Revert "Move skills watcher to app-server" (#21460)

Reverts openai/codex#21287

codex-rs/app-server/src/thread_state.rs

@@ -7,7 +7,6 @@ use codex_app_server_protocol::Turn;
 use codex_app_server_protocol::TurnError;
 use codex_core::CodexThread;
 use codex_core::ThreadConfigSnapshot;
-use codex_core::file_watcher::WatchRegistration;
 use codex_protocol::ThreadId;
 use codex_protocol::protocol::EventMsg;
 use codex_protocol::protocol::RolloutItem;
@@ -78,7 +77,6 @@ pub(crate) struct ThreadState {
     listener_command_tx: Option<mpsc::UnboundedSender<ThreadListenerCommand>>,
     current_turn_history: ThreadHistoryBuilder,
     listener_thread: Option<Weak<CodexThread>>,
-    watch_registration: WatchRegistration,
 }
 
 impl ThreadState {
@@ -93,7 +91,6 @@ impl ThreadState {
         &mut self,
         cancel_tx: oneshot::Sender<()>,
         conversation: &Arc<CodexThread>,
-        watch_registration: WatchRegistration,
     ) -> (mpsc::UnboundedReceiver<ThreadListenerCommand>, u64) {
         if let Some(previous) = self.cancel_tx.replace(cancel_tx) {
             let _ = previous.send(());
@@ -102,7 +99,6 @@ impl ThreadState {
         let (listener_command_tx, listener_command_rx) = mpsc::unbounded_channel();
         self.listener_command_tx = Some(listener_command_tx);
         self.listener_thread = Some(Arc::downgrade(conversation));
-        self.watch_registration = watch_registration;
         (listener_command_rx, self.listener_generation)
     }
 
@@ -113,7 +109,6 @@ impl ThreadState {
         self.listener_command_tx = None;
         self.current_turn_history.reset();
         self.listener_thread = None;
-        self.watch_registration = WatchRegistration::default();
     }
 
     pub(crate) fn set_experimental_raw_events(&mut self, enabled: bool) {