After a remote backend update restarts the gateway, the window WebSocket often dies without a close event (SSH/tailscale tunnels) and users force-quit to recover. finishBackendApply now nudges the registered reconnect handler, which rides the new ping liveness probe: healthy sockets are left untouched, dead ones are force-closed and re-dialed. The old blind gateway.close() on every wake signal is removed in favor of the probe.
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