Remove plugin hooks feature flag (#22552)

# Why

This is a follow-up stacked on top of the `plugin_hooks` default-on
change. Once we are comfortable making plugin hooks part of the normal
plugin behavior, the separate feature flag stops buying us much and
leaves extra branching/cache state behind.

# What

- remove the `PluginHooks` feature and generated config-schema entries
- make plugin hook loading/listing follow plugin enablement directly
- drop plugin-manager cache/state that only existed to distinguish
hook-flag toggles
- remove tests and fixtures that modeled `plugin_hooks = true/false`

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

@@ -101,18 +101,6 @@ fn run_git(repo: &Path, args: &[&str]) {
 }
 
 fn plugin_config_toml(enabled: bool, plugins_feature_enabled: bool) -> String {
-    plugin_config_toml_with_plugin_hooks(
-        enabled,
-        plugins_feature_enabled,
-        /*plugin_hooks_feature_enabled*/ false,
-    )
-}
-
-fn plugin_config_toml_with_plugin_hooks(
-    enabled: bool,
-    plugins_feature_enabled: bool,
-    plugin_hooks_feature_enabled: bool,
-) -> String {
     let mut root = toml::map::Map::new();
 
     let mut features = toml::map::Map::new();
@@ -120,10 +108,6 @@ fn plugin_config_toml_with_plugin_hooks(
         "plugins".to_string(),
         Value::Boolean(plugins_feature_enabled),
     );
-    features.insert(
-        "plugin_hooks".to_string(),
-        Value::Boolean(plugin_hooks_feature_enabled),
-    );
     root.insert("features".to_string(), Value::Table(features));
 
     let mut plugin = toml::map::Map::new();
@@ -1133,61 +1117,6 @@ async fn load_plugins_returns_empty_when_feature_disabled() {
     assert_eq!(outcome, PluginLoadOutcome::default());
 }
 
-#[tokio::test]
-async fn plugins_for_config_reloads_when_plugin_hooks_enablement_changes() {
-    let codex_home = TempDir::new().unwrap();
-    let plugin_root = codex_home
-        .path()
-        .join("plugins/cache")
-        .join("test/sample/local");
-
-    write_file(
-        &plugin_root.join(".codex-plugin/plugin.json"),
-        r#"{"name":"sample"}"#,
-    );
-    write_file(
-        &plugin_root.join("hooks/hooks.json"),
-        r#"{
-  "hooks": {
-    "PreToolUse": [
-      {
-        "hooks": [{ "type": "command", "command": "echo plugin hook" }]
-      }
-    ]
-  }
-}"#,
-    );
-
-    let manager = PluginsManager::new(codex_home.path().to_path_buf());
-    write_file(
-        &codex_home.path().join(CONFIG_TOML_FILE),
-        &plugin_config_toml_with_plugin_hooks(
-            /*enabled*/ true, /*plugins_feature_enabled*/ true,
-            /*plugin_hooks_feature_enabled*/ false,
-        ),
-    );
-    let config_without_plugin_hooks = load_config(codex_home.path(), codex_home.path()).await;
-    let without_plugin_hooks = manager
-        .plugins_for_config(&config_without_plugin_hooks)
-        .await;
-    assert!(
-        without_plugin_hooks
-            .effective_plugin_hook_sources()
-            .is_empty()
-    );
-
-    write_file(
-        &codex_home.path().join(CONFIG_TOML_FILE),
-        &plugin_config_toml_with_plugin_hooks(
-            /*enabled*/ true, /*plugins_feature_enabled*/ true,
-            /*plugin_hooks_feature_enabled*/ true,
-        ),
-    );
-    let config_with_plugin_hooks = load_config(codex_home.path(), codex_home.path()).await;
-    let with_plugin_hooks = manager.plugins_for_config(&config_with_plugin_hooks).await;
-    assert_eq!(with_plugin_hooks.effective_plugin_hook_sources().len(), 1);
-}
-
 #[tokio::test]
 async fn load_plugins_rejects_invalid_plugin_keys() {
     let codex_home = TempDir::new().unwrap();
@@ -2032,7 +1961,6 @@ async fn read_plugin_for_config_installed_git_source_reads_from_cache_without_cl
         &tmp.path().join(CONFIG_TOML_FILE),
         r#"[features]
 plugins = true
-plugin_hooks = true
 
 [plugins."toolkit@debug"]
 enabled = true
@@ -3741,7 +3669,6 @@ async fn load_plugins_ignores_project_config_files() {
         std::collections::HashMap::new(),
         &PluginStore::new(codex_home.path().to_path_buf()),
         Some(Product::Codex),
-        /*plugin_hooks_enabled*/ false,
     )
     .await;