iOS: degrade gracefully where the Android-only native services are missing

Share/pick/sync calls and streams no longer throw MissingPluginException at
startup; upload/download/sync-now show 'X isn't available on this platform
yet'. Offline/sync mirror dir no longer uses the Android-only external dir.
Info.plist: Face ID and photo library usage strings.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

lib/services/download_service.dart

@@ -38,6 +38,9 @@ class DownloadService {
           .toList(),
     );
 
-    await _channel.invokeMethod('startDownload', {...args, 'files': filesJson});
+    await invokeOrExplain(_channel, 'startDownload', 'Downloading', {
+      ...args,
+      'files': filesJson,
+    });
   }
 }

lib/services/native_channel.dart

@@ -1,3 +1,4 @@
+import 'package:flutter/services.dart';
 import '../providers/session_controller.dart';
 
 /// The "get this account's auth header, or bail" guard every native-
@@ -21,3 +22,57 @@ Map<String, String> baseChannelArgs(SessionController session) {
     'authHeader': requireAuthHeader(session),
   };
 }
+
+/// Thrown by user-triggered native services (upload, download, sync now...)
+/// on a platform whose native side isn't implemented yet - the message is
+/// shown to the user as-is, e.g. in a snackbar.
+class NativeServiceUnavailable implements Exception {
+  final String feature;
+
+  const NativeServiceUnavailable(this.feature);
+
+  @override
+  String toString() => "$feature isn't available on this platform yet.";
+}
+
+/// Calls [method], treating a missing native implementation (no
+/// `MethodChannel` handler registered, as on iOS until each service is
+/// built there) as "nothing to report": returns null instead of throwing
+/// `MissingPluginException`. For cold-start checks, scheduling and other
+/// calls nobody is waiting on.
+Future<T?> invokeIfAvailable<T>(
+  MethodChannel channel,
+  String method, [
+  Object? arguments,
+]) async {
+  try {
+    return await channel.invokeMethod<T>(method, arguments);
+  } on MissingPluginException {
+    return null;
+  }
+}
+
+/// Like [invokeIfAvailable], but for an action the user just asked for:
+/// throws [NativeServiceUnavailable] naming [feature] rather than silently
+/// doing nothing.
+Future<T?> invokeOrExplain<T>(
+  MethodChannel channel,
+  String method,
+  String feature, [
+  Object? arguments,
+]) async {
+  try {
+    return await channel.invokeMethod<T>(method, arguments);
+  } on MissingPluginException {
+    throw NativeServiceUnavailable(feature);
+  }
+}
+
+/// [channel]'s broadcast stream mapped through [convert], with the
+/// "no native implementation" error dropped - the stream just never emits.
+Stream<T> quietEvents<T>(EventChannel channel, T Function(dynamic) convert) {
+  return channel
+      .receiveBroadcastStream()
+      .handleError((Object _) {}, test: (e) => e is MissingPluginException)
+      .map(convert);
+}

lib/services/pick_intent_service.dart

@@ -1,5 +1,6 @@
 import 'package:flutter/services.dart';
 import '../models/pick_request.dart';
+import 'native_channel.dart';
 
 /// Talks to `MainActivity.kt`'s hand-rolled GET_CONTENT picker handling
 /// (mirrors `ShareIntentService`'s split between a cold-start check and a
@@ -14,7 +15,8 @@ class PickIntentService {
   /// Non-null if the app was launched cold as another app's file/photo
   /// picker.
   static Future<PickRequest?> getPickRequest() async {
-    final result = await _methodChannel.invokeMethod<Map<dynamic, dynamic>>(
+    final result = await invokeIfAvailable<Map<dynamic, dynamic>>(
+      _methodChannel,
       'getPickRequest',
     );
     return result == null ? null : PickRequest.fromMap(result);
@@ -23,7 +25,8 @@ class PickIntentService {
   /// Emits whenever the app is asked to act as a picker while already
   /// running.
   static Stream<PickRequest> get onNewPickRequest {
-    return _newPickChannel.receiveBroadcastStream().map(
+    return quietEvents(
+      _newPickChannel,
       (event) => PickRequest.fromMap(event as Map<dynamic, dynamic>),
     );
   }
@@ -34,7 +37,7 @@ class PickIntentService {
     List<String> localPaths,
     List<String> mimeTypes,
   ) {
-    return _methodChannel.invokeMethod('finishPick', {
+    return invokeIfAvailable(_methodChannel, 'finishPick', {
       'paths': localPaths,
       'mimeTypes': mimeTypes,
     });
@@ -42,6 +45,6 @@ class PickIntentService {
 
