feat(mcp): add runtime chart plugin enable/disable via _PluginFilterConfig

Introduces a dynamic filter layer in the chart type registry so operators can
disable individual plugins (e.g. `handlebars`) without a code deploy:

- `MCP_DISABLED_CHART_PLUGINS: frozenset[str]` — static deny-list in mcp_config.py
- `MCP_CHART_PLUGIN_ENABLED_FUNC: Callable[[str], bool] | None` — dynamic hook
  for Harness/Split/per-user targeting; takes precedence over the deny-list
- Both keys are propagated through `get_mcp_config()` defaults

registry.py changes:
- `_PluginFilterConfig` frozen dataclass replaces two bare globals so
  configure() replaces them atomically (no torn reads under concurrency)
- `configure(disabled, enabled_func)` — called at app init; accepts any
  iterable for `disabled`; validates `enabled_func` is callable
- `_is_plugin_enabled()` — reads config once, fails closed on callable exception
- `get()` / `all_types()` / `is_enabled()` apply the filter at lookup time;
  `is_registered()` and `display_name_for_viz_type()` intentionally bypass it
  so callers can distinguish "unknown" vs "disabled" and existing charts still
  resolve display names for disabled viz types

schema_validator.py: two-step pre-check — `is_registered()` for unknown types,
`is_enabled()` for disabled ones, with distinct `DISABLED_CHART_TYPE` error code.

Wiring:
- `SupersetAppInitializer.configure_mcp_chart_registry()` called after
  `configure_feature_flags()` in `init_app()`
- `flask_singleton.py` re-calls `registry.configure()` after the MCP config
  overlay so MCP-specific overrides in `superset_config.py` take effect in
  standalone MCP mode

Tests: 28 cases in test_registry_filters.py covering deny-list, callable hook,
fail-closed on exception, all_types() filtering, display_name bypass, atomic
reconfigure, and configure() with list/tuple/frozenset inputs.

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

superset/initialization/__init__.py

@@ -747,6 +747,7 @@ class SupersetAppInitializer:  # pylint: disable=too-many-public-methods
         # Configuration of feature_flags must be done first to allow init features
         # conditionally
         self.configure_feature_flags()
+        self.configure_mcp_chart_registry()
         self.configure_db_encrypt()
         self.setup_db()
 
@@ -821,6 +822,22 @@ class SupersetAppInitializer:  # pylint: disable=too-many-public-methods
     def configure_feature_flags(self) -> None:
         feature_flag_manager.init_app(self.superset_app)
 
+    def configure_mcp_chart_registry(self) -> None:
+        from superset.mcp_service.chart import registry
+        from superset.mcp_service.mcp_config import (
+            MCP_CHART_PLUGIN_ENABLED_FUNC,
+            MCP_DISABLED_CHART_PLUGINS,
+        )
+
+        registry.configure(
+            disabled=self.config.get(
+                "MCP_DISABLED_CHART_PLUGINS", MCP_DISABLED_CHART_PLUGINS
+            ),
+            enabled_func=self.config.get(
+                "MCP_CHART_PLUGIN_ENABLED_FUNC", MCP_CHART_PLUGIN_ENABLED_FUNC
+            ),
+        )
+
     def configure_sqlglot_dialects(self) -> None:
         extensions = self.config["SQLGLOT_DIALECTS_EXTENSIONS"]
 

superset/mcp_service/chart/registry.py

@@ -38,6 +38,8 @@ from __future__ import annotations
 
 import logging
 import threading
+from collections.abc import Callable, Iterable
+from dataclasses import dataclass, field
 from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
@@ -49,6 +51,22 @@ _REGISTRY: dict[str, "ChartTypePlugin"] = {}
 _plugins_loaded = False
 _plugins_lock = threading.Lock()
 
