fix: serialize file picker calls

lib/screens/settings/settings_screen.dart

@@ -1,6 +1,5 @@
 import 'dart:io';
 
-import 'package:file_picker/file_picker.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
@@ -15,6 +14,7 @@ import '../../i18n/strings.g.dart';
 import '../main_screen.dart';
 import '../../mixins/refreshable.dart';
 import '../../services/download_storage_service.dart';
+import '../../services/file_picker_service.dart';
 import '../../services/saf_storage_service.dart';
 import '../../providers/settings_provider.dart';
 import '../../providers/theme_provider.dart';
@@ -506,7 +506,7 @@ class _SettingsScreenState extends State<SettingsScreen> with FocusableTab {
           return;
         }
       } else {
-        final result = await FilePicker.platform.getDirectoryPath(dialogTitle: t.settings.selectFolder);
+        final result = await FilePickerService.instance.getDirectoryPath(dialogTitle: t.settings.selectFolder);
         selectedPath = result;
       }
 

lib/services/file_picker_service.dart

@@ -0,0 +1,46 @@
+import 'package:file_picker/file_picker.dart';
+import 'package:flutter/services.dart';
+
+import '../utils/app_logger.dart';
+
+/// Serializes file_picker invocations to avoid
+/// `PlatformException(already_active, File picker is already active)`.
+class FilePickerService {
+  static final FilePickerService _instance = FilePickerService._();
+  static FilePickerService get instance => _instance;
+  FilePickerService._();
+
+  bool _active = false;
+
+  Future<T?> _guard<T>(String opName, Future<T?> Function() body) async {
+    if (_active) return null;
+    _active = true;
+    try {
+      return await body();
+    } on PlatformException catch (e, st) {
+      if (e.code == 'already_active') return null;
+      appLogger.e('FilePicker.$opName failed', error: e, stackTrace: st);
+      rethrow;
+    } finally {
+      _active = false;
+    }
+  }
+
+  Future<FilePickerResult?> pickFiles({
+    FileType type = FileType.any,
+    List<String>? allowedExtensions,
+    bool withData = false,
+  }) {
+    return _guard('pickFiles', () => FilePicker.platform.pickFiles(
+      type: type,
+      allowedExtensions: allowedExtensions,
+      withData: withData,
+    ));
+  }
+
+  Future<String?> getDirectoryPath({String? dialogTitle}) {
+    return _guard('getDirectoryPath', () => FilePicker.platform.getDirectoryPath(
+      dialogTitle: dialogTitle,
+    ));
+  }
+}

lib/widgets/artwork_picker_dialog.dart

@@ -4,6 +4,7 @@ import 'package:material_symbols_icons/symbols.dart';
 import '../focus/focusable_button.dart';
 import '../focus/focusable_wrapper.dart';
 import '../i18n/strings.g.dart';
+import '../services/file_picker_service.dart';
 import '../services/plex_client.dart';
 import '../utils/dialogs.dart';
 import '../utils/snackbar_helper.dart';
@@ -105,7 +106,7 @@ class _ArtworkPickerDialogState extends State<ArtworkPickerDialog> {
   }
 
   Future<void> _uploadFile() async {
-    final result = await FilePicker.platform.pickFiles(
+    final result = await FilePickerService.instance.pickFiles(
       type: FileType.image,
       withData: true,
     );

lib/widgets/video_controls/sheets/video_settings_sheet.dart

@@ -13,6 +13,7 @@ import 'package:provider/provider.dart';
 import '../../../models/shader_preset.dart';
 import '../../../mpv/mpv.dart';
 import '../../../providers/shader_provider.dart';
+import '../../../services/file_picker_service.dart';
 import '../../../services/settings_service.dart';
 import '../../../services/shader_service.dart';
 import '../../../services/sleep_timer_service.dart';
@@ -744,7 +745,7 @@ class _VideoSettingsSheetState extends State<VideoSettingsSheet> {
   }
 
   Future<void> _importCustomShader(ShaderProvider shaderProvider) async {
-    final result = await FilePicker.platform.pickFiles(
+    final result = await FilePickerService.instance.pickFiles(
       type: FileType.custom,
       allowedExtensions: ['glsl'],
     );