app/src/androidTest/kotlin/org/libremail/ui/settings/SettingsScreenTest.kt

@@ -3,6 +3,7 @@ package org.libremail.ui.settings
 
 import androidx.activity.ComponentActivity
 import androidx.compose.ui.test.junit4.createAndroidComposeRule
+import androidx.compose.ui.test.onAllNodesWithText
 import androidx.compose.ui.test.onNodeWithText
 import androidx.compose.ui.test.performClick
 import androidx.compose.ui.test.performScrollTo
@@ -14,7 +15,6 @@ import org.junit.Rule
 import org.junit.Test
 import org.junit.runner.RunWith
 import org.libremail.R
-import org.libremail.data.security.AppLockAvailability
 import org.libremail.data.security.AppLockManager
 import org.libremail.data.security.DatabaseKeyCipher
 import org.libremail.data.security.DatabaseKeyStore
@@ -29,8 +29,10 @@ import org.libremail.ui.theme.LibreMailTheme
 import javax.inject.Provider
 
 /**
- * End-to-end test for the top-level message-downloading setting: tapping a policy must round-trip
- * through the real [SettingsRepository] (DataStore), proving the UI → ViewModel → persistence wiring.
+ * End-to-end tests for the global settings screen. Tapping a policy must round-trip through the real
+ * [SettingsRepository] (DataStore), proving the UI → ViewModel → persistence wiring; and enabling
+ * app-lock on a device with no secure lock must surface the rejection message via a snackbar — now
+ * visible to Compose semantics, unlike the former Toast it replaced.
  */
 @RunWith(AndroidJUnit4::class)
 class SettingsScreenTest {
@@ -38,27 +40,28 @@ class SettingsScreenTest {
     @get:Rule
     val composeTestRule = createAndroidComposeRule<ComponentActivity>()
 
+    private val context = InstrumentationRegistry.getInstrumentation().targetContext.applicationContext
+
+    // Device reports no secure lock, so enabling app-lock is rejected with a message.
+    private val insecureDevice = object : AppLockManager {
+        override fun isDeviceSecure() = false
+    }
+
     private fun string(resId: Int) = composeTestRule.activity.getString(resId)
 
-    @Test
-    fun selectingFetchPolicy_persistsThroughTheRepository() {
-        val context = InstrumentationRegistry.getInstrumentation().targetContext.applicationContext
-        val settingsRepository = SettingsRepository(context)
-        runBlocking { settingsRepository.setFetchPolicy(FetchPolicy.ALWAYS) } // known starting state
-        val appLockManager = object : AppLockManager {
-            override fun isDeviceSecure() = false
-            override fun availability() = AppLockAvailability.NONE_ENROLLED
-        }
+    private fun settingsViewModel(settingsRepository: SettingsRepository): SettingsViewModel {
         val keyStore = DatabaseKeyStore(context, KeystoreCrypto(), DatabaseKeyCipher(), PassphraseSession())
-        val viewModel = SettingsViewModel(
+        return SettingsViewModel(
             FakeAccountRepository(),
             settingsRepository,
-            appLockManager,
+            insecureDevice,
             keyStore,
             BatteryOptimizationManager(context),
             SyncScheduler(Provider { WorkManager.getInstance(context) }),
         )
+    }
 
+    private fun setContent(viewModel: SettingsViewModel) {
         composeTestRule.setContent {
             LibreMailTheme(darkTheme = false, dynamicColor = false) {
                 SettingsScreen(
@@ -70,6 +73,13 @@ class SettingsScreenTest {
                 )
             }
         }
+    }
+
+    @Test
+    fun selectingFetchPolicy_persistsThroughTheRepository() {
+        val settingsRepository = SettingsRepository(context)
+        runBlocking { settingsRepository.setFetchPolicy(FetchPolicy.ALWAYS) } // known starting state
+        setContent(settingsViewModel(settingsRepository))
 
         composeTestRule.onNodeWithText(string(R.string.fetch_on_demand)).performScrollTo().performClick()
 