+# ---------------------------------------------------------------------------
+# Plugin filter — replaced atomically by configure() at app startup.
+# Default: all registered plugins visible (no disabled set, no callable).
+# ---------------------------------------------------------------------------
+
+PluginEnabledFunc = Callable[[str], bool]
+
+
+@dataclass(frozen=True)
+class _PluginFilterConfig:
+    disabled_plugins: frozenset[str] = field(default_factory=frozenset)
+    enabled_func: PluginEnabledFunc | None = None
+
+
+_filter_config: _PluginFilterConfig = _PluginFilterConfig()
+
 
 def _ensure_plugins_loaded() -> None:
     """Lazily import the plugins package to populate _REGISTRY.
@@ -70,6 +88,60 @@ def _ensure_plugins_loaded() -> None:
                 logger.exception("Failed to load built-in chart type plugins")
 
 
+def configure(
+    disabled: Iterable[str] | None = None,
+    enabled_func: PluginEnabledFunc | None = None,
+) -> None:
+    """Set runtime plugin filters. Called once during app initialization.
+
+    Replaces the filter config atomically with a single assignment so concurrent
+    readers always observe a consistent (disabled_plugins, enabled_func) pair.
+
+    Args:
+        disabled: chart_type strings to suppress. Accepts any iterable (set,
+            frozenset, list, tuple). Ignored when enabled_func is provided.
+        enabled_func: callable(chart_type) -> bool.  When set, overrides
+            ``disabled``.  Must be cheap and in-process — no network I/O per
+            call.  On exception the registry fails *closed* (plugin hidden).
+    """
+    global _filter_config
+
+    if enabled_func is not None and not callable(enabled_func):
+        raise TypeError("enabled_func must be callable or None")
+
+    new_config = _PluginFilterConfig(
+        disabled_plugins=frozenset(disabled or ()),
+        enabled_func=enabled_func,
+    )
+    _filter_config = new_config
+
+    if new_config.disabled_plugins:
+        logger.info(
+            "MCP chart plugins disabled: %s", sorted(new_config.disabled_plugins)
+        )
+    if new_config.enabled_func is not None:
+        logger.info(
+            "MCP chart plugin dynamic filter configured: %r", new_config.enabled_func
+        )
+
+
+def _is_plugin_enabled(chart_type: str) -> bool:
+    """Return True if the plugin is currently enabled (not filtered out)."""
+    config = _filter_config  # read once — atomic reference in CPython
+    if config.enabled_func is not None:
+        try:
+            return bool(config.enabled_func(chart_type))
+        except Exception:
+            logger.warning(
+                "MCP_CHART_PLUGIN_ENABLED_FUNC raised for chart_type=%r; "
+                "failing closed (plugin hidden)",
+                chart_type,
+                exc_info=True,
+            )
+            return False
+    return chart_type not in config.disabled_plugins
+
+
 def register(plugin: "ChartTypePlugin") -> None:
     """Register a chart type plugin in the global registry."""
     if not plugin.chart_type:
@@ -83,23 +155,35 @@ def register(plugin: "ChartTypePlugin") -> None:
 
 
 def get(chart_type: str) -> "ChartTypePlugin | None":
-    """Return the plugin for a given chart_type, or None if not registered."""
+    """Return the plugin for chart_type, or None if unknown or disabled."""
     _ensure_plugins_loaded()
-    return _REGISTRY.get(chart_type)
+    if chart_type not in _REGISTRY or not _is_plugin_enabled(chart_type):
+        return None
+    return _REGISTRY[chart_type]
 
 
 def all_types() -> list[str]:
-    """Return all registered chart type strings in insertion order."""
+    """Return enabled registered chart type strings in insertion order."""
     _ensure_plugins_loaded()
-    return list(_REGISTRY.keys())
+    return [ct for ct in _REGISTRY if _is_plugin_enabled(ct)]
 
 
 def is_registered(chart_type: str) -> bool:
-    """Return True if chart_type has a registered plugin."""
+    """Return True if chart_type has a registered plugin, regardless of enabled state.
+
+    Use this to distinguish an unknown chart type from a disabled one.
+    Use is_enabled() to check whether the plugin is currently available.
+    """
     _ensure_plugins_loaded()
     return chart_type in _REGISTRY
 
 
+def is_enabled(chart_type: str) -> bool:
+    """Return True if chart_type is registered AND currently enabled."""
+    _ensure_plugins_loaded()
+    return chart_type in _REGISTRY and _is_plugin_enabled(chart_type)
+
+
 def display_name_for_viz_type(viz_type: str) -> str | None:
     """Return the user-facing display name for a Superset-internal viz_type.
 
