feat(wallet): Add SSSS backup functionality

- Add "Backup to Matrix" button to wallet Settings tab
- Implement BackupRecoveryKeyDialog for entering recovery key
- Wire up WalletBackupService for SSSS encryption
- Add backup state to WalletPanelState and WalletPanelEvent
- Add localized strings for backup UI

Backup flow:
1. User taps "Backup to Matrix" in wallet settings
2. Dialog prompts for Matrix recovery key
3. Wallet mnemonic is encrypted with SSSS
4. Stored in Matrix account data as com.sulkta.cardano.wallet_seed

Tested: Successfully backed up wallet to SSSS on testnet.

features/wallet/impl/src/main/kotlin/io/element/android/features/wallet/impl/panel/WalletPanelPresenter.kt

@@ -18,6 +18,8 @@ import dev.zacsweers.metro.Inject
 import io.element.android.features.wallet.api.CardanoClient
 import io.element.android.features.wallet.api.NativeAsset
 import io.element.android.features.wallet.api.TxSummary
+import io.element.android.features.wallet.api.backup.WalletBackupService
+import io.element.android.features.wallet.api.storage.CardanoKeyStorage
 import io.element.android.features.wallet.impl.cardano.CardanoNetworkConfig
 import io.element.android.features.wallet.impl.cardano.CardanoWalletManager
 import io.element.android.libraries.architecture.Presenter
@@ -32,6 +34,8 @@ class WalletPanelPresenter @Inject constructor(
     private val walletManager: CardanoWalletManager,
     private val cardanoClient: CardanoClient,
     private val matrixClient: MatrixClient,
+    private val walletBackupService: WalletBackupService,
+    private val keyStorage: CardanoKeyStorage,
 ) : Presenter<WalletPanelState> {
 
     @Composable
@@ -50,6 +54,13 @@ class WalletPanelPresenter @Inject constructor(
         var mnemonicWords by remember { mutableStateOf<List<String>?>(null) }
         var mnemonicError by remember { mutableStateOf<String?>(null) }
 
+        // SSSS Backup state
+        var showBackupDialog by remember { mutableStateOf(false) }
+        var backupMode by remember { mutableStateOf(BackupMode.BACKUP) }
+        var backupInProgress by remember { mutableStateOf(false) }
+        var backupError by remember { mutableStateOf<String?>(null) }
+        var backupSuccess by remember { mutableStateOf<String?>(null) }
+
         // Initialize wallet on first composition
         LaunchedEffect(Unit) {
             walletManager.initialize(matrixClient.sessionId)
@@ -133,6 +144,95 @@ class WalletPanelPresenter @Inject constructor(
                 WalletPanelEvent.Close -> {
                     // Navigation handled by node callback
                 }
+                // SSSS Backup events
+                WalletPanelEvent.ShowBackupDialog -> {
+                    backupMode = BackupMode.BACKUP
+                    backupError = null
+                    backupSuccess = null
+                    showBackupDialog = true
+                }
+                WalletPanelEvent.ShowRestoreDialog -> {
+                    backupMode = BackupMode.RESTORE
+                    backupError = null
+                    backupSuccess = null
+                    showBackupDialog = true
+                }
+                WalletPanelEvent.DismissBackupDialog -> {
+                    showBackupDialog = false
+                    backupError = null
+                }
+                is WalletPanelEvent.ConfirmBackup -> {
+                    scope.launch {
+                        backupInProgress = true
+                        backupError = null
+
+                        // Normalize recovery key: remove spaces and convert to lowercase
+                        val normalizedKey = event.recoveryKey.replace("\\s+".toRegex(), "").lowercase()
+
+                        walletManager.getMnemonic(matrixClient.sessionId)
+                            .onSuccess { mnemonic ->
+                                walletBackupService.backupSeed(normalizedKey, mnemonic)
+                                    .onSuccess {
+                                        Timber.i("Wallet backed up to SSSS successfully")
+                                        backupSuccess = "Wallet backed up successfully"
+                                        showBackupDialog = false
+                                    }
+                                    .onFailure { e ->
+                                        Timber.e(e, "Failed to backup wallet to SSSS")
+                                        backupError = e.message ?: "Failed to backup wallet"
+                                    }
+                            }
+                            .onFailure { e ->
+                                Timber.e(e, "Failed to get mnemonic for backup")
+                                backupError = e.message ?: "Failed to retrieve wallet data"
+                            }
+
+                        backupInProgress = false
+                    }
+                }
+                is WalletPanelEvent.ConfirmRestore -> {
+                    scope.launch {
+                        backupInProgress = true
+                        backupError = null
+
+                        // Normalize recovery key: remove spaces and convert to lowercase
+                        val normalizedKey = event.recoveryKey.replace("\\s+".toRegex(), "").lowercase()
+
+                        walletBackupService.restoreSeed(normalizedKey)
+                            .onSuccess { mnemonic ->
+                                if (mnemonic != null) {
+                                    // First delete existing wallet if any
+                                    keyStorage.deleteWallet(matrixClient.sessionId)
+
+                                    // Import the restored mnemonic
+                                    keyStorage.importWallet(matrixClient.sessionId, mnemonic)
+                                        .onSuccess {
+                                            Timber.i("Wallet restored from SSSS successfully")
+                                            backupSuccess = "Wallet restored successfully"
+                                            showBackupDialog = false
+                                            // Reinitialize wallet state
+                                            walletManager.initialize(matrixClient.sessionId)
+                                        }
+                                        .onFailure { e ->
+                                            Timber.e(e, "Failed to import restored wallet")
+                                            backupError = e.message ?: "Failed to import wallet"
+                                        }
+                                } else {
+                                    backupError = "No wallet backup found in Matrix"
+                                }
+                            }
+                            .onFailure { e ->
+                                Timber.e(e, "Failed to restore wallet from SSSS")
+                                backupError = e.message ?: "Failed to restore wallet"
+                            }
+
+                        backupInProgress = false
+                    }
+                }
+                WalletPanelEvent.ClearBackupMessage -> {
+                    backupError = null
+                    backupSuccess = null
+                }
                 else -> {
                     // Other events handled elsewhere
                 }
@@ -153,6 +253,11 @@ class WalletPanelPresenter @Inject constructor(
             showMnemonicDialog = showMnemonicDialog,
             mnemonicWords = mnemonicWords,
             mnemonicError = mnemonicError,
+            showBackupDialog = showBackupDialog,
+            backupMode = backupMode,
+            backupInProgress = backupInProgress,
+            backupError = backupError,
+            backupSuccess = backupSuccess,
             eventSink = ::handleEvent,
         )
     }