   /// Backs out of picking mode with no result, closing the picker.
   static Future<void> cancelPick() {
-    return _methodChannel.invokeMethod('cancelPick');
+    return invokeIfAvailable(_methodChannel, 'cancelPick');
   }
 }

lib/services/share_intent_service.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/services.dart';
+import 'native_channel.dart';
 
 /// A file shared to Noo from another app's "Share to..." sheet, before its
 /// bytes have been touched - just the `content://` Uri and whatever cheap
@@ -40,7 +41,8 @@ class ShareIntentService {
   /// Whatever was shared to launch the app cold (empty if it was launched
   /// normally, not via a share).
   static Future<List<SharedFileRef>> getInitialShare() async {
-    final result = await _methodChannel.invokeMethod<List<dynamic>>(
+    final result = await invokeIfAvailable<List<dynamic>>(
+      _methodChannel,
       'getInitialShare',
     );
     return (result ?? [])
@@ -51,7 +53,7 @@ class ShareIntentService {
 
   /// Emits whenever another share arrives while the app is already running.
   static Stream<List<SharedFileRef>> get onNewShare {
-    return _newShareChannel.receiveBroadcastStream().map((event) {
+    return quietEvents(_newShareChannel, (event) {
       return (event as List<dynamic>)
           .cast<Map<dynamic, dynamic>>()
           .map(SharedFileRef.fromMap)

lib/services/sync_service.dart

@@ -10,6 +10,7 @@ import '../models/saved_account.dart';
 import '../providers/files_controller.dart';
 import '../providers/session_controller.dart';
 import '../providers/sync_status_controller.dart';
+import 'native_channel.dart';
 
 /// A snapshot of native device-sync status - see `SyncStatusBus.kt` (the
 /// in-process pub/sub it mirrors) and `MainActivity.kt`'s `syncStatusMap`.
@@ -110,7 +111,7 @@ class SyncService {
           await cancelAccount(account.id);
           continue;
         }
-        await _channel.invokeMethod('reschedule', {
+        await invokeIfAvailable(_channel, 'reschedule', {
           'accountId': account.id,
           'serverUrl': account.serverUrl,
           'username': account.username,
@@ -132,7 +133,7 @@ class SyncService {
   /// Stops [accountId]'s periodic job (the account was removed, or has
   /// nothing left to sync).
   static Future<void> cancelAccount(String accountId) async {
-    await _channel.invokeMethod('cancel', {'accountId': accountId});
+    await invokeIfAvailable(_channel, 'cancel', {'accountId': accountId});
   }
 
   /// Runs a one-off sync pass immediately, independent of the periodic
@@ -158,7 +159,7 @@ class SyncService {
     }
 
