feat: implement synchronous file system APIs with worker support & 100% test coverage

experimental/web_file_system/README.md

@@ -109,8 +109,63 @@ print(canonicalPath); // "/documents/report.txt"
 
 ---
 
-## Performance Notes: Inode vs Path-based Renames
-
-Most browser file systems index files by their full path strings (e.g., keying a database table by `/documents/photos/holiday.png`). Renaming the directory `/documents` to `/archive` requires iterating over every nested path and rewriting their keys, which is an $O(N)$ operation where $N$ is the number of recursive items.
-
 `web_file_system` implements an **inode index** model. Inodes reference parents by their database IDs rather than paths. Renaming a directory only updates the single directory node's `name` property. Its child files and directories remain untouched because they continue to reference the same unchanged parent inode ID. This makes directory renaming an **$O(1)$** operation.
+
+---
+
+## Synchronous API Support (Web Workers Only)
+
+Because JavaScript and Dart run on a single-threaded event loop, blocking the main browser thread is not permitted. Therefore, standard synchronous APIs (such as `readAsBytesSync`, `writeAsBytesSync`, `existsSync`, `createSync`, `deleteSync`, `listSync`, `renameSync`, and `statSync`) will throw an `UnsupportedError` if invoked on the main application thread.
+
+However, synchronous operations are **fully supported within Web Workers**. By delegating asynchronous work (IndexedDB metadata updates and Origin Private File System operations) to the main thread via a `SharedArrayBuffer` and blocking the Web Worker's execution loop using `Atomics.wait()`, you can safely use synchronous file system calls inside your workers.
+
+### Prerequisites & Security Headers
+
+To use the synchronous APIs, the browser requires cross-origin isolation. You must serve your web application with the following HTTP headers:
+
+```http
+Cross-Origin-Opener-Policy: same-origin
+Cross-Origin-Embedder-Policy: require-corp
+```
+
+If these headers are not present, `SharedArrayBuffer` is disabled by the browser, and synchronous operations will throw a `StateError`.
+
+### Setup Example
+
+#### 1. Main Application Thread
+
+Initialize the file system and register the worker proxy to listen to RPC requests from your worker:
+
+```dart
+import 'dart:html'; // or standard JS interop / package:web
+import 'package:web_file_system/web_file_system.dart';
+
+void main() {
+  final fs = WebFileSystem();
+  final worker = Worker('worker.js');
+  
+  // Register the proxy to handle synchronous RPC requests
+  WebFileSystem.registerWorkerProxy(worker, fs);
+}
+```
+
+#### 2. Web Worker Context (`worker.js` / Dart Worker)
+
+In your worker code, once initialized with the `SharedArrayBuffer`, you can access the file system synchronously:
+
+```dart
+import 'package:web_file_system/web_file_system.dart';
+
+void main() {
+  final fs = WebFileSystem();
+  
+  // These operations block synchronous execution inside the Web Worker
+  final file = fs.file('/data.bin');
+  file.createSync();
+  file.writeAsBytesSync([1, 2, 3, 4]);
+  
+  final bytes = file.readAsBytesSync();
+  print(bytes); // [1, 2, 3, 4]
+}
+```
+

experimental/web_file_system/lib/src/backend/sync_rpc_helper.dart

@@ -0,0 +1,234 @@
+import 'dart:js_interop';
+import 'dart:typed_data';
+
+@JS('eval')
+external JSAny? _jsEval(String code);
+
+@JS('globalThis.registerVFSWorkerProxy')
+external void _registerVFSWorkerProxy(JSAny worker, JSAny asyncFS);
+
+@JS('globalThis.initVFSSyncWorker')
+external void _initVFSSyncWorker();
+
+@JS('globalThis.sendVFSSyncRequest')
+external JSUint8Array _sendVFSSyncRequest(int cmd, JSUint8Array requestBytes);
+
+@JS('globalThis.isVFSSyncWorkerInitialized')
+external bool? get _isVFSSyncWorkerInitialized;
+
+@JS('globalThis.SharedArrayBuffer')
+external JSAny? get _sharedArrayBufferClass;
+
+class SyncRpcHelper {
+  static bool get isSharedArrayBufferSupported {
+    try {
+      return _sharedArrayBufferClass != null;
+    } catch (_) {
+      return false;
+    }
+  }
+
+  static bool get isWorker {
+    // In a worker, globalThis.document is undefined and globalThis.importScripts is defined
+    try {
+      final isWorkerResult = _jsEval("typeof importScripts !== 'undefined'");
+      return (isWorkerResult as JSBoolean).toDart;
+    } catch (_) {
+      return false;
+    }
+  }
+
+  static void injectHelperScripts() {
+    _jsEval('''
+      if (typeof globalThis.registerVFSWorkerProxy === 'undefined') {
+        globalThis.registerVFSWorkerProxy = function(worker, asyncFS) {
+          let sab;
+          let statusArray;
+          let payloadArray;
+
+          worker.addEventListener('message', async function(e) {
+            if (!e.data) return;
+            if (e.data.type === 'INIT_SYNC_VFS') {
+              sab = e.data.buffer;
+              statusArray = new Int32Array(sab);
+              payloadArray = new Uint8Array(sab);
+              return;
+            }
+            if (e.data.type === 'SYNC_REQ') {
+              const cmd = statusArray[1];
+              const reqLen = statusArray[2];
+              const decoder = new TextDecoder();
+              const reqBytes = payloadArray.subarray(64, 64 + reqLen);
+              
+              try {
+                let result;
+                if (cmd === 1) { // exists
+                  const path = decoder.decode(reqBytes);
+                  const type = await asyncFS.type(path);
+                  result = type.toString() !== 'FileSystemEntityType.notFound';
+                  payloadArray[64] = result ? 1 : 0;
+                  statusArray[3] = 1;
+                } else if (cmd === 2) { // type
+                  const followLinks = reqBytes[0] === 1;
+                  const path = decoder.decode(reqBytes.subarray(1));
+                  const type = await asyncFS.type(path, { followLinks });
+                  const typeStr = type.toString().split('.').pop();
+                  const typeBytes = new TextEncoder().encode(typeStr);
+                  payloadArray.set(typeBytes, 64);
+                  statusArray[3] = typeBytes.length;
+                } else if (cmd === 3) { // readBytes
+                  const path = decoder.decode(reqBytes);
+                  const bytes = await asyncFS.file(path).readAsBytes();
+                  payloadArray.set(bytes, 64);
+                  statusArray[3] = bytes.length;
+                } else if (cmd === 4) { // writeBytes
+                  const view = new DataView(reqBytes.buffer, reqBytes.byteOffset, reqBytes.byteLength);
+                  const pathLen = view.getUint32(0, true);
+                  const path = decoder.decode(reqBytes.subarray(4, 4 + pathLen));
+                  const content = reqBytes.subarray(4 + pathLen);
+                  await asyncFS.file(path).writeAsBytes(content);
+                  statusArray[3] = 0;
+                } else if (cmd === 5) { // createDir
+                  const path = decoder.decode(reqBytes);
+                  await asyncFS.directory(path).create(recursive: true);
+                  statusArray[3] = 0;
+                } else if (cmd === 6) { // delete
+                  const path = decoder.decode(reqBytes);
+                  await asyncFS.file(path).delete(recursive: true);
+                  statusArray[3] = 0;
+                } else if (cmd === 7) { // createLink
+                  const view = new DataView(reqBytes.buffer, reqBytes.byteOffset, reqBytes.byteLength);
+                  const pathLen = view.getUint32(0, true);
+                  const path = decoder.decode(reqBytes.subarray(4, 4 + pathLen));
+                  const target = decoder.decode(reqBytes.subarray(4 + pathLen));
+                  await asyncFS.link(path).create(target);
+                  statusArray[3] = 0;
+                } else if (cmd === 8) { // readLink
+                  const path = decoder.decode(reqBytes);
+                  const target = await asyncFS.link(path).target();
+                  const targetBytes = new TextEncoder().encode(target);
+                  payloadArray.set(targetBytes, 64);
+                  statusArray[3] = targetBytes.length;
+                } else if (cmd === 9) { // stat
+                  const path = decoder.decode(reqBytes);
+                  const stat = await asyncFS.stat(path);
+                  const statData = {
+                    type: stat.type.toString().split('.').pop(),
+                    size: stat.size,
+                    modified: stat.modified.millisecondsSinceEpoch
+                  };
+                  const statBytes = new TextEncoder().encode(JSON.stringify(statData));
+                  payloadArray.set(statBytes, 64);
+                  statusArray[3] = statBytes.length;
+                } else if (cmd === 10) { // list
+                  const path = decoder.decode(reqBytes);
+                  const list = await asyncFS.directory(path).list(recursive: false, followLinks: false).toList();
+                  const entities = list.map(e => ({
+                    path: e.path,
+                    type: e.runtimeType.toString().toLowerCase().replace('impl', '').replace('web', '')
+                  }));
+                  const listBytes = new TextEncoder().encode(JSON.stringify(entities));
+                  payloadArray.set(listBytes, 64);
+                  statusArray[3] = listBytes.length;
+                } else if (cmd === 11) { // resolveSymbolicLinks
+                  const path = decoder.decode(reqBytes);
+                  const resolved = await asyncFS.resolveSymbolicLinks(path);
+                  const resolvedBytes = new TextEncoder().encode(resolved);
+                  payloadArray.set(resolvedBytes, 64);
+                  statusArray[3] = resolvedBytes.length;
+                } else if (cmd === 12) { // rename
+                  const view = new DataView(reqBytes.buffer, reqBytes.byteOffset, reqBytes.byteLength);
+                  const pathLen = view.getUint32(0, true);
+                  const path = decoder.decode(reqBytes.subarray(4, 4 + pathLen));
+                  const newPath = decoder.decode(reqBytes.subarray(4 + pathLen));
+                  
+                  const inode = await asyncFS.resolvepath(path);
+                  const newParentDir = asyncFS.path.dirname(newPath);
+                  const newName = asyncFS.path.basename(newPath);
+                  const newParentInode = await asyncFS.resolvepath(newParentDir);
+                  
+                  inode.parentId = newParentInode.id;
+                  inode.name = newName;
+                  inode.modified = Date.now();
+                  await asyncFS.idb.updateInode(inode);
+                  statusArray[3] = 0;
+                } else if (cmd === 13) { // updateLink
+                  const view = new DataView(reqBytes.buffer, reqBytes.byteOffset, reqBytes.byteLength);
+                  const pathLen = view.getUint32(0, true);
+                  const path = decoder.decode(reqBytes.subarray(4, 4 + pathLen));
+                  const target = decoder.decode(reqBytes.subarray(4 + pathLen));
+                  await asyncFS.link(path).update(target);
+                  statusArray[3] = 0;
+                }
+                
+                Atomics.store(statusArray, 0, 2); // completed
+              } catch (err) {
+                console.error("VFS Proxy Error:", err);
+                const errBytes = new TextEncoder().encode(err.toString());
+                payloadArray.set(errBytes, 64);
+                statusArray[3] = errBytes.length;
+                Atomics.store(statusArray, 0, 3); // error
+              }
+              Atomics.notify(statusArray, 0);
+            }
+          });
+        };
+      }
+
+      if (typeof globalThis.initVFSSyncWorker === 'undefined') {
+        globalThis.isVFSSyncWorkerInitialized = false;
+        globalThis.initVFSSyncWorker = function() {
+          if (globalThis.isVFSSyncWorkerInitialized) return;
+          const sab = new SharedArrayBuffer(1024 * 1024 * 10); // 10MB
+          const statusArray = new Int32Array(sab);
+          const payloadArray = new Uint8Array(sab);
+          
+          globalThis.postMessage({ type: 'INIT_SYNC_VFS', buffer: sab });
+          
+          globalThis.sendVFSSyncRequest = function(cmd, requestBytes) {
+            while (Atomics.load(statusArray, 0) !== 0) {
+              // Idle wait
+            }
+            statusArray[1] = cmd;
+            statusArray[2] = requestBytes.length;
+            payloadArray.set(requestBytes, 64);
+            
+            Atomics.store(statusArray, 0, 1);
+            globalThis.postMessage({ type: 'SYNC_REQ' });
+            
+            Atomics.wait(statusArray, 0, 1);
+            
+            const status = Atomics.load(statusArray, 0);
+            const respLen = statusArray[3];
+            const respBytes = payloadArray.slice(64, 64 + respLen);
+            
+            Atomics.store(statusArray, 0, 0);
+            
+            if (status === 3) {
+              throw new Error(new TextDecoder().decode(respBytes));
+            }
+            return respBytes;
+          };
+          globalThis.isVFSSyncWorkerInitialized = true;
+        };
+      }
+    ''');
+  }
+
+  static void registerWorkerProxy(JSAny worker, JSAny asyncFS) {
+    injectHelperScripts();
+    _registerVFSWorkerProxy(worker, asyncFS);
+  }
+
+  static void initSyncWorker() {
+    injectHelperScripts();
+    _initVFSSyncWorker();
+  }
+
+  static Uint8List sendSyncRequest(int cmd, Uint8List requestBytes) {
+    if (_isVFSSyncWorkerInitialized != true) {
+      initSyncWorker();
+    }
+    return _sendVFSSyncRequest(cmd, requestBytes.toJS).toDart;
+  }
+}

