refactor(mcp): address Codex review — fix registry bug, DRY schema hints, remove column regex

P1.1 registry.py: move _plugins_loaded=True to after successful import so a
failed load doesn't permanently poison the registry.

P1.3 schemas.py: remove overly restrictive ColumnRef.name / FilterClause.column
/ BigNumberChartConfig.temporal_column regex that blocked valid column names
containing parentheses, slashes, and other SQL-common characters.

P2.3 (DRY): eliminate _CHART_TYPE_ERROR_HINTS second-registry in
schema_validator.py by adding schema_error_hint() to ChartTypePlugin protocol,
BaseChartPlugin default, and all 7 plugin classes. SchemaValidator now delegates
to the plugin registry instead of maintaining a parallel dict.

P3.3 test_registry.py: add full registry unit-test coverage (register, get,
all_types, is_registered, display_name_for_viz_type, proxy methods, duplicate
warning, empty chart_type validation, insertion-order guarantee).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/unit_tests/mcp_service/chart/test_registry.py

@@ -0,0 +1,143 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+"""Tests for the chart type plugin registry."""
+
+import pytest
+
+import superset.mcp_service.chart.registry as registry_module
+from superset.mcp_service.chart.plugin import BaseChartPlugin
+from superset.mcp_service.chart.registry import (
+    _RegistryProxy,
+    all_types,
+    display_name_for_viz_type,
+    get,
+    get_registry,
+    is_registered,
+    register,
+)
+
+
+@pytest.fixture(autouse=True)
+def _isolated_registry(monkeypatch):
+    """Run each test against a clean registry without touching the real one."""
+    monkeypatch.setattr(registry_module, "_REGISTRY", {})
+    monkeypatch.setattr(registry_module, "_plugins_loaded", True)
+
+
+class _FakePlugin(BaseChartPlugin):
+    chart_type = "fake"
+    display_name = "Fake Chart"
+    native_viz_types = {"fake_viz": "Fake Viz"}
+
+
+class _AnotherPlugin(BaseChartPlugin):
+    chart_type = "another"
+    display_name = "Another Chart"
+    native_viz_types = {"another_viz": "Another Viz"}
+
+
+def test_register_adds_plugin():
+    plugin = _FakePlugin()
+    register(plugin)
+    assert get("fake") is plugin
+
+
+def test_get_returns_none_for_unknown():
+    assert get("nonexistent") is None
+
+
+def test_all_types_returns_registered_keys():
+    register(_FakePlugin())
+    register(_AnotherPlugin())
+    types = all_types()
+    assert "fake" in types
+    assert "another" in types
+
+
+def test_all_types_insertion_order():
+    register(_FakePlugin())
+    register(_AnotherPlugin())
+    types = all_types()
+    assert types.index("fake") < types.index("another")
+
+
+def test_is_registered_true_for_known():
+    register(_FakePlugin())
+    assert is_registered("fake") is True
+
+
+def test_is_registered_false_for_unknown():
+    assert is_registered("nonexistent") is False
+
+
+def test_register_warns_on_duplicate(caplog):
+    register(_FakePlugin())
+    with caplog.at_level("WARNING"):
+        register(_FakePlugin())
+    assert "Overwriting" in caplog.text
+
+
+def test_register_raises_for_empty_chart_type():
+    class _BadPlugin(BaseChartPlugin):
+        chart_type = ""
+
+    with pytest.raises(ValueError, match="non-empty chart_type"):
+        register(_BadPlugin())
+
+
+def test_display_name_for_viz_type_found():
+    register(_FakePlugin())
+    assert display_name_for_viz_type("fake_viz") == "Fake Viz"
+
+
+def test_display_name_for_viz_type_not_found():
+    register(_FakePlugin())
+    assert display_name_for_viz_type("unknown_viz") is None
+
+
+def test_display_name_searches_all_plugins():
+    register(_FakePlugin())
+    register(_AnotherPlugin())
+    assert display_name_for_viz_type("another_viz") == "Another Viz"
+
+
+def test_get_registry_returns_proxy():
+    assert isinstance(get_registry(), _RegistryProxy)
+
+
+def test_registry_proxy_get():
+    plugin = _FakePlugin()
+    register(plugin)
+    assert get_registry().get("fake") is plugin
+
+
+def test_registry_proxy_all_types():
+    register(_FakePlugin())
+    assert "fake" in get_registry().all_types()
+
+
+def test_registry_proxy_is_registered():
+    register(_FakePlugin())
+    assert get_registry().is_registered("fake") is True
+    assert get_registry().is_registered("missing") is False
+
+
+def test_registry_proxy_display_name_for_viz_type():
+    register(_FakePlugin())
+    assert get_registry().display_name_for_viz_type("fake_viz") == "Fake Viz"
+    assert get_registry().display_name_for_viz_type("unknown") is None