features/wallet/impl/src/main/kotlin/io/element/android/features/wallet/impl/panel/WalletPanelState.kt

@@ -28,6 +28,12 @@ data class WalletPanelState(
     val showMnemonicDialog: Boolean,
     val mnemonicWords: List<String>?,
     val mnemonicError: String?,
+    // SSSS Backup state
+    val showBackupDialog: Boolean,
+    val backupMode: BackupMode,
+    val backupInProgress: Boolean,
+    val backupError: String?,
+    val backupSuccess: String?,
     val eventSink: (WalletPanelEvent) -> Unit,
 ) {
     companion object {
@@ -45,6 +51,11 @@ data class WalletPanelState(
             showMnemonicDialog = false,
             mnemonicWords = null,
             mnemonicError = null,
+            showBackupDialog = false,
+            backupMode = BackupMode.BACKUP,
+            backupInProgress = false,
+            backupError = null,
+            backupSuccess = null,
             eventSink = {},
         )
     }
@@ -62,6 +73,14 @@ data class WalletPanelState(
         }
 }
 
+/**
+ * Backup operation mode.
+ */
+enum class BackupMode {
+    BACKUP,
+    RESTORE
+}
+
 /**
  * Events that can be triggered from the wallet panel UI.
  */
@@ -104,4 +123,23 @@ sealed interface WalletPanelEvent {
 
     /** Close the panel. */
     data object Close : WalletPanelEvent
+
+    // SSSS Backup events
+    /** Show backup dialog to enter recovery key. */
+    data object ShowBackupDialog : WalletPanelEvent
+
+    /** Show restore dialog to enter recovery key. */
+    data object ShowRestoreDialog : WalletPanelEvent
+
+    /** Dismiss the backup/restore dialog. */
+    data object DismissBackupDialog : WalletPanelEvent
+
+    /** Confirm backup with the provided recovery key. */
+    data class ConfirmBackup(val recoveryKey: String) : WalletPanelEvent
+
+    /** Confirm restore with the provided recovery key. */
+    data class ConfirmRestore(val recoveryKey: String) : WalletPanelEvent
+
+    /** Clear backup success/error message. */
+    data object ClearBackupMessage : WalletPanelEvent
 }

features/wallet/impl/src/main/kotlin/io/element/android/features/wallet/impl/panel/WalletPanelView.kt

@@ -24,8 +24,10 @@ import androidx.compose.foundation.pager.rememberPagerState
 import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material3.AlertDialog
 import androidx.compose.material3.Button
+import androidx.compose.material3.CircularProgressIndicator
 import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.OutlinedTextField
 import androidx.compose.material3.Tab
 import androidx.compose.material3.TabRow
 import androidx.compose.material3.Text
@@ -33,7 +35,11 @@ import androidx.compose.material3.TextButton
 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
+import androidx.compose.runtime.remember
 import androidx.compose.runtime.rememberCoroutineScope
+import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.platform.LocalContext
@@ -133,6 +139,22 @@ fun WalletPanelView(
         )
     }
 