@@ -77,4 +87,20 @@ class SettingsScreenTest {
             runBlocking { settingsRepository.fetchPolicy() } == FetchPolicy.ON_DEMAND
         }
     }
+
+    @Test
+    fun enablingAppLockWithoutSecureDevice_showsRejectionSnackbar() {
+        val settingsRepository = SettingsRepository(context)
+        runBlocking { settingsRepository.setAppLock(false) } // known starting state: off
+        setContent(settingsViewModel(settingsRepository))
+
+        // App-lock lives under the collapsed "Advanced" section: expand it, then toggle the switch on.
+        composeTestRule.onNodeWithText(string(R.string.settings_advanced)).performScrollTo().performClick()
+        composeTestRule.onNodeWithText(string(R.string.settings_adv_app_lock)).performScrollTo().performClick()
+
+        val message = string(R.string.app_lock_needs_device_lock)
+        composeTestRule.waitUntil(5_000) {
+            composeTestRule.onAllNodesWithText(message).fetchSemanticsNodes().isNotEmpty()
+        }
+    }
 }

app/src/main/kotlin/org/libremail/data/security/AppLockManager.kt

@@ -3,40 +3,21 @@ package org.libremail.data.security
 
 import android.app.KeyguardManager
 import android.content.Context
-import androidx.biometric.BiometricManager
 import androidx.biometric.BiometricManager.Authenticators.BIOMETRIC_STRONG
 import androidx.biometric.BiometricManager.Authenticators.DEVICE_CREDENTIAL
 import dagger.hilt.android.qualifiers.ApplicationContext
 import javax.inject.Inject
 import javax.inject.Singleton
 
-/** Whether a usable device authenticator (strong biometric or device credential) is available. */
-enum class AppLockAvailability {
-    /** A biometric or device credential can be presented right now. */
-    AVAILABLE,
-
-    /** Hardware exists but nothing (biometric or PIN/pattern/password) is enrolled. */
-    NONE_ENROLLED,
-
-    /** No suitable authentication hardware, or it is temporarily unavailable. */
-    NO_HARDWARE,
-
-    /** Availability could not be determined (unknown status / security update required). */
-    UNAVAILABLE,
-}
-
 /**
- * Queries device-lock and biometric availability for the app-lock feature. Real behavior depends on
- * the device keyguard and BiometricManager, so it is validated on-device, not in JVM tests.
+ * Reports whether the device has a secure lock, for the app-lock feature. Real behavior depends on
+ * the device keyguard, so it is validated on-device, not in JVM tests.
  */
 interface AppLockManager {
 
     /** True when the device has a secure lock screen (PIN, pattern, password, or biometric). */
     fun isDeviceSecure(): Boolean
 
-    /** Whether a biometric or device-credential prompt can currently be shown. */
-    fun availability(): AppLockAvailability
-
     companion object {
         /** Accept a strong biometric OR the device credential (PIN/pattern/password) as fallback. */
         const val AUTHENTICATORS: Int = BIOMETRIC_STRONG or DEVICE_CREDENTIAL
@@ -50,14 +31,4 @@ class AndroidAppLockManager @Inject constructor(@ApplicationContext private val
         get() = context.getSystemService(Context.KEYGUARD_SERVICE) as? KeyguardManager
 
     override fun isDeviceSecure(): Boolean = keyguardManager?.isDeviceSecure == true
-
-    override fun availability(): AppLockAvailability =
-        when (BiometricManager.from(context).canAuthenticate(AppLockManager.AUTHENTICATORS)) {
-            BiometricManager.BIOMETRIC_SUCCESS -> AppLockAvailability.AVAILABLE
-            BiometricManager.BIOMETRIC_ERROR_NONE_ENROLLED -> AppLockAvailability.NONE_ENROLLED
-            BiometricManager.BIOMETRIC_ERROR_NO_HARDWARE,
-            BiometricManager.BIOMETRIC_ERROR_HW_UNAVAILABLE,
-            -> AppLockAvailability.NO_HARDWARE
-            else -> AppLockAvailability.UNAVAILABLE
-        }
 }

app/src/main/kotlin/org/libremail/ui/lock/AppLockGateHost.kt

@@ -1,13 +1,13 @@
 // SPDX-License-Identifier: GPL-3.0-or-later
 package org.libremail.ui.lock
 
+import androidx.activity.compose.LocalActivity
 import androidx.biometric.BiometricPrompt
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Surface
 import androidx.compose.runtime.Composable
-import androidx.compose.runtime.DisposableEffect
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
@@ -15,14 +15,12 @@ import androidx.compose.runtime.remember
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.input.pointer.pointerInput
-import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.res.stringResource
 import androidx.core.content.ContextCompat
 import androidx.fragment.app.FragmentActivity
 import androidx.hilt.navigation.compose.hiltViewModel
 import androidx.lifecycle.Lifecycle
-import androidx.lifecycle.LifecycleEventObserver
-import androidx.lifecycle.compose.LocalLifecycleOwner
+import androidx.lifecycle.compose.LifecycleEventEffect
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import org.libremail.R
 import org.libremail.data.security.AppLockManager
@@ -38,35 +36,29 @@ import org.libremail.data.security.AppLockManager
 @Composable
 fun AppLockGateHost(viewModel: AppLockViewModel = hiltViewModel(), content: @Composable () -> Unit) {
     val uiState by viewModel.uiState.collectAsStateWithLifecycle()
-    val lifecycleOwner = LocalLifecycleOwner.current
-    val context = LocalContext.current
-    val activity = context.findFragmentActivity()
 
