Gate plugin recommendation cache warming on feature flags (#60721)

## Why

Background plugin cache refreshes fetched recommendations even when plugin recommendations were disabled.

## What changed

Pass the effective recommendation feature state into `PluginsConfigInput` and skip recommendation cache warming unless apps, plugins, and either `tool_suggest` or `recommended_plugins` are enabled. Installed-plugin cache refreshes continue independently.

Disable `tool_suggest` and `recommended_plugins` by default in core and app-server test helpers, with explicit overrides for recommendation tests.

## Testing

Update cache-warming and external-login recommendation tests to opt in explicitly. Update config RPC assertions to verify the test helpers' session flag overrides.

GitOrigin-RevId: dc04e2847c94e2b15842fcd95cc0cf1f104e1fac

codex-rs/core-plugins/src/manager.rs

@@ -175,6 +175,7 @@ pub struct PluginsConfigInput {
     pub remote_plugin_enabled: bool,
     pub chatgpt_base_url: String,
     pub product_sku: Option<String>,
+    plugin_recommendations_enabled: bool,
     http_client_factory: HttpClientFactory,
     remote_http_clients: Arc<OnceLock<Arc<dyn HttpClientSelector>>>,
     runtime_http_clients: Arc<OnceLock<Arc<dyn HttpClientSelector>>>,
@@ -203,12 +204,18 @@ impl PluginsConfigInput {
             chatgpt_base_url,
             http_client_factory,
             product_sku,
+            plugin_recommendations_enabled: false,
             remote_http_clients: Arc::new(OnceLock::new()),
             runtime_http_clients: Arc::new(OnceLock::new()),
             runtime_auth_mode: None,
         }
     }
 
+    pub fn with_plugin_recommendations_enabled(mut self, enabled: bool) -> Self {
+        self.plugin_recommendations_enabled = enabled;
+        self
+    }
+
     pub fn with_runtime_auth_mode(mut self, mode: Option<RuntimeAuthMode>) -> Self {
         self.runtime_auth_mode = mode;
         self
@@ -1699,6 +1706,10 @@ impl PluginsManager {
             EffectivePluginsChange::default(),
         );
 
+        if !config.plugin_recommendations_enabled {
+            return;
+        }
+
         let manager = Arc::clone(self);
         let config = config.clone();
         tokio::spawn(async move {

codex-rs/core-plugins/src/manager_tests.rs

@@ -6151,7 +6151,9 @@ plugins = true
         .mount(&server)
         .await;
 
-    let mut config = load_config(tmp.path(), tmp.path()).await;
+    let mut config = load_config(tmp.path(), tmp.path())
+        .await
+        .with_plugin_recommendations_enabled(/*enabled*/ true);
     config.chatgpt_base_url = server.uri();
     let manager = std::sync::Arc::new(test_plugins_manager(tmp.path().to_path_buf()));
     let auth = CodexAuth::create_dummy_chatgpt_auth_for_testing();