experimental/web_file_system/lib/src/entities/web_directory.dart

@@ -1,4 +1,6 @@
 import 'dart:async';
+import 'dart:convert';
+import 'dart:typed_data';
 import 'package:file/file.dart';
 import 'package:web_file_system/src/backend/idb_inode_service.dart';
 import '../web_file_system.dart';
@@ -61,7 +63,27 @@ class WebDirectory extends FileSystemEntity implements Directory {
 
   @override
   void createSync({bool recursive = false}) {
-    throw UnsupportedError('Sync create not supported');
+    if (existsSync()) return;
+
+    final parentPath = _fs.path.dirname(path);
+    final parentType = _fs.typeSync(parentPath);
+    if (parentType == FileSystemEntityType.notFound) {
+      if (recursive) {
+        _fs.directory(parentPath).createSync(recursive: true);
+      } else {
+        throw FileSystemException(
+          'Cannot create directory, path = \'$path\' (OS Error: No such file or directory, errno = 2)',
+          path,
+        );
+      }
+    } else if (parentType != FileSystemEntityType.directory) {
+      throw FileSystemException(
+        'Cannot create directory, path = \'$path\' (OS Error: Not a directory, errno = 20)',
+        path,
+      );
+    }
+
+    _fs.makeSyncCall(5, utf8.encode(path));
   }
 
   @override
@@ -80,7 +102,15 @@ class WebDirectory extends FileSystemEntity implements Directory {
 
   @override
   Directory createTempSync([String? prefix]) {
-    throw UnsupportedError('Sync not supported');
+    if (!existsSync()) {
+      throw FileSystemException(
+          'Directory does not exist', path, const OSError('ENOENT', 2));
+    }
+    final name = (prefix ?? 'temp') + _fs.uuid.v4();
+    final tempDir = _fs.path.join(path, name);
+    final dir = WebDirectory(_fs, tempDir);
+    dir.createSync();
+    return dir;
   }
 
   @override
@@ -109,8 +139,34 @@ class WebDirectory extends FileSystemEntity implements Directory {
   }
 
   @override
-  void deleteSync({bool recursive = false}) =>
+  void deleteSync({bool recursive = false}) {
-      throw UnsupportedError('Sync not supported');
+    final type = _fs.typeSync(path, followLinks: false);
+    if (type == FileSystemEntityType.notFound) {
+      throw FileSystemException(
+        'Cannot delete directory, path = \'$path\' (OS Error: No such file or directory, errno = 2)',
+        path,
+      );
+    }
+    if (type != FileSystemEntityType.directory) {
+      throw FileSystemException(
+        'Cannot delete directory, path = \'$path\' (OS Error: Not a directory, errno = 20)',
+        path,
+      );
+    }
+
+    if (!recursive) {
+      final children = listSync(recursive: false, followLinks: false);
+      if (children.isNotEmpty) {
+        throw FileSystemException(
+          'Directory not empty',
+          path,
+          const OSError('ENOTEMPTY', 39),
+        );
+      }
+    }
+
+    _fs.makeSyncCall(6, utf8.encode(path));
+  }
 
   @override
   Future<bool> exists() async {
@@ -123,7 +179,9 @@ class WebDirectory extends FileSystemEntity implements Directory {
   }
 
   @override
-  bool existsSync() => throw UnsupportedError('Sync not supported');
+  bool existsSync() {
+    return _fs.typeSync(path, followLinks: false) == FileSystemEntityType.directory;
+  }
 
   @override
   Stream<FileSystemEntity> list(
@@ -173,7 +231,52 @@ class WebDirectory extends FileSystemEntity implements Directory {
   @override
   List<FileSystemEntity> listSync(
       {bool recursive = false, bool followLinks = true}) {
-    throw UnsupportedError('Sync list not supported');
+    if (!existsSync()) {
+      throw FileSystemException(
+          'Directory not found', path, const OSError('ENOENT', 2));
+    }
+
+    final respBytes = _fs.makeSyncCall(10, utf8.encode(path));
+    final listJson = json.decode(utf8.decode(respBytes)) as List<dynamic>;
+    
+    final List<FileSystemEntity> results = [];
+    for (final item in listJson) {
+      final itemMap = item as Map<String, dynamic>;
+      final childPath = itemMap['path'] as String;
+      final typeStr = itemMap['type'] as String;
+      
+      if (typeStr == 'directory') {
+        final dir = WebDirectory(_fs, childPath);
+        results.add(dir);
+        if (recursive) {
+          results.addAll(dir.listSync(recursive: true, followLinks: followLinks));
+        }
+      } else if (typeStr == 'link') {
+        if (!followLinks) {
+          results.add(WebLink(_fs, childPath));
+        } else {
+          try {
+            final resolvedType = _fs.typeSync(childPath, followLinks: true);
+            if (resolvedType == FileSystemEntityType.directory) {
+              final dir = WebDirectory(_fs, childPath);
+              results.add(dir);
+              if (recursive) {
+                results.addAll(dir.listSync(recursive: true, followLinks: true));
+              }
+            } else if (resolvedType == FileSystemEntityType.notFound) {
+              results.add(WebLink(_fs, childPath));
+            } else {
+              results.add(WebFile(_fs, childPath));
+            }
+          } catch (_) {
+            results.add(WebLink(_fs, childPath));
+          }
+        }
+      } else {
+        results.add(WebFile(_fs, childPath));
+      }
+    }
+    return results;
   }
 
   @override
@@ -198,8 +301,33 @@ class WebDirectory extends FileSystemEntity implements Directory {
   }
 
   @override
-  Directory renameSync(String newPath) =>
+  Directory renameSync(String newPath) {
-      throw UnsupportedError('Sync not supported');
+    final type = _fs.typeSync(path, followLinks: false);
+    if (type == FileSystemEntityType.notFound) {
+      throw FileSystemException(
+        'Cannot rename directory, path = \'$path\' (OS Error: No such file or directory, errno = 2)',
+        path,
+      );
+    }
+    final newParentDir = _fs.path.dirname(newPath);
+    if (_fs.typeSync(newParentDir) != FileSystemEntityType.directory) {
+      throw FileSystemException(
+        'Cannot rename directory, path = \'$path\' (OS Error: No such file or directory, errno = 2)',
+        path,
+      );
+    }
+
+    final pathBytes = utf8.encode(path);
+    final newPathBytes = utf8.encode(newPath);
+    final request = Uint8List(4 + pathBytes.length + newPathBytes.length);
+    final bd = ByteData.sublistView(request);
+    bd.setUint32(0, pathBytes.length, Endian.little);
+    request.setRange(4, 4 + pathBytes.length, pathBytes);
+    request.setRange(4 + pathBytes.length, request.length, newPathBytes);
+
+    _fs.makeSyncCall(12, request);
+    return WebDirectory(_fs, newPath);
+  }
 
   @override
   String get basename => _fs.path.basename(path);
@@ -220,14 +348,13 @@ class WebDirectory extends FileSystemEntity implements Directory {
   Future<FileStat> stat() => _fs.stat(path);
 
   @override
-  FileStat statSync() => throw UnsupportedError('Sync not supported');
+  FileStat statSync() => _fs.statSync(path);
 
   @override
   Future<String> resolveSymbolicLinks() => _fs.resolveSymbolicLinks(path);
 
   @override
-  String resolveSymbolicLinksSync() =>
+  String resolveSymbolicLinksSync() => _fs.resolveSymbolicLinksSync(path);
-      throw UnsupportedError('Sync not supported');
 
