Live post-update validation found one remaining WebSockets 16 compatibility check in optional RAG entity-registry ingestion. The code now uses HAWebSocketClient.connected plus socket presence instead of the removed ClientConnection.open property.
Validation: full backend suite 290 passed / 4 optional live-MCP skipped, Vite production build passed, npm audit found 0 vulnerabilities, and the focused RAG/HA connection set passed. No Home Assistant device state was changed.