semi implemented and features implemented save checkpoint

docs/features/unchecked/gateway/gateway-connection-lifecycle-management.md

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+# Gateway Connection Lifecycle Management
+
+## Module
+Gateway
+
+## Status
+IMPLEMENTED
+
+## Description
+HELLO frame processing for microservice registration, connection lifecycle management with cleanup on disconnect, and `ConnectionManager` hosted service for monitoring active connections.
+
+## Implementation Details
+- **Gateway hosted service**: `src/Gateway/StellaOps.Gateway.WebService/Services/GatewayHostedService.cs` -- connection lifecycle management background service
+- **Health monitoring**: `src/Gateway/StellaOps.Gateway.WebService/Services/GatewayHealthMonitorService.cs` -- monitors active connections, detects stale instances
+- **Metrics**: `src/Gateway/StellaOps.Gateway.WebService/Services/GatewayMetrics.cs` -- connection metrics tracking
+- **Configuration**: `src/Gateway/StellaOps.Gateway.WebService/Configuration/GatewayOptions.cs`, `GatewayOptionsValidator.cs`
+- **Source**: batch_51/file_22.md
+
+## E2E Test Plan
+- [ ] Verify HELLO frame processing registers new microservice connections
+- [ ] Test connection cleanup on client disconnect
+- [ ] Verify GatewayHealthMonitorService detects stale connections
+- [ ] Verify edge cases and error handling