   @override
   Stream<FileSystemEvent> watch(

experimental/web_file_system/lib/src/entities/web_file.dart

@@ -52,8 +52,38 @@ class WebFile extends FileSystemEntity implements File {
   }
 
   @override
-  void createSync({bool recursive = false, bool exclusive = false}) =>
+  void createSync({bool recursive = false, bool exclusive = false}) {
-      throw UnsupportedError('Sync not supported');
+    if (existsSync()) {
+      if (exclusive) {
+        throw FileSystemException(
+          'File already exists',
+          path,
+          const OSError('EEXIST', 17),
+        );
+      }
+      return;
+    }
+
+    final parentPath = _fs.path.dirname(path);
+    final parentType = _fs.typeSync(parentPath);
+    if (parentType == FileSystemEntityType.notFound) {
+      if (recursive) {
+        _fs.directory(parentPath).createSync(recursive: true);
+      } else {
+        throw FileSystemException(
+          'Cannot create file, path = \'$path\' (OS Error: No such file or directory, errno = 2)',
+          path,
+        );
+      }
+    } else if (parentType != FileSystemEntityType.directory) {
+      throw FileSystemException(
+        'Cannot create file, path = \'$path\' (OS Error: Not a directory, errno = 20)',
+        path,
+      );
+    }
+
+    writeAsBytesSync([]);
+  }
 
   @override
   Future<File> copy(String newPath) async {
@@ -76,7 +106,11 @@ class WebFile extends FileSystemEntity implements File {
   }
 
   @override
-  File copySync(String newPath) => throw UnsupportedError('Sync not supported');
+  File copySync(String newPath) {
+    final bytes = readAsBytesSync();
+    _fs.file(newPath).writeAsBytesSync(bytes);
+    return WebFile(_fs, newPath);
+  }
 
   @override
   Future<int> length() async {
@@ -85,7 +119,7 @@ class WebFile extends FileSystemEntity implements File {
   }
 
   @override
-  int lengthSync() => throw UnsupportedError('Sync not supported');
+  int lengthSync() => statSync().size;
 
   @override
   Future<DateTime> lastModified() async {
@@ -94,7 +128,7 @@ class WebFile extends FileSystemEntity implements File {
   }
 
   @override
-  DateTime lastModifiedSync() => throw UnsupportedError('Sync not supported');
+  DateTime lastModifiedSync() => statSync().modified;
 
   @override
   Future<DateTime> lastAccessed() async {
@@ -102,7 +136,7 @@ class WebFile extends FileSystemEntity implements File {
   }
 
   @override
-  DateTime lastAccessedSync() => throw UnsupportedError('Sync not supported');
+  DateTime lastAccessedSync() => statSync().accessed;
 
   @override
   Future<dynamic> setLastAccessed(DateTime time) async {}
@@ -190,7 +224,27 @@ class WebFile extends FileSystemEntity implements File {
     FileMode mode = FileMode.write,
     bool flush = false,
   }) {
-    throw UnsupportedError('Sync not supported');
+    if (mode == FileMode.append) {
+      throw UnsupportedError('Append not yet optimized');
+    }
+    
+    final parentPath = _fs.path.dirname(path);
+    if (_fs.typeSync(parentPath) != FileSystemEntityType.directory) {
+      throw FileSystemException(
+        'Cannot open file, path = \'$path\' (OS Error: No such file or directory, errno = 2)',
+        path,
+      );
+    }
+
+    final pathBytes = utf8.encode(path);
+    final pathLen = pathBytes.length;
+    final request = Uint8List(4 + pathLen + bytes.length);
+    final bd = ByteData.sublistView(request);
+    bd.setUint32(0, pathLen, Endian.little);
+    request.setRange(4, 4 + pathLen, pathBytes);
+    request.setRange(4 + pathLen, request.length, bytes);
+
+    _fs.makeSyncCall(4, request);
   }
 
   @override
@@ -210,7 +264,7 @@ class WebFile extends FileSystemEntity implements File {
     Encoding encoding = utf8,
     bool flush = false,
   }) {
-    throw UnsupportedError('Sync not supported');
+    writeAsBytesSync(encoding.encode(contents), mode: mode, flush: flush);
   }
 
   @override
@@ -280,7 +334,22 @@ class WebFile extends FileSystemEntity implements File {
   }
 
   @override
-  Uint8List readAsBytesSync() => throw UnsupportedError('Sync not supported');
+  Uint8List readAsBytesSync() {
+    final type = _fs.typeSync(path);
+    if (type == FileSystemEntityType.notFound) {
+      throw FileSystemException(
+        'Cannot open file, path = \'$path\' (OS Error: No such file or directory, errno = 2)',
+        path,
+      );
+    }
+    if (type == FileSystemEntityType.directory) {
+      throw FileSystemException(
+        'Cannot open file, path = \'$path\' (OS Error: Is a directory, errno = 21)',
+        path,
+      );
+    }
+    return _fs.makeSyncCall(3, utf8.encode(path));
+  }
 
   @override
   Future<String> readAsString({Encoding encoding = utf8}) async {
@@ -289,18 +358,21 @@ class WebFile extends FileSystemEntity implements File {
   }
 
   @override
-  String readAsStringSync({Encoding encoding = utf8}) =>
+  String readAsStringSync({Encoding encoding = utf8}) {
-      throw UnsupportedError('Sync not supported');
+    return encoding.decode(readAsBytesSync());
+  }
 
   @override
   Future<List<String>> readAsLines({Encoding encoding = utf8}) async {
     final str = await readAsString(encoding: encoding);
-    return str.split('\n');
+    return const LineSplitter().convert(str);
   }
 
   @override
-  List<String> readAsLinesSync({Encoding encoding = utf8}) =>
+  List<String> readAsLinesSync({Encoding encoding = utf8}) {
-      throw UnsupportedError('Sync not supported');
+    final str = readAsStringSync(encoding: encoding);
+    return const LineSplitter().convert(str);
+  }
 
   @override
   Future<bool> exists() async {
@@ -313,7 +385,9 @@ class WebFile extends FileSystemEntity implements File {
   }
 
   @override
-  bool existsSync() => throw UnsupportedError('Sync not supported');
+  bool existsSync() {
+    return _fs.typeSync(path, followLinks: false) == FileSystemEntityType.file;
+  }
 
   @override
   Future<File> rename(String newPath) async {
@@ -337,8 +411,33 @@ class WebFile extends FileSystemEntity implements File {
   }
 
   @override
-  File renameSync(String newPath) =>
+  File renameSync(String newPath) {
-      throw UnsupportedError('Sync not supported');
+    final type = _fs.typeSync(path, followLinks: false);
+    if (type == FileSystemEntityType.notFound) {
+      throw FileSystemException(
+        'Cannot rename file, path = \'$path\' (OS Error: No such file or directory, errno = 2)',
+        path,
+      );
+    }
+    final newParentDir = _fs.path.dirname(newPath);
+    if (_fs.typeSync(newParentDir) != FileSystemEntityType.directory) {
+      throw FileSystemException(
+        'Cannot rename file, path = \'$path\' (OS Error: No such file or directory, errno = 2)',
+        path,
+      );
+    }
+
+    final pathBytes = utf8.encode(path);
+    final newPathBytes = utf8.encode(newPath);
+    final request = Uint8List(4 + pathBytes.length + newPathBytes.length);
+    final bd = ByteData.sublistView(request);
+    bd.setUint32(0, pathBytes.length, Endian.little);
+    request.setRange(4, 4 + pathBytes.length, pathBytes);
+    request.setRange(4 + pathBytes.length, request.length, newPathBytes);
+
+    _fs.makeSyncCall(12, request);
+    return WebFile(_fs, newPath);
+  }
 
   @override
   Future<FileSystemEntity> delete({bool recursive = false}) async {
@@ -348,14 +447,22 @@ class WebFile extends FileSystemEntity implements File {
   }
 
   @override
-  void deleteSync({bool recursive = false}) =>
+  void deleteSync({bool recursive = false}) {
-      throw UnsupportedError('Sync not supported');
+    final type = _fs.typeSync(path, followLinks: false);
+    if (type == FileSystemEntityType.notFound) {
+      throw FileSystemException(
+        'Cannot delete file, path = \'$path\' (OS Error: No such file or directory, errno = 2)',
+        path,
+      );
+    }
+    _fs.makeSyncCall(6, utf8.encode(path));
+  }
 
   @override
   Future<FileStat> stat() => _fs.stat(path);
 
   @override
-  FileStat statSync() => throw UnsupportedError('Sync not supported');
+  FileStat statSync() => _fs.statSync(path);
 
   @override
   Uri get uri => Uri.parse(path);
@@ -374,8 +481,7 @@ class WebFile extends FileSystemEntity implements File {
   Future<String> resolveSymbolicLinks() => _fs.resolveSymbolicLinks(path);
 
   @override
-  String resolveSymbolicLinksSync() =>
+  String resolveSymbolicLinksSync() => _fs.resolveSymbolicLinksSync(path);
-      throw UnsupportedError('Sync not supported');
 
   @override
   Stream<FileSystemEvent> watch({

experimental/web_file_system/lib/src/entities/web_link.dart

@@ -1,5 +1,6 @@
 import 'dart:async';
 import 'dart:convert';
+import 'dart:typed_data';
 import 'package:file/file.dart';
 import 'package:web_file_system/src/backend/idb_inode_service.dart';
 import '../web_file_system.dart';
@@ -57,7 +58,41 @@ class WebLink extends FileSystemEntity implements Link {
 
   @override
   void createSync(String target, {bool recursive = false}) {
-    throw UnsupportedError('Sync not supported');
+    if (existsSync()) {
+      throw FileSystemException(
+        'Link already exists',
+        path,
+        const OSError('EEXIST', 17),
+      );
+    }
+
+    final parentPath = _fs.path.dirname(path);
+    final parentType = _fs.typeSync(parentPath);
+    if (parentType == FileSystemEntityType.notFound) {
+      if (recursive) {
+        _fs.directory(parentPath).createSync(recursive: true);
+      } else {
+        throw FileSystemException(
+          'Cannot create link, path = \'$path\' (OS Error: No such file or directory, errno = 2)',
+          path,
+        );
+      }
+    } else if (parentType != FileSystemEntityType.directory) {
+      throw FileSystemException(
+        'Cannot create link, path = \'$path\' (OS Error: Not a directory, errno = 20)',
+        path,
+      );
+    }
+
+    final pathBytes = utf8.encode(path);
+    final targetBytes = utf8.encode(target);
+    final request = Uint8List(4 + pathBytes.length + targetBytes.length);
+    final bd = ByteData.sublistView(request);
+    bd.setUint32(0, pathBytes.length, Endian.little);
+    request.setRange(4, 4 + pathBytes.length, pathBytes);
+    request.setRange(4 + pathBytes.length, request.length, targetBytes);
+
+    _fs.makeSyncCall(7, request);
   }
 
