[app-server] send account/rateLimits/updated notifications (#5477)

Codex will now send an `account/rateLimits/updated` notification
whenever the user's rate limits are updated.

This is implemented by just transforming the existing TokenCount event.

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

@@ -875,6 +875,11 @@ pub struct AuthStatusChangeNotification {
 #[serde(tag = "method", content = "params", rename_all = "camelCase")]
 #[strum(serialize_all = "camelCase")]
 pub enum ServerNotification {
+    #[serde(rename = "account/rateLimits/updated")]
+    #[ts(rename = "account/rateLimits/updated")]
+    #[strum(serialize = "account/rateLimits/updated")]
+    AccountRateLimitsUpdated(RateLimitSnapshot),
+
     /// Authentication status changed
     AuthStatusChange(AuthStatusChangeNotification),
 
@@ -888,6 +893,7 @@ pub enum ServerNotification {
 impl ServerNotification {
     pub fn to_params(self) -> Result<serde_json::Value, serde_json::Error> {
         match self {
+            ServerNotification::AccountRateLimitsUpdated(params) => serde_json::to_value(params),
             ServerNotification::AuthStatusChange(params) => serde_json::to_value(params),
             ServerNotification::LoginChatGptComplete(params) => serde_json::to_value(params),
             ServerNotification::SessionConfigured(params) => serde_json::to_value(params),

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

@@ -1436,6 +1436,15 @@ async fn apply_bespoke_event_handling(
                 on_exec_approval_response(event_id, rx, conversation).await;
             });
         }
+        EventMsg::TokenCount(token_count_event) => {
+            if let Some(rate_limits) = token_count_event.rate_limits {
+                outgoing
+                    .send_server_notification(ServerNotification::AccountRateLimitsUpdated(
+                        rate_limits,
+                    ))
+                    .await;
+            }
+        }
         // If this is a TurnAborted, reply to any pending interrupt requests.
         EventMsg::TurnAborted(turn_aborted_event) => {
             let pending = {

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

@@ -142,6 +142,8 @@ pub(crate) struct OutgoingError {
 #[cfg(test)]
 mod tests {
     use codex_app_server_protocol::LoginChatGptCompleteNotification;
+    use codex_protocol::protocol::RateLimitSnapshot;
+    use codex_protocol::protocol::RateLimitWindow;
     use pretty_assertions::assert_eq;
     use serde_json::json;
     use uuid::Uuid;
@@ -171,4 +173,34 @@ mod tests {
             "ensure the strum macros serialize the method field correctly"
         );
     }
+
+    #[test]
+    fn verify_account_rate_limits_notification_serialization() {
+        let notification = ServerNotification::AccountRateLimitsUpdated(RateLimitSnapshot {
+            primary: Some(RateLimitWindow {
+                used_percent: 25.0,
+                window_minutes: Some(15),
+                resets_at: Some(123),
+            }),
+            secondary: None,
+        });
+
+        let jsonrpc_notification = OutgoingMessage::AppServerNotification(notification);
+        assert_eq!(
+            json!({
+                "method": "account/rateLimits/updated",
+                "params": {
+                    "primary": {
+                        "used_percent": 25.0,
+                        "window_minutes": 15,
+                        "resets_at": 123,
+                    },
+                    "secondary": null,
+                },
+            }),
+            serde_json::to_value(jsonrpc_notification)
+                .expect("ensure the notification serializes correctly"),
+            "ensure the notification serializes correctly"
+        );
+    }
 }