OVERLAY_UNICAST_CHANNEL

The room-channel name an admitted client's app-unicast spoke rides on — the two-peer server↔client link a server hands to OverlayServer.admit as the local delivery seam for cross-core routed unicasts.

It is a distinct channel from the Raft transport's "raft" channel so the two dialects never share framing: a client reading this channel by the same name sees exactly the overlay's per-recipient traffic, never Raft envelopes. A server calls room.channel(OVERLAY_UNICAST_CHANNEL) for each admitted connection and registers it as that client's local spoke via OverlayServer.admit.