14 @@ private fun VolumeControl(
             valueRange = 0f..playback.volumeMax.coerceAtLeast(1).toFloat(),
             enabled = enabled && playback.volumeMax > 0,
             onValueChange = {
-                dragging = true
-                value = it
+                sliderState.drag(it)
             },
             onValueChangeFinished = {
-                onVolume(value.toInt())
-                dragging = false
+                if (enabled && playback.volumeMax > 0) {
+                    sliderState.finish(playback.volumeCurrent, playback.volumeMax)?.let(onVolume)
+                } else {
+                    sliderState.cancel()
+                }
             },
             modifier = Modifier.weight(1f)
         )

ControllerApp/src/main/java/com/example/controllerapp/ui/VolumeSliderState.kt

@@ -0,0 +1,24 @@
+package com.example.controllerapp.ui
+
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.setValue
+
+/** Remote acknowledgements may update playback while the local edit stays authoritative. */
+internal class VolumeSliderState {
+    var draggedValue by mutableStateOf<Float?>(null)
+        private set
+
+    fun displayedValue(current: Int, maximum: Int): Float =
+        (draggedValue ?: current.toFloat()).coerceIn(0f, maximum.coerceAtLeast(0).toFloat())
+
+    fun drag(value: Float) { draggedValue = value }
+
+    fun finish(current: Int, maximum: Int): Int? {
+        val finalValue = draggedValue?.let { displayedValue(current, maximum).toInt() }
+        cancel()
+        return finalValue
+    }
+
+    fun cancel() { draggedValue = null }
+}

ControllerApp/src/test/java/com/example/controllerapp/ui/VolumeSliderStateTest.kt

@@ -0,0 +1,33 @@
+package com.example.controllerapp.ui
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Test
+
+class VolumeSliderStateTest {
+    @Test
+    fun delayedRemoteAckDoesNotOverwriteDragOrFinalCommand() {
+        val state = VolumeSliderState()
+        assertEquals(5f, state.displayedValue(5, 15), 0.001f)
+        state.drag(8f)
+        state.drag(12f)
+        assertEquals(12f, state.displayedValue(8, 15), 0.001f)
+        assertEquals(12, state.finish(8, 15))
+        assertNull(state.draggedValue)
+        assertEquals(12f, state.displayedValue(12, 15), 0.001f)
+        assertNull(state.finish(12, 15))
+    }
+
+    @Test
+    fun changedMaximumClampsFinalValueAndDisconnectCancelsEdit() {
+        val state = VolumeSliderState()
+        state.drag(14f)
+        assertEquals(7f, state.displayedValue(3, 7), 0.001f)
+        assertEquals(7, state.finish(3, 7))
+        state.drag(9f)
+        state.cancel()
+        assertEquals(3f, state.displayedValue(3, 15), 0.001f)
+        assertNull(state.finish(3, 15))
+        assertEquals(0f, state.displayedValue(3, 0), 0.001f)
+    }
+}