diff --git a/virtual_fs.py b/virtual_fs.py
index bcfe2a7..5d1e24d 100644
--- a/virtual_fs.py
+++ b/virtual_fs.py
@@ -1,76 +1,39 @@
 """
-Virtual file system for the deep agent.
-
-This module implements a simple in-memory file system that allows the agent to create
-and modify files during its execution.  At the end of the run the virtual files can
-be dumped to the real file system.
+Virtual file system used by the deep agent.
+It stores files in memory and can be dumped to the real file system.
 """
 
-from __future__ import annotations
-
+import os
 from pathlib import Path
-from typing import Dict, Iterable, Tuple
-
+from typing import Dict, Optional
 
 class VirtualFileSystem:
-    """A minimal in‑memory file system.
+    """A simple in‑memory file system.
 
-    The files are stored in a dictionary mapping a relative path to its content.
-    The content is stored as a string.  The class provides methods for writing
-    files, reading files and dumping all files to a real directory.
+    Files are stored as a mapping from a relative path to its content.
     """
 
-    def __init__(self) -> None:
-        self._files: Dict[str, str] = {}
+    def __init__(self, base_dir: str = "virtual_fs"):
+        self.base_dir = Path(base_dir)
+        self.files: Dict[str, str] = {}
 
-    def write(self, path: str | Path, content: str) -> None:
-        """Write *content* to *path*.
+    def write_file(self, path: str, content: str) -> None:
+        norm_path = Path(path).as_posix()
+        self.files[norm_path] = content
 
-        Parameters
-        ----------
-        path:
-            The relative path of the file.  ``Path`` objects are accepted for
-            convenience.
-        content:
-            The textual content to store.
-        """
-        path = str(path).lstrip("./")
-        self._files[path] = content
+    def read_file(self, path: str) -> Optional[str]:
+        norm_path = Path(path).as_posix()
+        return self.files.get(norm_path)
 
-    def read(self, path: str | Path) -> str:
-        """Return the content of *path*.
+    def list_files(self) -> Dict[str, str]:
+        return dict(self.files)
 
-        Raises
-        ------
-        KeyError
-            If the file does not exist.
-        """
-        path = str(path).lstrip("./")
-        return self._files[path]
-
-    def list_files(self) -> Iterable[Tuple[str, str]]:
-        """Yield ``(path, content)`` for all stored files."""
-        for path, content in self._files.items():
-            yield path, content
-
-    def dump_to_disk(self, root: str | Path) -> None:
-        """Write all virtual files to *root*.
-
-        Parameters
-        ----------
-        root:
-            The directory on the real file system where the files should be
-            created.
-        """
-        root = Path(root)
-        for path, content in self._files.items():
-            file_path = root / path
+    def dump_to_real_fs(self, real_root: str = "real_fs") -> None:
+        real_root_path = Path(real_root)
+        for rel_path, content in self.files.items():
+            file_path = real_root_path / rel_path
             file_path.parent.mkdir(parents=True, exist_ok=True)
             file_path.write_text(content, encoding="utf-8")
 
-    def __repr__(self) -> str:  # pragma: no cover
-        return f"VirtualFileSystem({len(self._files)} files)"
-
-
-# Singleton instance used by the tools.
-virtual_fs = VirtualFileSystem()
+    def __repr__(self) -> str:
+        return f"VirtualFileSystem(files={list(self.files.keys())})"