fix(plugins): clean failed sibling modules

plugins/plugin_loader.py

@@ -110,6 +110,8 @@ def load_plugin_module(module_name: str, plugin_dir: Path, *, parents: Tuple[str
         sub_mod = _new_module(full_sub_name, sub_file)
         if _exec(sub_mod, logger):
             loaded_submodules.append((sub_file.stem, sub_mod))
+        else:
+            sys.modules.pop(full_sub_name, None)
     if not _exec(mod, logger):
         sys.modules.pop(module_name, None)
         return None

tests/plugins/test_plugin_loader.py

@@ -0,0 +1,70 @@
+"""Regression tests for directory-plugin module loading."""
+
+from __future__ import annotations
+
+import logging
+import sys
+
+from plugins.plugin_loader import load_plugin_module
+
+
+def test_failed_sibling_is_removed_before_init_handles_missing_import(tmp_path):
+    """A failed eager sibling import must remain catchable as ModuleNotFoundError."""
+    plugin_dir = tmp_path / "plugin"
+    plugin_dir.mkdir()
+    (plugin_dir / "broken.py").write_text(
+        "from .missing_dependency import value\n",
+        encoding="utf-8",
+    )
+    (plugin_dir / "__init__.py").write_text(
+        "try:\n"
+        "    from .broken import value\n"
+        "except ModuleNotFoundError:\n"
+        "    fallback_used = True\n",
+        encoding="utf-8",
+    )
+    module_name = "test_plugin_loader_package.failed_sibling"
+
+    try:
+        module = load_plugin_module(
+            module_name,
+            plugin_dir,
+            parents=(),
+            logger=logging.getLogger(__name__),
+        )
+
+        assert module is not None
+        assert module.fallback_used is True
+        assert f"{module_name}.broken" not in sys.modules
+    finally:
+        for name in tuple(sys.modules):
+            if name == module_name or name.startswith(f"{module_name}."):
+                sys.modules.pop(name, None)
+
+
+def test_successful_sibling_remains_available_on_loaded_module(tmp_path):
+    """Cleaning failed siblings must not alter the eager success path."""
+    plugin_dir = tmp_path / "plugin"
+    plugin_dir.mkdir()
+    (plugin_dir / "helper.py").write_text("value = 42\n", encoding="utf-8")
+    (plugin_dir / "__init__.py").write_text(
+        "from .helper import value\n",
+        encoding="utf-8",
+    )
+    module_name = "test_plugin_loader_package.successful_sibling"
+
+    try:
+        module = load_plugin_module(
+            module_name,
+            plugin_dir,
+            parents=(),
+            logger=logging.getLogger(__name__),
+        )
+
+        assert module is not None
+        assert module.value == 42
+        assert module.helper.value == 42
+    finally:
+        for name in tuple(sys.modules):
+            if name == module_name or name.startswith(f"{module_name}."):
+                sys.modules.pop(name, None)