app-server: Silence thread status changes caused by thread being created (#13079)

Currently we emit `thread/status/changed` with `Idle` status right
before sending `thread/started` event (which also has `Idle` status in
it).
It feels that there is no point in that as client has no way to know
prior state of the thread as it didn't exist yet, so silence these kinds
of notifications.

codex-rs/app-server/tests/suite/v2/review.rs

@@ -8,6 +8,7 @@ use app_test_support::to_response;
 use codex_app_server_protocol::ItemCompletedNotification;
 use codex_app_server_protocol::ItemStartedNotification;
 use codex_app_server_protocol::JSONRPCError;
+use codex_app_server_protocol::JSONRPCMessage;
 use codex_app_server_protocol::JSONRPCNotification;
 use codex_app_server_protocol::JSONRPCResponse;
 use codex_app_server_protocol::RequestId;
@@ -19,9 +20,12 @@ use codex_app_server_protocol::ServerRequest;
 use codex_app_server_protocol::ThreadItem;
 use codex_app_server_protocol::ThreadStartParams;
 use codex_app_server_protocol::ThreadStartResponse;
+use codex_app_server_protocol::ThreadStartedNotification;
+use codex_app_server_protocol::ThreadStatusChangedNotification;
 use codex_app_server_protocol::TurnStartParams;
 use codex_app_server_protocol::TurnStatus;
 use codex_app_server_protocol::UserInput as V2UserInput;
+use pretty_assertions::assert_eq;
 use serde_json::json;
 use tempfile::TempDir;
 use tokio::time::timeout;
@@ -301,6 +305,31 @@ async fn review_start_with_detached_delivery_returns_new_thread_id() -> Result<(
         "detached review should run on a different thread"
     );
 
+    let deadline = tokio::time::Instant::now() + DEFAULT_READ_TIMEOUT;
+    let notification = loop {
+        let remaining = deadline.saturating_duration_since(tokio::time::Instant::now());
+        let message = timeout(remaining, mcp.read_next_message()).await??;
+        let JSONRPCMessage::Notification(notification) = message else {
+            continue;
+        };
+        if notification.method == "thread/status/changed" {
+            let status_changed: ThreadStatusChangedNotification =
+                serde_json::from_value(notification.params.expect("params must be present"))?;
+            if status_changed.thread_id == review_thread_id {
+                anyhow::bail!(
+                    "detached review threads should be introduced without a preceding thread/status/changed"
+                );
+            }
+            continue;
+        }
+        if notification.method == "thread/started" {
+            break notification;
+        }
+    };
+    let started: ThreadStartedNotification =
+        serde_json::from_value(notification.params.expect("params must be present"))?;
+    assert_eq!(started.thread.id, review_thread_id);
+
     Ok(())
 }
 
@@ -389,6 +418,11 @@ async fn start_default_thread(mcp: &mut McpProcess) -> Result<String> {
     )
     .await??;
     let ThreadStartResponse { thread, .. } = to_response::<ThreadStartResponse>(thread_resp)?;
+    timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_notification_message("thread/started"),
+    )
+    .await??;
     Ok(thread.id)
 }