relay

<!-- CAPABILITIES_SUMMARY: - channel_adapter_design: Platform-agnostic adapter for Slack/Discord/Telegram/WhatsApp/LINE, write-once-deploy-everywhere (Vercel Chat SDK, LangBot, Bottender) - webhook_handler_design: HMAC-SHA256 over raw bytes, timing-safe comparison, ≤5 min timestamp window, idempotency keys (TTL 7-30 days), async processing (2xx within 3s), ≤100KB payload cap, TLS-only, DLQ with full context - websocket_server_design: Connection lifecycle, heartbeat/reconnect, rooms, horizontal scaling with externalized session state, KEDA/HPA autoscaling, Prometheus metrics, WebSocketStream backpressure - bot_framework_design: Command parser, slash commands, conversation state machine, middleware chain, LLM-native runner integration, unified bot SDK - event_routing_design: Discriminated-union event schema, CloudEvents envelope, AsyncAPI documentation, routing matrix, fan-out/fan-in, choreography pattern - webhook_standards_awareness: Standard Webhooks headers plus provider-specific formats (Stripe-Signature, x-hub-signature-256, x-slack-signature) - unified_message_format: Platform-agnostic message normalization and outbound adaptation via adapter rendering - realtime_communication: SSE, WebSocket, WebTransport, long polling — selection and implementation - message_queue_integration: Redis Pub/Sub, BullMQ, RabbitMQ, Kafka/Redpanda for reliable delivery and event streaming - circuit_breaker_design: ≥50%-over-1-min or 5/10 failure threshold, auto-open with DLQ routing, immediat...