     final paths = sync.syncEverything ? ['/'] : sync.syncedPaths;
-    await _channel.invokeMethod('syncNow', {
+    await invokeOrExplain(_channel, 'syncNow', 'Syncing', {
       'accountId': accountId,
       'serverUrl': session.serverUrl,
       'username': session.username,
@@ -178,7 +179,8 @@ class SyncService {
   /// app start - the native bus only knows an account once a sync pass has
   /// run in this process.
   static Future<SyncStatusSnapshot> getStatus(String? accountId) async {
-    final result = await _channel.invokeMethod<Map<dynamic, dynamic>>(
+    final result = await invokeIfAvailable<Map<dynamic, dynamic>>(
+      _channel,
       'getSyncStatus',
       {'accountId': accountId},
     );
@@ -196,11 +198,10 @@ class SyncService {
   /// (`SyncStatusController`), so sync badges stopped updating until the app
   /// was restarted. This is a broadcast stream, so any number of Dart
   /// listeners share the one native subscription.
-  static final Stream<SyncStatusSnapshot> statusStream = _statusChannel
-      .receiveBroadcastStream()
-      .map(
-        (event) => SyncStatusSnapshot.fromMap(event as Map<dynamic, dynamic>),
-      );
+  static final Stream<SyncStatusSnapshot> statusStream = quietEvents(
+    _statusChannel,
+    (event) => SyncStatusSnapshot.fromMap(event as Map<dynamic, dynamic>),
+  );
 
   /// In-app conflict resolution (the header's "Keep local"/"Use server"
   /// buttons) - shares the exact same native `ConflictResolveWorker`
@@ -213,7 +214,7 @@ class SyncService {
   ) async {
     final authHeader = session.service?.authHeaders['Authorization'];
     if (authHeader == null) throw Exception('Not logged in.');
-    await _channel.invokeMethod('resolveConflict', {
+    await invokeOrExplain(_channel, 'resolveConflict', 'Resolving conflicts', {
       'accountId': conflict.accountId,
       'serverUrl': session.serverUrl,
       'username': session.username,
@@ -236,12 +237,23 @@ class SyncService {
   ) async {
     final accountId = session.activeAccountId;
     if (accountId == null) return;
-    await _channel.invokeMethod('removeLocalSync', {
+    await invokeIfAvailable(_channel, 'removeLocalSync', {
       'accountId': accountId,
       'path': path,
     });
   }
 
+  /// Where the `sync/<accountId>/...` mirror lives: Android's app-specific
+  /// external files dir (what `SyncEngine.kt` writes to); everywhere else -
+  /// iOS has no external storage, `getExternalStorageDirectory` throws
+  /// there - the app's private support directory.
+  static Future<Directory?> baseDirectory() async {
+    if (defaultTargetPlatform == TargetPlatform.android) {
+      return getExternalStorageDirectory();
+    }
+    return getApplicationSupportDirectory();
+  }
+
   /// The deterministic local mirror path for [remoteItemPath] under
   /// account [accountId] - mirrors `SyncEngine.kt#syncRoot`'s
   /// `<externalFilesDir>/sync/<accountId>/...` layout exactly, so this
@@ -251,7 +263,7 @@ class SyncService {
     String accountId,
     String remoteItemPath,
   ) async {
-    final base = await getExternalStorageDirectory();
+    final base = await baseDirectory();
     if (base == null) return null;
     final relPath = remoteItemPath.startsWith('/')
         ? remoteItemPath.substring(1)

lib/services/upload_service.dart

@@ -56,7 +56,7 @@ class UploadService {
           .toList(),
     );
 
-    await _channel.invokeMethod('startUpload', {
+    await invokeOrExplain(_channel, 'startUpload', 'Uploading', {
       ...args,
       'files': filesJson,
       'remoteFolder': files.currentFolderPath,
@@ -70,7 +70,8 @@ class UploadService {
   /// deliberately: see `SyncService.statusStream`'s identical doc comment -
   /// `EventChannel.receiveBroadcastStream()` opens its own native
   /// subscription per call, and the native side only keeps the latest one.
-  static final Stream<UploadCompletion> completions = _statusChannel
-      .receiveBroadcastStream()
-      .map((event) => UploadCompletion.fromMap(event as Map<dynamic, dynamic>));
+  static final Stream<UploadCompletion> completions = quietEvents(
+    _statusChannel,
+    (event) => UploadCompletion.fromMap(event as Map<dynamic, dynamic>),
+  );
 }