diff --git a/codex-lens/src/codexlens/config.py b/codex-lens/src/codexlens/config.py
index 7e49b70d..7436b18d 100644
--- a/codex-lens/src/codexlens/config.py
+++ b/codex-lens/src/codexlens/config.py
@@ -122,8 +122,21 @@ class Config:
             self.data_dir = self.data_dir.expanduser().resolve()
             self.venv_path = self.venv_path.expanduser().resolve()
             self.data_dir.mkdir(parents=True, exist_ok=True)
+        except PermissionError as exc:
+            raise ConfigError(
+                f"Permission denied initializing paths (data_dir={self.data_dir}, venv_path={self.venv_path}) "
+                f"[{type(exc).__name__}]: {exc}"
+            ) from exc
+        except OSError as exc:
+            raise ConfigError(
+                f"Filesystem error initializing paths (data_dir={self.data_dir}, venv_path={self.venv_path}) "
+                f"[{type(exc).__name__}]: {exc}"
+            ) from exc
         except Exception as exc:
-            raise ConfigError(f"Failed to initialize data_dir at {self.data_dir}: {exc}") from exc
+            raise ConfigError(
+                f"Unexpected error initializing paths (data_dir={self.data_dir}, venv_path={self.venv_path}) "
+                f"[{type(exc).__name__}]: {exc}"
+            ) from exc
 
     @cached_property
     def cache_dir(self) -> Path:
@@ -145,8 +158,18 @@ class Config:
         for directory in (self.cache_dir, self.index_dir):
             try:
                 directory.mkdir(parents=True, exist_ok=True)
+            except PermissionError as exc:
+                raise ConfigError(
+                    f"Permission denied creating directory {directory} [{type(exc).__name__}]: {exc}"
+                ) from exc
+            except OSError as exc:
+                raise ConfigError(
+                    f"Filesystem error creating directory {directory} [{type(exc).__name__}]: {exc}"
+                ) from exc
             except Exception as exc:
-                raise ConfigError(f"Failed to create directory {directory}: {exc}") from exc
+                raise ConfigError(
+                    f"Unexpected error creating directory {directory} [{type(exc).__name__}]: {exc}"
+                ) from exc
 
     def language_for_path(self, path: str | Path) -> str | None:
         """Infer a supported language ID from a file path."""
diff --git a/codex-lens/tests/test_config.py b/codex-lens/tests/test_config.py
index 75e42b28..96b7e7b5 100644
--- a/codex-lens/tests/test_config.py
+++ b/codex-lens/tests/test_config.py
@@ -118,6 +118,57 @@ class TestConfig:
             config = Config(data_dir=data_dir)
             assert data_dir.exists()
 
+    def test_post_init_permission_error_includes_path_and_cause(self, monkeypatch):
+        """PermissionError during __post_init__ should raise ConfigError with context."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            data_dir = Path(tmpdir) / "blocked"
+            venv_path = Path(tmpdir) / "venv"
+            expected_data_dir = data_dir.expanduser().resolve()
+
+            real_mkdir = Path.mkdir
+
+            def guarded_mkdir(self, *args, **kwargs):
+                if self == expected_data_dir:
+                    raise PermissionError("Permission denied")
+                return real_mkdir(self, *args, **kwargs)
+
+            monkeypatch.setattr(Path, "mkdir", guarded_mkdir)
+
+            with pytest.raises(ConfigError) as excinfo:
+                Config(data_dir=data_dir, venv_path=venv_path)
+
+            message = str(excinfo.value)
+            assert str(expected_data_dir) in message
+            assert "permission" in message.lower()
+            assert "PermissionError" in message
+            assert isinstance(excinfo.value.__cause__, PermissionError)
+
+    def test_post_init_os_error_includes_path_and_cause(self, monkeypatch):
+        """OSError during __post_init__ should raise ConfigError with context."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            data_dir = Path(tmpdir) / "invalid"
+            venv_path = Path(tmpdir) / "venv"
+            expected_data_dir = data_dir.expanduser().resolve()
+
+            real_mkdir = Path.mkdir
+
+            def guarded_mkdir(self, *args, **kwargs):
+                if self == expected_data_dir:
+                    raise OSError("Invalid path")
+                return real_mkdir(self, *args, **kwargs)
+
+            monkeypatch.setattr(Path, "mkdir", guarded_mkdir)
+
+            with pytest.raises(ConfigError) as excinfo:
+                Config(data_dir=data_dir, venv_path=venv_path)
+
+            message = str(excinfo.value)
+            assert str(expected_data_dir) in message
+            assert "permission" not in message.lower()
+            assert "filesystem" in message.lower()
+            assert "OSError" in message
+            assert isinstance(excinfo.value.__cause__, OSError)
+
     def test_supported_languages(self):
         """Test default supported languages."""
         with tempfile.TemporaryDirectory() as tmpdir:
@@ -158,6 +209,55 @@ class TestConfig:
             assert config.cache_dir.exists()
             assert config.index_dir.exists()
 
+    def test_ensure_runtime_dirs_permission_error_includes_path_and_cause(self, monkeypatch):
+        """PermissionError during ensure_runtime_dirs should raise ConfigError with context."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            config = Config(data_dir=Path(tmpdir))
+            target_dir = config.cache_dir
+
+            real_mkdir = Path.mkdir
+
+            def guarded_mkdir(self, *args, **kwargs):
+                if self == target_dir:
+                    raise PermissionError("Permission denied")
+                return real_mkdir(self, *args, **kwargs)
+
+            monkeypatch.setattr(Path, "mkdir", guarded_mkdir)
+
+            with pytest.raises(ConfigError) as excinfo:
+                config.ensure_runtime_dirs()
+
+            message = str(excinfo.value)
+            assert str(target_dir) in message
+            assert "permission" in message.lower()
+            assert "PermissionError" in message
+            assert isinstance(excinfo.value.__cause__, PermissionError)
+
+    def test_ensure_runtime_dirs_os_error_includes_path_and_cause(self, monkeypatch):
+        """OSError during ensure_runtime_dirs should raise ConfigError with context."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            config = Config(data_dir=Path(tmpdir))
+            target_dir = config.cache_dir
+
+            real_mkdir = Path.mkdir
+
+            def guarded_mkdir(self, *args, **kwargs):
+                if self == target_dir:
+                    raise OSError("Invalid path")
+                return real_mkdir(self, *args, **kwargs)
+
+            monkeypatch.setattr(Path, "mkdir", guarded_mkdir)
+
+            with pytest.raises(ConfigError) as excinfo:
+                config.ensure_runtime_dirs()
+
+            message = str(excinfo.value)
+            assert str(target_dir) in message
+            assert "permission" not in message.lower()
+            assert "filesystem" in message.lower()
+            assert "OSError" in message
+            assert isinstance(excinfo.value.__cause__, OSError)
+
     def test_language_for_path_python(self):
         """Test language detection for Python files."""
         with tempfile.TemporaryDirectory() as tmpdir: