@@ -0,0 +1,194 @@
+# Copyright 2026 Query Farm LLC - https://query.farm
+
+"""Importing vgi, and defining functions, must not touch the filesystem.
+
+``Function.storage`` resolves the default SQLite store lazily, on first access.
+``TableFunctionBase.__init_subclass__`` used to defeat that: it detected
+abstract classes with a plain ``getattr`` over ``dir(cls)``, which invoked the
+storage descriptor, which created ``vgi_storage.db`` under the user's state
+directory. Because vgi defines subclasses of its own, a bare ``import vgi`` did
+it — and failed outright wherever that directory was not writable, such as a
+container running as a non-root user whose home belongs to root.
+
+The import checks run in a subprocess with ``HOME`` and the XDG directories
+pointed at an empty temporary directory, because the storage descriptor caches
+its backend per process and the test process has usually resolved it already.
+"""
+
+import os
+import subprocess
+import sys
+from abc import abstractmethod
+from pathlib import Path
+
+import pytest
+
+from vgi.table_function import TableFunctionGenerator
+
+#: Imports every function base class and defines a concrete table function, so
+#: both vgi's own class definitions and a worker's go through __init_subclass__.
+_IMPORT_AND_DEFINE = """
+import pyarrow as pa
+import vgi
+import vgi.aggregate_function
+import vgi.scalar_function
+import vgi.table_in_out_function
+from vgi.invocation import BindResponse
+from vgi.table_function import TableFunctionGenerator
+
+
+class Concrete(TableFunctionGenerator[None, None]):
+    @classmethod
+    def on_bind(cls, params):
+        return BindResponse(output_schema=pa.schema([("n", pa.int64())]))
+
+    @classmethod
+    def process(cls, params, state, out):
+        out.finish()
+"""
+
+
+def _isolated_env(home: Path) -> dict[str, str]:
+    """Environment whose every per-user directory lives under ``home``.
+
+    ``VGI_*`` variables are dropped so the default file-backed SQLite store is
+    the one in play; a test run configured with ``VGI_WORKER_SHARED_STORAGE``
+    set to ``memory`` would otherwise pass without the fix.
+    """
+    env = {k: v for k, v in os.environ.items() if not k.startswith(("VGI_", "XDG_"))}
+    env["HOME"] = str(home)
+    for name in ("XDG_STATE_HOME", "XDG_DATA_HOME", "XDG_CACHE_HOME", "XDG_CONFIG_HOME"):
+        env[name] = str(home / name.lower())
+    return env
+
+
+def _run(code: str, home: Path) -> subprocess.CompletedProcess[str]:
+    """Run ``code`` in a fresh interpreter with per-user directories under ``home``."""
+    return subprocess.run(
+        [sys.executable, "-c", code],
+        env=_isolated_env(home),
+        capture_output=True,
+        text=True,
+        timeout=120,
+        check=False,
+    )
+
+
+def _files_under(root: Path) -> list[str]:
+    """Every file below ``root``, relative to it."""
+    return sorted(str(p.relative_to(root)) for p in root.rglob("*") if p.is_file())
+
+
+class TestImportWritesNothing:
+    """The storage store is created when it is used, not when vgi is imported."""
+
+    def test_import_and_define_create_no_files(self, tmp_path: Path) -> None:
+        """Importing vgi and defining a function leaves the home directory empty."""
+        result = _run(_IMPORT_AND_DEFINE, tmp_path)
+        assert result.returncode == 0, result.stderr
+        assert _files_under(tmp_path) == []
+
+    @pytest.mark.skipif(
+        sys.platform == "win32" or os.geteuid() == 0,
+        reason="a read-only directory does not stop root, and POSIX modes do not apply on Windows",
+    )
+    def test_import_succeeds_when_home_is_not_writable(self, tmp_path: Path) -> None:
+        """A read-only home — a container's non-root user, say — does not stop the import."""
+        home = tmp_path / "home"
+        home.mkdir()
+        home.chmod(0o555)
+        try:
+            result = _run(_IMPORT_AND_DEFINE, home)
+        finally:
+            home.chmod(0o755)
+        assert result.returncode == 0, result.stderr
+
+    def test_storage_is_still_created_on_first_use(self, tmp_path: Path) -> None:
+        """Laziness, not removal: touching Function.storage still creates the store."""
+        result = _run("from vgi.function import Function\nFunction.storage", tmp_path)
+        assert result.returncode == 0, result.stderr
+        assert any(name.endswith("vgi_storage.db") for name in _files_under(tmp_path))
+
+
+class _NotADataclass:
+    """An argument type a concrete function would be rejected for."""
+
+
+class TestAbstractDetection:
+    """Reading attributes statically must still recognize every kind of abstract member.
+
+    An abstract class skips validation of its argument type; a concrete one is
