Implements IDataConnection + IBrowsableDataConnection over the IMxGatewayClient
seam: connect/disconnect with once-only Disconnected guard + background event
loop, subscribe/unsubscribe with tag routing, read/write batch with per-tag
error classification, WriteBatchAndWait, and Galaxy browse mapping. Covers plan
Tasks 6-10. Full unit coverage via FakeMxGatewayClient (12 tests).
Joseph Doherty