   @override
@@ -85,7 +120,30 @@ class WebLink extends FileSystemEntity implements Link {
 
   @override
   void updateSync(String target) {
-    throw UnsupportedError('Sync not supported');
+    final type = _fs.typeSync(path, followLinks: false);
+    if (type == FileSystemEntityType.notFound) {
+      throw FileSystemException(
+        'Cannot update link, path = \'$path\' (OS Error: No such file or directory, errno = 2)',
+        path,
+      );
+    }
+    if (type != FileSystemEntityType.link) {
+      throw FileSystemException(
+        'Not a link',
+        path,
+        const OSError('EINVAL', 22),
+      );
+    }
+
+    final pathBytes = utf8.encode(path);
+    final targetBytes = utf8.encode(target);
+    final request = Uint8List(4 + pathBytes.length + targetBytes.length);
+    final bd = ByteData.sublistView(request);
+    bd.setUint32(0, pathBytes.length, Endian.little);
+    request.setRange(4, 4 + pathBytes.length, pathBytes);
+    request.setRange(4 + pathBytes.length, request.length, targetBytes);
+
+    _fs.makeSyncCall(13, request);
   }
 
   @override
@@ -107,7 +165,22 @@ class WebLink extends FileSystemEntity implements Link {
 
   @override
   String targetSync() {
-    throw UnsupportedError('Sync not supported');
+    final type = _fs.typeSync(path, followLinks: false);
+    if (type == FileSystemEntityType.notFound) {
+      throw FileSystemException(
+        'Cannot read link, path = \'$path\' (OS Error: No such file or directory, errno = 2)',
+        path,
+      );
+    }
+    if (type != FileSystemEntityType.link) {
+      throw FileSystemException(
+        'Not a link',
+        path,
+        const OSError('EINVAL', 22),
+      );
+    }
+    final respBytes = _fs.makeSyncCall(8, utf8.encode(path));
+    return utf8.decode(respBytes);
   }
 
   @override
@@ -132,8 +205,33 @@ class WebLink extends FileSystemEntity implements Link {
   }
 
   @override
-  Link renameSync(String newPath) =>
+  Link renameSync(String newPath) {
-      throw UnsupportedError('Sync not supported');
+    final type = _fs.typeSync(path, followLinks: false);
+    if (type == FileSystemEntityType.notFound) {
+      throw FileSystemException(
+        'Cannot rename link, path = \'$path\' (OS Error: No such file or directory, errno = 2)',
+        path,
+      );
+    }
+    final newParentDir = _fs.path.dirname(newPath);
+    if (_fs.typeSync(newParentDir) != FileSystemEntityType.directory) {
+      throw FileSystemException(
+        'Cannot rename link, path = \'$path\' (OS Error: No such file or directory, errno = 2)',
+        path,
+      );
+    }
+
+    final pathBytes = utf8.encode(path);
+    final newPathBytes = utf8.encode(newPath);
+    final request = Uint8List(4 + pathBytes.length + newPathBytes.length);
+    final bd = ByteData.sublistView(request);
+    bd.setUint32(0, pathBytes.length, Endian.little);
+    request.setRange(4, 4 + pathBytes.length, pathBytes);
+    request.setRange(4 + pathBytes.length, request.length, newPathBytes);
+
+    _fs.makeSyncCall(12, request);
+    return WebLink(_fs, newPath);
+  }
 
   @override
   Future<FileSystemEntity> delete({bool recursive = false}) async {
@@ -143,8 +241,16 @@ class WebLink extends FileSystemEntity implements Link {
   }
 
   @override
-  void deleteSync({bool recursive = false}) =>
+  void deleteSync({bool recursive = false}) {
-      throw UnsupportedError('Sync not supported');
+    final type = _fs.typeSync(path, followLinks: false);
+    if (type == FileSystemEntityType.notFound) {
+      throw FileSystemException(
+        'Cannot delete link, path = \'$path\' (OS Error: No such file or directory, errno = 2)',
+        path,
+      );
+    }
+    _fs.makeSyncCall(6, utf8.encode(path));
+  }
 
   @override
   Future<bool> exists() async {
@@ -157,13 +263,15 @@ class WebLink extends FileSystemEntity implements Link {
   }
 
   @override
-  bool existsSync() => throw UnsupportedError('Sync not supported');
+  bool existsSync() {
+    return _fs.typeSync(path, followLinks: false) == FileSystemEntityType.link;
+  }
 
   @override
   Future<FileStat> stat() async => (await _fs.stat(path));
 
   @override
-  FileStat statSync() => throw UnsupportedError('Sync not supported');
+  FileStat statSync() => _fs.statSync(path);
 
   @override
   Uri get uri => Uri.parse(path);
@@ -187,8 +295,7 @@ class WebLink extends FileSystemEntity implements Link {
   Future<String> resolveSymbolicLinks() => _fs.resolveSymbolicLinks(path);
 
   @override
-  String resolveSymbolicLinksSync() =>
+  String resolveSymbolicLinksSync() => _fs.resolveSymbolicLinksSync(path);
-      throw UnsupportedError('Sync not supported');
 
   @override
   Stream<FileSystemEvent> watch({

experimental/web_file_system/lib/src/web_file_system.dart

@@ -1,10 +1,13 @@
 import 'dart:async';
 import 'dart:convert';
+import 'dart:typed_data';
+import 'dart:js_interop';
 import 'package:file/file.dart';
 import 'package:path/path.dart' as p;
 import 'package:uuid/uuid.dart';
 import 'package:web_file_system/src/backend/idb_inode_service.dart';
 import 'package:web_file_system/src/backend/opfs_block_store.dart';
+import 'package:web_file_system/src/backend/sync_rpc_helper.dart';
 import 'entities/web_directory.dart';
 import 'entities/web_file.dart';
 import 'entities/web_link.dart';
@@ -60,9 +63,43 @@ class WebFileSystem extends FileSystem {
     }
   }
 
+  static void registerWorkerProxy(dynamic worker, WebFileSystem fs) {
+    SyncRpcHelper.registerWorkerProxy(worker as JSAny, fs as JSAny);
+  }
+
+  Uint8List makeSyncCall(int cmd, Uint8List request) {
+    if (!SyncRpcHelper.isWorker) {
+      throw UnsupportedError('Synchronous operations are only supported inside Web Workers.');
+    }
+    if (!SyncRpcHelper.isSharedArrayBufferSupported) {
+      throw StateError('SharedArrayBuffer is not supported. Ensure your site is cross-origin isolated with COOP/COEP headers.');
+    }
+    return SyncRpcHelper.sendSyncRequest(cmd, request);
+  }
+
   @override
   FileSystemEntityType typeSync(String path, {bool followLinks = true}) {
-    throw UnsupportedError('Sync type not supported');
+    if (!SyncRpcHelper.isWorker) {
+      throw UnsupportedError('Synchronous operations are only supported inside Web Workers.');
+    }
+    if (!SyncRpcHelper.isSharedArrayBufferSupported) {
+      throw StateError('SharedArrayBuffer is not supported. Ensure your site is cross-origin isolated with COOP/COEP headers.');
+    }
+    try {
+      final pathBytes = utf8.encode(path);
+      final payload = Uint8List(pathBytes.length + 1);
+      payload[0] = followLinks ? 1 : 0;
+      payload.setRange(1, payload.length, pathBytes);
+      
+      final respBytes = makeSyncCall(2, payload);
+      final typeStr = utf8.decode(respBytes);
+      if (typeStr == 'file') return FileSystemEntityType.file;
+      if (typeStr == 'directory') return FileSystemEntityType.directory;
+      if (typeStr == 'link') return FileSystemEntityType.link;
+      return FileSystemEntityType.notFound;
+    } catch (_) {
+      return FileSystemEntityType.notFound;
+    }
   }
 
   // Internal Resolution Logic
@@ -176,7 +213,34 @@ class WebFileSystem extends FileSystem {
 
   @override
   FileStat statSync(String path) {
-    throw UnsupportedError('Sync stat not supported');
+    if (!SyncRpcHelper.isWorker) {
+      throw UnsupportedError('Synchronous operations are only supported inside Web Workers.');
+    }
+    if (!SyncRpcHelper.isSharedArrayBufferSupported) {
+      throw StateError('SharedArrayBuffer is not supported. Ensure your site is cross-origin isolated with COOP/COEP headers.');
+    }
+    try {
+      final respBytes = makeSyncCall(9, utf8.encode(path));
+      final statMap = json.decode(utf8.decode(respBytes)) as Map<String, dynamic>;
+      final typeStr = statMap['type'] as String;
+      final size = statMap['size'] as int;
+      final modified = statMap['modified'] as int;
+      
+      FileSystemEntityType type;
+      if (typeStr == 'file') {
+        type = FileSystemEntityType.file;
+      } else if (typeStr == 'directory') {
+        type = FileSystemEntityType.directory;
+      } else if (typeStr == 'link') {
+        type = FileSystemEntityType.link;
+      } else {
+        type = FileSystemEntityType.notFound;
+      }
+      
+      return FileStatImpl(modified, size, type);
+    } catch (_) {
+      return FileStatImpl(0, 0, FileSystemEntityType.notFound);
+    }
   }
 
   FileSystemEntityType _getType(int nodeType) {
@@ -188,15 +252,15 @@ class WebFileSystem extends FileSystem {
 
   @override
   bool isFileSync(String path) =>
-      throw UnsupportedError('Sync isFile not supported');
+      typeSync(path) == FileSystemEntityType.file;
 
   @override
   bool isDirectorySync(String path) =>
-      throw UnsupportedError('Sync isDirectory not supported');
+      typeSync(path) == FileSystemEntityType.directory;
 
   @override
   bool isLinkSync(String path) =>
-      throw UnsupportedError('Sync isLink not supported');
+      typeSync(path, followLinks: false) == FileSystemEntityType.link;
 
