Fall back to HTTP immediately for oversized WebSocket requests (#60840)

## Why

A WebSocket close with code `1009` before any text arrives indicates that the request exceeds the peer's message size limit. Retrying the request over another WebSocket does not address that limit.

## What changed

- Classify these early size rejections as requiring HTTP fallback and switch transports without exhausting WebSocket retries, including during prewarming.
- Preserve ordinary stream retry behavior for size closes after any text frame and for other close codes.

## Testing

Add integration coverage for early size rejections during generation and prewarming, size closes after metadata, rate limits, or response creation, and ordinary closes.

GitOrigin-RevId: 4550d289bb414fec1faae2a195bcc635d394117b

codex-rs/codex-api/src/api_bridge.rs

@@ -30,6 +30,7 @@ pub fn map_api_error(err: ApiError) -> CodexErr {
         ApiError::Transport(_)
         | ApiError::Api { .. }
         | ApiError::Stream(_)
+        | ApiError::WebsocketMessageTooLarge
         | ApiError::ContentFilter
         | ApiError::ResponseIncomplete(_)
         | ApiError::ContextWindowExceeded
@@ -67,6 +68,9 @@ fn map_api_error_details(err: ApiError) -> CodexErr {
             CodexErr::new(CodexErrorDetails::RateLimitExceeded(message))
         }
         ApiError::Stream(msg) => CodexErr::Stream(msg),
+        ApiError::WebsocketMessageTooLarge => {
+            CodexErr::new(CodexErrorDetails::WebsocketMessageTooLarge)
+        }
         ApiError::ContentFilter => CodexErr::new(CodexErrorDetails::ContentFilter),
         ApiError::ResponseIncomplete(incomplete) => {
             CodexErr::new(CodexErrorDetails::ResponseIncomplete(incomplete))

codex-rs/codex-api/src/endpoint/responses_websocket.rs

@@ -47,6 +47,7 @@ use tokio_tungstenite::tungstenite::handshake::client::Response;
 use tokio_tungstenite::tungstenite::protocol::CloseFrame;
 use tokio_tungstenite::tungstenite::protocol::frame::Fragment;
 use tokio_tungstenite::tungstenite::protocol::frame::Frame;
+use tokio_tungstenite::tungstenite::protocol::frame::coding::CloseCode;
 use tokio_tungstenite::tungstenite::protocol::frame::coding::Data;
 use tracing::Instrument;
 use tracing::Span;
@@ -848,6 +849,7 @@ async fn run_websocket_response_stream(
     let mut interrupt_request = interrupt.clone().fuse();
     let mut interruption = None;
     let mut response_id = None;
+    let mut received_text = false;
     let mut awaiting_interrupt_ack = false;
     loop {
         let poll_start = Instant::now();
@@ -896,6 +898,7 @@ async fn run_websocket_response_stream(
 
         match message {
             Message::Text(text) => {
+                received_text = true;
                 let event = serde_json::from_str::<ResponsesStreamEvent>(&text);
                 let kind = event.as_ref().ok().map(ResponsesStreamEvent::kind);
                 if let Some(t) = telemetry.as_ref() {
@@ -1033,6 +1036,9 @@ async fn run_websocket_response_stream(
             Message::Binary(_) => {
                 return Err(ApiError::Stream("unexpected binary websocket event".into()));
             }
+            Message::Close(Some(frame)) if frame.code == CloseCode::Size && !received_text => {
+                return Err(ApiError::WebsocketMessageTooLarge);
+            }
             Message::Close(_) => {
                 return Err(ApiError::Stream(
                     "websocket closed by server before response.completed".into(),

codex-rs/codex-api/src/error.rs

@@ -15,6 +15,8 @@ pub enum ApiError {
     Api { status: StatusCode, message: String },
     #[error("stream error: {0}")]
     Stream(String),
+    #[error("websocket request exceeds the peer's message size limit (close code 1009)")]
+    WebsocketMessageTooLarge,
     #[error("stream error: Incomplete response returned, reason: content_filter")]
     ContentFilter,
     #[error(transparent)]