Classify streaming rate-limit errors (#40931)

## What changed

- Classify `response.failed` events with the `rate_limit_exceeded` code as a distinct retryable error while preserving any parsed retry delay.
- Expose the error as `rateLimitExceeded` through the core protocol and app-server schemas after stream retries are exhausted.
- Preserve the upstream message for TUI display while keeping it out of telemetry summaries.

## Testing

- Cover SSE classification, retry metadata, protocol conversion and serialization, exhausted stream retries, telemetry redaction, and TUI rendering.

GitOrigin-RevId: 02dab4d3477dcd7653a58c49c4bd38687a616579

codex-rs/response-debug-context/src/lib.rs

@@ -80,6 +80,7 @@ pub fn telemetry_api_error_message(error: &ApiError) -> String {
         ApiError::QuotaExceeded => "quota exceeded".to_string(),
         ApiError::UsageNotIncluded => "usage not included".to_string(),
         ApiError::Retryable { .. } => "retryable error".to_string(),
+        ApiError::RateLimitExceeded { .. } => "rate limit exceeded".to_string(),
         ApiError::RateLimit(_) => "rate limit".to_string(),
         ApiError::InvalidRequest { .. } => "invalid request".to_string(),
         ApiError::CyberPolicy { .. } => "cyber policy".to_string(),
@@ -134,7 +135,7 @@ mod tests {
     }
 
     #[test]
-    fn telemetry_error_messages_omit_http_bodies() {
+    fn telemetry_error_messages_omit_upstream_bodies() {
         let transport = TransportError::Http {
             status: StatusCode::UNAUTHORIZED,
             url: Some("https://chatgpt.com/backend-api/codex/responses".to_string()),
@@ -147,6 +148,13 @@ mod tests {
             telemetry_api_error_message(&ApiError::Transport(transport)),
             "http 401"
         );
+        assert_eq!(
+            telemetry_api_error_message(&ApiError::RateLimitExceeded {
+                message: "private upstream diagnostic".to_string(),
+                delay: Some(std::time::Duration::from_secs(1)),
+            }),
+            "rate limit exceeded"
+        );
     }
 
     #[test]