The Node main thread was saturated at about 39 uploads/s, overflowing the
listen queue so uploads timed out connecting from nginx.
- Enable keepAlive on the S3 agent; every upload did a full TLS handshake
- Remove OpenTelemetry tracing
- Cache the system key lookup for 60s
- Use lean queries when listing calls
- Serialize each call once in notify_clients, not per recipient
- Add an nginx upstream keepalive pool, and hold Node's keepAliveTimeout
above it so nginx never reuses a connection Node has closed
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>