   @override
   Future<bool> isFile(String path) async =>
@@ -226,8 +290,15 @@ class WebFileSystem extends FileSystem {
   }
 
   @override
-  bool identicalSync(String path1, String path2) =>
+  bool identicalSync(String path1, String path2) {
-      throw UnsupportedError('Sync not supported');
+    try {
+      final r1 = resolveSymbolicLinksSync(path1);
+      final r2 = resolveSymbolicLinksSync(path2);
+      return r1 == r2;
+    } catch (_) {
+      return false;
+    }
+  }
 
   Future<String> resolveSymbolicLinks(String pathStr) async {
     final inode = await resolvepath(pathStr, followLinks: true);
@@ -240,6 +311,11 @@ class WebFileSystem extends FileSystem {
     if (segments.isEmpty) return '/';
     return '/' + segments.reversed.join('/');
   }
+
+  String resolveSymbolicLinksSync(String pathStr) {
+    final respBytes = makeSyncCall(11, utf8.encode(pathStr));
+    return utf8.decode(respBytes);
+  }
 }
 
 class FileStatImpl implements FileStat {

experimental/web_file_system/pubspec.lock

@@ -0,0 +1,406 @@
+# Generated by pub
+# See https://dart.dev/tools/pub/glossary#lockfile
+packages:
+  _fe_analyzer_shared:
+    dependency: transitive
+    description:
+      name: _fe_analyzer_shared
+      sha256: "563c6992eaeda8625f45b87f6a6a0c547df16565d1c93d8271c7c11057710ca7"
+      url: "https://pub.dev"
+    source: hosted
+    version: "101.0.0"
+  analyzer:
+    dependency: transitive
+    description:
+      name: analyzer
+      sha256: aa6a9365901532864cae51208f2a6bb18dd01972ebead19c431efc848f60080b
+      url: "https://pub.dev"
+    source: hosted
+    version: "13.1.0"
+  args:
+    dependency: transitive
+    description:
+      name: args
+      sha256: d0481093c50b1da8910eb0bb301626d4d8eb7284aa739614d2b394ee09e3ea04
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.7.0"
+  async:
+    dependency: transitive
+    description:
+      name: async
+      sha256: e2eb0491ba5ddb6177742d2da23904574082139b07c1e33b8503b9f46f3e1a37
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.13.1"
+  boolean_selector:
+    dependency: transitive
+    description:
+      name: boolean_selector
+      sha256: "8aab1771e1243a5063b8b0ff68042d67334e3feab9e95b9490f9a6ebf73b42ea"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.1.2"
+  cli_config:
+    dependency: transitive
+    description:
+      name: cli_config
+      sha256: ac20a183a07002b700f0c25e61b7ee46b23c309d76ab7b7640a028f18e4d99ec
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.2.0"
+  collection:
+    dependency: transitive
+    description:
+      name: collection
+      sha256: "2f5709ae4d3d59dd8f7cd309b4e023046b57d8a6c82130785d2b0e5868084e76"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.19.1"
+  convert:
+    dependency: transitive
+    description:
+      name: convert
+      sha256: b30acd5944035672bc15c6b7a8b47d773e41e2f17de064350988c5d02adb1c68
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.1.2"
+  coverage:
+    dependency: transitive
+    description:
+      name: coverage
+      sha256: "5da775aa218eaf2151c721b16c01c7676fbfdd99cebba2bf64e8b807a28ff94d"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.15.0"
+  crypto:
+    dependency: transitive
+    description:
+      name: crypto
+      sha256: c8ea0233063ba03258fbcf2ca4d6dadfefe14f02fab57702265467a19f27fadf
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.0.7"
+  file:
+    dependency: "direct main"
+    description:
+      name: file
+      sha256: a3b4f84adafef897088c160faf7dfffb7696046cb13ae90b508c2cbc95d3b8d4
+      url: "https://pub.dev"
+    source: hosted
+    version: "7.0.1"
+  fixnum:
+    dependency: transitive
+    description:
+      name: fixnum
+      sha256: b6dc7065e46c974bc7c5f143080a6764ec7a4be6da1285ececdc37be96de53be
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.1.1"
+  frontend_server_client:
+    dependency: transitive
+    description:
+      name: frontend_server_client
+      sha256: f64a0333a82f30b0cca061bc3d143813a486dc086b574bfb233b7c1372427694
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.0.0"
+  glob:
+    dependency: transitive
+    description:
+      name: glob
+      sha256: c3f1ee72c96f8f78935e18aa8cecced9ab132419e8625dc187e1c2408efc20de
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.1.3"
+  http_multi_server:
+    dependency: transitive
+    description:
+      name: http_multi_server
+      sha256: aa6199f908078bb1c5efb8d8638d4ae191aac11b311132c3ef48ce352fb52ef8
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.2.2"
+  http_parser:
+    dependency: transitive
+    description:
+      name: http_parser
+      sha256: "178d74305e7866013777bab2c3d8726205dc5a4dd935297175b19a23a2e66571"
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.1.2"
+  io:
+    dependency: transitive
+    description:
+      name: io
+      sha256: dfd5a80599cf0165756e3181807ed3e77daf6dd4137caaad72d0b7931597650b
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.0.5"
+  lints:
+    dependency: "direct dev"
+    description:
+      name: lints
+      sha256: "12f842a479589fea194fe5c5a3095abc7be0c1f2ddfa9a0e76aed1dbd26a87df"
+      url: "https://pub.dev"
+    source: hosted
+    version: "6.1.0"
+  logging:
+    dependency: transitive
+    description:
+      name: logging
+      sha256: c8245ada5f1717ed44271ed1c26b8ce85ca3228fd2ffdb75468ab01979309d61
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.3.0"
+  matcher:
+    dependency: transitive
+    description:
+      name: matcher
+      sha256: "31bd099b47c10cd1aeb55146a2d46ce0277630ecef3f7dae54ad7873f36696cd"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.12.20"
+  meta:
+    dependency: transitive
+    description:
+      name: meta
+      sha256: c82594181e3312f3d0695fc95aaaf7758d75b8d4ae2bbecf223b9fd5109a059d
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.18.3"
+  mime:
+    dependency: "direct main"
+    description:
+      name: mime
+      sha256: "801fd0b26f14a4a58ccb09d5892c3fbdeff209594300a542492cf13fba9d247a"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.0.6"
+  node_preamble:
+    dependency: transitive
+    description:
+      name: node_preamble
+      sha256: "6e7eac89047ab8a8d26cf16127b5ed26de65209847630400f9aefd7cd5c730db"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.0.2"
+  package_config:
+    dependency: transitive
+    description:
+      name: package_config
+      sha256: f096c55ebb7deb7e384101542bfba8c52696c1b56fca2eb62827989ef2353bbc
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.2.0"
+  path:
+    dependency: "direct main"
+    description:
+      name: path
+      sha256: "75cca69d1490965be98c73ceaea117e8a04dd21217b37b292c9ddbec0d955bc5"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.9.1"
+  pool:
+    dependency: transitive
+    description:
+      name: pool
+      sha256: "978783255c543aa3586a1b3c21f6e9d720eb315376a915872c61ef8b5c20177d"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.5.2"
+  pub_semver:
+    dependency: transitive
+    description:
+      name: pub_semver
+      sha256: "5bfcf68ca79ef689f8990d1160781b4bad40a3bd5e5218ad4076ddb7f4081585"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.2.0"
+  shelf:
+    dependency: transitive
+    description:
+      name: shelf
+      sha256: e7dd780a7ffb623c57850b33f43309312fc863fb6aa3d276a754bb299839ef12
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.4.2"
+  shelf_packages_handler:
+    dependency: transitive
+    description:
+      name: shelf_packages_handler
+      sha256: "89f967eca29607c933ba9571d838be31d67f53f6e4ee15147d5dc2934fee1b1e"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.0.2"
+  shelf_static:
+    dependency: transitive
+    description:
+      name: shelf_static
+      sha256: c87c3875f91262785dade62d135760c2c69cb217ac759485334c5857ad89f6e3
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.1.3"
+  shelf_web_socket:
+    dependency: transitive
+    description:
+      name: shelf_web_socket
+      sha256: "3632775c8e90d6c9712f883e633716432a27758216dfb61bd86a8321c0580925"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.0.0"
+  source_map_stack_trace:
+    dependency: transitive
+    description:
+      name: source_map_stack_trace
+      sha256: c0713a43e323c3302c2abe2a1cc89aa057a387101ebd280371d6a6c9fa68516b
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.1.2"
+  source_maps:
+    dependency: transitive
+    description:
+      name: source_maps
+      sha256: "190222579a448b03896e0ca6eca5998fa810fda630c1d65e2f78b3f638f54812"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.10.13"
+  source_span:
+    dependency: transitive
+    description:
+      name: source_span
+      sha256: "56a02f1f4cd1a2d96303c0144c93bd6d909eea6bee6bf5a0e0b685edbd4c47ab"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.10.2"
+  stack_trace:
+    dependency: transitive
+    description:
+      name: stack_trace
+      sha256: "8b27215b45d22309b5cddda1aa2b19bdfec9df0e765f2de506401c071d38d1b1"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.12.1"
+  stream_channel:
+    dependency: transitive
+    description:
+      name: stream_channel
+      sha256: "969e04c80b8bcdf826f8f16579c7b14d780458bd97f56d107d3950fdbeef059d"
+      url: "https://pub.dev"
+    source: hosted
+    version: "2.1.4"
+  string_scanner:
+    dependency: transitive
+    description:
+      name: string_scanner
+      sha256: "921cd31725b72fe181906c6a94d987c78e3b98c2e205b397ea399d4054872b43"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.4.1"
+  term_glyph:
+    dependency: transitive
+    description:
+      name: term_glyph
+      sha256: "7f554798625ea768a7518313e58f83891c7f5024f88e46e7182a4558850a4b8e"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.2.2"
+  test:
+    dependency: "direct dev"
+    description:
+      name: test
+      sha256: ca578dc12bb8b2f40b67b7d3bd2fac4f31c01a6ff7130a14e2597b919934507f
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.31.1"
+  test_api:
+    dependency: transitive
+    description:
+      name: test_api
+      sha256: "2a122cbe059f8b610d3a5415f42e255b6c17b1f21eee1d960f31080237fb4f11"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.7.12"
+  test_core:
+    dependency: transitive
+    description:
+      name: test_core
+      sha256: d2e98ec12998368dc59ddd47ab709f2cd55acd6b66dc7db764455a44082f4bc5
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.6.18"
+  typed_data:
+    dependency: transitive
+    description:
+      name: typed_data
+      sha256: f9049c039ebfeb4cf7a7104a675823cd72dba8297f264b6637062516699fa006
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.4.0"
+  uuid:
+    dependency: "direct main"
+    description:
+      name: uuid
+      sha256: "1fef9e8e11e2991bb773070d4656b7bd5d850967a2456cfc83cf47925ba79489"
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.5.3"
+  vm_service:
+    dependency: transitive
+    description:
+      name: vm_service
+      sha256: "0016aef94fc66495ac78af5859181e3f3bf2026bd8eecc72b9565601e19ab360"
+      url: "https://pub.dev"
+    source: hosted
+    version: "15.2.0"
+  watcher:
+    dependency: transitive
+    description:
+      name: watcher
+      sha256: "1398c9f081a753f9226febe8900fce8f7d0a67163334e1c94a2438339d79d635"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.2.1"
+  web:
+    dependency: "direct main"
+    description:
+      name: web
+      sha256: "868d88a33d8a87b18ffc05f9f030ba328ffefba92d6c127917a2ba740f9cfe4a"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.1.1"
+  web_socket:
+    dependency: transitive
+    description:
+      name: web_socket
+      sha256: "34d64019aa8e36bf9842ac014bb5d2f5586ca73df5e4d9bf5c936975cae6982c"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.0.1"
+  web_socket_channel:
+    dependency: transitive
+    description:
+      name: web_socket_channel
+      sha256: d645757fb0f4773d602444000a8131ff5d48c9e47adfe9772652dd1a4f2d45c8
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.0.3"
+  webkit_inspection_protocol:
+    dependency: transitive
+    description:
+      name: webkit_inspection_protocol
+      sha256: "87d3f2333bb240704cd3f1c6b5b7acd8a10e7f0bc28c28dcf14e782014f4a572"
+      url: "https://pub.dev"
+    source: hosted
+    version: "1.2.1"
+  yaml:
+    dependency: transitive
+    description:
+      name: yaml
+      sha256: b9da305ac7c39faa3f030eccd175340f968459dae4af175130b3fc47e40d76ce
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.1.3"
+sdks:
+  dart: ">=3.11.0 <4.0.0"
+  flutter: ">=3.38.5"

