Dedupe native transfer/notification code and split ServerProvider into focused controllers

Consolidates duplicated GET/PUT/notification-channel logic across
DownloadService/ShareUploadService/SyncEngine into shared Kotlin helpers,
gives upload/download real batch queueing instead of dropping a second
concurrent batch, and dedupes repeated Dart channel-argument boilerplate.

Replaces the 2300+ line ServerProvider god object with ten focused
ChangeNotifiers (SessionController, SettingsController, FilesController,
PhotosController, FavoritesController, TrashController, SharesController,
RecentController, SyncStatusController, PickController) plus ItemOperations,
a plain coordinator for cross-domain item mutations - fixing the coupling
where device-sync status, per-tab data, and global UI prefs all lived in
one object. Updates every view/widget call site accordingly and refreshes
the architecture/server/standards/styling docs to match.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

lib/providers/sync_status_controller.dart

@@ -0,0 +1,215 @@
+import 'dart:async';
+import 'dart:convert';
+import 'package:flutter/material.dart';
+import '../models/nextcloud_item.dart';
+import '../models/sync_status.dart';
+import '../services/sync_service.dart';
+import 'session_controller.dart';
+
+/// Device-sync state and settings: which remote paths (files or folders,
+/// per account) get mirrored locally by the native `SyncWorker`, whether
+/// its periodic background runs are allowed on cellular, and live status
+/// pushed from `SyncStatusBus.kt` (syncing-now/per-file-syncing/synced/
+/// conflicts) - see `server.md`'s "Device sync" section. Split out of the
+/// former single `ServerProvider` god object specifically because this
+/// state used to reach directly into Files/Photos/Favorites item lists
+/// (`syncStatusFor`) despite living in an unrelated domain; now it's a
+/// second, focused provider those views read alongside their own tab
+/// controller.
+class SyncStatusController extends ChangeNotifier {
+  final SessionController session;
+
+  static const _prefSyncedPaths = 'ui_synced_folders';
+  static const _prefSyncEverything = 'ui_sync_everything';
+  static const _prefSyncOnCellular = 'ui_sync_on_cellular';
+
+  List<String> _syncedPaths = [];
+  bool _syncEverything = false;
+  bool _syncOnCellular = false;
+
+  bool _isSyncingNow = false;
+  Set<String> _syncingFileIds = {};
+  Set<String> _syncedFileIds = {};
+  List<SyncConflictInfo> _syncConflicts = [];
+  StreamSubscription<SyncStatusSnapshot>? _statusSub;
+
+  SyncStatusController(this.session) {
+    session.addAccountClearedListener(_onAccountCleared);
+    session.addAccountActivatedListener(_onAccountActivated);
+    _statusSub = SyncService.statusStream.listen(_applySnapshot);
+    _loadGlobalPrefs();
+  }
+
+  List<String> get syncedPaths => List.unmodifiable(_syncedPaths);
+  bool get syncEverything => _syncEverything;
+  bool get syncOnCellular => _syncOnCellular;
+
+  bool get isSyncingNow => _isSyncingNow;
+  List<SyncConflictInfo> get syncConflicts => List.unmodifiable(_syncConflicts);
+
+  SyncHeaderStatus get syncHeaderStatus {
+    if (_syncConflicts.isNotEmpty) return SyncHeaderStatus.alert;
+    if (_isSyncingNow) return SyncHeaderStatus.syncing;
+    if (!_syncEverything && _syncedPaths.isEmpty) return SyncHeaderStatus.off;
+    return SyncHeaderStatus.done;
+  }
+
+  SyncItemStatus syncStatusFor(NextcloudItem item) {
+    if (_syncingFileIds.contains(item.id)) return SyncItemStatus.syncing;
+    if (_syncConflicts.any((c) => c.fileId == item.id)) {
+      return SyncItemStatus.conflict;
+    }
+    if (_syncedFileIds.contains(item.id)) return SyncItemStatus.synced;
+    return SyncItemStatus.none;
+  }
+
+  Future<void> _loadGlobalPrefs() async {
+    final prefs = await session.prefsFuture;
+    _syncOnCellular = prefs.getBool(_prefSyncOnCellular) ?? _syncOnCellular;
+    notifyListeners();
+  }
+
+  void _onAccountCleared() {
+    _syncedPaths = [];
+    _syncEverything = false;
+    _isSyncingNow = false;
+    _syncingFileIds = {};
+    _syncedFileIds = {};
+    _syncConflicts = [];
+    notifyListeners();
+  }
+
+  Future<void> _onAccountActivated() async {
+    final id = session.activeAccountId;
+    if (id != null) {
+      final prefs = await session.prefsFuture;
