feat(mcp): warn on native_viz_types collision at plugin registration

If two plugins claim the same viz_type, display_name_for_viz_type()
silently resolves to the iteration-order winner. Surface a warning at
register() time so plugin authors catch the shadowing immediately.

superset/mcp_service/chart/registry.py

@@ -160,6 +160,21 @@ def register(plugin: "ChartTypePlugin") -> None:
             logger.warning(
                 "Overwriting existing plugin for chart_type=%r", plugin.chart_type
             )
+        for existing in _REGISTRY.values():
+            if existing.chart_type == plugin.chart_type:
+                continue
+            colliding = plugin.native_viz_types.keys() & existing.native_viz_types
+            if colliding:
+                # display_name_for_viz_type() resolves to the first plugin in
+                # iteration order, making the later registration unreachable.
+                logger.warning(
+                    "Plugin %r declares native_viz_types %s already claimed by "
+                    "plugin %r; viz_type display-name lookups will resolve to "
+                    "the earlier registration",
+                    plugin.chart_type,
+                    sorted(colliding),
+                    existing.chart_type,
+                )
         _REGISTRY[plugin.chart_type] = plugin
     logger.debug("Registered chart plugin: %r", plugin.chart_type)
 

tests/unit_tests/mcp_service/chart/test_registry.py

@@ -98,6 +98,29 @@ def test_register_warns_on_duplicate(caplog):
     assert "Overwriting" in caplog.text
 
 
+def test_register_warns_on_viz_type_collision(caplog):
+    register(_FakePlugin())
+
+    class _CollidingPlugin(BaseChartPlugin):
+        chart_type = "colliding"
+        display_name = "Colliding Chart"
+        native_viz_types = {"fake_viz": "Shadowed Viz", "own_viz": "Own Viz"}
+
+    with caplog.at_level("WARNING"):
+        register(_CollidingPlugin())
+    assert "already claimed by" in caplog.text
+    assert "fake_viz" in caplog.text
+    # Earlier registration wins in display-name lookups
+    assert display_name_for_viz_type("fake_viz") == "Fake Viz"
+
+
+def test_register_same_plugin_no_collision_warning(caplog):
+    register(_FakePlugin())
+    with caplog.at_level("WARNING"):
+        register(_FakePlugin())
+    assert "already claimed by" not in caplog.text
+
+
 def test_register_raises_for_empty_chart_type():
     class _BadPlugin(BaseChartPlugin):
         chart_type = ""