Without this UA tag the Feishu server does not push group @mention events over the WebSocket transport. The "channel" tag tells the server to use the Channel protocol which enables group-message routing in addition to P2P direct messages. Root cause: FeishuWSClient was created without any UA signaling tag, so the server defaulted to the basic DM-only push mode. Group @mention events were silently dropped before reaching Hermes. Fixes https://github.com/NousResearch/hermes-agent/issues/50656 Also adds a regression test verifying the UA tag is present in the FeishuWSClient constructor call.