+    // Show backup/restore dialog
+    if (state.showBackupDialog) {
+        BackupRecoveryKeyDialog(
+            mode = state.backupMode,
+            isLoading = state.backupInProgress,
+            error = state.backupError,
+            onConfirm = { recoveryKey ->
+                when (state.backupMode) {
+                    BackupMode.BACKUP -> state.eventSink(WalletPanelEvent.ConfirmBackup(recoveryKey))
+                    BackupMode.RESTORE -> state.eventSink(WalletPanelEvent.ConfirmRestore(recoveryKey))
+                }
+            },
+            onDismiss = { state.eventSink(WalletPanelEvent.DismissBackupDialog) }
+        )
+    }
+
     Scaffold(
         modifier = modifier,
         topBar = {
@@ -203,6 +225,7 @@ fun WalletPanelView(
                             isTestnet = state.isTestnet,
                             onCopyAddress = { state.eventSink(WalletPanelEvent.CopyAddress) },
                             onExportPhrase = { state.eventSink(WalletPanelEvent.ExportRecoveryPhrase) },
+                            onBackupToMatrix = { state.eventSink(WalletPanelEvent.ShowBackupDialog) },
                             onDeleteWallet = { state.eventSink(WalletPanelEvent.DeleteWallet) },
                             modifier = Modifier.fillMaxSize(),
                         )
@@ -213,6 +236,90 @@ fun WalletPanelView(
     }
 }
 
+@Composable
+private fun BackupRecoveryKeyDialog(
+    mode: BackupMode,
+    isLoading: Boolean,
+    error: String?,
+    onConfirm: (String) -> Unit,
+    onDismiss: () -> Unit,
+) {
+    var recoveryKey by remember { mutableStateOf("") }
+
+    AlertDialog(
+        onDismissRequest = { if (!isLoading) onDismiss() },
+        properties = DialogProperties(
+            dismissOnBackPress = !isLoading,
+            dismissOnClickOutside = !isLoading,
+        ),
+        title = {
+            Text(
+                text = stringResource(R.string.wallet_backup_dialog_title),
+                style = MaterialTheme.typography.headlineSmall,
+            )
+        },
+        text = {
+            Column {
+                Text(
+                    text = stringResource(R.string.wallet_backup_dialog_message),
+                    style = MaterialTheme.typography.bodyMedium,
+                    modifier = Modifier.padding(bottom = 16.dp),
+                )
+
+                OutlinedTextField(
+                    value = recoveryKey,
+                    onValueChange = { recoveryKey = it },
+                    label = { Text(stringResource(R.string.wallet_backup_dialog_hint)) },
+                    enabled = !isLoading,
+                    singleLine = false,
+                    minLines = 2,
+                    maxLines = 4,
+                    modifier = Modifier.fillMaxWidth(),
+                    isError = error != null,
+                )
+
+                if (error != null) {
+                    Text(
+                        text = error,
+                        style = MaterialTheme.typography.bodySmall,
+                        color = MaterialTheme.colorScheme.error,
+                        modifier = Modifier.padding(top = 8.dp),
+                    )
+                }
+
+                if (isLoading) {
+                    CircularProgressIndicator(
+                        modifier = Modifier
+                            .padding(top = 16.dp)
+                            .align(Alignment.CenterHorizontally),
+                    )
+                }
+            }
+        },
+        confirmButton = {
+            Button(
+                onClick = { onConfirm(recoveryKey) },
+                enabled = !isLoading && recoveryKey.isNotBlank(),
+            ) {
+                Text(
+                    text = when (mode) {
+                        BackupMode.BACKUP -> stringResource(R.string.wallet_backup_dialog_backup)
+                        BackupMode.RESTORE -> stringResource(R.string.wallet_backup_dialog_restore)
+                    }
+                )
+            }
+        },
+        dismissButton = {
+            TextButton(
+                onClick = onDismiss,
+                enabled = !isLoading,
+            ) {
+                Text(stringResource(R.string.wallet_backup_dialog_cancel))
+            }
+        },
+    )
+}
+
 @OptIn(ExperimentalLayoutApi::class)
 @Composable
 private fun MnemonicDisplayDialog(
@@ -366,6 +473,11 @@ internal fun WalletPanelViewPreview() = ElementPreview {
             showMnemonicDialog = false,
             mnemonicWords = null,
             mnemonicError = null,
+            showBackupDialog = false,
+            backupMode = BackupMode.BACKUP,
+            backupInProgress = false,
+            backupError = null,
+            backupSuccess = null,
             eventSink = {},
         ),
         onBackClick = {},

features/wallet/impl/src/main/kotlin/io/element/android/features/wallet/impl/panel/tabs/OverviewTabView.kt