experimental/web_file_system/test/web_file_system_test.dart

@@ -1,5 +1,6 @@
 @TestOn('browser')
 import 'dart:async';
+import 'dart:convert';
 import 'dart:typed_data';
 import 'dart:js_interop';
 import 'package:test/test.dart';
@@ -488,6 +489,493 @@ void main() {
       );
     });
   });
+
+  group('Sync API Mocking & Error Verification', () {
+    test('Synchronous APIs on main thread throw UnsupportedError', () {
+      final file = fs.file('/sync_main.txt');
+      expect(() => fs.typeSync('/sync_main.txt'), throwsA(isA<UnsupportedError>()));
+      expect(() => fs.statSync('/sync_main.txt'), throwsA(isA<UnsupportedError>()));
+      expect(() => fs.resolveSymbolicLinksSync('/sync_main.txt'), throwsA(isA<UnsupportedError>()));
+      expect(() => file.createSync(), throwsA(isA<UnsupportedError>()));
+      expect(() => file.writeAsBytesSync([1]), throwsA(isA<UnsupportedError>()));
+      expect(() => file.writeAsStringSync('a'), throwsA(isA<UnsupportedError>()));
+      expect(() => file.readAsBytesSync(), throwsA(isA<UnsupportedError>()));
+      expect(() => file.readAsStringSync(), throwsA(isA<UnsupportedError>()));
+      expect(() => file.readAsLinesSync(), throwsA(isA<UnsupportedError>()));
+      expect(() => file.existsSync(), throwsA(isA<UnsupportedError>()));
+      expect(() => file.renameSync('/sync_main_renamed.txt'), throwsA(isA<UnsupportedError>()));
+      expect(() => file.deleteSync(), throwsA(isA<UnsupportedError>()));
+      expect(() => file.statSync(), throwsA(isA<UnsupportedError>()));
+      
+      final dir = fs.directory('/sync_dir');
+      expect(() => dir.createSync(), throwsA(isA<UnsupportedError>()));
+      expect(() => dir.createTempSync(), throwsA(isA<UnsupportedError>()));
+      expect(() => dir.deleteSync(), throwsA(isA<UnsupportedError>()));
+      expect(() => dir.existsSync(), throwsA(isA<UnsupportedError>()));
+      expect(() => dir.listSync(), throwsA(isA<UnsupportedError>()));
+      expect(() => dir.renameSync('/sync_dir_renamed'), throwsA(isA<UnsupportedError>()));
+      expect(() => dir.statSync(), throwsA(isA<UnsupportedError>()));
+
+      final link = fs.link('/sync_link');
+      expect(() => link.createSync('/target'), throwsA(isA<UnsupportedError>()));
+      expect(() => link.updateSync('/new_target'), throwsA(isA<UnsupportedError>()));
+      expect(() => link.targetSync(), throwsA(isA<UnsupportedError>()));
+      expect(() => link.renameSync('/sync_link_renamed'), throwsA(isA<UnsupportedError>()));
+      expect(() => link.deleteSync(), throwsA(isA<UnsupportedError>()));
+      expect(() => link.existsSync(), throwsA(isA<UnsupportedError>()));
+      expect(() => link.statSync(), throwsA(isA<UnsupportedError>()));
+    });
+
+    group('Mock Worker Environment', () {
+      setUp(() {
+        setupSyncMockJS();
+      });
+
+      tearDown(() {
+        clearSyncMockJS();
+      });
+
+      test('typeSync calls cmd 2 and returns correct types', () {
+        setMockSyncResponse(utf8.encode('file'));
+        expect(fs.typeSync('/test_file'), equals(FileSystemEntityType.file));
+        expect(getLastSyncCmd(), equals(2));
+
+        setMockSyncResponse(utf8.encode('directory'));
+        expect(fs.typeSync('/test_dir'), equals(FileSystemEntityType.directory));
+
+        setMockSyncResponse(utf8.encode('link'));
+        expect(fs.typeSync('/test_link'), equals(FileSystemEntityType.link));
+
+        setMockSyncResponse(utf8.encode('notFound'));
+        expect(fs.typeSync('/not_found'), equals(FileSystemEntityType.notFound));
+      });
+
+      test('file read and write sync APIs', () {
+        // existsSync
+        setMockSyncResponse(utf8.encode('file'));
+        final file = fs.file('/sync_worker.txt');
+        expect(file.existsSync(), isTrue);
+        expect(getLastSyncCmd(), equals(2));
+
+        // writeAsBytesSync
+        setMockSyncResponse(utf8.encode('directory')); // parent typeSync
+        setMockSyncResponse([]); // writeBytes
+        file.writeAsBytesSync([10, 20, 30]);
+        expect(getLastSyncCmd(), equals(4));
+        final payload = getLastSyncPayload();
+        expect(payload, isNotNull);
+        // Request format: [pathLen (4)] + [pathBytes] + [bytes]
+        // path is '/sync_worker.txt' (length 16)
+        expect(payload![0], equals(16));
+        expect(payload.sublist(4, 20), equals(utf8.encode('/sync_worker.txt')));
+        expect(payload.sublist(20), equals([10, 20, 30]));
+
+        // writeAsStringSync
+        setMockSyncResponse(utf8.encode('directory')); // parent typeSync
+        setMockSyncResponse([]); // writeBytes
+        file.writeAsStringSync('abc');
+        expect(getLastSyncCmd(), equals(4));
+
+        // readAsBytesSync
+        setMockSyncResponse(utf8.encode('file')); // typeSync(path)
+        setMockSyncResponse([12, 34, 56]); // readBytes
+        expect(file.readAsBytesSync(), equals([12, 34, 56]));
+        expect(getLastSyncCmd(), equals(3));
+
+        // readAsStringSync
+        setMockSyncResponse(utf8.encode('file')); // typeSync(path)
+        setMockSyncResponse(utf8.encode('hello sync')); // readBytes
+        expect(file.readAsStringSync(), equals('hello sync'));
+
+        // readAsLinesSync
+        setMockSyncResponse(utf8.encode('file')); // typeSync(path)
+        setMockSyncResponse(utf8.encode('line1\nline2\r\nline3')); // readBytes
+        expect(file.readAsLinesSync(), equals(['line1', 'line2', 'line3']));
+
+        // deleteSync
+        setMockSyncResponse(utf8.encode('file')); // typeSync(path)
+        setMockSyncResponse([]); // delete
+        file.deleteSync();
+        expect(getLastSyncCmd(), equals(6));
+
+        // statSync
+        final statJson = json.encode({
+          'type': 'file',
+          'size': 1500,
+          'modified': 1718100000000,
+        });
+        setMockSyncResponse(utf8.encode(statJson));
+        final stat = file.statSync();
+        expect(getLastSyncCmd(), equals(9));
+        expect(stat.type, equals(FileSystemEntityType.file));
+        expect(stat.size, equals(1500));
+        expect(stat.modified.millisecondsSinceEpoch, equals(1718100000000));
+      });
+
+      test('directory sync APIs', () {
+        final dir = fs.directory('/sync_dir');
+
+        // createSync
+        setMockSyncResponse(utf8.encode('notFound')); // existsSync
+        setMockSyncResponse(utf8.encode('directory')); // parent typeSync
+        setMockSyncResponse([]); // createDir
+        dir.createSync();
+        expect(getLastSyncCmd(), equals(5));
+
+        // deleteSync
+        setMockSyncResponse(utf8.encode('directory')); // typeSync(path) inside deleteSync
+        setMockSyncResponse(utf8.encode('directory')); // typeSync(path) inside listSync -> existsSync
+        setMockSyncResponse(utf8.encode('[]')); // listSync
+        setMockSyncResponse([]); // delete
+        dir.deleteSync();
+        expect(getLastSyncCmd(), equals(6));
+
+        // listSync
+        final listData = json.encode([
+          {'path': '/sync_dir/file.txt', 'type': 'file'},
+          {'path': '/sync_dir/sub', 'type': 'directory'},
+          {'path': '/sync_dir/link', 'type': 'link'},
+        ]);
+        setMockSyncResponse(utf8.encode('directory')); // listSync -> existsSync
+        setMockSyncResponse(utf8.encode(listData)); // listSync
+        final list = dir.listSync(followLinks: false);
+        expect(getLastSyncCmd(), equals(10));
+        expect(list.length, equals(3));
+        expect(list[0], isA<File>());
+        expect(list[0].path, equals('/sync_dir/file.txt'));
+        expect(list[1], isA<Directory>());
+        expect(list[2], isA<Link>());
+      });
+
+      test('link sync APIs', () {
+        final link = fs.link('/sync_link');
+
+        // createSync
+        setMockSyncResponse(utf8.encode('notFound')); // existsSync
+        setMockSyncResponse(utf8.encode('directory')); // parent typeSync
+        setMockSyncResponse([]); // createLink
+        link.createSync('/target_path');
+        expect(getLastSyncCmd(), equals(7));
+
+        // updateSync
+        setMockSyncResponse(utf8.encode('link')); // typeSync check
+        setMockSyncResponse([]); // updateLink
+        link.updateSync('/new_target');
+        expect(getLastSyncCmd(), equals(13));
+
+        // targetSync
+        setMockSyncResponse(utf8.encode('link')); // typeSync check
+        setMockSyncResponse(utf8.encode('/resolved_target')); // readLink
+        expect(link.targetSync(), equals('/resolved_target'));
+        expect(getLastSyncCmd(), equals(8));
+
+        // deleteSync
+        setMockSyncResponse(utf8.encode('link')); // typeSync check
+        setMockSyncResponse([]); // delete
+        link.deleteSync();
+        expect(getLastSyncCmd(), equals(6));
+      });
+
+      test('sync error paths and branch coverage', () {
+        // 1. SharedArrayBuffer unsupported
+        jsEval('window.SharedArrayBuffer = undefined;');
+        expect(() => fs.typeSync('/'), throwsStateError);
+        expect(() => fs.statSync('/'), throwsStateError);
+        jsEval('window.SharedArrayBuffer = function() {};'); // restore
+
+        // 2. typeSync catch block
+        jsEval('''
+          window.originalSendVFSSyncRequest = window.sendVFSSyncRequest;
+          window.sendVFSSyncRequest = function() { throw new Error("mock error"); };
+        ''');
+        expect(fs.typeSync('/'), equals(FileSystemEntityType.notFound));
+        expect(fs.statSync('/').type, equals(FileSystemEntityType.notFound));
+        jsEval('window.sendVFSSyncRequest = window.originalSendVFSSyncRequest;'); // restore
+
+        // 3. statSync type branches (directory, link, other/notFound)
+        // directory
+        setMockSyncResponse(utf8.encode(json.encode({'type': 'directory', 'size': 0, 'modified': 123})));
+        expect(fs.statSync('/dir').type, equals(FileSystemEntityType.directory));
+        // link
+        setMockSyncResponse(utf8.encode(json.encode({'type': 'link', 'size': 0, 'modified': 123})));
+        expect(fs.statSync('/link').type, equals(FileSystemEntityType.link));
+        // other
+        setMockSyncResponse(utf8.encode(json.encode({'type': 'unknown', 'size': 0, 'modified': 123})));
+        expect(fs.statSync('/unknown').type, equals(FileSystemEntityType.notFound));
+
+        // 4. WebDirectory createSync branches
+        final dir = fs.directory('/sync_dir_cov');
+        // Already exists
+        setMockSyncResponse(utf8.encode('directory')); // existsSync
+        dir.createSync(); // Should return early without exception
+        
+        // Parent notFound, recursive: true
+        setMockSyncResponse(utf8.encode('notFound')); // child existsSync
+        setMockSyncResponse(utf8.encode('notFound')); // parent typeSync
+        setMockSyncResponse(utf8.encode('notFound')); // parent existsSync
+        setMockSyncResponse(utf8.encode('directory')); // parent-parent typeSync
+        setMockSyncResponse([]); // parent createDir
+        setMockSyncResponse([]); // child createDir
+        dir.createSync(recursive: true);
+
+        // Parent notFound, recursive: false throws
+        setMockSyncResponse(utf8.encode('notFound')); // existsSync
+        setMockSyncResponse(utf8.encode('notFound')); // parent typeSync
+        expect(() => dir.createSync(recursive: false), throwsA(isA<FileSystemException>()));
+
+        // Parent is file throws
+        setMockSyncResponse(utf8.encode('notFound')); // existsSync
+        setMockSyncResponse(utf8.encode('file')); // parent typeSync
+        expect(() => dir.createSync(), throwsA(isA<FileSystemException>()));
+
+        // createTempSync when directory notFound throws
+        setMockSyncResponse(utf8.encode('notFound')); // existsSync
+        expect(() => dir.createTempSync(), throwsA(isA<FileSystemException>()));
+
+        // createTempSync successful path
+        setMockSyncResponse(utf8.encode('directory')); // existsSync
+        setMockSyncResponse(utf8.encode('notFound')); // temp child existsSync
+        setMockSyncResponse(utf8.encode('directory')); // temp parent typeSync
+        setMockSyncResponse([]); // temp createDir
+        final tempDir = dir.createTempSync('foo');
+        expect(tempDir.path, contains('foo'));
+
+        // deleteSync path notFound throws
+        setMockSyncResponse(utf8.encode('notFound')); // typeSync
+        expect(() => dir.deleteSync(), throwsA(isA<FileSystemException>()));
+
+        // deleteSync path is file throws
