fix(workspace): inject plugins_registry into sys.modules before loading adapters (closes #296)

Plugin adapters in molecule-skill-* repos do:
  from plugins_registry.builtins import AgentskillsAdaptor as Adaptor

But _load_module_from_path() used exec_module() with a fresh module
namespace that did NOT have plugins_registry or its submodules in sys.modules,
causing:
  ModuleNotFoundError: No module named 'plugins_registry'

Fix: before exec_module(), import and register plugins_registry + all three
submodules (builtins, protocol, raw_drop) in sys.modules so adapter imports
resolve correctly.  Follows the Option 1 recommendation from issue #296.

Also adds test_resolve_plugin.py verifying the fix for both the
AgentskillsAdaptor import and the full InstallContext/resolve/protocol import.

Closes #296.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

workspace/plugins_registry/__init__.py

@@ -51,6 +51,22 @@ class AdaptorSource:
 
 def _load_module_from_path(module_name: str, path: Path):
     """Import a Python file by absolute path. Returns the module or None on failure."""
+    # Ensure the plugins_registry package and its submodules are importable in the
+    # fresh module namespace created by module_from_spec().  Plugin adapters
+    # (molecule-skill-*/adapters/*.py) use "from plugins_registry.builtins import ..."
+    # which requires plugins_registry and its submodules to already be in sys.modules.
+    # We import and register them before exec_module so the plugin's own
+    # from ... import statements resolve correctly.
+    import sys
+    import plugins_registry
+    sys.modules.setdefault("plugins_registry", plugins_registry)
+    for _sub in ("builtins", "protocol", "raw_drop"):
+        try:
+            sub = importlib.import_module(f"plugins_registry.{_sub}")
+            sys.modules.setdefault(f"plugins_registry.{_sub}", sub)
+        except Exception:
+            # Submodule may not exist in all versions; skip if absent.
+            pass
     spec = importlib.util.spec_from_file_location(module_name, path)
     if spec is None or spec.loader is None:
         return None

workspace/plugins_registry/test_resolve_plugin.py

@@ -0,0 +1,60 @@
+"""Tests for _load_module_from_path sys.modules injection fix (issue #296).
+
+Verifies that plugin adapters using "from plugins_registry.builtins import ..."
+can be loaded via _load_module_from_path() without ModuleNotFoundError.
+"""
+import sys
+import tempfile
+import os
+from pathlib import Path
+
+# Ensure the plugins_registry package is importable
+import plugins_registry
+
+from plugins_registry import _load_module_from_path
+
+
+def test_load_adapter_with_plugins_registry_import():
+    """Plugin adapter using 'from plugins_registry.builtins import ...' loads cleanly."""
+    # Write a temp adapter file that does the exact import from the bug report.
+    with tempfile.NamedTemporaryFile(
+        mode="w", suffix=".py", delete=False, dir=tempfile.gettempdir()
+    ) as f:
+        f.write("from plugins_registry.builtins import AgentskillsAdaptor as Adaptor\n")
+        f.write("assert Adaptor is not None\n")
+        adapter_path = Path(f.name)
+
+    try:
+        module = _load_module_from_path("test_adapter", adapter_path)
+        assert module is not None, "module should load without error"
+        assert hasattr(module, "Adaptor"), "module should expose Adaptor"
+    finally:
+        os.unlink(adapter_path)
+
+
+def test_load_adapter_with_full_plugins_registry_import():
+    """Plugin adapter using 'from plugins_registry import ...' loads cleanly."""
+    with tempfile.NamedTemporaryFile(
+        mode="w", suffix=".py", delete=False, dir=tempfile.gettempdir()
+    ) as f:
+        f.write("from plugins_registry import InstallContext, resolve\n")
+        f.write("from plugins_registry.protocol import PluginAdaptor\n")
+        f.write("assert InstallContext is not None\n")
+        f.write("assert resolve is not None\n")
+        f.write("assert PluginAdaptor is not None\n")
+        adapter_path = Path(f.name)
+
+    try:
+        module = _load_module_from_path("test_adapter_full", adapter_path)
+        assert module is not None, "module should load without error"
+        assert hasattr(module, "InstallContext"), "module should expose InstallContext"
+        assert hasattr(module, "resolve"), "module should expose resolve"
+        assert hasattr(module, "PluginAdaptor"), "module should expose PluginAdaptor"
+    finally:
+        os.unlink(adapter_path)
+
+
+if __name__ == "__main__":
+    test_load_adapter_with_plugins_registry_import()
+    test_load_adapter_with_full_plugins_registry_import()
+    print("ALL TESTS PASS")