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DataSource (C++): - New optional config: MulticastGroup (e.g. "239.0.0.1") and DataPort (default Port+1); when set, enables multicast mode; absent = unicast - Control plane: BasicTCPSocket listener on Port; CONNECT received over TCP triggers HandleTCPConnect() which sends CONFIG via the same TCP connection - Data plane: BasicUDPSocket aimed at MulticastGroup:DataPort; all DATA fragments sent via dataSocket.Write() so any joined client receives them - useMulticast is the single branch point; every unicast code path is unchanged when MulticastGroup is absent - New methods: HandleTCPConnect(), IsMulticast() - 5 new unit tests (ports 44710-44729); all 38 tests passing WebUI hub (Go): - SourceConfig gains MulticastGroup and DataPort fields (JSON, optional) - UDPClient gains multicastGroup/dataPort; Run() routes to new runMulticastSession() when multicastGroup is non-empty - runMulticastSession(): TCP dial for CONNECT/CONFIG, net.ListenMulticastUDP for DATA, background goroutine watches TCP for DISCONNECT/close - All existing sm.Add() call sites updated (unicast callers pass "", 0) Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>