feat: add auto refresh on thread listeners (#9105)

This PR is in the scope of multi-agent work. 

An agent (=thread) can now spawn other agents. Those other agents are
not attached to any clients. We need a way to make sure that the clients
are aware of the new threads to look at (for approval for example). This
PR adds a channel to the `ThreadManager` that pushes the ID of those
newly created agents such that the client (here the app-server) can also
subscribe to those ones.

codex-rs/core/src/thread_manager.rs

@@ -31,8 +31,11 @@ use std::sync::Arc;
 #[cfg(any(test, feature = "test-support"))]
 use tempfile::TempDir;
 use tokio::sync::RwLock;
+use tokio::sync::broadcast;
 use tracing::warn;
 
+const THREAD_CREATED_CHANNEL_CAPACITY: usize = 1024;
+
 /// Represents a newly created Codex thread (formerly called a conversation), including the first event
 /// (which is [`EventMsg::SessionConfigured`]).
 pub struct NewThread {
@@ -54,6 +57,7 @@ pub struct ThreadManager {
 /// function to require an `Arc<&Self>`.
 pub(crate) struct ThreadManagerState {
     threads: Arc<RwLock<HashMap<ThreadId, Arc<CodexThread>>>>,
+    thread_created_tx: broadcast::Sender<ThreadId>,
     auth_manager: Arc<AuthManager>,
     models_manager: Arc<ModelsManager>,
     skills_manager: Arc<SkillsManager>,
@@ -70,9 +74,11 @@ impl ThreadManager {
         auth_manager: Arc<AuthManager>,
         session_source: SessionSource,
     ) -> Self {
+        let (thread_created_tx, _) = broadcast::channel(THREAD_CREATED_CHANNEL_CAPACITY);
         Self {
             state: Arc::new(ThreadManagerState {
                 threads: Arc::new(RwLock::new(HashMap::new())),
+                thread_created_tx,
                 models_manager: Arc::new(ModelsManager::new(
                     codex_home.clone(),
                     auth_manager.clone(),
@@ -108,9 +114,11 @@ impl ThreadManager {
         codex_home: PathBuf,
     ) -> Self {
         let auth_manager = AuthManager::from_auth_for_testing(auth);
+        let (thread_created_tx, _) = broadcast::channel(THREAD_CREATED_CHANNEL_CAPACITY);
         Self {
             state: Arc::new(ThreadManagerState {
                 threads: Arc::new(RwLock::new(HashMap::new())),
+                thread_created_tx,
                 models_manager: Arc::new(ModelsManager::with_provider(
                     codex_home.clone(),
                     auth_manager.clone(),
@@ -174,6 +182,10 @@ impl ThreadManager {
         }
     }
 
+    pub fn subscribe_thread_created(&self) -> broadcast::Receiver<ThreadId> {
+        self.state.thread_created_tx.subscribe()
+    }
+
     pub async fn get_thread(&self, thread_id: ThreadId) -> CodexResult<Arc<CodexThread>> {
         self.state.get_thread(thread_id).await
     }
@@ -348,6 +360,10 @@ impl ThreadManagerState {
             session_configured,
         })
     }
+
+    pub(crate) fn notify_thread_created(&self, thread_id: ThreadId) {
+        let _ = self.thread_created_tx.send(thread_id);
+    }
 }
 
 /// Return a prefix of `items` obtained by cutting strictly before the nth user message