-    DisposableEffect(lifecycleOwner) {
-        val observer = LifecycleEventObserver { _, event ->
-            when (event) {
-                Lifecycle.Event.ON_START -> viewModel.onForeground()
-                Lifecycle.Event.ON_STOP -> viewModel.onBackground()
-                else -> Unit
-            }
-        }
-        lifecycleOwner.lifecycle.addObserver(observer)
-        onDispose { lifecycleOwner.lifecycle.removeObserver(observer) }
-    }
+    LifecycleEventEffect(Lifecycle.Event.ON_START) { viewModel.onForeground() }
+    LifecycleEventEffect(Lifecycle.Event.ON_STOP) { viewModel.onBackground() }
+
+    // BiometricPrompt must be hosted by a FragmentActivity; LocalActivity is the hosting Activity.
+    val activity = LocalActivity.current
+    val fragmentActivity = remember(activity) { activity as? FragmentActivity }
 
     val promptTitle = stringResource(R.string.app_lock_prompt_title)
     val promptSubtitle = stringResource(R.string.app_lock_prompt_subtitle)
-    val authenticate: () -> Unit = authenticate@{
-        val host = activity ?: run {
-            viewModel.onAuthError(null)
-            return@authenticate
+    val authenticate: () -> Unit = remember(fragmentActivity, viewModel, promptTitle, promptSubtitle) {
+        authenticate@{
+            val host = fragmentActivity ?: run {
+                viewModel.onAuthError(null)
+                return@authenticate
+            }
+            host.showAppLockPrompt(
+                title = promptTitle,
+                subtitle = promptSubtitle,
+                onSuccess = viewModel::onAuthenticated,
+                onError = { message -> viewModel.onAuthError(message) },
+            )
         }
-        host.showAppLockPrompt(
-            title = promptTitle,
-            subtitle = promptSubtitle,
-            onSuccess = viewModel::onAuthenticated,
-            onError = { message -> viewModel.onAuthError(message) },
-        )
     }
 
     // Once unlocked, keep [content] in the composition across later re-locks so its state (navigation
@@ -149,9 +141,3 @@ private fun FragmentActivity.showAppLockPrompt(
         .build()
     prompt.authenticate(info)
 }
-
-private tailrec fun android.content.Context.findFragmentActivity(): FragmentActivity? = when (this) {
-    is FragmentActivity -> this
-    is android.content.ContextWrapper -> baseContext.findFragmentActivity()
-    else -> null
-}

app/src/main/kotlin/org/libremail/ui/lock/AppLockViewModel.kt

@@ -97,8 +97,18 @@ class AppLockViewModel @Inject constructor(
         }
     }
 
-    private fun emitLocked(error: String? = null) {
-        _uiState.value = AppLockUiState.Locked(error, ++lockSeq)
+    /**
+     * Single writer for the gated UI state: derive it from [AppLockGate.state] — the source of truth
+     * for whether the session is locked — instead of hand-mirroring the gate at each call site. [error]
+     * is a human-readable reason the previous unlock attempt failed. The transient
+     * [AppLockUiState.Checking] cover and the "app-lock off / just disabled" unlocked states are driven
+     * by settings/lifecycle rather than the session gate, so their sites set [_uiState] directly.
+     */
+    private fun publish(error: String? = null) {
+        _uiState.value = when (gate.state) {
+            LockState.UNLOCKED -> AppLockUiState.Unlocked
+            LockState.LOCKED -> AppLockUiState.Locked(error, ++lockSeq)
+        }
     }
 
     /** Recompute the lock state when the app comes to the foreground (lifecycle ON_START). */
@@ -136,18 +146,15 @@ class AppLockViewModel @Inject constructor(
                 LockAction.CLEAR_AND_REQUIRE_AUTH -> clearCacheAndRestart(disableAppLock = false)
 