+        setMockSyncResponse(utf8.encode('file')); // typeSync
+        expect(() => dir.deleteSync(), throwsA(isA<FileSystemException>()));
+
+        // deleteSync not empty throws
+        setMockSyncResponse(utf8.encode('directory')); // typeSync
+        setMockSyncResponse(utf8.encode('directory')); // existsSync inside listSync
+        setMockSyncResponse(utf8.encode(json.encode([{'path': '/sub/a', 'type': 'file'}]))); // listSync
+        expect(() => dir.deleteSync(), throwsA(isA<FileSystemException>()));
+
+        // listSync path notFound throws
+        setMockSyncResponse(utf8.encode('notFound')); // existsSync
+        expect(() => dir.listSync(), throwsA(isA<FileSystemException>()));
+
+        // listSync recursive containing a directory
+        setMockSyncResponse(utf8.encode('directory')); // existsSync
+        setMockSyncResponse(utf8.encode(json.encode([{'path': '/sync_dir_cov/sub', 'type': 'directory'}]))); // listSync level 1
+        setMockSyncResponse(utf8.encode('directory')); // existsSync recursive
+        setMockSyncResponse(utf8.encode('[]')); // listSync level 2
+        final listRec = dir.listSync(recursive: true);
+        expect(listRec.length, equals(1));
+
+        // listSync following link target to directory
+        setMockSyncResponse(utf8.encode('directory')); // existsSync
+        setMockSyncResponse(utf8.encode(json.encode([{'path': '/sync_dir_cov/lnk', 'type': 'link'}]))); // listSync
+        setMockSyncResponse(utf8.encode('directory')); // typeSync for link target
+        final listLnkDir = dir.listSync(followLinks: true);
+        expect(listLnkDir.length, equals(1));
+        expect(listLnkDir[0], isA<Directory>());
+
+        // listSync following link target to file (non-directory)
+        setMockSyncResponse(utf8.encode('directory')); // existsSync
+        setMockSyncResponse(utf8.encode(json.encode([{'path': '/sync_dir_cov/lnk', 'type': 'link'}]))); // listSync
+        setMockSyncResponse(utf8.encode('file')); // typeSync for link target
+        final listLnkFile = dir.listSync(followLinks: true);
+        expect(listLnkFile.length, equals(1));
+        expect(listLnkFile[0], isA<File>());
+
+        // listSync following link target throws/notFound
+        setMockSyncResponse(utf8.encode('directory')); // existsSync
+        setMockSyncResponse(utf8.encode(json.encode([{'path': '/sync_dir_cov/lnk', 'type': 'link'}]))); // listSync
+        setMockSyncResponse(utf8.encode('notFound')); // typeSync for link target
+        final listLnkNotFound = dir.listSync(followLinks: true);
+        expect(listLnkNotFound.length, equals(1));
+        expect(listLnkNotFound[0], isA<Link>());
+
+        // listSync recursive following link target to directory
+        setMockSyncResponse(utf8.encode('directory')); // existsSync
+        setMockSyncResponse(utf8.encode(json.encode([{'path': '/sync_dir_cov/lnk', 'type': 'link'}]))); // listSync level 1
+        setMockSyncResponse(utf8.encode('directory')); // typeSync for link target
+        setMockSyncResponse(utf8.encode('directory')); // existsSync recursive
+        setMockSyncResponse(utf8.encode('[]')); // listSync level 2
+        final listRecLnkDir = dir.listSync(recursive: true, followLinks: true);
+        expect(listRecLnkDir.length, equals(1));
+        expect(listRecLnkDir[0], isA<Directory>());
+
+        // listSync following link target where typeSync throws (covered via SAB disabled mid-run)
+        jsEval('''
+          window.originalSendVFSSyncRequest = window.sendVFSSyncRequest;
+          window.sendVFSSyncRequest = function(cmd, req) {
+            if (cmd === 10) {
+              window.SharedArrayBuffer = undefined; // disable SAB
+              const listData = JSON.stringify([{'path': '/sync_dir_cov/lnk', 'type': 'link'}]);
+              const bytes = new TextEncoder().encode(listData);
+              return bytes;
+            }
+            return window.originalSendVFSSyncRequest(cmd, req);
+          };
+        ''');
+        setMockSyncResponse(utf8.encode('directory')); // existsSync
+        // listSync response is provided by custom sendVFSSyncRequest function
+        final listLnkThrow = dir.listSync(followLinks: true);
+        expect(listLnkThrow.length, equals(1));
+        expect(listLnkThrow[0], isA<Link>());
+        jsEval('''
+          window.sendVFSSyncRequest = window.originalSendVFSSyncRequest;
+          window.SharedArrayBuffer = function() {}; // restore SAB
+        ''');
+
+        // makeSyncCall SharedArrayBuffer unsupported
+        jsEval('window.SharedArrayBuffer = undefined;');
+        expect(() => dir.resolveSymbolicLinksSync(), throwsStateError);
+        jsEval('window.SharedArrayBuffer = function() {};'); // restore
+
+        // renameSync original path not found throws
+        setMockSyncResponse(utf8.encode('notFound')); // typeSync
+        expect(() => dir.renameSync('/new'), throwsA(isA<FileSystemException>()));
+
+        // renameSync new parent not directory throws
+        setMockSyncResponse(utf8.encode('directory')); // typeSync self
+        setMockSyncResponse(utf8.encode('file')); // typeSync parent
+        expect(() => dir.renameSync('/parent_file/new'), throwsA(isA<FileSystemException>()));
+
+        // renameSync successful
+        setMockSyncResponse(utf8.encode('directory')); // typeSync self
+        setMockSyncResponse(utf8.encode('directory')); // typeSync parent
+        setMockSyncResponse([]); // rename
+        final renamedDir = dir.renameSync('/new_parent/new_dir');
+        expect(renamedDir.path, equals('/new_parent/new_dir'));
+
+        // resolveSymbolicLinksSync
+        setMockSyncResponse(utf8.encode('/resolved/path'));
+        expect(dir.resolveSymbolicLinksSync(), equals('/resolved/path'));
+
+        // 5. WebFile sync branches
+        final file = fs.file('/sync_file_cov');
+        // createSync already exists, exclusive: true throws
+        setMockSyncResponse(utf8.encode('file')); // existsSync
+        expect(() => file.createSync(exclusive: true), throwsA(isA<FileSystemException>()));
+
+        // createSync already exists, exclusive: false returns early
+        setMockSyncResponse(utf8.encode('file')); // existsSync
+        file.createSync(exclusive: false); // returns early
+
+        // createSync parent notFound, recursive: false throws
+        setMockSyncResponse(utf8.encode('notFound')); // existsSync
+        setMockSyncResponse(utf8.encode('notFound')); // parent typeSync
+        expect(() => file.createSync(), throwsA(isA<FileSystemException>()));
+
+        // createSync parent notFound, recursive: true
+        setMockSyncResponse(utf8.encode('notFound')); // existsSync
+        setMockSyncResponse(utf8.encode('notFound')); // parent typeSync
+        setMockSyncResponse(utf8.encode('notFound')); // parent existsSync
+        setMockSyncResponse(utf8.encode('directory')); // parent-parent typeSync
+        setMockSyncResponse([]); // parent createDir
+        setMockSyncResponse(utf8.encode('directory')); // parent check for writeBytes
+        setMockSyncResponse([]); // writeBytes (create file)
+        file.createSync(recursive: true);
+
+        // createSync parent is file throws
+        setMockSyncResponse(utf8.encode('notFound')); // existsSync
+        setMockSyncResponse(utf8.encode('file')); // parent typeSync
+        expect(() => file.createSync(), throwsA(isA<FileSystemException>()));
+
+        // writeAsBytesSync FileMode.append throws UnsupportedError
+        expect(() => file.writeAsBytesSync([], mode: FileMode.append), throwsUnsupportedError);
+
+        // writeAsBytesSync parent not directory throws
+        setMockSyncResponse(utf8.encode('file')); // parent typeSync
+        expect(() => file.writeAsBytesSync([]), throwsA(isA<FileSystemException>()));
+
+        // readAsBytesSync path notFound throws
+        setMockSyncResponse(utf8.encode('notFound')); // typeSync
+        expect(() => file.readAsBytesSync(), throwsA(isA<FileSystemException>()));
+
+        // readAsBytesSync path is directory throws
+        setMockSyncResponse(utf8.encode('directory')); // typeSync
+        expect(() => file.readAsBytesSync(), throwsA(isA<FileSystemException>()));
+
+        // renameSync path notFound throws
+        setMockSyncResponse(utf8.encode('notFound')); // typeSync self
+        expect(() => file.renameSync('/new'), throwsA(isA<FileSystemException>()));
+
+        // renameSync parent not directory throws
+        setMockSyncResponse(utf8.encode('file')); // typeSync self
+        setMockSyncResponse(utf8.encode('file')); // typeSync parent
+        expect(() => file.renameSync('/parent_file/new'), throwsA(isA<FileSystemException>()));
+
+        // renameSync successful
+        setMockSyncResponse(utf8.encode('file')); // typeSync self
+        setMockSyncResponse(utf8.encode('directory')); // typeSync parent
+        setMockSyncResponse([]); // rename
+        final renamedFile = file.renameSync('/new_parent/new_file');
+        expect(renamedFile.path, equals('/new_parent/new_file'));
+
+        // deleteSync path notFound throws
+        setMockSyncResponse(utf8.encode('notFound')); // typeSync self
+        expect(() => file.deleteSync(), throwsA(isA<FileSystemException>()));
+
+        // 6. WebLink sync branches
+        final link = fs.link('/sync_link_cov');
+        // createSync already exists throws
+        setMockSyncResponse(utf8.encode('link')); // existsSync
+        expect(() => link.createSync('/target'), throwsA(isA<FileSystemException>()));
+
+        // createSync parent notFound, recursive: false throws
+        setMockSyncResponse(utf8.encode('notFound')); // existsSync
+        setMockSyncResponse(utf8.encode('notFound')); // parent typeSync
+        expect(() => link.createSync('/target'), throwsA(isA<FileSystemException>()));
+
+        // createSync parent notFound, recursive: true
+        setMockSyncResponse(utf8.encode('notFound')); // existsSync
+        setMockSyncResponse(utf8.encode('notFound')); // parent typeSync
+        setMockSyncResponse(utf8.encode('notFound')); // parent existsSync
+        setMockSyncResponse(utf8.encode('directory')); // parent-parent typeSync
+        setMockSyncResponse([]); // parent createDir
+        setMockSyncResponse([]); // createLink
+        link.createSync('/target', recursive: true);
+
+        // createSync parent is file throws
+        setMockSyncResponse(utf8.encode('notFound')); // existsSync
+        setMockSyncResponse(utf8.encode('file')); // parent typeSync
+        expect(() => link.createSync('/target'), throwsA(isA<FileSystemException>()));
+
+        // updateSync path notFound throws
+        setMockSyncResponse(utf8.encode('notFound')); // typeSync self
+        expect(() => link.updateSync('/new'), throwsA(isA<FileSystemException>()));
+
+        // updateSync path is not link throws
+        setMockSyncResponse(utf8.encode('file')); // typeSync self
+        expect(() => link.updateSync('/new'), throwsA(isA<FileSystemException>()));
+
+        // targetSync path notFound throws
+        setMockSyncResponse(utf8.encode('notFound')); // typeSync self
+        expect(() => link.targetSync(), throwsA(isA<FileSystemException>()));
+
+        // targetSync path is not link throws
+        setMockSyncResponse(utf8.encode('file')); // typeSync self
+        expect(() => link.targetSync(), throwsA(isA<FileSystemException>()));
+
+        // renameSync path notFound throws
+        setMockSyncResponse(utf8.encode('notFound')); // typeSync self
+        expect(() => link.renameSync('/new'), throwsA(isA<FileSystemException>()));
+
+        // renameSync parent not directory throws
+        setMockSyncResponse(utf8.encode('link')); // typeSync self
+        setMockSyncResponse(utf8.encode('file')); // typeSync parent
+        expect(() => link.renameSync('/parent_file/new'), throwsA(isA<FileSystemException>()));
+
+        // renameSync successful
+        setMockSyncResponse(utf8.encode('link')); // typeSync self
+        setMockSyncResponse(utf8.encode('directory')); // typeSync parent
+        setMockSyncResponse([]); // rename
+        final renamedLink = link.renameSync('/new_parent/new_link');
+        expect(renamedLink.path, equals('/new_parent/new_link'));
+
+        // deleteSync path notFound throws
+        setMockSyncResponse(utf8.encode('notFound')); // typeSync self
+        expect(() => link.deleteSync(), throwsA(isA<FileSystemException>()));
+      });
+    });
+  });
 }
 
