CompleteRead logged a Warning for every non-Good status on every poll and
latched Degraded for all of them. Now a bad tag warns once per bad episode
(re-armed when it reads Good, and on re-initialise), a comms-class status
(BadCommunicationError / BadTimeout) degrades with LastSuccessfulRead
preserved, and any other status - the device answered and refused this tag -
advances LastSuccessfulRead with no state change. Read-path exception
handlers now go through MarkCommsFault, so they never downgrade Faulted.
Refs #739
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT
Joseph Doherty
4083b4aada