android: predictive back scale for settings pages and remediation detail

src/frontends/android/app/src/main/java/org/strongswan/android/ui/RemediationInstructionsActivity.kt

@@ -61,6 +61,7 @@ import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
 import org.strongswan.android.R
+import org.strongswan.android.ui.compose.components.PredictiveBackScale
 import org.strongswan.android.logic.imc.RemediationInstruction
 import org.strongswan.android.ui.compose.components.ShxCard
 import org.strongswan.android.ui.compose.components.ShxEmptyState
@@ -127,7 +128,8 @@ private fun RemediationUi(
 	onFinish: () -> Unit,
 )
 {
-	BackHandler(enabled = selected != null) { onSelect(null) }
+	PredictiveBackScale(enabled = selected != null, onBack = { onSelect(null) }, modifier = Modifier.fillMaxSize())
+	{
 	Column(Modifier.fillMaxSize())
 	{
 		TopAppBar(
@@ -246,4 +248,5 @@ private fun RemediationUi(
 			}
 		}
 	}
+	}
 }

src/frontends/android/app/src/main/java/org/strongswan/android/ui/compose/SettingsScreen.kt

@@ -96,6 +96,7 @@ import androidx.compose.material3.Icon
 import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.widthIn
+import org.strongswan.android.ui.compose.components.PredictiveBackScale
 import org.strongswan.android.R
 import org.strongswan.android.data.VpnProfile
 import org.strongswan.android.logic.StrongSwanApplication
@@ -178,14 +179,18 @@ fun SettingsScreen(profiles: List<VpnProfile>, showTitle: Boolean = true)
 
 	var pageState by rememberSaveable { mutableStateOf(SettingsPage.ROOT) }
 	/* from a sub page "back" returns to the settings list, not out of the tab */
-	BackHandler(enabled = pageState != SettingsPage.ROOT) { pageState = SettingsPage.ROOT }
 	val effects = MaterialTheme.motionScheme.defaultEffectsSpec<Float>()
 	val spatial = MaterialTheme.motionScheme.defaultSpatialSpec<androidx.compose.ui.unit.IntOffset>()
 
 	Box(Modifier.fillMaxSize(), contentAlignment = Alignment.TopCenter)
 	{
+	PredictiveBackScale(
+		enabled = pageState != SettingsPage.ROOT,
+		onBack = { pageState = SettingsPage.ROOT },
+		modifier = Modifier.widthIn(max = 640.dp).fillMaxSize(),
+	)
+	{
 	AnimatedContent(
-		modifier = Modifier.widthIn(max = 640.dp),
 		targetState = pageState,
 		transitionSpec = {
 			val forward = targetState != SettingsPage.ROOT
@@ -533,6 +538,7 @@ fun SettingsScreen(profiles: List<VpnProfile>, showTitle: Boolean = true)
 		)
 	}
 	}
+	}
 	ShxSnackbarHost(
 		hostState = snackbarHostState,
 		modifier = Modifier.align(Alignment.BottomCenter),

src/frontends/android/app/src/main/java/org/strongswan/android/ui/compose/components/PredictiveBack.kt

@@ -0,0 +1,65 @@
+/*
+ * Copyright (C) 2026 SHX VPN
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ */
+
+package org.strongswan.android.ui.compose.components
+
+import androidx.activity.compose.PredictiveBackHandler
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableFloatStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.graphics.graphicsLayer
+import androidx.compose.ui.unit.dp
+import kotlin.coroutines.cancellation.CancellationException
+
+/**
+ * Handles the system back gesture for in-screen navigation (a sub page that returns
+ * to its parent): while the user drags, the content shrinks slightly and rounds its
+ * corners, then [onBack] runs when the gesture is committed.
+ */
+@Composable
+fun PredictiveBackScale(
+	enabled: Boolean,
+	onBack: () -> Unit,
+	modifier: Modifier = Modifier,
+	content: @Composable () -> Unit,
+)
+{
+	var progress by remember { mutableFloatStateOf(0f) }
+	PredictiveBackHandler(enabled = enabled) { events ->
+		try
+		{
+			events.collect { progress = it.progress }
+			onBack()
+			progress = 0f
+		}
+		catch (e: CancellationException)
+		{
+			progress = 0f
+			throw e
+		}
+	}
+	Box(
+		modifier
+			.graphicsLayer {
+				val scale = 1f - 0.08f * progress
+				scaleX = scale
+				scaleY = scale
+			}
+			.clip(RoundedCornerShape((progress * 28f).dp)),
+	)
+	{
+		content()
+	}
+}