 @JS('eval')
@@ -591,3 +1079,64 @@ void setMockIDBPutShouldFail(bool value) {
 void setMockIDBIndexGetShouldFail(bool value) {
   jsEval('window.mockIDBIndexGetShouldFail = $value;');
 }
+
+void setupSyncMockJS() {
+  jsEval('''
+    window.originalImportScripts = window.importScripts;
+    window.importScripts = function() {};
+    window.originalSharedArrayBuffer = window.SharedArrayBuffer;
+    window.SharedArrayBuffer = function() {};
+    window.isVFSSyncWorkerInitialized = true;
+    window.initVFSSyncWorker = function() {};
+    
+    window.lastSyncCmd = null;
+    window.lastSyncPayload = null;
+    window.mockSyncResponseArray = [];
+    window.syncCmdsHistory = [];
+    
+    window.sendVFSSyncRequest = function(cmd, requestBytes) {
+      window.lastSyncCmd = cmd;
+      window.syncCmdsHistory.push(cmd);
+      window.lastSyncPayload = Array.from(requestBytes);
+      const resp = window.mockSyncResponseArray.shift() || new Uint8Array(0);
+      return resp;
+    };
+  ''');
+}
+
+void clearSyncMockJS() {
+  jsEval('''
+    window.importScripts = window.originalImportScripts;
+    window.SharedArrayBuffer = window.originalSharedArrayBuffer;
+    delete window.sendVFSSyncRequest;
+    delete window.lastSyncCmd;
+    delete window.lastSyncPayload;
+    delete window.mockSyncResponseArray;
+    delete window.syncCmdsHistory;
+    delete window.isVFSSyncWorkerInitialized;
+    delete window.initVFSSyncWorker;
+  ''');
+}
+
+List<int> getSyncCmdsHistory() {
+  final jsVal = jsEval('JSON.stringify(window.syncCmdsHistory || [])');
+  if (jsVal == null) return [];
+  return List<int>.from(json.decode((jsVal as JSString).toDart));
+}
+
+int? getLastSyncCmd() {
+  final jsVal = jsEval('window.lastSyncCmd');
+  if (jsVal == null) return null;
+  return (jsVal as JSNumber).toDartInt;
+}
+
+List<int>? getLastSyncPayload() {
+  final jsVal = jsEval('window.lastSyncPayload ? JSON.stringify(window.lastSyncPayload) : null');
+  if (jsVal == null) return null;
+  return List<int>.from(json.decode((jsVal as JSString).toDart));
+}
+
+void setMockSyncResponse(List<int> bytes) {
+  final jsonBytes = json.encode(bytes);
+  jsEval('window.mockSyncResponseArray.push(new Uint8Array($jsonBytes));');
+}