fix: prompt to confirm discarding unsaved changes in config screens

Fixes #5283 by introducing an UnsavedChangesDialog component and integrating it into RadioConfigScreenList and ChannelConfigScreen. Utilizes PlatformBackHandler to guard against accidental system back gestures.

core/resources/src/commonMain/composeResources/values/strings.xml

@@ -182,6 +182,8 @@
     <string name="accept">Accept</string>
     <string name="cancel">Cancel</string>
     <string name="discard_changes">Discard</string>
+    <string name="unsaved_changes_message">You have unsaved changes. Are you sure you want to discard them?</string>
+    <string name="stay">Stay</string>
     <string name="save_changes">Save</string>
     <string name="new_channel_rcvd">New Channel URL received</string>
     <string name="report">Report</string>

core/ui/src/commonMain/kotlin/org/meshtastic/core/ui/component/UnsavedChangesDialog.kt

@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2025-2026 Meshtastic LLC
+ *
+ * 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 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package org.meshtastic.core.ui.component
+
+import androidx.compose.runtime.Composable
+import org.meshtastic.core.resources.Res
+import org.meshtastic.core.resources.cancel
+import org.meshtastic.core.resources.discard_changes
+import org.meshtastic.core.resources.stay
+import org.meshtastic.core.resources.unsaved_changes_message
+
+@Composable
+fun UnsavedChangesDialog(onDiscard: () -> Unit, onStay: () -> Unit) {
+    MeshtasticDialog(
+        titleRes = Res.string.cancel,
+        messageRes = Res.string.unsaved_changes_message,
+        confirmTextRes = Res.string.discard_changes,
+        onConfirm = onDiscard,
+        dismissTextRes = Res.string.stay,
+        onDismiss = onStay,
+    )
+}

feature/settings/src/commonMain/kotlin/org/meshtastic/feature/settings/radio/channel/ChannelConfigScreen.kt

@@ -137,6 +137,27 @@ private fun ChannelConfigScreen(
 
     var showEditChannelDialog: Int? by rememberSaveable { mutableStateOf(null) }
     var showChannelLegendDialog by rememberSaveable { mutableStateOf(false) }
+    var showExitConfirmation by rememberSaveable { mutableStateOf(false) }
+
+    val handleBack = {
+        if (isEditing) {
+            showExitConfirmation = true
+        } else {
+            onBack()
+        }
+    }
+
+    org.meshtastic.core.ui.util.PlatformBackHandler(enabled = isEditing) { showExitConfirmation = true }
+
+    if (showExitConfirmation) {
+        org.meshtastic.core.ui.component.UnsavedChangesDialog(
+            onDiscard = {
+                showExitConfirmation = false
+                onBack()
+            },
+            onStay = { showExitConfirmation = false },
+        )
+    }
 
     if (showEditChannelDialog != null) {
         val index = showEditChannelDialog ?: return
@@ -164,7 +185,7 @@ private fun ChannelConfigScreen(
             MainAppBar(
                 title = title,
                 canNavigateUp = true,
-                onNavigateUp = onBack,
+                onNavigateUp = handleBack,
                 ourNode = null,
                 showNodeChip = false,
                 actions = {},

feature/settings/src/commonMain/kotlin/org/meshtastic/feature/settings/radio/component/RadioConfigScreenList.kt

@@ -31,6 +31,10 @@ import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.LazyListScope
 import androidx.compose.material3.Scaffold
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.saveable.rememberSaveable
+import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.platform.LocalFocusManager
 import androidx.compose.ui.unit.dp
@@ -41,6 +45,8 @@ import org.meshtastic.core.resources.discard_changes
 import org.meshtastic.core.resources.save_changes
 import org.meshtastic.core.ui.component.MainAppBar
 import org.meshtastic.core.ui.component.PreferenceFooter
+import org.meshtastic.core.ui.component.UnsavedChangesDialog
+import org.meshtastic.core.ui.util.PlatformBackHandler
 import org.meshtastic.feature.settings.radio.ResponseState
 
 @Suppress("LongMethod")
@@ -60,14 +66,38 @@ fun <T : Message<T, *>> RadioConfigScreenList(
     content: LazyListScope.() -> Unit,
 ) {
     val focusManager = LocalFocusManager.current
+    val isEditing = configState.isDirty || additionalDirtyCheck()
+    var showExitConfirmation by rememberSaveable { mutableStateOf(false) }
+
+    val handleBack = {
+        if (isEditing) {
+            showExitConfirmation = true
+        } else {
+            onBack()
+        }
+    }
+
+    PlatformBackHandler(enabled = isEditing) { showExitConfirmation = true }
 
     Box(modifier = modifier) {
+        if (showExitConfirmation) {
+            UnsavedChangesDialog(
+                onDiscard = {
+                    showExitConfirmation = false
+                    configState.reset()
+                    onDiscard()
+                    onBack()
+                },
+                onStay = { showExitConfirmation = false },
+            )
+        }
+
         Scaffold(
             topBar = {
                 MainAppBar(
                     title = title,
                     canNavigateUp = true,
-                    onNavigateUp = onBack,
+                    onNavigateUp = handleBack,
                     ourNode = null,
                     showNodeChip = false,
                     actions = actions,
@@ -75,7 +105,7 @@ fun <T : Message<T, *>> RadioConfigScreenList(
                 )
             },
         ) { innerPadding ->
-            val showFooterButtons = configState.isDirty || additionalDirtyCheck()
+            val showFooterButtons = isEditing
 
             LazyColumn(
                 modifier = Modifier.padding(innerPadding).fillMaxSize(),