@@ -137,5 +221,8 @@ class _RegistryProxy:
     def is_registered(self, chart_type: str) -> bool:
         return is_registered(chart_type)
 
+    def is_enabled(self, chart_type: str) -> bool:
+        return is_enabled(chart_type)
+
     def display_name_for_viz_type(self, viz_type: str) -> str | None:
         return display_name_for_viz_type(viz_type)

superset/mcp_service/chart/validation/schema_validator.py

@@ -172,6 +172,21 @@ class SchemaValidator:
                 error_code="INVALID_CHART_TYPE",
             )
 
+        if not registry.is_enabled(chart_type):
+            valid_types = ", ".join(registry.all_types())
+            return False, ChartGenerationError(
+                error_type="disabled_chart_type",
+                message=f"Chart type '{chart_type}' is not enabled on this instance",
+                details=f"Chart type '{chart_type}' is registered but has been "
+                f"disabled by the operator. "
+                f"Enabled chart types: {valid_types}",
+                suggestions=[
+                    f"Use one of the enabled chart types: {valid_types}",
+                    "Contact your administrator if you believe this is an error",
+                ],
+                error_code="DISABLED_CHART_TYPE",
+            )
+
         plugin = registry.get(chart_type)
         if plugin is None:
             return False, ChartGenerationError(

superset/mcp_service/flask_singleton.py

@@ -81,6 +81,17 @@ try:
         mcp_config = get_mcp_config(_mcp_app.config)
         _mcp_app.config.update(mcp_config)
 
+        # Re-configure chart registry so MCP-specific overrides (e.g.
+        # MCP_DISABLED_CHART_PLUGINS set by the operator) take effect after
+        # the MCP config overlay.  SupersetAppInitializer.configure_mcp_chart_registry()
+        # ran earlier with pre-overlay values; this call corrects them.
+        from superset.mcp_service.chart import registry as _chart_registry
+
+        _chart_registry.configure(
+            disabled=_mcp_app.config.get("MCP_DISABLED_CHART_PLUGINS"),
+            enabled_func=_mcp_app.config.get("MCP_CHART_PLUGIN_ENABLED_FUNC"),
+        )
+
         with _mcp_app.app_context():
             from superset.core.mcp.core_mcp_injection import (
                 initialize_core_mcp_dependencies,

superset/mcp_service/mcp_config.py

@@ -18,6 +18,7 @@
 
 import logging
 import secrets
+from collections.abc import Callable
 from typing import Any, Dict, Optional
 
 from flask import Flask
@@ -56,6 +57,46 @@ MCP_DEBUG = False
 # against the FAB security_manager before execution.
 MCP_RBAC_ENABLED = True
 
