fix(plugins): discovery must not instantiate an imported base class

inspect.getmembers() returns members ALPHABETICALLY, and the name-based
detection strategy takes the first class ending in 'Plugin'. Every plugin
does 'from plugin_system import PredBatPlugin', so the abstract base sits
in the module namespace — and any plugin class sorting after
'PredBatPlugin' gets the base instantiated instead of itself.

The plugin then logs as loaded successfully and silently does nothing: no
hooks registered, no behaviour. Whether a plugin works depends on the
luck of its class name. Hit in the wild with a class named
SocKeepPublishPlugin; ColdWeatherPlugin and CurtailmentPlugin sort before
the base, so they were unaffected.

Fix: require obj.__module__ == plugin_module.__name__, so only classes
actually DEFINED in the plugin file are candidates. The two fallback
strategies (PREDBAT_PLUGIN marker, initialize_plugin function) are
unchanged.

Test discovers a temp plugin whose class name sorts after PredBatPlugin
and asserts the right class was instantiated. Verified it fails without
the fix:
  ERROR: discovery instantiated PredBatPlugin, expected ZzSortsLastPlugin

Author: warksit

apps/predbat/plugin_system.py

@@ -121,9 +121,16 @@ def load_plugin(self, plugin_dir: str, plugin_name: str):
 
         # Plugin discovery fallthrough (try in order of preference):
 
-        # 1. MOST PREFERRED: Class name ends with "Plugin"
+        # 1. MOST PREFERRED: Class name ends with "Plugin" AND is defined in this
+        # module. inspect.getmembers() returns members ALPHABETICALLY, so without the
+        # __module__ check a plugin whose class sorts after an imported one silently
+        # gets the wrong class instantiated: `from plugin_system import PredBatPlugin`
+        # puts the base class in the namespace, so e.g. SocKeepPublishPlugin (sorting
+        # after PredBatPlugin) had the abstract base constructed instead — the plugin
+        # logged as loaded successfully and did nothing. Whether a plugin works should
+        # not depend on the alphabet.
         for name, obj in inspect.getmembers(plugin_module, inspect.isclass):
-            if name.endswith("Plugin"):
+            if name.endswith("Plugin") and obj.__module__ == plugin_module.__name__:
                 try:
                     self.log(f"Initialising plugin class (name-based): {name}")
                     plugin_instance = obj(self.base)

apps/predbat/tests/test_plugin_startup.py

@@ -7,8 +7,12 @@
 # pylint: disable=consider-using-f-string
 # pylint: disable=line-too-long
 # pylint: disable=attribute-defined-outside-init
+import os
+import shutil
+import tempfile
 from unittest.mock import MagicMock, patch
 from predbat import PredBat
+from plugin_system import PluginSystem
 
 
 def test_plugin_startup_order(my_predbat):
@@ -143,3 +147,44 @@ def register_hooks(self, plugin_system):
         print(f"OK: Plugin successfully registered endpoint /test")
 
     return failed
+
+
+def test_plugin_discovery_skips_imported_base_class(my_predbat):
+    """
+    Discovery must instantiate the class DEFINED in the plugin file, not a class
+    it merely imports.
+
+    inspect.getmembers() returns members alphabetically and the name-based strategy
+    takes the first class ending in "Plugin". Every plugin does
+    `from plugin_system import PredBatPlugin`, so any plugin class sorting AFTER
+    "PredBatPlugin" had the abstract base instantiated instead of itself — the
+    plugin logged as loaded successfully, registered no hooks, and did nothing.
+    """
+    print("*** Running test: Plugin discovery skips imported base classes")
+    failed = 0
+
+    base = MagicMock()
+    base.log = MagicMock()
+
+    tmpdir = tempfile.mkdtemp()
+    try:
+        # Class name deliberately sorts AFTER "PredBatPlugin".
+        with open(os.path.join(tmpdir, "zz_sorts_last_plugin.py"), "w", encoding="utf-8") as fh:
+            fh.write("from plugin_system import PredBatPlugin\n\n\nclass ZzSortsLastPlugin(PredBatPlugin):\n    pass\n")
+
+        plugin_system = PluginSystem(base)
+        plugin_system.discover_plugins([tmpdir])
+        loaded = list(plugin_system.plugins.values())
+
+        if len(loaded) != 1:
+            print("ERROR: expected exactly one discovered plugin, got {}".format(len(loaded)))
+            failed = 1
+        elif type(loaded[0]).__name__ != "ZzSortsLastPlugin":
+            print("ERROR: discovery instantiated {}, expected ZzSortsLastPlugin".format(type(loaded[0]).__name__))
+            failed = 1
+        else:
+            print("OK: discovery instantiated the plugin class, not the imported base")
+    finally:
+        shutil.rmtree(tmpdir, ignore_errors=True)
+
+    return failed

apps/predbat/unit_test.py

@@ -49,7 +49,7 @@
 from tests.test_nordpool import run_nordpool_test
 from tests.test_futurerate_auto import test_futurerate_auto
 from tests.test_car_charging_smart import run_car_charging_smart_tests
-from tests.test_plugin_startup import test_plugin_startup_order
+from tests.test_plugin_startup import test_plugin_startup_order, test_plugin_discovery_skips_imported_base_class
 from tests.test_active_flag import test_active_flag
 from tests.test_component_health_status import test_component_health_status
 from tests.test_optimise_levels import run_optimise_levels_tests
@@ -398,6 +398,7 @@ def main():
         ("add_now_to_octopus_slot", test_add_now_to_octopus_slot, "Add now to Octopus slot tests", False),
         ("octopus_slots_change", test_octopus_slots_change, "Octopus slots change-detection signature tests (in-progress re-clock vs genuine change)", False),
         ("plugin_startup", test_plugin_startup_order, "Plugin startup order tests", False),
+        ("plugin_discovery", test_plugin_discovery_skips_imported_base_class, "Plugin discovery skips imported base classes", False),
         ("active_flag", test_active_flag, "Active flag cleared on exception tests", False),
         ("component_health_status", test_component_health_status, "Component errors fail the recorded run status tests", False),
         ("dynamic_load_car", test_dynamic_load_car_slot_cancellation, "Dynamic load car slot cancellation tests", False),