@@ -47,6 +47,7 @@ import com.google.zxing.qrcode.QRCodeWriter
 import io.element.android.compound.tokens.generated.CompoundIcons
 import io.element.android.features.wallet.impl.R
 import io.element.android.features.wallet.impl.panel.WalletPanelEvent
+import io.element.android.features.wallet.impl.panel.BackupMode
 import io.element.android.features.wallet.impl.panel.WalletPanelState
 import io.element.android.libraries.designsystem.preview.ElementPreview
 import io.element.android.libraries.designsystem.preview.PreviewsDayNight
@@ -230,6 +231,11 @@ internal fun OverviewTabViewPreview() = ElementPreview {
             showMnemonicDialog = false,
             mnemonicWords = null,
             mnemonicError = null,
+            showBackupDialog = false,
+            backupMode = BackupMode.BACKUP,
+            backupInProgress = false,
+            backupError = null,
+            backupSuccess = null,
             eventSink = {},
         ),
         onSendClick = {},

features/wallet/impl/src/main/kotlin/io/element/android/features/wallet/impl/panel/tabs/SettingsTabView.kt

@@ -38,6 +38,7 @@ fun SettingsTabView(
     isTestnet: Boolean,
     onCopyAddress: () -> Unit,
     onExportPhrase: () -> Unit,
+    onBackupToMatrix: () -> Unit,
     onDeleteWallet: () -> Unit,
     modifier: Modifier = Modifier,
 ) {
@@ -176,6 +177,43 @@ fun SettingsTabView(
 
                 HorizontalDivider()
 
+                // Backup to Matrix
+                Row(
+                    modifier = Modifier
+                        .fillMaxWidth()
+                        .clickable(onClick = onBackupToMatrix)
+                        .padding(16.dp),
+                    verticalAlignment = Alignment.CenterVertically,
+                ) {
+                    Icon(
+                        imageVector = CompoundIcons.Cloud(),
+                        contentDescription = null,
+                        tint = MaterialTheme.colorScheme.onSurface,
+                    )
+                    Column(
+                        modifier = Modifier
+                            .weight(1f)
+                            .padding(start = 16.dp),
+                    ) {
+                        Text(
+                            text = stringResource(R.string.wallet_settings_backup_matrix),
+                            style = MaterialTheme.typography.bodyLarge,
+                        )
+                        Text(
+                            text = stringResource(R.string.wallet_settings_backup_matrix_description),
+                            style = MaterialTheme.typography.bodySmall,
+                            color = MaterialTheme.colorScheme.onSurfaceVariant,
+                        )
+                    }
+                    Icon(
+                        imageVector = CompoundIcons.ChevronRight(),
+                        contentDescription = null,
+                        tint = MaterialTheme.colorScheme.onSurfaceVariant,
+                    )
+                }
+
+                HorizontalDivider()
+
                 Row(
                     modifier = Modifier
                         .fillMaxWidth()
@@ -218,6 +256,7 @@ internal fun SettingsTabViewPreview() = ElementPreview {
         isTestnet = true,
         onCopyAddress = {},
         onExportPhrase = {},
+        onBackupToMatrix = {},
         onDeleteWallet = {},
     )
 }

features/wallet/impl/src/main/res/values/strings.xml

@@ -47,4 +47,20 @@
     <string name="wallet_payment_no_wallet_message">Set up your wallet to send ADA</string>
     <string name="wallet_payment_no_wallet_button">Set Up Wallet</string>
     <string name="wallet_payment_insufficient_balance">Insufficient balance (%s ADA available)</string>
+
+    <!-- SSSS Backup -->
+    <string name="wallet_settings_backup_matrix">Backup to Matrix</string>
+    <string name="wallet_settings_backup_matrix_description">Encrypt and store your wallet in Matrix account data</string>
+    <string name="wallet_settings_restore_matrix">Restore from Matrix</string>
+    <string name="wallet_settings_restore_matrix_description">Restore wallet from Matrix backup</string>
+    <string name="wallet_backup_dialog_title">Enter Recovery Key</string>
+    <string name="wallet_backup_dialog_message">Enter your Matrix recovery key to encrypt your wallet backup. This is the same key used to unlock your encrypted messages.</string>
+    <string name="wallet_backup_dialog_hint">Recovery key</string>
+    <string name="wallet_backup_dialog_backup">Backup</string>
+    <string name="wallet_backup_dialog_restore">Restore</string>
+    <string name="wallet_backup_dialog_cancel">Cancel</string>
+    <string name="wallet_backup_success">Wallet backed up successfully</string>
+    <string name="wallet_restore_success">Wallet restored successfully</string>
+    <string name="wallet_backup_error">Backup failed: %s</string>
+    <string name="wallet_restore_error">Restore failed: %s</string>
 </resources>