+    rejected at class creation when that type is not a dataclass. So a class
+    with an invalid argument type is defined successfully only if it is seen as
+    abstract.
+    """
+
+    def test_a_concrete_class_is_validated(self) -> None:
+        """Control: without an abstract member, the invalid argument type is rejected."""
+        with pytest.raises(TypeError, match="must be a dataclass"):
+
+            class Concrete(TableFunctionGenerator[_NotADataclass, None]):  # type: ignore[type-var]
+                @classmethod
+                def on_bind(cls, params):  # type: ignore[no-untyped-def]
+                    raise NotImplementedError
+
+                @classmethod
+                def process(cls, params, state, out):  # type: ignore[no-untyped-def]
+                    raise NotImplementedError
+
+    def test_an_abstract_classmethod_marks_the_class_abstract(self) -> None:
+        """An inherited-concrete class that adds an abstract classmethod skips validation."""
+
+        class WithAbstractClassmethod(TableFunctionGenerator[_NotADataclass, None]):  # type: ignore[type-var]
+            @classmethod
+            def on_bind(cls, params):  # type: ignore[no-untyped-def]
+                raise NotImplementedError
+
+            @classmethod
+            def process(cls, params, state, out):  # type: ignore[no-untyped-def]
+                raise NotImplementedError
+
+            @classmethod
+            @abstractmethod
+            def extra(cls) -> None:
+                """Left for a subclass to implement."""
+
+        assert WithAbstractClassmethod._setting_params == {}
+
+    def test_an_abstract_staticmethod_marks_the_class_abstract(self) -> None:
+        """An abstract staticmethod is recognized through its raw attribute too."""
+
+        class WithAbstractStaticmethod(TableFunctionGenerator[_NotADataclass, None]):  # type: ignore[type-var]
+            @classmethod
+            def on_bind(cls, params):  # type: ignore[no-untyped-def]
+                raise NotImplementedError
+
+            @classmethod
+            def process(cls, params, state, out):  # type: ignore[no-untyped-def]
+                raise NotImplementedError
+
+            @staticmethod
+            @abstractmethod
+            def extra() -> None:
+                """Left for a subclass to implement."""
+
+        assert WithAbstractStaticmethod._setting_params == {}
+
+    def test_an_abstract_property_marks_the_class_abstract(self) -> None:
+        """An abstract property is recognized through its raw attribute too."""
+
+        class WithAbstractProperty(TableFunctionGenerator[_NotADataclass, None]):  # type: ignore[type-var]
+            @classmethod
+            def on_bind(cls, params):  # type: ignore[no-untyped-def]
+                raise NotImplementedError
+
+            @classmethod
+            def process(cls, params, state, out):  # type: ignore[no-untyped-def]
+                raise NotImplementedError
+
+            @property
+            @abstractmethod
+            def extra(self) -> int:
+                """Left for a subclass to implement."""
+
+        assert WithAbstractProperty._setting_params == {}
@@ -8,6 +8,7 @@
 
 from __future__ import annotations
 
+import inspect
 import uuid
 from abc import abstractmethod
 from collections.abc import Mapping
@@ -854,8 +855,19 @@ def __init_subclass__(cls) -> None:
                             cls.FunctionArguments = type_args[0]
                         break
 
-        # Skip validation for abstract base classes
-        is_abstract = any(getattr(getattr(cls, name, None), "__isabstractmethod__", False) for name in dir(cls))
+        # Skip validation for abstract base classes. Each attribute is read with
+        # getattr_static, which returns the raw class attribute without invoking
+        # descriptors: a plain getattr() here resolved the inherited
+        # `Function.storage` descriptor, whose first access builds the default
+        # SQLite store on disk. Because vgi defines subclasses of its own, that
+        # made `import vgi` alone create a database under the user's state
+        # directory, and fail outright where that directory is not writable (a
+        # container's non-root user, say). The raw attribute answers the same
+        # question: classmethod, staticmethod and property objects all expose
+        # the `__isabstractmethod__` of what they wrap.
+        is_abstract = any(
+            getattr(inspect.getattr_static(cls, name, None), "__isabstractmethod__", False) for name in dir(cls)
+        )
         if is_abstract:
             cls._setting_params = {}
             cls._secret_params = {}