+# =============================================================================
+# MCP Chart Plugin Filtering
+# =============================================================================
+#
+# Overview:
+# ---------
+# These two settings let operators enable/disable individual chart type plugins
+# at runtime without a code deploy.
+#
+# Use cases:
+#   - Emergency kill switch: add "handlebars" to MCP_DISABLED_CHART_PLUGINS and
+#     restart to immediately hide it from all callers.
+#   - Dynamic per-request control (A/B test, gradual rollout): set
+#     MCP_CHART_PLUGIN_ENABLED_FUNC to an in-process predicate that can vary
+#     by user, request header, or any other context available at call time.
+#
+# Priority:
+#   MCP_CHART_PLUGIN_ENABLED_FUNC takes precedence over MCP_DISABLED_CHART_PLUGINS.
+#   When the callable is set, the deny-list is ignored entirely.
+#
+# MCP_CHART_PLUGIN_ENABLED_FUNC contract:
+#   - Called as enabled_func(chart_type: str) -> bool for every registry lookup.
+#   - Must be cheap and in-process: consult already-loaded feature flags or
+#     request-local context (e.g. Flask g). Do NOT perform network I/O per call.
+#   - On exception, the registry fails CLOSED (plugin hidden) and logs a warning.
+#   - Example (Harness / Split via pre-fetched flags in g):
+#       from flask import g
+#       def MCP_CHART_PLUGIN_ENABLED_FUNC(chart_type: str) -> bool:
+#           flags = getattr(g, "feature_flags", {})
+#           return flags.get(f"mcp_chart_{chart_type}", True)
+# =============================================================================
+
+# Chart types in this set are hidden from all registry lookups.
+# Use frozenset to avoid accidental mutation.
+MCP_DISABLED_CHART_PLUGINS: frozenset[str] = frozenset()
+
+# Dynamic per-call predicate. When set, overrides MCP_DISABLED_CHART_PLUGINS.
+# Signature: (chart_type: str) -> bool
+MCP_CHART_PLUGIN_ENABLED_FUNC: Callable[[str], bool] | None = None
+
 # MCP JWT Debug Errors - controls server-side JWT debug logging.
 # When False (default), uses the default JWTVerifier with minimal logging.
 # When True, uses DetailedJWTVerifier with tiered logging:
@@ -402,6 +443,8 @@ def get_mcp_config(app_config: Dict[str, Any] | None = None) -> Dict[str, Any]:
         "MCP_SERVICE_PORT": MCP_SERVICE_PORT,
         "MCP_DEBUG": MCP_DEBUG,
         "MCP_RBAC_ENABLED": MCP_RBAC_ENABLED,
+        "MCP_DISABLED_CHART_PLUGINS": MCP_DISABLED_CHART_PLUGINS,
+        "MCP_CHART_PLUGIN_ENABLED_FUNC": MCP_CHART_PLUGIN_ENABLED_FUNC,
         **MCP_SESSION_CONFIG,
         **MCP_CSRF_CONFIG,
     }

