Against opc-plc (opc.tcp://10.100.0.35:50000): a shutdown with three live
subscriptions is bounded and the same instance re-initialises and reads (O-9 +
lifecycle generation through the real SDK); a server-refused write
(BadTypeMismatch) passes through and keeps the driver Healthy with its stamp
advanced (health contract); the browse side-panel reports a live variable's type,
shape and access (O-5).
Against the MTConnect fixture Agent: the headers-only ping reaches it and fails on
a dead port (T-7); a delivering /sample stream serves reads and reports its lag and
effective count on the diagnostics bag (T-4/T-5).
Refs #743
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT
Joseph Doherty