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/ext/guardian-v2/src/async_scorer/sampler.rs

@@ -359,7 +359,10 @@ impl LunaSampler {
         let retryable = match error {
             LunaSamplerError::ConnectionTimeout
             | LunaSamplerError::Api(
-                ApiError::Retryable { .. } | ApiError::Stream(_) | ApiError::ServerOverloaded,
+                ApiError::Retryable { .. }
+                | ApiError::RateLimitExceeded { .. }
+                | ApiError::Stream(_)
+                | ApiError::ServerOverloaded,
             )
             | LunaSamplerError::Api(ApiError::Transport(
                 TransportError::RetryLimit