fix(plugin-system): load/enable failures, atomic state files, pip lock, test-double parity (#645)

- load_plugin: an on_enable() that raises unregisters the instance, so the
  next load retries instead of returning True "already loaded".
- get_plugin_info: guard plugin.get_info(); one plugin raising no longer
  breaks /api/v3/plugins/installed.
- plugin_state.json and the operation history are written with
  atomic_write_text under their lock.
- plugin_loader: module-level lock serialises pip installs across the
  parallel startup loaders.
- store_manager._install_via_download: extract dir cleanup moved to finally.
- Test doubles: draw_image() warns (DeprecationWarning; the real
  DisplayManager has none), MockDisplayManager.draw_text accepts the real
  signature's optional params, VisualTestDisplayManager logs draw errors at
  WARNING.
- Docs/comments: compatibility.py method name, PluginState.LOADED meaning,
  brittle schema count, why _report_skip_once uses setdefault.
- Remove unused PluginOperationQueue.get_active_operations().

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

test/test_testing_mocks.py

@@ -9,6 +9,8 @@ get_cached_data_with_strategy() and previously hit an AttributeError that
 its own broad except swallowed, producing an empty-but-green render).
 """
 
+import pytest
+
 from src.plugin_system.testing.mocks import MockCacheManager
 
 
@@ -43,3 +45,64 @@ class TestMockCacheManagerStrategyMethod:
         cm.get_cached_data_with_strategy("k", "sports_live")
         cm.reset()
         assert cm.get_cached_data_with_strategy_calls == []
+
+
+class TestDisplayDoublesMatchTheRealDisplayManager:
+    """The real DisplayManager has no draw_image(); the doubles keep it so
+    existing plugin test suites still pass, but warn, because a plugin that
+    calls it passes its tests and then raises AttributeError on the Pi."""
+
+    @staticmethod
+    def _real_display_manager(monkeypatch):
+        # Without EMULATOR the import needs the hardware rgbmatrix module.
+        monkeypatch.setenv("EMULATOR", "true")
+        from src.display_manager import DisplayManager
+        return DisplayManager
+
+    def test_real_display_manager_has_no_draw_image(self, monkeypatch):
+        DisplayManager = self._real_display_manager(monkeypatch)
+        assert not hasattr(DisplayManager, 'draw_image')
+
+    def test_mock_draw_image_warns_and_still_records(self):
+        from PIL import Image
+        from src.plugin_system.testing.mocks import MockDisplayManager
+
+        dm = MockDisplayManager()
+        with pytest.warns(DeprecationWarning, match=r"image\.paste\(img, \(x, y\)\)"):
+            dm.draw_image(Image.new('RGB', (4, 4)), 1, 2)
+        assert dm.draw_calls[-1]['type'] == 'image'
+
+    @pytest.mark.parametrize("cls_name", ["VisualTestDisplayManager", "BoundsCheckingDisplayManager"])
+    def test_visual_draw_image_warns_and_still_pastes(self, cls_name):
+        from PIL import Image
+        import src.plugin_system.testing as testing
+
+        dm = getattr(testing, cls_name)(width=16, height=8)
+        with pytest.warns(DeprecationWarning, match="DisplayManager has no such method"):
+            dm.draw_image(Image.new('RGB', (2, 2), (0, 0, 255)), 3, 3)
+        assert dm.image.getpixel((3, 3)) == (0, 0, 255)
+
+    def test_mock_draw_text_accepts_the_real_signature(self, monkeypatch):
+        import inspect
+        DisplayManager = self._real_display_manager(monkeypatch)
+        from src.plugin_system.testing.mocks import MockDisplayManager
+
+        real = inspect.signature(DisplayManager.draw_text).parameters
+        mock = inspect.signature(MockDisplayManager.draw_text).parameters
+        for name, param in real.items():
+            assert name in mock, name
+            assert mock[name].default == param.default, name
+
+        dm = MockDisplayManager()
+        dm.draw_text("hi", small_font=True, centered=True)
+        assert dm.draw_calls[-1]['text'] == "hi"
+
+    def test_visual_draw_failure_is_logged_at_warning(self, caplog):
+        import logging
+        from src.plugin_system.testing import VisualTestDisplayManager
+
+        dm = VisualTestDisplayManager(width=16, height=8)
+        with caplog.at_level(logging.WARNING):
+            dm.draw_image(object(), 0, 0)  # not an image: paste raises
+        assert any(r.levelno == logging.WARNING and "Error drawing image" in r.getMessage()
+                   for r in caplog.records)