ADR-013 Phase 2: import guard hardening (round-3 review fixes)

tests/test_plugin_importguard.py

@@ -142,6 +142,52 @@ def test_tampered_submodule_import_raises(guarded):
         importlib.import_module(f'plugins.{name}.models')
 
 
+def test_planted_extension_module_refused(guarded):
+    """Finding (round 3): a planted .so standing in for a would-be submodule must
+    be refused, not handed to the stdlib ExtensionFileLoader unverified."""
+    import importlib.machinery
+    guard, plugins_dir, priv, name = guarded
+    pdir = _write_pkg_plugin(plugins_dir, name)
+    _stamp(pdir, priv, name)
+
+    ext = importlib.machinery.EXTENSION_SUFFIXES[0]
+    (pdir / 'models' / f'evil{ext}').write_bytes(b'\x7fELF-not-really')
+    with pytest.raises(PluginVerificationError):
+        guard.find_spec(f'plugins.{name}.models.evil')
+
+
+def test_planted_sourceless_pyc_refused(guarded):
+    """A sourceless .pyc for a name with no .py must be refused."""
+    guard, plugins_dir, priv, name = guarded
+    pdir = _write_pkg_plugin(plugins_dir, name)
+    _stamp(pdir, priv, name)
+
+    (pdir / 'models' / 'evil.pyc').write_bytes(b'\x00garbage')
+    with pytest.raises(PluginVerificationError):
+        guard.find_spec(f'plugins.{name}.models.evil')
+
+
+def test_absent_module_defers(guarded):
+    """A genuinely-absent module returns None (normal ModuleNotFoundError)."""
+    guard, plugins_dir, priv, name = guarded
+    pdir = _write_pkg_plugin(plugins_dir, name)
+    _stamp(pdir, priv, name)
+    assert guard.find_spec(f'plugins.{name}.models.notthere') is None
+
+
+def test_top_level_plugins_body_neutralized(guarded):
+    """Finding (round 3): the top-level plugins/__init__.py runs first and is in
+    no provenance; the guard must exec an EMPTY body so an attacker-overwritten
+    plugins/__init__.py cannot execute."""
+    guard, plugins_dir, priv, name = guarded
+    (plugins_dir / '__init__.py').write_text('raise RuntimeError("attacker code")')
+    spec = guard.find_spec('plugins')
+    assert spec is not None
+    # the loader carries empty source, not the on-disk body
+    assert spec.loader._source == b''
+    assert str(plugins_dir) in spec.submodule_search_locations
+
+
 def test_install_uninstall_idempotent(tmp_path, keypair):
     _, pub_path = keypair
     plugins_dir = tmp_path / 'plugins'