+      String k(String base) => session.accountStore.accountPrefKey(id, base);
+      final pathsJson = prefs.getString(k(_prefSyncedPaths));
+      if (pathsJson != null) {
+        try {
+          _syncedPaths = (jsonDecode(pathsJson) as List).cast<String>();
+        } catch (e) {
+          debugPrint('[SyncStatusController] Synced paths restore failed: $e');
+          _syncedPaths = [];
+        }
+      } else {
+        _syncedPaths = [];
+      }
+      _syncEverything = prefs.getBool(k(_prefSyncEverything)) ?? false;
+      notifyListeners();
+    }
+    unawaited(SyncService.reschedule(session, this));
+    unawaited(SyncService.getStatus().then(_applySnapshot));
+  }
+
+  void _applySnapshot(SyncStatusSnapshot snapshot) {
+    if (snapshot.accountId != null &&
+        snapshot.accountId != session.activeAccountId) {
+      return;
+    }
+    _isSyncingNow = snapshot.syncing;
+    _syncingFileIds = snapshot.syncingFileIds;
+    _syncedFileIds = snapshot.syncedFileIds;
+    _syncConflicts = snapshot.conflicts;
+    notifyListeners();
+  }
+
+  void _persistSyncedPaths() {
+    final id = session.activeAccountId;
+    if (id == null) return;
+    session.prefsFuture.then(
+      (p) => p.setString(
+        session.accountStore.accountPrefKey(id, _prefSyncedPaths),
+        jsonEncode(_syncedPaths),
+      ),
+    );
+  }
+
+  bool isPathSynced(String path) => _syncedPaths.contains(path);
+
+  void addSyncedPath(String path) {
+    if (_syncedPaths.contains(path)) return;
+    _syncedPaths = [..._syncedPaths, path];
+    notifyListeners();
+    _persistSyncedPaths();
+    unawaited(SyncService.reschedule(session, this));
+  }
+
+  void removeSyncedPath(String path) {
+    if (!_syncedPaths.contains(path)) return;
+    _syncedPaths = _syncedPaths.where((f) => f != path).toList();
+    notifyListeners();
+    _persistSyncedPaths();
+    unawaited(SyncService.reschedule(session, this));
+  }
+
+  void setSyncEverything(bool value) {
+    if (_syncEverything == value) return;
+    _syncEverything = value;
+    notifyListeners();
+    final id = session.activeAccountId;
+    if (id != null) {
+      session.prefsFuture.then(
+        (p) => p.setBool(
+          session.accountStore.accountPrefKey(id, _prefSyncEverything),
+          value,
+        ),
+      );
+    }
+    unawaited(SyncService.reschedule(session, this));
+  }
+
+  void setSyncOnCellular(bool value) {
+    if (_syncOnCellular == value) return;
+    _syncOnCellular = value;
+    notifyListeners();
+    session.prefsFuture.then((p) => p.setBool(_prefSyncOnCellular, value));
+    unawaited(SyncService.reschedule(session, this));
+  }
+
+  /// In-app conflict resolution (the sync header's "Keep local"/"Use
+  /// server" buttons) - see `SyncService.resolveConflict`'s doc comment
+  /// for why this shares the exact same native path the notification
+  /// actions use.
+  Future<void> resolveSyncConflict(
+    SyncConflictInfo conflict, {
+    required bool useLocal,
+  }) {
+    return SyncService.resolveConflict(
+      session,
+      conflict,
+      useLocal ? 'local' : 'server',
+    );
+  }
+
+  /// The local mirror path for [item] if it falls under a synced folder
+  /// *and* has actually been synced down already - a pure function of the
+  /// remote path once a folder's marked synced (mirrors
+  /// `SyncEngine.kt#syncRoot`'s `<externalFilesDir>/sync/<accountId>/...`
+  /// layout exactly), so this never needs to read the native sync-state
+  /// SharedPreferences from Dart. Callers (Share/Download) use this to
+  /// skip a fresh WebDAV fetch when a local copy already exists.
+  Future<String?> localSyncedFilePath(NextcloudItem item) async {
+    final id = session.activeAccountId;
+    if (id == null) return null;
+    final itemPath = item.path.endsWith('/')
+        ? item.path.substring(0, item.path.length - 1)
+        : item.path;
+    final isSynced =
+        _syncEverything ||
+        _syncedPaths.any((folder) {
+          final f = folder.endsWith('/')
+              ? folder.substring(0, folder.length - 1)
+              : folder;
+          return itemPath == f || itemPath.startsWith('$f/');
+        });
+    if (!isSynced) return null;
+    return SyncService.localSyncedFilePath(id, item.path);
+  }
+
+  @override
+  void dispose() {
+    _statusSub?.cancel();
+    super.dispose();
+  }
+}