Create Codex threads on first message after clear

PLAN.md

@@ -249,6 +249,10 @@ That notification retries the waiting queue, so delivery does not depend on a
 later message happening to retry it. A message accepted while initialization or
 recovery is still finding a thread is recorded as queued; the phone can therefore
 reopen without losing the only visible copy before Codex acknowledges it.
+Clearing does not eagerly create that replacement: it forgets the old id and
+the next message starts a thread and its first turn together. An empty replacement
+would become exactly the unresumable id above if the app-server restarted between
+the clear and the next message.
 
 Codex subscription limits come from the CLI's `account/rateLimits/read`
 app-server request on the machine that runs Codex. This keeps login and

server/src/session/codex.rs

@@ -213,9 +213,9 @@ impl Driver for CodexDriver {
         // a thread to receive this yet. Announce that wait just like one behind an active turn: the
         // phone stops preserving its local bridge once this method returns, so the server event is
         // the durable copy until Codex acknowledges the message.
-        let waiting_for_protocol = state.initialize_request.is_some()
-            || state.thread_request.is_some()
-            || read_thread(&self.inner.session_dir).is_none();
+        let missing_thread = read_thread(&self.inner.session_dir).is_none();
+        let waiting_for_protocol =
+            state.initialize_request.is_some() || state.thread_request.is_some() || missing_thread;
         let id = (state.running || waiting_for_protocol)
             .then(super::random_hex)
             .unwrap_or_default();
@@ -228,6 +228,14 @@ impl Driver for CodexDriver {
             text: text.clone(),
             attachments: attachments.clone(),
         });
+        let start_thread = (missing_thread
+            && state.initialize_request.is_none()
+            && state.thread_request.is_none())
+        .then(|| {
+            let request = request_id();
+            state.thread_request = Some(request.clone());
+            request
+        });
         drop(state);
         save_state(&self.inner);
         if !id.is_empty() {
@@ -237,6 +245,16 @@ impl Driver for CodexDriver {
                 attachments,
             });
         }
+        if let Some(request) = start_thread {
+            send_json(
+                &self.inner,
+                json!({
+                    "id": request,
+                    "method": "thread/start",
+                    "params": thread_params(&self.inner)
+                }),
+            );
+        }
         dispatch_waiting(&self.inner);
     }
 
@@ -333,13 +351,11 @@ impl Driver for CodexDriver {
             });
             return;
         }
-        let request = request_id();
-        self.inner.state.lock().unwrap().thread_request = Some(request.clone());
+        // A thread has no durable rollout until its first turn. Creating an empty replacement here
+        // leaves an id that a restarted app-server cannot resume; start it with the next message
+        // instead, when Codex can make the thread and its first turn together.
+        self.inner.state.lock().unwrap().thread_request = None;
         save_state(&self.inner);
-        send_json(
-            &self.inner,
-            json!({"id": request, "method": "thread/start", "params": thread_params(&self.inner)}),
-        );
         let _ = self.inner.sink.send(Event::Cleared);
     }
 
@@ -1399,6 +1415,61 @@ mod tests {
         assert!(!state.waiting[0].id.is_empty());
     }
 
+    #[test]
+    fn clear_defers_the_replacement_thread_until_its_first_message() {
+        let dir = tempfile::tempdir().expect("tempdir");
+        write_thread(dir.path(), "old-thread");
+        let (sink, mut events) = mpsc::unbounded_channel();
+        let (to_child, mut requests) = mpsc::unbounded_channel();
+        let inner = Arc::new(Inner {
+            sink,
+            state: Mutex::new(ProtocolState::default()),
+            settings: Mutex::new(Settings {
+                model: None,
+                permission_mode: None,
+                effort: None,
+            }),
+            to_child,
+            transport: Transport::Here,
+            session_dir: dir.path().to_path_buf(),
+            subagents: Arc::new(Subagents::new(dir.path().to_path_buf())),
+            reading: AtomicBool::new(true),
+        });
+        let driver = CodexDriver {
+            inner: Arc::clone(&inner),
+        };
+
+        driver.clear();
+
+        assert_eq!(events.try_recv().expect("clear boundary"), Event::Cleared);
+        assert_eq!(read_thread(dir.path()), None);
+        assert!(
+            requests.try_recv().is_err(),
+            "clear eagerly started a thread"
+        );
+
+        driver.send_user_message("first new message".to_string(), Vec::new());
+
+        assert!(matches!(
+            events.try_recv().expect("durable queue event"),
+            Event::MessageQueued { text, .. } if text == "first new message"
+        ));
+        let start: Value = serde_json::from_str(&requests.try_recv().expect("thread start"))
+            .expect("request json");
+        assert_eq!(start["method"], "thread/start");
+        let request_id = start["id"].as_str().expect("request id");
+
+        handle_response(
+            &inner,
+            &json!({"id": request_id, "result": {"thread": {"id": "new-thread"}}}),
+        );
+
+        let turn: Value =
+            serde_json::from_str(&requests.try_recv().expect("first turn")).expect("request json");
+        assert_eq!(turn["method"], "turn/start");
+        assert_eq!(turn["params"]["threadId"], "new-thread");
+    }
+
     #[test]
     fn a_replacement_thread_notification_releases_its_waiting_message() {
         let dir = tempfile::tempdir().expect("tempdir");