tests/unit_tests/mcp_service/chart/test_registry_filters.py

@@ -0,0 +1,222 @@
+# 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 registry plugin filtering (configure / is_enabled / get / all_types)."""
+
+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 (
+    _PluginFilterConfig,
+    all_types,
+    configure,
+    display_name_for_viz_type,
+    get,
+    is_enabled,
+    is_registered,
+    register,
+)
+
+
+@pytest.fixture(autouse=True)
+def _isolated_registry(monkeypatch):
+    """Isolated registry with two known plugins and a clean filter for each test."""
+    monkeypatch.setattr(registry_module, "_REGISTRY", {})
+    monkeypatch.setattr(registry_module, "_plugins_loaded", True)
+    monkeypatch.setattr(registry_module, "_filter_config", _PluginFilterConfig())
+    register(_AlphaPlugin())
+    register(_BetaPlugin())
+
+
+class _AlphaPlugin(BaseChartPlugin):
+    chart_type = "alpha"
+    display_name = "Alpha Chart"
+    native_viz_types = {"alpha_viz": "Alpha Viz"}
+
+
+class _BetaPlugin(BaseChartPlugin):
+    chart_type = "beta"
+    display_name = "Beta Chart"
+    native_viz_types = {"beta_viz": "Beta Viz"}
+
+
+# ---------------------------------------------------------------------------
+# Static deny-list tests
+# ---------------------------------------------------------------------------
+
+
+def test_get_returns_plugin_when_enabled():
+    assert get("alpha") is not None
+    assert get("beta") is not None
+
+
+def test_get_returns_none_for_disabled_plugin():
+    configure(disabled={"alpha"})
+    assert get("alpha") is None
+
+
+def test_get_still_returns_other_plugins_when_one_is_disabled():
+    configure(disabled={"alpha"})
+    assert get("beta") is not None
+
+
+def test_all_types_excludes_disabled():
+    configure(disabled={"alpha"})
+    types = all_types()
+    assert "alpha" not in types
+    assert "beta" in types
+
+
+def test_all_types_empty_when_all_disabled():
+    configure(disabled={"alpha", "beta"})
+    assert all_types() == []
+
+
+def test_is_registered_ignores_deny_list():
+    configure(disabled={"alpha"})
+    assert is_registered("alpha") is True
+
+
+def test_is_enabled_returns_false_for_disabled():
+    configure(disabled={"alpha"})
+    assert is_enabled("alpha") is False
+
+
+def test_is_enabled_returns_true_when_not_disabled():
+    configure(disabled={"alpha"})
+    assert is_enabled("beta") is True
+
+
+def test_is_enabled_returns_false_for_unknown():
+    assert is_enabled("nonexistent") is False
+
+
+# ---------------------------------------------------------------------------
+# configure() accepts different iterable shapes
+# ---------------------------------------------------------------------------
+
+
+def test_configure_accepts_list():
+    configure(disabled=["alpha"])
+    assert get("alpha") is None
+
+
+def test_configure_accepts_tuple():
+    configure(disabled=("alpha",))
+    assert get("alpha") is None
+
+
+def test_configure_accepts_frozenset():
+    configure(disabled=frozenset({"alpha"}))
+    assert get("alpha") is None
+
+
+def test_configure_accepts_none_disabled():
+    configure(disabled=None)
+    assert get("alpha") is not None
+
+
+def test_configure_rejects_noncallable_enabled_func():
+    with pytest.raises(TypeError):
+        configure(enabled_func="not_a_callable")
+
+
+# ---------------------------------------------------------------------------
+# Dynamic callable hook tests
+# ---------------------------------------------------------------------------
+
+
+def test_enabled_func_overrides_deny_list():
+    # alpha is in deny-list but callable says True → should be visible
+    configure(disabled={"alpha"}, enabled_func=lambda ct: ct == "alpha")
+    assert get("alpha") is not None
+
+
+def test_enabled_func_can_disable_plugin():
+    configure(enabled_func=lambda ct: ct != "beta")
+    assert get("beta") is None
+    assert get("alpha") is not None
+
+
+def test_enabled_func_called_per_lookup():
+    calls = []
+
+    def hook(ct: str) -> bool:
+        calls.append(ct)
+        return True
+
+    configure(enabled_func=hook)
+    get("alpha")
+    get("alpha")
+    assert calls.count("alpha") == 2
+
+
+def test_enabled_func_exception_fails_closed(caplog):
+    import logging
+
+    def bad_hook(ct: str) -> bool:
+        raise RuntimeError("Harness down")
+
+    configure(enabled_func=bad_hook)
+    with caplog.at_level(logging.WARNING, logger="superset.mcp_service.chart.registry"):
+        result = get("alpha")
+
+    assert result is None  # fail closed
+    assert "failing closed" in caplog.text.lower() or "alpha" in caplog.text
+
+
+def test_enabled_func_all_types_respects_hook():
+    configure(enabled_func=lambda ct: ct == "alpha")
+    assert all_types() == ["alpha"]
+
+
+# ---------------------------------------------------------------------------
+# display_name_for_viz_type is NOT filtered
+# ---------------------------------------------------------------------------
+
+
+def test_display_name_unaffected_by_deny_list():
+    configure(disabled={"alpha"})
+    # Even though alpha is disabled, its viz_type should still resolve
+    assert display_name_for_viz_type("alpha_viz") == "Alpha Viz"
+
+
+def test_display_name_unaffected_by_callable():
+    configure(enabled_func=lambda ct: False)
+    assert display_name_for_viz_type("beta_viz") == "Beta Viz"
+
+
+# ---------------------------------------------------------------------------
+# configure() atomicity: replacing config is visible to next lookup
+# ---------------------------------------------------------------------------
+
+
+def test_reconfigure_replaces_previous_filter():
+    configure(disabled={"alpha"})
+    assert get("alpha") is None
+    configure(disabled=set())
+    assert get("alpha") is not None
+
+
+def test_reconfigure_with_func_then_none_falls_back_to_deny_list():
+    configure(enabled_func=lambda ct: False)
+    assert get("alpha") is None
+
+    configure(disabled={"beta"}, enabled_func=None)
+    assert get("alpha") is not None
+    assert get("beta") is None