                 LockAction.REQUIRE_AUTH -> {
-                    val state = gate.onForeground(foregroundAt, appLockEnabled = true)
-                    if (state == LockState.UNLOCKED) {
-                        _uiState.value = AppLockUiState.Unlocked
-                    } else {
-                        // Re-lock on grace expiry (timeout). The SQLCipher passphrase is intentionally
-                        // NOT evicted here: PassphraseSession is the only separately-held copy, but
-                        // clearing it flips EncryptedCacheGuard to "locked" and would stall background
-                        // sync/push while locked, and the already-open Room handle keeps the key
-                        // resident regardless. Full eviction needs the DB close/reopen owned by #93 /
-                        // #111 — see PassphraseSession's KDoc.
-                        emitLocked()
-                    }
+                    // Advance the gate for this foreground pass, then publish its decision (UNLOCKED
+                    // within the grace window, otherwise LOCKED). Re-locking on grace expiry
+                    // intentionally does NOT evict the SQLCipher passphrase: PassphraseSession is the
+                    // only separately-held copy, but clearing it flips EncryptedCacheGuard to "locked"
+                    // and would stall background sync/push while locked, and the already-open Room handle
+                    // keeps the key resident regardless. Full eviction needs the DB close/reopen owned by
+                    // #93 / #111 — see PassphraseSession's KDoc.
+                    gate.onForeground(foregroundAt, appLockEnabled = true)
+                    publish()
                 }
             }
         }
@@ -169,7 +176,7 @@ class AppLockViewModel @Inject constructor(
             when (withContext(Dispatchers.Default) { unlockOrArm() }) {
                 UnlockResult.OK -> {
                     gate.onAuthenticated()
-                    _uiState.value = AppLockUiState.Unlocked
+                    publish()
                 }
 
                 UnlockResult.UNRECOVERABLE -> {
@@ -181,7 +188,7 @@ class AppLockViewModel @Inject constructor(
 
                 UnlockResult.RETRY -> {
                     gate.lock()
-                    emitLocked(context.getString(R.string.app_lock_unlock_failed))
+                    publish(context.getString(R.string.app_lock_unlock_failed))
                 }
             }
         }
@@ -190,7 +197,7 @@ class AppLockViewModel @Inject constructor(
     /** Called by the host when the prompt is cancelled or errors. */
     fun onAuthError(message: String?) {
         gate.lock()
-        emitLocked(message)
+        publish(message)
     }
 
     /** Outcome of unwrapping/arming the auth-bound passphrase after a successful device auth. */

app/src/main/kotlin/org/libremail/ui/settings/SettingsScreen.kt

@@ -1,7 +1,6 @@
 // SPDX-License-Identifier: GPL-3.0-or-later
 package org.libremail.ui.settings
 
-import android.widget.Toast
 import androidx.compose.animation.AnimatedVisibility
 import androidx.compose.foundation.clickable
 import androidx.compose.foundation.layout.Column
@@ -18,11 +17,14 @@ import androidx.compose.material3.HorizontalDivider
 import androidx.compose.material3.Icon
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Scaffold
+import androidx.compose.material3.SnackbarHost
+import androidx.compose.material3.SnackbarHostState
 import androidx.compose.material3.Text
 import androidx.compose.material3.TopAppBar
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
+import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.rotate
@@ -55,10 +57,14 @@ fun SettingsScreen(
     val batteryUnrestricted by viewModel.batteryUnrestricted.collectAsStateWithLifecycle()
     val context = LocalContext.current
     val resources = LocalResources.current
+    val snackbarHostState = remember { SnackbarHostState() }
 
+    // Surface a rejected app-lock toggle via the canonical snackbar pattern (matches MailboxScreen).
+    // The ViewModel holds the @StringRes id; resolve it here via LocalResources (so it re-resolves on
+    // configuration changes) at the display boundary, then clear it.
     LaunchedEffect(appLockMessage) {
-        appLockMessage?.let {
-            Toast.makeText(context, resources.getString(it), Toast.LENGTH_LONG).show()
+        appLockMessage?.let { messageId ->
+            snackbarHostState.showSnackbar(resources.getString(messageId))
             viewModel.clearAppLockMessage()
         }
     }
@@ -69,6 +75,7 @@ fun SettingsScreen(
     Scaffold(
         topBar = { TopAppBar(title = { Text(stringResource(R.string.title_settings)) }) },
         bottomBar = { LibreMailBottomBar(current = TopDest.SETTINGS, onSelect = onSelectTab) },
+        snackbarHost = { SnackbarHost(snackbarHostState) },
     ) { padding ->
         Column(
             modifier = Modifier