Honor managed plugin disablement for executor capabilities (#40640)

## Why

Selected executor plugin roots could still expose capabilities when managed
requirements disabled the `plugins` feature.

## What changed

- Suppress MCP servers, skills, apps, and connectors from selected executor
  plugins when `plugins` is disabled, while preserving the selected-root
  identity used to filter those capabilities.
- Apply the policy consistently to direct selected-root discovery and batched
  executor capability discovery.

## Testing

- Add contributor-level and app-server coverage that verifies disabled plugin
  capabilities are absent and their MCP servers never start.

GitOrigin-RevId: e30bd8a936c4b0e083908b89a65f4d02e01747de

codex-rs/ext/mcp/tests/executor_plugin_mcp.rs

@@ -157,6 +157,61 @@ async fn selected_plugin_package_is_contributed_without_servers_or_connectors()
     Ok(())
 }
 
+#[tokio::test]
+async fn managed_plugins_requirement_disables_selected_executor_plugin_capabilities() -> TestResult
+{
+    let codex_home = tempfile::tempdir()?;
+    let plugin_root = tempfile::tempdir()?;
+    std::fs::create_dir_all(plugin_root.path().join(".codex-plugin"))?;
+    std::fs::write(
+        plugin_root.path().join(".codex-plugin/plugin.json"),
+        r#"{"name":"selected-root","interface":{"displayName":"Selected Root"}}"#,
+    )?;
+    std::fs::write(
+        plugin_root.path().join(".mcp.json"),
+        r#"{"mcpServers":{"probe":{"command":"probe-command"}}}"#,
+    )?;
+    let mut config = ConfigBuilder::default()
+        .codex_home(codex_home.path().to_path_buf())
+        .fallback_cwd(Some(codex_home.path().to_path_buf()))
+        .cloud_config_bundle(
+            CloudConfigBundleFixture::loader_with_enterprise_requirement(
+                r#"
+[features]
+plugins = false
+"#,
+            ),
+        )
+        .build()
+        .await?;
+    assert!(!config.features.enabled(Feature::Plugins));
+
+    let direct = raw_selected_plugin_contributions(&config, plugin_root.path()).await?;
+    assert!(
+        matches!(
+            direct.as_slice(),
+            [McpServerContribution::SelectedPluginPackage { selected_root_id, .. }]
+                if selected_root_id == "selected-root"
+        ),
+        "managed Plugins disable should preserve only the direct selected-root identity"
+    );
+
+    config
+        .features
+        .enable(Feature::ExecutorCapabilityDiscovery)
+        .expect("test config should allow feature update");
+    let discovered = raw_selected_plugin_contributions(&config, plugin_root.path()).await?;
+    assert!(
+        matches!(
+            discovered.as_slice(),
+            [McpServerContribution::SelectedPluginPackage { selected_root_id, .. }]
+                if selected_root_id == "selected-root"
+        ),
+        "managed Plugins disable should preserve only the discovered selected-root identity"
+    );
+    Ok(())
+}
+
 #[tokio::test]
 async fn high_level_discovery_matches_the_existing_plugin_provider() -> TestResult {
     let codex_home = tempfile::tempdir()?;